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www.microchip.com
www.microchip.com/analogtools
Analog & Interface Solutions
Fall 2012
Signal Chain Design Guide
Devices For Use With Sensors
Design ideas in this guide use the following devices.
A complete device list and corresponding data sheets for these products can be found at www.microchip.com/analog.
Operational
AmpliïŹers
Instrumentation
AmpliïŹers
Comparators Analog-to-Digital
Converters
Digital
Potentiometers
Digital-to-Analog
Converters
Voltage
References
Temperature
Sensors
MCP6XX
MCP6XXX
MCP6VXX
MCP6HXX
MCP6NXX MCP654X
MCP656X
MCP65R4X
MCP30XX
MCP32XX
MCP33XX
MCP34XX
MCP35XX
MCP39XX
MCP40XX
MCP40D1X
MCP41XX
MCP42XX
MCP43XX
MCP45XX
MCP46XX
MCP41XXX
MCP42XXX
MCP47XX
MCP48XX
MCP49XX
MCP47DA1
MCP47A1
TC132X
MCP1525
MCP1541
MCP98XX
MCP9700/A
MCP9701/A
2Signal Chain Design Guide
Signal Chain Overview
Typical Sensor Signal Chain Control Loop
Digital DomainAnalog Domain
Driver
(MOSFET)
Op Amp DAC/PWM
Actuators
Motors, Valves,
Relays, Switches,
Speakers, Horns,
LEDs
ADC/
V-to-Freq
Amp
Sensors
Filter
Reference
Voltage
MUX
PICÂź MCU
or dsPICÂź
DSC
Indicator
(LCD, LED)
Digital
Potentiometer
Typical sensor applications involve the monitoring of
sensor parameters and controlling of actuators. The
sensor signal chain, as shown below, consists of analog
and digital domains. Typical sensors output very low
amplitude analog signals. These weak analog signals
are amplified and filtered, and converted to digital values
using op amps, analog-to-digital or voltage-to-frequency
converters, and are processed at the MCU. The analog
sensor output typically needs proper signal conditioning
before it gets converted to a digital signal.
The MCU controls the actuators and maintains the
operation of the sensor signal conditioning circuits based
on the condition of the signal detection. In the digital
to analog feedback path, the digital-to-analog converter
(DAC), digital potentiometer and Pulse-Width-Modulator
(PWM) devices are most commonly used. The MOSFET
driver is commonly used for the interface between the
feedback circuit and actuators such as motors and valves.
Microchip offers a large portfolio of devices for signal
chain applications.
3
Signal Chain Design Guide
Many system applications require the measurement of a
physical or electrical condition, or the presence or absence
of a known physical, electrical or chemical quantity. Analog
sensors are typically used to indicate the magnitude or
change in the environmental condition, by reacting to the
condition and generating a change in an electrical property
as a result.
Typical phenomena that are measured are:
■Electrical signal and properties
■Magnetic signal and properties
■Temperature
■Humidity
■Force, weight, torque and pressure
■Motion and vibration
■Flow
■Fluid level and volume
■Light and infrared
■Chemistry/gas
Summary Of Common Physical Conditions and Related Sensor Types
Phenomena Sensor Electrical Output
Magnetic Hall Effect Voltage
Magneto-Resistive Resistance
Temperature
Thermocouple Voltage
RTD Resistance
Thermistor Resistance
IC Voltage
Infrared Current
Humidity Capacitive Capacitance
Infrared Current
Force, Weight, Torque, Pressure
Strain Gauge Resistance/Voltage
Load Cell Resistance
Piezoelectric Voltage or Charge
Mechanical Transducer Resistance, Voltage, Capacitance
Motion and Vibration
LVDT AC Voltage
Piezoelectric Voltage or Charge
Microphone Voltage
Ultrosonic Voltage, Resistive, Current
Accelerometer Voltage
Flow
Magnetic Flowmeter Voltage
Mass Flowmeter Resistance/Voltage
Ultrasound/Doppler Frequency
Hot-wire Anemometer Resistance
Mechanical Transducer (turbine) Voltage
Fluid Level and Volume
Ultrasound Time Delay
Mechanical Transducer Resistance/Voltage
Capacitor Capacitance
Switch On/Off
Thermal Voltage
Touch
Capacitance Voltage
Inductance Current
Resistance Frequency
Proximity
Capacitance Voltage, Frequency
Inductance Current, Frequency
Resistance Voltage, Current
Light Photodiode Current
Chemical
pH Electrode Voltage
Solution Conductivity Resistance/Current
CO Sensor Voltage or Charge
Photodiode (turbidity, colorimeter) Current
Ion Sensor Current
Sensor Overview
There are sensors that respond to these phenomena by
producing the following electrical properties:
■Voltage
■Current
■Resistance
■Capacitance
■Charge
This electrical property is then conditioned by an analog
circuit before being driven to a digital circuit. In this way,
the environmental condition can be “measured” and the
system can make decisions based on the result.
The table below provides an overview of typical
phenomena, the type of sensor commonly used to measure
the phenomena and electrical output of the sensor.
For additional information, please refer to
Application Note AN990.
4Signal Chain Design Guide
Operational AmpliïŹers (Op Amps)
Microchip Technology offers a broad portfolio of op amp
families built on advanced CMOS technology. These
families are offered in single, dual and quad configurations,
which are available in space saving packages.
These op amp families include devices with Quiescent
Current (I ) per amplifier between 0.45 ”A and 6 mA, q
with a Gain Bandwidth Product (GBWP) between 9 kHz
and 60MHz, respectively. The op amp with lowest supply
voltage (V ) operates between 1.4V and 6.0V, while the op dd
amp with highest V operates between 6.5V and 16.0V.dd
These op amp families fall into the following categories:
General Purpose, Precision (including EPROM Trimmed and
mCal Technology) and Zero-Drift.
Instrumentation AmpliïŹers (INA)
Microchip has expanded its portfolio of amplifiers with the
industry’s first instrumentation amplifier featuring mCal
technology. The features rail-to-rail input and MCP6N11
output, 1.8V operation and low offset/offset drift.
Comparators
Microchip offers a broad portfolio of low-power and
high-speed comparators. The and MCP6541 MCP6561
family of comparators provide ultra low power, 600 nA
typical, and higher speed with 40 ns propagation delay,
respectively. Both families of comparators are available
with single, dual and quad, as well as with push-pull and
open-drain output options (for and ).MCP6546 MCP6566
The and family of push-pull and MCP65R41 MCP65R46
open-drain output comparators are offered with integrated
reference voltages of 1.21V and 2.4V receptively. This
family provides ±1% typical tolerance while consuming
2.5 ÎŒA and high speed with 4ÎŒs propagation delay. These
comparators operate with a single-supply voltage as low
as 1.8V to 5.5V, which makes them ideal for low cost
and/or battery powered applications.
Product Overviews
Programmable Gain AmpliïŹer (PGA)
The and PGA families MCP6S21/2/6/8 MCP6S91/2/3
give the designer digital control over an amplifier using
a serial interface (SPI bus). An input analog multiplexer
with 1, 2, 6 or 8 inputs can be set to the desired input
signal. The gain can be set to one of eight non-inverting
gains: + 1, 2, 4, 5, 8, 10, 16 and 32 V/V. In addition, a
software shutdown mode offers significant power savings
for portable embedded designs. This is all achieved in
one simple integrated part that allows for considerably
greater bandwidth, while maintaining a low supply current.
Systems with multiple sensors are significantly simplified.
The MCP6G01 family are analog Selectable Gain Amplifiers
(SGA). The Gain Select input pin(s) set a gain of + 1V/V,
+10 V/V and + 50 V/V. The Chip Select pin on the
MCP6G03 puts it into shutdown to conserve power.
Analog-to-Digital Converters (ADC)
Microchip offers a broad portfolio of high-precision
Delta-Sigma, SAR and Dual Slope A/D Converters. The
MCP3550/1/3 Delta-Sigma ADCs offer up to 22-bit
resolution with only 120 ÎŒA typical current consumption
in a small 8-pin MSOP package. The is a single MCP3421
channel 18-bit Delta-Sigma ADC and is available in a small
6-pin SOT-23 package. It includes a voltage reference
and PGA. The user can select the conversion resolution
up to 18 bits. The and the are MCP3422/3 MCP3424
two channel and four channel versions, respectively, of
the device. The (10-bit), MCP3421 MCP300X MCP320X
(12-bit) and (13-bit) SAR ADCs combine high MCP330X
performance and low power consumption in a small
package, making them ideal for embedded control
applications. The analog front end offer two MCP3911
simultaneously sampled 24-bit Delta-Sigma ADCs making
it ideal for voltage and current measurement, and other
data acquisition applications.
The “Analog-to-Digital Converter Design Guide” (Microchip
Document No. 21841) shows various application
examples of the ADC devices.
Microchip also offers many high accuracy energy metering
devices which are based on the Delta-Sigma ADC cores.
The “Complete Utility Metering Solution Guide” (Microchip
Document No: 24930) offers detailed solutions for
metering applications.
5
Signal Chain Design Guide
Voltage References
Microchip offers the family of low power and low MCP15XX
dropout precision Voltage References. The family includes
the with an output voltage of 2.5V and the MCP1525
MCP1541 with an output voltage of 4.096V. Microchip’s
voltage references are offered in SOT23-3 and TO-92
packages.
Temperature Sensors
Microchip offers a broad portfolio of thermal management
products, including Logic Output, Voltage Output and
Serial Output temperature sensors. These products allow
the system designer to implement the device that best
meets the application requirements. Key features include
high accuracy (such as , with ±0.5°C maximum MCP9808
accuracy from −20°C to 100°C), low power, extended
temperature range and small packages. In addition, other
Microchip products can be used to support Thermocouple,
RTD and Thermistor applications.
Digital Potentiometers
Microchip’s family of digital potentiometers offer a wide
range of options. These devices support the 6-bit through
8-bit applications. Offering both volatile and non-volatile
options, with digital interfaces from the simple Up/Down
interface to the standard SPI and I2Cℱ interfaces. These
devices are offered in small packages such as 6-lead
SC70 and 8-lead DFN for the single potentiometer devices,
14-lead TSSOP and 16-lead QFN packages for the dual
potentiometer devices, and 20-lead TSSOP and QFN
packages for the quad potentiometer devices. Non-volatile
devices offer a Wiperlockℱ Technology feature, while
volatile devices will operate down to 1.8V. Resistances
are offered from 2.1kΩ to 100 kΩ. Over 50 device
configurations are currently available.
The “Digital Potentiometer Design Guide” (Microchip
Document No. 22017), shows various application
examples of the digital potentiometer devices.
Product Overviews
Digital-to-Analog Converters (DAC)
Microchip’s family of Digital-to-Analog Converters (DACs)
offer a wide range of options. These devices support the
6-bit through 12-bit applications. Offering both volatile
and non-volatile options, and standard SPI and I2C digital
interfaces. These devices are offered in small packages
such as 6-lead SC70, SOT-23 and DFN (2 × 2) for the
single output devices and 10-pin MSOP for quad output
devices. Some versions support selecting either the
device V , the external voltage reference or an internally dd
generated voltage reference source from the DAC circuitry.
Devices with nonvolatile memory (EEPROM) allow the
device to retain the programmed output code and DAC
state through power down events.
These DAC devices provide high accuracy and low noise
and are ideal for industrial applications where calibration
or compensation of signals (such as temperature,
pressure or humidity) is required.
6Signal Chain Design Guide
Local Sensing
Local sensors are located relatively close to their signal
conditioning circuits, and the noise environment is not
severe; most of these sensors are single ended (not
differential). Non-inverting amplifiers are a good choice for
amplifying most of these sensors’ output because they
have high input impedance, and require a minimal amount
of discrete components.
Key AmpliïŹer Features
■Low cost
‱   
General purpose op amps
■High precision
‱    Low offset op amps
‱    Zero-drift op amps
‱    Low noise op amps
■Rail-to-rail input/output
‱    Most op amp families
■High input impedance
‱    Op amps with CMOS inputs
■Low power and portable applications
‱    Low power op amps
■High voltage
‱    High voltage op amps
■High bandwidth and slew rate
‱    High speed op amps
■Load drive
‱    High output drive op amps
Classic Gain AmpliïŹer
High Side Current Sensing AmpliïŹer
+
pH Monitor
VOUT
MCP6XX,
MCP6XXX
-
–
+
R
SEN ISEN
R
1
R
2
VOUT
VREF
R1R2
V1
V2
–
+
MCP6HXX
VDD
RSEN << R1, R2
V = (VOUT 1 – V2) + VREF
R2
R1
( )
Local Sensors
Sensors and Applications
Single Sensors
■
Thermistors for battery chargers and power supply
temperature protection
■Humidity Sensors for process control
■Pyroelectric infrared intrusion alarms, motion detection
and garage door openers
■Smoke and ïŹre sensors for home and ofïŹce
■Charge ampliïŹer for Piezoelectric Transducer detection
■Thermistor for battery chargers and home thermostats
■LVDT position and rotation sensors for industrial control
■Hall effect sensors for engine speed sensing and
door openers
■Photoelectric infrared detector
■Photoelectric motion detectors, ïŹ‚ame detectors,
intrusion alarms
■Sensing resistor for current detection
Multiple Local Sensors
■Temperature measurement at multiple points on a Printed
Circuit Board (PCB)
■Sensors that require temperature correction
■Weather measurements (temperature, pressure,
humidity, light)
Capacitive Humidity Sensor Circuit
(PIC16F690DM-PCTLHS)
PIC16F690
MCP6291
VDD_DIG
C1
U1
P4
100 nF
VCM
VDD
VSEN
VINT
RINT
6.65 M℩
CSEN
IINT
RCM
1
20 k℩
RCM
2
20 k℩
CCM
100 nF
100 nF
CCG
C
2
P3
P1
P2
U
2
–
+
Comparator
VREF
SR
Latch
Timer1
7
Signal Chain Design Guide
Remote Sensing
All sensors in a high noise environment should be
considered as remote sensors. Also, sensors not located
on the same PCB as the signal conditioning circuitry are
remote. Remote sensing applications typically use a
differential amplifier or an instrumentation amplifier.
Key AmpliïŹer Features
■Differential input
■Large CMR
■Small Vos
Products
■High Precision
‱    Low Offset Op Amps
‱    Auto-zeroed Op Amps
‱    Low Noise Op Amps
Sensors and Applications
■High temperature sensors
‱    Thermocouples for stoves, engines and process
control
‱    RTDs for ovens and process control
■Wheatstone Bridges
‱    Pressure sensors for automotive and industrial
control
‱    Strain gauges for engines
■Low side current monitors for motors and batteries
Differential AmpliïŹer
Thermocouple Circuit Using an INA
VOUT
EMI
EMI
VREF
MCP6VXX
MCP616
–
+
TCJ
(Cold Junction)
Input
Filter
Temp. Sensor
THJ
(Hot Junction
)
INA
–
+
–
+
ADC
MCU
VREF
2
2
Remote Sensors
8Signal Chain Design Guide
Weight and pressure measurement have been among
the most popular applications for medical, industrial,
automotive and consumer industries. In recent years,
the MEMS pressure/accelerometer devices have
become widely used in many applications and support
our modern life style. The majority of weight scale and
pressure measurement circuits use bridge type ratiometric
configuration. In this case, the output voltage range
from the sensor circuit is proportional to the excitation
voltage. The following circuit shows an example weight
measurement application. In the figure, the output from
the load cell is amplified by the low noise op amplifier and
fed to the 18-bit delta sigma ADC.MCP3421
Example of Weight Measurement Circuit
ConïŹguration (MCP3421DM-WS)
MCP3421
PIC Âź
MCU
–
+
–
+
ADC
œ MCP6V02
œ MCP6V02
V
E
xcitation
Load Cell
Sensor Signal Conditioning
Weight and Pressure Sensing Applications
The following circuit shows an example of pressure
measurement using the 22-bit Delta-Sigma MCP3551
ADC. In this example, the is directly connected MCP3551
to the sensor output without using the sensor NPP-301
signal conditioning circuit. Since the uses an MCP3551
external reference input, the same supply voltage is used
for the ADC reference and V , and the sensor excitation. dd
Therefore, the variation in the sensor excitation source is
naturally cancelled out.
Example of Pressure Measurement Circuit
ConïŹguration using the MCP3551 Device
R
2
SPI
V
REF
SCK
SDO
CS
MCP3551
5, 6, 7
1
2
3
4
8
V
SS
V
IN+
V
IN-
To V
DD
V
DD
0.1 ”F 1.0 ”F
NPP-301
R
1
R
4
R
3
MCU
∆V ~ [(∆R
2
+ ∆R
4
) - (∆R
1
+∆R
3
)]/4R * V
DD
With R
1
= R
2
= R
3
= R
4
= R
0.00
PSI
9
Signal Chain Design Guide
DC Voltage and Current Measurement
DC voltage and current measurement can be easily done
by using low speed high resolution Delta Sigma ADC such
as and family devices. The MCP3421 MCP3422 MCP3421
is a single channel device while the is a dual MCP3422
channel device, which can measure the voltage and
current using the same device.
The following circuits show simple example of Battery
voltage and current measurement using the . MCP3421
The uses internal reference voltage of 2.048V. MCP3421
If the input voltage is greater than the reference, it needs
a voltage divider to bring down the input full scale range
below the reference voltage. This example is shown in
example circuit (a). In the current measurement, the ADC
is simply connected across a simple shunt current sensor
as shown in the figure. The current is calculated using the
measured voltage value and a known shunt’s resistance
value. The has a differential input and the MSb MCP3421
in the output bit represents the direction of the current.
Voltage Measurement Using MCP3421 Device
Current Measurement Using MCP3421 Device
(a) If V
REF
< V
BAT
ADC
V
BAT
–
+
R
2
R
1
(b) If V
REF
> V
BAT
R2
V
IN
= ( ________ ) ● (V
BAT)
R1 R2+
R2
VMeasured = ADC Output Codes ● LSB ● _________ ● _____
( + )R1 R2
PGA
1
2
N
–1
LSB = ________________
Reference ltageVo
2.048V
2
17
2
N
–1
LSB of 18-bit ADC = ________________ = ______ = 15.625 ”V
Reference ltageVo
ADC
V
BAT
–
+
MCP3421
MCP3421
MCU MCU
V
IN
Current = (Measured Voltage)/(Kn n Resistance Value of Current Sensorow )
Direction of current is determined by sign bit (Msb bit) of the ADC output code.
ADC
Battery
Charging
Current
Discharging
Current
Current Sensor
To Load
–
+
MCP3421
MCU
Voltage and Current Measurement
Battery Fuel Management by Measuring
Battery Voltage and Current
By measuring the battery voltage and current, an intelligent
battery fuel management algorithm can be developed.
The figure below shows an example of battery fuel
management circuit. The measures both voltage MCP3422
and current draws of the battery, and the system tracks
how much the battery fuel has been used and remained.
The MCU controls the for the recharging of the MCP73831
single cell Li-Ion battery
Example Circuit for Battery Fuel Management by
measuring Battery Voltage and Current
Battery
MCU
MCP73831
MCP3422
CH B
R2
CH A
Charging Current
Decharging
Current
Battery Fuel Measurement
Battery Fuel Charger
VBAT
S2
S1
R1
STAT PROG
R3
Load
10 Signal Chain Design Guide
Voltage and Current Measurement
Example of Three-Phase Current and Voltage Measurement Using the MCP3911 Energy Metering Delta-Sigma ADC
Current Measurement Using Rogowski Coil
PIC24FJ256GA110
Family
Flash
128–256 kB
ADC
10-bit
16 ch
RAM
16 kB
UART
UART
UART
UART
RTCC
32 KHz
RS485
PLC
IrDA
Âź
RS485
I
2
Cℱ
SPI Smart Card
Reader
Prepayment
Card
EEPROM
GPIO
SPI
LCD Driver LCD Panel
NTC Thermistor
Battery
MCP3911
Current
Sampling
Voltage
Sampling
×3
Low Voltage
Detect
Power Supply
Load
~ AC
Shunt
R2
I( )t
1
R1
C1
ADC
VDD
VOUT
2
VIN
B-Field
AC Voltage and Current Measurement
AC voltage and current measurement can be done
by using energy metering Delta Sigma ADC such as
MCP39XX devices. The Three-Phase Current and Voltage
Measurement figure below shows an example of
measuring three-phase current using the . The MCP3911
measured data is processed by the PIC24F.
Shunt resistors are a common and low cost method for
current sensing. Isolated methods include the use of Current
transformers and Rogowski coils. The Current Measurement
using Rogowski Coil figure shows an example of the current
measurement using the Rogowski coil. The Rogowski coil
picks-up the electro-magnetic field (EMF) produced by the
current at the center. This EMF is measured as voltage. The
voltage is integrated so that the output is a voltage that
represents the current waveform.
11
Signal Chain Design Guide
Temperature Sensing Solutions
Thermistor Solution
Thermistors are non-linear and require a look up table for
compensation. The solution is to use Microchip’s Linear
Active Thermistors, the and the . MCP9700 MCP9701
These are low-cost voltage output temperature sensors
that replace almost any Thermistor application solutions.
Unlike resistive type sensors such as Thermistors, the
signal conditioning at the non-linear region and noise
immunity circuit development overhead can be avoided by
using the low-cost Linear Active Thermistors. The voltage
output pin (Vout) can be directly connected to the ADC
input of a microcontroller. The and MCP9700/9700A
MCP9701/9701A temperature coefficients are scaled
to provide a 1°C/bit resolution for an 8-bit ADC with a
reference voltage of 2.5V and 5V, respectively.The MCP9700
and MCP9701 sensors output can be compensated for
improved sensor accuracy as shown below, refer to the
AN1001 application note.
MCP9700 and MCP9701 Key Features
■SC70, TO92 packages
■Operating temperature range: −40°C to +150°C
■Temperature CoefïŹ cient: 10 mV/°C (MCP9700)
■Temperature CoefïŹ cient: 19.5 mV/°C (MCP9701)
■Low power: 6 ÎŒA (typ.)
Applications
■Refrigeration equipment
■Power supply over temperature protection
■General purpose temperature monitoring
Typical Sensor Accuracy Before and After
Compensation
Resistive Temperature Detector (RTD)
Solutions
RTD Solution with Precision Delta-Sigma ADC
Resistive Temperature Detectors (RTDs) are highly accurate
and repeatable temperature sensing elements. When
using these sensors a robust instrumentation circuit is
required and it is typically used in high performance thermal
management applications such as medical instrumentation.
Microchip’s RTD solution uses a high performance Delta-
Sigma Analog to Digital converter, two external resistors, and a
reference voltage to measure RTD resistance or temperature
ratiometrically. A ±0.1°C accuracy and ±0.01°C measurement
resolution can be achieved across the RTD temperature range
of −200°C to +800°C with a single point calibration.
This solution uses a common reference voltage to bias
the RTD and the ADC which provides a ratio-metric relation
between the ADC resolution and the RTD temperature
resolution. Only one biasing resistor, R
A, is needed to set the
measurement resolution ratio (shown in equation below).
RTD Resistance
For instance, a 2V ADC reference voltage (Vref) results in
a 1ΌV/LSb (Least Significant Bit) resolution. Setting R
A=
RB=6.8 kΩ provides 111.6 ÎŒV/°C temperature coefficient
(PT100 RTD with 0.385Ω/°C temperature coefficient). This
provides 0.008°C/LSb temperature measurement resolution
for the entire range of 20Ω to 320Ω or −200°C to +800°C.
A single point calibration with a 0.1% 100Ω resistor provides
±0.1°C accuracy as shown in the figure below.
This approach provides a plug-and-play solution with
minimum adjustment. However, the system accuracy
depends on several factors such as the RTD type, biasing
circuit tolerance and stability, error due to power dissipation
or self-heat, and RTD non-linear characteristics.
This solution can be evaluated using Microchip’s RTD
Reference Design Board (TMPSNSRD-RTD2).
Code
RRTD = RA
(
2n 1 − − Code
)
Where:
Code = ADC output code
RA = Biasing resistor
n = ADC number of bits
(22 bits with sign, MCP3551)
RTD Instrumentation Circuit Block Diagram and Output Performance (see Application Note AN1154)
Measured Accuracy (°C)
-200 0
Temperature (°C)
600400200
0.1
0.05
0
-0.05
-0.1
800
V
REF
V
DD
1 ”F
MCP3551
–
+
RTD
R
B
5%
R
A
1%
V
DD
V
REF
SPI
LDO
V
LDO
C* C*
3
*See LDO Data Sheet at: www.microchip.com/LDO
PICÂź
MCU
12 Signal Chain Design Guide
Temperature Sensing Solutions
Resistive Temperature Detector (RTD)
Solutions
RTD Solution with RC Oscillators
RC oscillators offer several advantages in precision
sensing applications. They do not require an Analog-to-
Digital Converter (ADC), and oscillator can be directly
connected to an Input/Output pin of a microcontroller
to measure change in frequency proportional to sensor
output. The accuracy of the frequency measurement is
directly related to the quality of the microcontroller’s clock
signal, and high-frequency oscillators for the controller are
available with accuracies of better than 10 ppm.
The oscillator circuits shown in the Oscillator Circuits
For Sensors section can be used for this method. The
variable resistor of the circuits (Figure: Oscillator Circuits
for Resistive Sensors) are replaced with the RTD sensor.
There is an example of a state variable RC oscillator, which
provides an output frequency that is proportional to the
square root of the product of the two RTD resistances
( 1/(R1 × R2)α1/2). A second example shows the
relaxation oscillator (or astable multi-vibrator), which
provides a square wave output with a single comparator.
The state variable RC oscillator is good for precision
applications, while the relaxation oscillator is an
alternative for cost-sensitive applications.
RTD Solution with Instrumentation AmpliïŹer
This Wheatstone bridge reference design board
demonstrates the performance of Microchip’s MCP6N11
instrumentation amplifier (INA) and a traditional three op amp
INA using Microchip’s and auto-zeroed MCP6V26 MCP6V27
op amps. The input signal comes from an RTD temperature
sensor in a Wheatstone bridge. Real world interference is
added to the bridge’s output, to provide realistic performance
comparisons. Data is gathered and displayed on a PC, for
ease of use. The USB PICÂź microcontroller and included
Graphical User Interface (GUI) provides the means to
configure the board and collect sample data.
MCP6N11 and MCP6V2X Wheatstone Bridge
Reference Design (ARD00354)
–
+
RTD
Using USB
PWM
Coupling
PC
(Thermal Management Software)
VREF
12-bit ADC Module
PIC18F2550 (USB) Microcontroller
PWM
Input
Filter
VDD
Output
Filter
INA
Thermocouple Sensor Solutions
Thermocouple Solution with Precision
Delta-Sigma ADC
Delta-Sigma ADCs can be used to directly measure
thermocouple voltage. Microchip’s ADC can MCP3421
be used to accurately measure temperature using a
Thermocouple. The device provides a plug and play solution
for various types of thermocouples, greatly simplifying the
circuit design. In this case, the Thermocouple linearization
routine is implemented in firmware or software. Cold
Junction Compensation is implemented using Microchip’s
stand alone digital temperature sensors, such as the
±0.5C accurate MCP9808.
This solution can be evaluated using Microchip’s
Thermocouple Reference Design Board (TMPSNSRD-TCPL1).
Thermocouple Solution with Auto-Zero’ed Op Amp
Microchip’s auto-zeroed op amp can be used to accurately
measure thermocouple voltage. The MCP6V01 op amp
ultra low offset voltage and high common mode rejection
makes it ideal for low cost thermocouple applications.
The Thermocouple Auto-Zeroed Reference MCP6V01
design demonstrates how to accurately measure
temperature (MCP6V01RD-TCPL).
Wireless Temperature Monitoring Solution
MCP9804
Temp. Sensor
PIC18F2550
USB PICÂź
Microcontroller 2
2
MCP3421
18-bit ADC
Thermocouple
Thermal Pad
MCP3421
–
+
(Thermocouple)
Heat
PICÂź MCU
18-bit ∆
∑
ADC
MRF24J40
MCP9804
Temp Sensor
±1°C
13
Signal Chain Design Guide
Temperature Measurements Using 4 Channel ADC (MCP3424)
See Thermocouple Reference Design (TMPSNSRD-TCPL1)
12
14
13
11
10
9
8
MCP3424
Delta-Sigma ADC
V
DD
SCL
SDA
Isothermal Block
(Cold Junction)
Thermocouple Sensor
Heat
SCL
0.1 ”F
10 ”F
SCL
SDA
V
DD
5 k℩
To MCU
SDA
SCL
SDA
SCL
3
1
2
4
5
6
7
CH1+
CH1-
CH2+
CH2-
V
SS
V
DD
SDA
CH4-
CH4+
CH3-
CH3+
Adr1
Adr0
SCL
5 k℩
SDA
Isothermal Block
(Cold Junction)
MCP9804 MCP9804
MCP9804MCP9804
Temperature Sensing Solutions
14 Signal Chain Design Guide
The feedback capacitor (C ) is used for circuit stability. f
The device’s wiper resistance (R ) is ignored for first order w
calculations. This is due to it being in series with the op
amp input resistance and the op amp input impedance is
very large.
Circuit Gain Equation
Programmable Gain AmpliïŹer
The PGA Thermistor PICtail Demo Board MCP6SX2
features the and Programmable Gain MCP6S22 MCP6S92
Amplifiers (PGA). These devices overcome the non-linear
response of a NTC thermistor, multiplex between two
inputs and provide gain. It demonstrates the possibility of
measuring multiple sensors and reducing the number of
PIC microcontroller I/O pins used. Two on-board variable
resistors allow users to experiment with different designs
on the bench.
A complete solution is achieved by interfacing this board
to the PICkitℱ 1 Flash Starter Kit (see DS40051) and the
Signal Analysis PICtail Daughter Board (see DS51476).
MCP6SX2 PGA Thermistor PICtailℱ Demo Board
(MCP6SX2DM-PICTLTH)
V
out
= − R
bw
× V
in
R
aw
r
bw
= r
ab
× Wiper Code
# of Resistors
R
aw
= # of Resistors − Wiper Code × R
ab
# of Resistors
PICkitℱ 1 Serial Analysis
PC Program
PICkit 1
Flash Starter Kit
PC
USB
Hardware Software
PICkit 1
Firmware
PICA2Dlab.hex
Firmware
14
14
Signal Analysis
PICtail Daughter Board
MCP6SX2 PG ThermistorA
PICtail Demo Board
PGA
MCP6S22
Thermistor
Te
mperature
MCP6SX2 PGA Thermistor
PICtailℱ Demo Board
+5
Test Point
GND
Test Point
CH0 Input
Test Point
CH1 Input
Test Point
Thermistor
Voltage
Divider
Signal Analysis
PICtail Daughter Board
PICkitℱ 1
Flash Starter Kit
Serial
EEPROM
PIC16F684
ADC
PIC16F745
GND
+5
4
SPI Bus
V
OUT
4
SPIℱ Bus
GND
+5
to PC
USB
Programmable Gain
Programmable AmpliïŹer Gain Using a
Digital Potentiometer
Many sensors require their signal to be amplified before
being converted to a digital representation. This signal
gain may be done with and operational amplifier. Since
all sensors will have some variation in their operational
characteristics, it may be desirable to calibrate the gain
of the operational amplifier to ensure an optimal output
voltage range.
The figure below shows two inverting amplifier with
programmable gain circuits. The generic circuit (a) where
R
1, R2, and Pot1 can be used to tune the gain of the
inverting amplifier, and the simplified circuit (b) which
removes resistors R1 and R2 and just uses the digital
potentiometers Raw and Rbw ratio to control the gain.
The simplified circuit reduces the cost and board area
but there are trade-offs (for the same resistance and
resolution), Using the R1 and R2 resistors allows the
range of the gain to be limited and therefore each digital
potentiometer step is a fine adjust within that range.
While in the simplified circuit, the range is not limited and
therefore each digital potentiometer step causes a larger
variation in the gain.
The following equation shows how to calculate the gain
for the simplified circuit (figure below). The gain is the
ratio of the digital potentiometers wiper position on the
Rab resistor ladder. As the wiper moves away from the
midscale value, the gain will either become greater then
one (as wiper moves towards Terminal A), or less then one
(as wiper moves towards Terminal B).
Inverting AmpliïŹer with Programmable Gain Circuits
Generic Circuit (a)
Pot1
V
OUT
VIN
R2R1
W
A B
Simplified Circuit (b)
Pot1
VOUT
Input
CF
W
A B
Note 1: A general purpose op amp, such as the MCP6001.
Op Amp
(1)
+
–
CF
Op Amp
(1)
+
–
15
Signal Chain Design Guide
Sensor Calibration/Compensation
Sensor Characteristics
Sensor characteristics vary, both for device to device as
well as for a given device over the operating conditions. To
optimize system operation, this sensor variation may
require some compensation. This compensation may
simply address device to device variation, or be more
dynamic to also address the variations of the device over
the operating conditions. The system voltage and
temperature may effect the sensor output characteristics
such as output voltage offset and linearity. This
conditioning circuit can also be used to optimize the range
of the sensors conditioned signal into the Analog-to-Digital
conversion circuit.
Depending on the sensor, the sensor’s output may either
be voltage or a current. A possible compensation circuit
for each output type will be discussed.
In this first case, the sensor generates an output voltage.
Temperature sensors are typical sensors that generate a
voltage output which varies unit to unit.
Voltage Control
A simple voltage control circuit (see figure below) can
ensure that the sensors output voltage is optimized to
the input range of the next stage in the signal chain. This
circuit is a gain amplifier, where the R
1 and R2 resistances
determine the amplifier’s gain. The amplifier’s output
voltage range is limited by the V and V voltages. dd ss
Controlling the V voltage can optimize the V voltage os out
profile, based on the sensor’s output voltage (V ).sen
Inverting AmpliïŹer (Voltage Gain)
Either a DAC or a Digital Potentiometer can be used to
control the voltage at V . This device can be a non-os
volatile version so that at system power up the V os
voltage is at the calibrated voltage, programmed during
manufacturing test, to address the sensor’s device to
device variation. If dynamic control is desired, the DAC or
Digital Potentiometer can be interfaced to a microcontroller
so that dynamic changes to the V voltage compensate os
for the system conditions and non-linearity of the sensor.
Analog-to-Digital
Conversion
Conditioning
Circuit
(Optimizes Sensor ’s
Output)
Sensor
V
OUT
R2
R1
VOS
V
SEN INV
VDD
Op Amp
+
–
VDD
Typically during the manufacturing stage the test system
will write this compensation data into some non-volatile
memory in the system which the microcontroller will use
during normal operation to adjust the V voltage. os
In this second case, the sensor generates an output
current. Photodiodes are a typical sensors that generate a
current output, and can vary ±30% at +25°C (unit-to-unit).
Current to Voltage
A simple current to voltage converter circuit (see Figure
below), is used to create a voltage on the output of the op
amp (V1), which can then be compensated. In this circuit,
the photodiodes I current times the R resistance equals pd f
the voltage at the op amps output (V
1
). The R resistance f
needs to be selected so that at the minimum I pd max( )
current, the V voltage is at the maximum input voltage out
for the next stage of the signal chain. Typically this will
be done when the DAC or Digital Potentiometer is at Full
Scale (so V ≈ Vout 1). For photodiodes where the I pd max( )
current exceeds the minimum I current (increasing pd max( )
the V1 voltage), the DAC or Digital Potentiometer Wiper
code be programmed to attenuate the that V1 voltage to
the desired V max voltage. This then compensates for out
the variation of the photodiode‘s I current.pd
Photodiode Calibration (Trans-Impedance AmpliïŹer)
This device can be a non-volatile version so that at
system power up the voltage attenuation is at the level,
programmed during manufacturing test, to address the
sensor’s device to device variation. If dynamic control
is desired, the DAC or Digital Potentiometer can be
interfaced to a microcontroller so that dynamic changes
to the voltage attenuation compensate for the system
conditions and non-linearity of the sensor. Typically during
the manufacturing stage the test system will write this
compensation data into some non-volatile memory in the
system which the microcontroller will use during normal
operation to adjust the voltage attenuation.
C may be used to stabilize the op amp. Additional f
information on Amplifying High-Impedance Sensors is
available in Application Note AN951.
RF
VPD
Op Amp
+
–
C
F
RAB
V1
A
BCN
V
OUT
IPD
C(1)
16 Signal Chain Design Guide
Setting the DC Set Point for Sensor Circuit
A common DAC application is digitally controlling the set
point and/or calibration of parameters in a signal chain.
The figure below shows controlling the DC set point of a
light detector sensor using the 12-bit quad DAC MCP4728
device. The DAC provides 4096 output steps. If G = 1 and
internal reference voltage options are selected, then the
internal 2.048 V would produce 500 ”V of resolution. ref
If G = 2 is selected, the internal 2.048 Vref would
produce 1 mV of resolution. If a smaller output step size
is desired, the output range would need to be reduced.
So, using gain of 1 is a better choice than using gain of 2
configuration option for smaller step size, but its full-scale
range is one half of that of the gain of 2. Using a voltage
divider at the DAC output is another method for obtaining
a smaller step size.
Sensor Calibration/Compensation
Setting the DC Set Point
LDAC
8
10
9
7
6
VDD
3
1
2
4
5
V
SS
V
OUT
A
V
OUT
D
V
OUT
C
V
OUT
B
V
DD
SCL
SDA
RDY/BSY
R
6
R
3
R
5
R
4
0.1 ”F
Analog Outputs
10 ”F
To MCU
R
1
R
2
Comparator 1
Light
VDD
VTRIP1
0.1 ”F
R
1
R
2
Comparator 2
Light
VDD
VTRIP2
0.1 ”F
R
1
R
2
Comparator 3
Light
VDD
VTRIP3
0.1 ”F
R
1
R
2
Comparator 4
Light
VDD
VTRIP4
0.1 ”F
ïŁ±
ïŁČ
ïŁł
V
OUT
= V
REF
x Dn G
X
V
TRIP
= V
OUT
x
R
1
+ R
2
Where Dn Input Code (0 to 4095) =
G
X
= Gain Selection (x1 or x2)
4096
R2
Quad DAC
RSENSE
MCP6544(1/4)
RSENSE
MCP6544(2/4)
RSENSE
MCP6544(3/4)
RSENSE
MCP6544(4/4)
–
+
MCP4728
–
+
–
+
–
+
17
Signal Chain Design Guide
Oscillator Circuits for Sensors
RC oscillators can accurately and quickly measure resistive
and capacitive sensors. The oscillator period (or frequency)
is measured against a reference clock signal, so no
analog-to-digital convertor is needed.
State-Variable Oscillators
State-variable oscillators have reliable start-up, low
sensitivity to stray capacitances and multiple output
configurations (sine wave or square wave). They can use
one or two resistive sensors, and they can use one or two
capacitive sensors.
Some of their advantages and features are:
■Precision
■Reliable oscillation startup
■Sine or square wave output
■Frequency /(R∝ 1 1R2C1C2)1/2
Relaxation Oscillators
Relaxation oscillators have reliable start-up, low cost and
square wave output. They can use a resistive sensor or a
capacitive sensor.
Oscillator Circuits For Sensors
Oscillator Circuits for Resistive Sensors
Oscillator Circuits for Capacitive Sensors
VOUT
C2C1
VREF
–
+
–
+
–
+
–
+
C
4
R4
R1R2
VREF VREF
R R R3 7 8
VREF
Notes: In AN895, R = RTD and R = RTD A resistive divider to V1 A 2 A. DD
sets V
REF
(V
DD
/2 is recommended).
MCP6XX4 MCP6XX4 MCP6XX4 MCP65X1
U1a U1b U1c U2
State Variable Oscillator:
–
+
. . . VREF
MCP6XX4
U1d
C1
VDD
–
+
R2
R3
MCP65X1
Relaxation Oscillator:
U1
R1
R4
VOUT
Note: In AN895, R = RTD1 .
VOUT
C2C1
VREF
–
+
–
+
–
+
–
+
C
4
R4
R1R2
V
REF VREF
R R R3 7 8
VREF
Notes: A resistive divider to V sets V (V /2 is recommended).DD REF DD
MCP6XX4 MCP6XX4 MCP6XX4 MCP65X1
U1a U1b U1c U2
State Variable Oscillator:
–
+
. . . VREF
MCP6XX4
U1d
C1
VDD
–
+
R2
R3
MCP65X1
Relaxation Oscillator:
U1
R1
R4
VOUT
Some of their advantages and features are:
■Low cost
■Reliable oscillation startup
■Square wave output
■Frequency /(R∝ 1 1C1)
Sensors and Applications
These oscillator circuits are applicable to various type of
sensors.
Resistive Sensors
■RTDs
■Thermistors
■Humidity
Capacitive Sensors
■Humidity
■Pressure (e.g., absolute quartz)
■Fluid Level
Related Application Notes:
AN895: Oscillator Circuits for RTD Temperature Sensors
AN866: Designing Operational Amplifier Oscillator Circuits
for Sensor Applications
Available on the Microchip web site at: www.microchip.com.
18 Signal Chain Design Guide
FilterLabÂź Software
Microchip’s FilterLab software is an innovative software
tool that simplifies analog active filter (using op amps)
design. Available at no cost from the Microchip website
at www.microchip.com/filterlab, the FilterLab design tool
provides full schematic diagrams of the filter circuit with
component values. It also outputs the filter circuit in
SPICE format, which can be used with the macro model to
simulate actual filter performance.
SPICE Macro Models
The SPICE macro models for linear ICs (op amps and
comparators) are available on the Microchip website
at www.microchip.com/spicemodels. The models were
written and tested in PSPICE owned by Orcad (Cadence).
For other simulators, they may require translation. The
models cover a wide aspect of the linear ICs’ electrical
specifications. Not only do the models cover voltage,
current and resistance of the linear ICs, but they also
cover the temperature and noise effects on the behavior of
the linear ICs. The models have not been verified outside
the specification range listed in the linear ICs’ datasheet.
The models’ behavior under these conditions cannot be
guaranteed to match the actual linear ICs’ performance.
Moreover, the models are intended to be an initial design
tool. Bench testing is a very important part of any design
and cannot be replaced with simulations. Also, simulation
results using these macro models need to be validated
by comparing them to the datasheet specifications and
characteristcs curves.
Filter Lab Window
SPICE Macro Model Example
Development Software
19
Signal Chain Design Guide
Development Tools
These following development boards support the
development of signal chain applications. These product
families may have other demonstration and evaluation
boards that may also be useful. For more information visit
www.microchip.com/analogtools.
Reference Designs
Battery
MCP3421 Battery Fuel Gauge Demo
(MCP3421DM-BFG)
he MCP3421 Battery Fuel Gauge
emo Board demonstrates how
o measure the battery voltage
nd discharging current using the
MCP3421. The MCU algorithm
calculates the battery fuel being used. This demo board
is shipped with 1.5V AAA non-rechargeable battery. The
board can also charge a single-cell 4.2V Li-Ion battery.
Pressure
MCP3551 Tiny Application (Pressure) Sensor Demo
(MCP355XDM-TAS)
his 1" × 1" board is designed to
emonstrate the performance of the
MCP3550/1/3 devices in a simple
ow-cost application. The circuit uses a
atiometric sensor configuration and uses
he system power supply as the voltage
reference. The extreme common mode rejection capability
of the MCP355X devices, along with their excellent normal
mode power supply rejection at 50 and 60 Hz, allows for
excellent system performance.
MCP3551 Sensor Application Developer’s Board
(MCP355XDV-MS1)
he MCP355X Sensor Developer’s Board
llows for easy system design of high
esolution systems such as weigh scale,
emperature sensing, or other small
ignal systems requiring precise signal
conditioning circuits. The reference design includes LCD
display firmware that performs all the necessary functions
including ADC sampling, USB communication for PC data
analysis, LCD display output, zero cancellation, full scale
calibration, and units display in gram (g), kilogram (kg) or
ADC output units.
Photodiode
MCP6031 Photodiode PICtail Plus Demo Board
(MCP6031DM-PTPLS)
he MCP6031 Photodiode PICtail Plus
emo Board demonstrates how to use a
ans impedance amplifier, which consists
f MCP6031 high precision op amp and
xternal resistors, to convert photo-current
o voltage.
Temperature Sensors
Thermocouple Reference Design (TMPSNSRD-TCPL1)
he Thermocouple Reference
esign demonstrates how to
nstrument a Thermocouple and
ccurately sense temperature over
the entire Thermocouple measurement range. This solution
uses the MCP3421 18-bit Analog-to-Digital Converter (ADC)
to measure voltage across the Thermocouple.
MCP6V01 Thermocouple Auto-Zero Reference
Design (MCP6V01RD-TCPL)
he MCP6V01 Thermocouple Auto-
eroed Reference Design demonstrates
ow to use a difference amplifier system
o measure electromotive force (EMF)
voltage at the cold junction of thermocouple in order to
accurately measure temperature at the hot junction. This
can be done by using the MCP6V01 auto-zeroed op amp
because of its ultra low offset voltage (V ) and high os
common mode rejection ratio (CMRR).
RTD Reference Design Board (TMPSNSRD-RTD2)
he RTD Reference Design demonstrates
ow to implement Resistive Temperature
etector (RTD) and accurately measure
emperature. This solution uses the
MCP3551 22-bit Analog-to-Digital
Converter (ADC) to measure voltage across the RTD.
The ADC and the RTD are referenced using an onboard
reference voltage and the ADC inputs are directly
connected to the RTD terminals. This provides a ratio
metric temperature measurement. The solution uses a
current limiting resistor to bias the RTD. It provides a
reliable and accurate RTD instrumentation without the need
for extensive circuit com pensation and calibration routines.
MCP6N11 and MCP6V2X Wheatstone Bridge
Reference Design (ARD00354)
his board demonstrates the performance
f Microchip’s MCP6N11 instrumentation
mplifier (INA) and a traditional three op
mp INA using Microchip’s MCP6V26 and
CP6V27 auto-zeroed op amps. The input
gnal comes from an RTD temperature
sensor in a Wheatstone bridge.
20 Signal Chain Design Guide
Development Tools
Demonstration Boards
ADCs
MCP3911 ADC Evaluation Board for 16-bit MCUs
(ADM00398)
he MCP3911 ADC Evaluation Board for
6-Bit MCUs system provides the ability to
valuate the performance of the MCP3911
ual-channel ADC. It also provides a
development platform for 16-bit PIC-based applications,
using existing 100-pin PIM systems compatible with the
Explorer-16 and other high pin count PIC demo boards. The
system comes with a programmed PIC24FJ256GA110 PIM
module that communicates with the included PC software
for data exchange and ADC configuration.
MCP3421 Weight Scale Demo Board
(MCP3421DM-WS)
he MCP3421 Weight Scale Demo Board
designed to evaluate the performance
f the low-power consumption, 18-bit
DC in an electronic weight scale design.
ext to the MCP3421 there is a low-
oise, auto-zero MCP6V07 op amp. This
an be used to investigate the impact
of extra gain added before the ADC for performance
improvement. The PIC18F4550 is controlling the LCD and
the USB communication with the PC. The GUI is used to
indicate the performance parameters of the design and for
calibration of the weight scale.
MCP3421 Battery Fuel Gage Demo Board
(MCP3421DM-BFG)
he MCP3421 Battery Fuel Gauge
emo Board demonstrates how to
measure the battery voltage and
ischarging current using the MCP3421.
The MCU algorithm calculates the
battery fuel being used. This demo board is shipped
with 1.5V AAA non-rechargeable battery. The demo board
displays the following parameters:
(a) Measured battery voltage.
(b) Measured battery discharging current.
(c) Battery Fuel Used (calculated).
The MCP3421 Battery Fuel Gauge Demo Board also can
charge a single-cell 4.2V
Li-Ion battery. This feature, however, is disabled by
firmware since the demo kit is shipped to customer with
non-rechargeable 1.5V AAA battery.
DACs
MCP4725 PICtail Plus Daughter Board
(MCP4725DM-PTPLS)
his daughter board demonstrates the
MCP4725 (12-bit DAC with non-volatile
memory) features using the Explorer
6 Development Board and the PICkit
erial Analyzer.
MCP4725 SOT-23-6 Evaluation Board
(MCP4725EV)
he MCP4725 SOT-23-6 Evaluation
oard is a quick and easy evaluation
ool for the MCP4725 12-bit DAC
evice. It works with Microchip’s
popular PICkit Serial Analyzer or independently with the
customer’s applications board. The PICkit Serial Analyzer
is sold separately.
MCP4728 Evaluation Board (MCP4728EV)
he MCP4728 Evaluation Board is a tool for
uick and easy evaluation of the MCP4728
-channel 12-bit DAC device. It contains the
MCP4728 device and connection pins for the
Microchip’s popular PICkit SerialAnalyzer. The
ICkit Serial Analyzer is sold separately.
Digital Potentiometers
MCP42XX PICtail Plus Daughter Board
(MCP42XXDM-TPTLS)
he MCP42XX PICtail Plus Daughter
oard is used to demonstrate the
peration of the MCP42XX Digital
otentiometers. This board is
esigned to be used in conjunction
with either the PIC24 Explorer 16 Demo Board or the
PICkit Serial Analyzer.
MCP402X Non-Volatile Digital Potentiometer
Evaluation Board (MCP402XEV)
he MCP402XEV is a low cost
valuation board that quickly enables
he user to exercise all of the features
f the MCP402X Non-Volatile Digital
otentiometer. A 6 pin PIC10F206-I/OT
with FLASH memory is utilized to generate all of the
Low-Voltage (LV) and High-Voltage (HV) MCP402X serial
commands when the 2 momentary switches are depressed
in various sequences. This enables the user to Increment
and Decrement the wiper, save the setting to EEPROM &
exercise the WiperLock feature.ℱ
Op Amps and PGAs
MCP651 Input Offset Evaluation Board
(MCP651EV-VOS)
he MCP651 Input Offset Evaluation
oard is intended to provide a simple
means to measure the MCP651 Input
ffset Evaluation Board op amp’s input
ffset voltage under a variety of operating
conditions. The measured input offset voltage (V ost
includes the input offset voltage specified in the data
sheet (V ) plus changes due to: power supply voltage os
(PSRR), common mode voltage (CMRR), output voltage
(AOL), input offset voltage drift over temperature (ΔV /os
ΔTA) and 1/f noise.
21
Signal Chain Design Guide
Development Tools
MCP6V01 Input Offset Demo Board
(MCP6V01DM-VOS)
he MCP6V01 Input Offset Demo Board
s intended to provide a simple means
o measure the MCP6V01/2/3 op amps
nput offset voltage (V ) under a variety os
f bias conditions. This Vos includes
he specified input offset voltage value
found in the data sheet plus changes due to power supply
voltage (PSRR), common mode voltage (CMRR), output
voltage (AOL) and temperature (IV /ITA).os
MCP661 Line Driver Demo Board (MCP661DM-LD)
his demo board uses the MCP661 in
very basic application for high speed
p amps; a 50℩ line (coax) driver.
0 MHz solution, high speed PCB
layout techniques and a means to test AC response, step
response and distortion. Both the input and the output are
connected to lab equipment with 50Ω BNC cables. There
are 50Ω terminating resistors and transmission lines on the
board. The op amp is set to a gain of 2V/V to overcome the
loss at its output caused by the 50Ω resistor at that point.
Connecting lab supplies to the board is simple; there are
three surface mount test points provided for this purpose.
AmpliïŹer Evaluation Board 1 (MCP6XXXEV-AMP1)
he MCP6XXX Amplifier Evaluation Board
is designed to support inverting/non-
nverting amplifiers, voltage followers,
nverting/non-inverting comparators,
nverting/non-inverting differentiators.
AmpliïŹer Evaluation Board 2 MCP6XXXEV-AMP2)(
he MCP6XXX Amplifier Evaluation Board 2
upports inverting summing amplifiers and
on-inverting summing amplifiers.
AmpliïŹer Evaluation Board 3 MCP6XXXEV-AMP3)(
he MCP6XXX Amplifier Evaluation Board
is designed to support the difference
mplifier circuits which are generated by
he Mindiℱ Amplifier Designer.
AmpliïŹer Evaluation Board 4 MCP6XXXEV-AMP4)(
he MCP6XXX Amplifier Evaluation Board
is designed to support the inverting
ntegrator circuit.
MCP6H04 Evaluation Board Instrumentation
AmpliïŹer (ADM00375)
he MCP6H04 Intrumentation Amplifier
oard is designed to support signal
onditioner from sensors example
urrent sensor.
MCP6SX2 PGA Thermistor PICtail Demo Board
(MCP6SX2DM-PCTLTH)
he MCP6SX2 PGA Thermistor PICtail
emo Board features the MCP6S22
nd MCP6S92 Programmable Gain
mplifiers (PGA). These devices help
vercome the non-linear response
of the on-board NTC thermistor. These devices have
user selectable inputs which allow the possibilities of
temperature correcting another sensor.
MCP6XXX Active Filter Demo (MCP6XXXDM-FLTR)
his kit supports Mindiℱ Active Filter
esigner & Simulator and active filters
esigned by FilterLab V2.0. These filters
re all pole and are built by cascading
rst and second order sections.
Humidity Sensor PICtail Demo Board
(PIC16F690DM-PCTLHS)
his board uses the MCP6291 and
IC16F690 to measure the capacitance
f a relative humidity sensor. The board
an also measure small capacitors in
ifferent ranges of values using a dual
slope integration method. This board also supports the
application note AN1016.
Temperature Sensors
MCP9800 Temp Sensor Demo Board
(MCP9800DM-TS1)
he MCP9800 Temperature Sensor
emo Board demonstrates the
ensor’s features. Users can connect
he demo board to a PC with USB
nterface and evaluate the sensor
performance. The 7-Segment LED displays temperature in
degrees Celsius or degrees Fahrenheit; the temperature
alert feature can be set by the users using an on board
potentiometer. An alert LED is used to indicate an over
temperature condition. In addition, temperature can be
data logged using the Microchip Thermal Management
Software Graphical User Interface (GUI). The sensor
registers can also be programmed using the GUI.
MCP6S26 PT100 RTD Evaluation Board
(TMPSNS-RTD1)
he PT100 RTD Evaluation Board
emonstrates how to bias a Resistive
emperature Detector (RTD) and
ccurately measure temperature.
p to two RTDs can be connected.
The RTDs are biased using constant current source and
the output voltage is scaled using a difference amplifier.
In addition to the difference amplifier, a multiple input
channel Programmable Gain Amplifier (PGA) MCP6S26 is
used to digitally switch between RTDs and increase the
scale up to 32 times.
22 Signal Chain Design Guide
Related Support Material
The following literature is available on the Microchip web
site: www.microchip.com/appnotes. There are additional
application notes that may be useful.
Application Related Documentation
Sensor Conditioning Circuits Overview
AN866: Designing Operational AmpliïŹer Oscillator
Circuits For Sensor Applications
Operational amplifier (op amp) oscillators can be used
to accurately measure resistive and capacitive sensors.
Oscillator design can be simplified by using the procedure
discussed in this application note. The derivation of
the design equations provides a method to select the
passive components and determine the influence of each
component on the frequency of oscillation. The procedure
will be demonstrated by analyzing two state-variable RC
op-amp oscillator circuits.
AN990: Analog Sensor Conditioning Circuits,
An Overview
Analog sensors produce a change in an electrical property
to indicate a change in its environment. This change in
electrical property needs to be conditioned by an analog
circuit before conversion to digital. Further processing
occurs in the digital domain but is not addressed in this
application note.
Delta-Sigma ADCs
AN1156: Battery Fuel Measurement Using Delta-
Sigma ADC Devices
This application note reviews the battery fuel measurement
using the MCU and ADC devices. Developing battery fuel
measurement in this manner provides flexible solutions
and enables economic management.
DS21841: Analog-to-Digital Converter Design Guide
SAR ADCs
AN246: Driving the Analog Inputs of a SAR
A/D Converter
This application note delves into the issues surrounding
the SAR converter’s input and conversion nuances to
insure that the converter is handled properly from the
beginning of the design phase.
AN688: Layout Tips for 12-Bit A/D Converter
Application
This application note provides basic 12-bit layout
guidelines, ending with a review of issues to be aware of.
Examples of good layout and bad layout implementations
are presented throughout.
AN693: Understanding A/D Converter
Performance SpeciïŹcations
This application note describes the specifications used to
quantify the performance of A/D converters and give the
reader a better understanding of the significance of those
specifications in an application.
AN842: Differential ADC Biasing Techniques,
Tips and Tricks
True differential converters can offer many advantages
over single-ended input A/D Converters (ADC). In addition
to their common mode rejection ability, these converters
can also be used to overcome many DC biasing limitations
of common signal conditioning circuits.
Utility Metering
DS01008: Utility Metering Solutions
Digital Potentiometers
AN691: Optimizing the Digital Potentiometer in
Precision Circuits
In this application note, circuit ideas are presented that
use the necessary design techniques to mitigate errors,
consequently optimizing the performance of the digital
potentiometer.
AN692: Using a Digital Potentiometer to Optimize a
Precision Single Supply Photo Detect
This application note shows how the adjustability of the
digital potentiometer can be used to an advantage in
photosensing circuits.
AN1080: Understanding Digital Potentiometer
Resistance Variations
This application note discusses how process, voltage and
temperature effect the resistor network’s characteristics,
specifications and techniques to improve system
performance.
AN1316A: Using Digital Potentiometers for
Programmable AmpliïŹer Gain
This application note discusses implementations of
programmable gain circuits using an op amp and a digital
potentiometer. This discussion includes implementation
details for the digital potentiometer’s resistor network.
23
Signal Chain Design Guide
Op Amps
AN1302: Current Sensing Circuit Concepts
and Fundamentals
This application note provides an overview of current
sensing circuit concepts and fundamentals. It introduces
current sensing techniques and focuses on three typical
high-side current sensing implementations, with their
specific advantages and disadvantages.
AN679: Temperature Sensing Technologies
Covers the most popular temperature sensor
technologies and helps determine the most appropriate
sensor for an application.
AN681: Reading and Using Fast Fourier
Transformation (FFT)
Discusses the use of frequency analysis (FFTs), time
analysis and DC analysis techniques. It emphasizes
Analog-to-Digital converter applications.
AN684: Single Supply Temperature Sensing
with Thermocouples
Focuses on thermocouple circuit solutions. It builds
from signal conditioning components to complete
application circuits.
AN695: Interfacing Pressure Sensors to Microchip’s
Analog Peripherals
Shows how to condition a Wheatstone bridge sensor
using simple circuits. A piezoresistive pressure sensor
application is used to illustrate the theory.
AN699: Anti-Aliasing, Analog Filters for Data
Acquisition Systems
A tutorial on active analog filters and their most
common applications.
AN722: Operational AmpliïŹer Topologies and
DC SpeciïŹcations
Defines op amp DC specifications found in a data sheet.
It shows where these specifications are critical in
application circuits.
AN723: Operational AmpliïŹer AC SpeciïŹcations
and Applications
Defines op amp AC specifications found in a data sheet.
It shows where these specifications are critical in
application circuits.
AN866: Designing Operational AmpliïŹer Oscillator
Circuits For Sensor Applications
Gives simple design procedures for op amp oscillators.
These circuits are used to accurately measure resistive
and capacitive sensors.
AN884: Driving Capacitive Loads With Op Amps
Explains why all op amps tend to have problems driving
large capacitive loads. A simple, one resistor compensation
scheme is given that gives much better performance.
AN951: Amplifying High-Impedance Sensors,
Photodiode Example
Shows how to condition the current out of a high-impedance
sensor. A photodiode detector illustrates the theory.
AN990: Analog Sensor Conditioning Circuits,
An Overview
Gives an overview of the many sensor types, applications
and conditioning circuits.
AN1014: Measuring Small Changes in
Capacitive Sensors
This application note shows a switched capacitor circuit
that uses a PIC microcontroller, and minimal external
passive components, to measure small changes in
capacitance. The values are very repeatable under
constant environmental conditions.
AN1177: Op Amp Precision Design: DC Errors
This application note covers the essential background
information and design theory needed to design a
precision DC circuit using op amps.
AN1228: Op Amp Precision Design: Random Noise
This application note covers the essential background
information and design theory needed to design low noise,
precision op amp circuits. The focus is on simple, results
oriented methods and approximations useful for circuits
with a low-pass response.
AN1258: Op Amp Precision Design: PCB
Layout Techniques
This application note covers Printed Circuit Board (PCB)
effects encountered in high (DC) precision op amp circuits.
It provides techniques for improving the performance,
giving more flexibility in solving a given design problem. It
demonstrates one important factor necessary to convert a
good schematic into a working precision design.
Related Support Material

Produktspezifikationen

Marke: Microchip
Kategorie: Nicht kategorisiert
Modell: MCP9801

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