Analog and Interface Product Solutions
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
Amplifiers
MCP6XX
MCP6XXX
MCP6V01/2/3
MCP6V06/7/8
Comparators
MCP654X
MCP656X
Analog-to-Digital
Converters
MCP3421
MCP3422/3/4
MCP355X
MCP3901
Temperature
Sensors
MCP9800
MCP9804
MCP9700/A
MCP9701/A
Voltage
References
MCP1525
MCP1541
Digital
Potentiometers
MCP40XX
MCP40D1X
MCP41XX
MCP42XX
MCP43XX
MCP45XX
MCP46XX
MCP41XXX
MCP42XXX
Digital-to-Analog
Converters
MCP4725
MCP4728
MCP482X
MCP492X
www.microchip.com/analog
Signal Chain Overview
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 using op amps, an analog-to-digital
or voltage-to-frequency converter, and is processed at the
MCU. The analog sensor output typically needs proper signal
conditioning before it gets converted to a digital signal.
Typical Sensor Signal Chain Control Loop
Analog Domain
Sensors
Reference
Voltage
MUX
Op
Amp
PIC
®
MCU
or dsPIC
®
DSC
Digital
Potentiometer
Actuators
Motors, Valves,
Relays, Switches,
Speakers, Horns,
LEDs
Driver
(MOSFET)
Op Amp
Filter
ADC/
V-to-Freq
Digital Domain
Indicator
(LCD, LED)
The MCU controls the actuators and maintains the operation
of the sensor signal conditioning circuits based on the
condition of the signal detection. For 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.
DAC/PWM
2
Signal Chain Design Guide
Sensor Overview
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
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 converted 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.
Summary Of Common Physical Conditions and Related Sensor Types
Phenomena
Magnetic
Temperature
Sensor
Hall Effect
Magneto-Resistive
Thermocouple
RTD
Thermistor
IC
Infrared
Thermopile
Capacitive
Infrared
Strain Gauge
Load Cell
Piezo-electric
Mechanical Transducer
LVDT
Piezo-electric
Microphone
Ultrasonic
Accelerometer
Magnetic Flowmeter
Mass Flowmeter
Ultrasound/Doppler
Hot-wire Anemometer
Mechanical Transducer (turbine)
Ultrasound
Mechanical Transducer
Capacitor
Switch
Thermal
Photodiode
pH Electrode
Solution Conductivity
CO Sensor
Photodiode (turbidity, colorimeter)
Electrical Output
Voltage
Resistance
Voltage
Resistance
Resistance
Voltage
Current
Voltage
Capacitance
Current
Resistance/Voltage
Resistance
Voltage or Charge
Resistance, Voltage, Capacitance
AC Voltage
Voltage or Charge
Voltage
Voltage, Resistive, Current
Voltage
Voltage
Resistance/Voltage
Frequency
Resistance
Voltage
Time Delay
Resistance, Voltage
Capacitance
On/Off
Voltage
Current
Voltage
Resistance/Current
Voltage or Charge
Current
Humidity
Force, Weight, Torque, Pressure
Motion and Vibration
Flow
Fluid Level and Volume
Light
Chemical
Signal Chain Design Guide
3
Product Overviews
Operational Amplifiers (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
Q
) per amplifier between 0.6 μA and 6 mA, with
a Gain Bandwidth Product (GBWP) between 10 kHz and
60 MHz, respectively. The op amp with lowest supply voltage
(V
DD
) operates between 1.4V and 6.0V, while the op amp
with highest V
DD
operates between 6.5V and 16.0V.
These op amp families fall into the following categories:
General Purpose, Low Offset, Auto-zeroed, High Speed, Low
Noise and mCal (self calibrating input offset voltage (V
OS
)).
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 μA typical current consumption in
a small 8-pin MSOP package. The
MCP3421
is a single
channel 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
MCP3422/3
and the
MCP3424
are two channel and
four channel versions, respectively, of the
MCP3421
device.
The
MCP300X
(10-bit),
MCP320X
(12-bit) and
MCP330X
(13-bit) SAR ADCs combine high performance and low
power consumption in a small package, making them ideal
for embedded control applications. The
TC5XX
Dual Slope
ADC devices offer another alternative with up to 17-bits of
conversion resolution.
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.
Comparators
The
MCP6541
and
MCP6561
family of comparators
provide ultra low power, 600 nA typical, and higher speed
with 40 ns propagation delay, respectively. The
MCP6541
family low operating current is suitable for battery powered
application and the output drive capability is ideal for alert
buzzer driver applications. The
MCP6561
family with greater
than 4 MHz toggle frequency is ideal for higher speed
embedded system applications where sinusoidal output
from sensors to square wave conversion is needed. The
47 ns typical propagation delay also makes this device ideal
for microprocessor interface. Both families of comparators
are available with single, dual and quad as well as with
push-pull and open-drain output options (MCP6546 and
MCP6566).
Voltage References
Microchip offers the
MCP15XX
family of low power and low
dropout precision Voltage References. The family includes
the
MCP1525
with an output voltage of 2.5V and the
MCP1541
with an output voltage of 4.096V. Microchip’s
voltage references are offered in SOT23-3 and TO-92
packages.
Programmable Gain Amplifier (PGA)
The
MCP6S21/2/6/8
and
MCP6S91/2/3
PGA families
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.
4
Signal Chain Design Guide
Product Overviews
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 I
2
C™ 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 Wiperlock™ 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.
Digital-to-Analog Converters (DAC)
Microchip has a number of Digital-to-Analog Converters that
range from high performance 12-bit devices to cost effective
8-bit devices.
The
MCP4725
is a single channel 12-bit DAC with non-
volatile memory (EEPROM). The user can store DAC input
code and configuration register bits into the EEPROM. This
non-volatile memory feature enables the device to hold
the DAC input code during power-off time allowing the DAC
output to be available immediately after power-up. This
feature is very useful when the DAC is used as a supporting
device for other device operations in systems. The
MCP4725
is availabe in a tiny SOT23-6 package.
The
MCP4728
is a 12-bit DAC with four analog outputs. This
device also has non-volatile memory (EEPROM) for each DAC
channel. The user can select internal reference or V
DD
as
reference individually for each channel. The
MCP4725
and
MCP4728
are available with I
2
C serial interface.
The
MCP4821/2
family of 12-bit DACs combines high
performance with an internal reference voltage and SPI
interface. The
MCP4921/2
family is similar and allows
for an external reference. 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 and humidity) is required.
The
TC1320/1
family of DACs has 8- and 10-bit precision
that uses the 2-wire SMBus/I
2
C serial interface protocol.
Signal Chain Design Guide
5
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