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What Is an Operational Amplifier?


An operational amplifier is a type of analog circuit that is designed to amplify the difference between the inputs non-inverting (positive) and inverting (negative) inputs. Operational amplifiers are commonly used to buffer or amplify signals, such as the signals from sensors, current shunts and resistive dividers. The Operational Amplifier (OPA) module on PIC® microcontrollers (MCUs) and the Analog Signal Conditioning (ASC) module on AVR® MCUs can feature internal resistor ladders that enable the peripheral to function as a Programmable Gain Amplifier (PGA), which increases the size of the signal to maximize the resolution in an Analog-to-Digital Converter (ADC).

What are Integrated OPAMPs?

This video is an overview of the integrated OPAMP peripheral on PIC and AVR microcontrollers and some of the common use cases.

Single Op Amp Circuits


Unity Gain

Non-Inverting Amplifier

Inverting Amplifier

Multi Op Amp Circuits


Differential Amplifier

Cascaded Inverting Amplifier

Instrumentation Amplifier

Embedded or Discrete Operational Amplifiers: Which Do You Need?


Embedded Operational Amplifiers

Embedded operational amplifiers are designed to be used as general-purpose operational amplifiers. A few of the common use cases that benefit from the peripheral are listed below:

  • Denser system integration and lower BOM cost: The module is integrated with the MCU, which reduces the number of components used and saves board space
  • Buffering the ADC input: The operational amplifier can be used to directly feed the ADC*, which can improve signal acquisition times
  • Synergy with other analog peripherals: Other analog peripherals, such as the Digital-to-Analog Converter (DAC) and Analog Comparator, can be used in conjunction with the operational amplifier to unlock new uses for existing peripherals

Discrete Operational Amplifiers

Some demanding analog applications require a discrete operational amplifier. Here are some of the benefits that our wide array of discrete operational amplifiers offer:

  • Bipolar power supply support: Discrete operational amplifiers are available in configurations that support bipolar power rails, enabling negative inputs and outputs
  • Exceptional performance: Generally, discrete operational amplifiers have more area on the die, which improves analog performance across the board
  • More output current: Discrete operational amplifiers can have larger output stages, which enables them to drive heavier loads

Advanced Features


Features vary by device. Please consult the device data sheet for more information on the features and feature configurations available on each device.

Selectable Input Pins

Optimize and Simplify Layout

The pins associated with the operational amplifier module are multiplexed. This feature can be used to select a different pin that is farther away from switching logic to reduce the amount of crosstalk or it can be used to simplify PCB layout.

Internal Resistor Ladder

Reduce the BOM

The internal resistor ladder removes the need for external resistors for most configurations. The ladder can be used to select and switch between the desired gains. For applications requiring gains that are not available on the ladder—or those requiring a greater degree of accuracy—the ladder can be disabled, and external feedback resistors can be used instead.  

Internal Unity Gain Override

The internal unity gain override forces the operational amplifier into unity gain by shorting the output and the inverting input*. Some devices may leave the negative input pin still connected, enabling this feature to be used as a discharge route for an integration capacitor.

 

Controllable Charge Pump

The internal charge pump in the OPA module can be enabled for enhanced analog performance for demanding applications, however, this increases the OPA module’s current consumption.

Internal Connection to ADC

The ADC on the device can directly sample the output of the operational amplifier without an external jumper to another pin. The module can also be used as a buffer for the ADC, which can improve signal acquisition time and resolution.

Input Offset Voltage Calibration Register

Each device is calibrated at the factory with a value that nulls the input offset voltage to within the specified data sheet tolerance. On some devices, this register can be overwritten at runtime for applications that contain a self-calibration routine. On a power-on reset, the factory value of the register is restored.

Software Override

The software override feature can be used to force the operational amplifier to a specific output, such as VDD, VSS, or tri-state*, while ignoring the inputs to the operational amplifier.

Tri-Stated Output

The output of the operational amplifier can be tri-stated, which allows for the creation of sample-and-hold circuits using the output and an external capacitor.

Hardware-Controlled Override

The hardware override can be used to switch the output configuration of the operational amplifier using an internal hardware signal, removing the need for core intervention.

Internal Connections to Other Analog Peripherals

Other on-chip analog peripherals can be connected to the operational amplifier’s inputs*. This could be used to mirror (and/or track) the DAC, to output the Fixed Voltage Reference (FVR) for external devices, or to build a cascade of internal operational amplifiers for more signal bandwidth.

*Implementation varies by device. Consult the MCU family data sheet for more information.

MPLAB® Mindi™ Analog Simulator

Uses a SIMetrix/SIMPLIS environment to model circuit behavior, reducing design time with software debugging for initial design verification

8-bit Microcontrollers with Operational Amplifiers


View All Parametrics
Product Number of Op Amps Max ADC Resolution (bits) Max I/O Pins Program Memory Size (KB)
AVR128DB28 2 12 23 128
AVR128DB32 2 12 27 128
AVR128DB48 3 12 41 128
AVR128DB64 3 12 56 128
AVR32DB28 2 12 23 32
AVR32DB32 2 12 27 32
AVR32DB48 3 12 41 32
AVR64DB28 2 12 23 64
AVR64DB32 2 12 27 64
AVR64DB48 3 12 41 64
AVR64DB64 3 12 56 64
PIC18F04Q41 1 12 12 16
PIC18F05Q41 1 12 12 32
PIC18F06Q41 1 12 12 64
PIC18F14Q41 1 12 18 16
PIC18F15Q41 1 12 18 32
PIC18F16Q41 1 12 18 64

Documentation

Title Download
Using the Operational Amplifier on PIC16 and PIC18 Download
Optimizing Internal Operational Amplifiers for Analog Signal Conditioning Download
AN3636 - Using the Internal OPAMP as Regulated Power Supply for MVIO Download
AN3632 - Constant-Current Driver Using the Analog Signal Conditioning (OPAMP) Peripheral Download
AN3633 - Gain and Offset Calibration of the Analog Signal Conditioning (OPAMP) Peripheral Download
Analog Sensor Measurement and Acquistion Download
TB3286 - Getting Started with Analog Signal Conditioning (OPAMP) Download
AN3631 - Low-BOM Microphone Interface Using the Analog Signal Conditioning (OPAMP) Peripheral Download