Opamp

April 26, 2026 · View on GitHub

A library for interfacing with the opamp peripheral on the AVR-DB series MCUs. These are reasonably decent opamps integrated as part of the chip - thus requiring no extra board space, and often no external components whatsoever. You can use them as a programmable gain amplifier to amplify an analog signal or differential amplifier to amplify the difference between two signals - and you would then most likely measure the output pin with the ADC. They can be used as voltage followers, and the trio together can even serve as an instrumentation amplifier. They come with a few notable limitations - for one thing, there is only one pin mapping. Certain input mux options are available only on some opamps, not all three. That it has a built-in resistor ladder is very helpful for reducing part counts, and is vital for some of the most exciting applications, but it's limited to only 8 combination of resistances, corresponding to a 15:1 ratio between the resistances (though do note that you can use the pin inputs and external resistors instead - it's just more parts and more soldering). One of Microchip's most often mentioned use cases (and understandably so) is generating the supply for the MVIO pins using the on-chip opamp. All you need to do is configure the opamp as a voltage vollower, with the DAC as the positive input, and connect the output to VDDIO2. You don't get very much current (especially near VDD), so you can't power much from it. But usually you're instead trying to match the lower operating voltage of something you want to talk to. This is a perfect application for it; see the below example for usage of the output_pin property, which demonstrates one way to

Developed by MCUdude.

The AVR DB-series parts with 48 or 64-pins have three built-in opamps, while the 28 and 32-pin versions have only two. At present, the on-chip opamps are present on the AVR DB-series parts, and no other devices featuring them have been announced within their AVR product line. It is likely that they will remain exclusive to the the top-end AVR devices as a premium feature. More useful information about the opamp peripheral can be found in the Microchip Application Note TB3286.

See also chapter 35: OPAMP - Analog Signal Processing of the datasheet. Section 35.3.7, "Applications Usage" is particularly valuable, showing the equivalent circuit and settings required for all registers to achieve a number of common opamp use cases - voltage followers, inverting and non-inverting programmable gain amplifiers, integrators (requires an external resistor and capacitor), differential amplifiers, and using all three opamps, even an instrumentation amplifier (a differential amplifier with each input buffered by a voltage follower)

Opamp	+ Pin	- Pin	OUT	Comments
Opamp0	PD1	PD3	PD2	48/64-pin parts only
Opamp1	PD4	PD7	PD5	PD6 is the DAC output
Opamp2	PE1	PD3	PE2	48/64-pin parts only

Opamp class

The Opamp class provides a wrapper around the on-chip opamps on the AVR DB-series parts. One instance of this class is created for each of the opamps present on the chip; the user should not be declaring new objects of class Opamp. The names are Opamp0, Opamp1 and (on 48 and 64-pin parts) Opamp2. Parts with less than 48 pins only have 2 opamps (they also lack the pins that the third opamp would use).

Note that there is both the static start() method (this enables or disables opamps in general) as well as each opamp's init() method, which writes all the settings you've configured using the properties to the peripheral registers (this triggers the settling time, a delay after enabling or reconfiguring an opamp before it can be used)

Summary

input_p

This property controls what the positive input of the opamp is connected to.

Accepted values

in_p::pin;         // Connect the inpuy to the external pin
in_p::wiper;       // Connect the input to the wiper internally
in_p::dac;         // Connect the input to the DAC internally
in_p::gnd;         // Connect the input to ground internally
in_p::vdd_div2;    // Connect the input to Vdd/2 internally, which is half the supply voltage
in_p::link_output; // Connect the input to the previous opamp's output internally (only available for Opamp1 and Opamp2)
in_p::link_wiper;  // Connect the input to the Opamp0 wiper internally (only available for Opamp2)

As noted above, unlike (for example) the CCL, for which one might imagine the Opamp's to be the "analog version" of, in_p::link_output does not wrap around; it's just not available on Opamp0, and in_p::link_wiper is only an option on Opamp2 (if present).

Value	R1	R2	R1:R2	gain (non)	gain (inv)
`wiper::wiper0`	15	1	15: 1	1 1/15	1/15
`wiper::wiper1`	7	1	14: 2	1 1/7	1/7
`wiper::wiper2`	3	1	12: 4	1 1/3	1/3
`wiper::wiper3`	1	1	8: 8	2	1
`wiper::wiper4`	3	5	6:10	2 2/3	1 2/3
`wiper::wiper5`	1	3	4:12	4	3
`wiper::wiper6`	1	7	2:14	8	7
`wiper::wiper7`	1	15	1:15	16	15

Opamp	+ Pin	- Pin	OUT	Comments
Opamp0	PD1	PD3	PD2
Opamp1	PD4	PD7	PD5	PD6 is the DAC output.
Opamp2	PE1	PE3	PE2	48/64-pin parts only.

Out[1]	Out[0]	Event	Alwayson	Result
0	0	0	0	Peripheral disabled.
0	0	0	1	Enabled? But output driver is not enabled without a `DRIVE` event, and event reception is not enabled. I believe this is pathological.
0	0	1	0	-
0	0	1	1	I think this enables events, but not ENABLE/DISABLE, since always on is described as having precedence - however, it will not output anything without a `DRIVE`.
0	1	0	0	Unclear. I believe
0	1	0	1	Opamp enabled with output driver on, without any events.
0	1	1	0	-
0	1	1	1	-
1	x	x	x	Invalid Configuration,

AC	+ Pin	- Pin	OUT
AC0	-	IN_N0	IN_P0
AC1	-	IN_N1	IN_P0
AC2	-	-	IN_P0

AC	+ Pin	- Pin	OUT
AC0	-	IN_N2	-
AC1	IN_P2	IN_N2	IN_N0
AC2	IN_P1	IN_N2	-

AC	+ Pin	- Pin	OUT
AC0	-	-	IN_P2
AC1	-	-	-
AC2	IN_P2	-	-