Digital gain control of OpAmp?

I would like to use a u-controller to control the gain around a low-voltage CMOS OpAmp. Gain Range: 0.5 to 50. ~256 gain steps. Frequency range: DC to ~300Khz. Using I2C as the digital interface would be convenient.

Anybody have a suggestion for a way to do this?

You could use a Digital Potentiometer to do that. They are applied just like a rotary potentiometer would be in a normal analog circuit, but its resistence is controlled by a uC, and not by the position of the pot.

There are several Digital Pots that works with I2C protocol (and SPI and Microwire as well).

They are also known as RDAC, because they can be thought of as a digital do analog converter too (the only difference is that the analog variable controlled is the resistance, and not voltage)..

There are some ICs from Microchip that I know are I2C (MCP45xx).

Take a look at:
Digital Potentiometers | Digital to Analog Converters | Analog Devices
https://www.electro-tech-online.com/custompdfs/2009/12/ds-22107a.pdf

Of course there are some integrated variable gain amplifiers, but I have never worked with one and I don't know how they behave... I think they may be more expensive, too.

Castilho

caster.cp said:

Of course there are some integrated variable gain amplifiers, but I have never worked with one and I don't know how they behave... I think they may be more expensive, too.

Castilho

Click to expand...

Microchip makes programmable gain op amps, but they only have 8 steps...
https://www.electro-tech-online.com/custompdfs/2009/12/21861e.pdf
The digital pot may be the best way to go, unless you could do it with a couple of analog switches?

BeeBop said:

Microchip makes programmable gain op amps, but they only have 8 steps...
https://www.electro-tech-online.com/custompdfs/2009/12/21861e-1.pdf
The digital pot may be the best way to go, unless you could do it with a couple of analog switches?

Click to expand...

Take a look at

https://www.analog.com/en/amplifier...tation-amplifiers/ad526/products/product.html

It's from a very expensive Software Programmable Gain Amplifier that provides 256 steps... (if two are cascaded...)

But I totally agree with you.


EDIT: When I first saw your post I thought you were talking about digital pots, and not programmable gain op amps =P My mistake.

Some DACs that use a ladder network internally can also be configured to provide a variable gain amp by putting the ladder network inside the amps feedback loop.