the best way to get gain on ADC signals?

Projects Networking, Protocols, and Devices
1

I am wondering, if I can get high speed ADC data, how can I apply a gain to it before it gets read to the native ADC of a micro-controller. I'm looking for a gain of at least 128, higher would probably be better, like 500. If neither of those are possible, I might have to resort to a lower gain but that is not ideal. the ADC rate I'm doing is ~10kHz I'd like to be able to do this for multiple channels.

I have another thread here asking how to get rapid ADC aquisition ( the right data logging equipment (ADC stuff). please help - Networking, Protocols, and Devices - Arduino Forum ) but gain wasn't discussed and I think it deserves it's own thread.

2

Most of the Atmega microprocessors - but NOT the 328 - have internal amplifiers for the AC input.

...R

3

You can buy fast, external ADC modules with built in, selectable gain values. This one works quite well. The maximum gain is 16X, but the six extra bits (over the Uno) should make up the difference for your project.

Note that this ADC is absolute, not ratiometric. To mimic a ratiometric ADC you need to use another channel to measure the reference voltage, and calculate the ratio in your code.

4

jremington:
You can buy fast, external ADC modules with built in, selectable gain values. This one works quite well. The maximum gain is 16X, but the six extra bits (over the Uno) should make up the difference for your project.

Note that this ADC is absolute, not ratiometric. To mimic a ratiometric ADC you need to use another channel to measure the reference voltage, and calculate the ratio in your code.

the ADC given there won't work as the sample rate is too low, I'm looking for 10kHz.

why does it matter that the ADC is absolute rather than ratiometric? Is it that ratiometric measurements are much more accurate?

5

voltagesurge:
the ADC given there won't work as the sample rate is too low, I'm looking for 10kHz.

Search for a suitable ADC on one of the big component suppliers websites - RS Components or DigiKey, for example. I have some ADCs from 20 years ago that can do 40 million samples per second - though they are only single channel and don't have amplification.

...R

6

why does it matter that the ADC is absolute rather than ratiometric?

It depends on what you are trying to measure.

If you want to measure a voltage, then absolute is often best. If you want to measure resistance, ratiometric is often best.

7

The answer is simple an operational amplifier. The solution is tough, if you are not an analog designer you might get it with a lot of luck. There are a lot of parts and reference designs available. Look at high performance audio amplifiers or instrument amplifier chips. This response is to help you get started in solving your problem, not solve it for you.
Good Luck & Have Fun!
Gil

8

gilshultz:
The answer is simple an operational amplifier.

As I mentioned earlier, many of the Atmega chips include OP Amps for the ADC

...R