# Interfacing instrumentation amplifier

I would like to interface several LTC6915 instrumentation amplifiers with a microcontroller. I have a schematic which looks something like below image:

What I figured out is that the two amplifiers are connected in parallel with each other and gain can be set simultaneously for both the amplifiers from microcontroller's GPIO.

Below is the image from datasheet which shows how to set gain.

What I understand is if I set D3, D2, D1 = 0 and D0 = 1 from GPIO of microcontroller, I would set gain 1. Is that correct? If I set different gain values, how can I interpret that what I have set is correct?

Also I would like to know what will happen if I set gain as 0. I read that gain increases the amplitude of the signal. So does gain 0 means it won't amplify the signal?

• Just to be certain: The LTC6915 uses a sample and hold operating at 3kHz. Your input signal (and any significant noise) must stay below 1.5 kHz. Anything above 1.5kHz wil be aliased back down to below 1.5kHz. So, a 2kHz signal would be 500Hz after the amplifier.
– JRE
May 7, 2019 at 11:29
• What do you mean with: If I set different gain values, how can I interpret that what I have set is correct? May 7, 2019 at 11:49
• Thankyou all @Huisman Let's say I set a gain of 1 initially and then 32. Will I get dfferent reading on both these settings?
– Alan
May 9, 2019 at 13:58
• Yes. The output shows the differential input voltage multiplied by the gain. So, a different gain will show different outputs. May 9, 2019 at 14:16
• Thankyou @Huisman for your time
– Alan
May 12, 2019 at 11:48

What I understand is if I set D3, D2, D1 = 0 and D0 = 1 from GPIO of microcontroller, I would set gain 1.

That's correct.

Also I would like to know what will happen if I set gain as 0. I read that gain increases the amplitude of the signal. So does gain 0 means it won't amplify the signal?

According the datasheet:

If the gain control code is 0000, the IC operates in software shutdown mode, i.e., the main op amp is turned off so that the PGA dissipates less power.

and

Send a gain code of 0000 to one IC to set its output to a high impedance state