Diff Amps and ADC's

- F
- Fibo
  
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posted
4 years ago

Thu, May 2, 2019 9:26 AM

Hello,

I have a 2Vpp signal that I'd like to send to a single ended to differential amplifier to drive an ADC... issue I'm running into is, I can't figure out how to set my diff amp's output common mode to the Vref of the ADC (1V).

I've been using Analog Devices Diff-Amp Calculator and it's made me notice that for the drivers I'm looking at AD8138, and ADA4932 the Vocm pin can't be less than 1.2V

I'm using the AD9238 ADC, which has a Vref of 1V and runs off a 3V supply

am I just using the wrong drivers for the job? I picked it cause it was called out in their eval board... but... maybe I'm just not understanding the Vocm pin right on the diff-amp.

Is Vocm the output DC bias of a diff-amp?

Much thanks!

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- M
- makolber
  
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posted
4 years ago

Thu, May 2, 2019 2:03 PM

I think your issue is that with a 2Vp-p signal and common mode = 1V, the outputs need to swing to 0V. So you need a negative supply or a rail to rail capable amp.

Mark

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