How to drive ADC with single to diff amp


I have a 1Vpp signal that I want to read with an AD9238 ADC, I would like to use a diff amp to gain the signal to 2Vpp first. The AD9238 has an internal Vref that I can set to 1V, so I'd like my input signal to be based around that reference.

I've been looking at both the ADA8138, and ADA4932 Diff Amps, but when I use Analog Device's Diff-Amp calculator I notice I can't set my Vocm less than 1.2V

I was looking at these diff amps cause the AD8138 is on the ADC's eval board... but if the Vref for the ADC can only be set to either 0.5V or 1V... do these not work for the AD9238 for those references?

I would like a 2Vpp centered around the ADC's 1V reference... am I just not able to do that with these diff amps? Is there a better single to diff amp for driving the AD9238?


  • Hi panfilero,

    You can use unbalanced supply for AD8138 or ADA4932 (-1V and 5V) since both these fully-differential amplifiers have a VOCM range within 1.2V from rails. When in single supply operation, the common-mode could go below 1.2V. Or you could actually let go of using the 1.0V reference as the VOCM for ADA4932/AD8138 and make use of AVDD/2. With this, you would need not to provide additional supply for the differential amplifiers.