Trying to understand AD8138 circuit from legacy design

Hi tgbe ,

Good day. To further help you with your inquiry, I would like to clarify some details of the question. May we clarify where did you get the circuit presented above? Also, is the input range +/- 3V is equivalent to C1R0H? Lastly, what was your intended output level?

Regards,
Gilbeys

Hi Gilbeys,

thank you for your reply. The circuit is from a legacy design we're working on, where the original designer is not available anymore. I'd like to understand the implications of the resistor circuits for a possible redesign.

The The C1ROH input range is supposedly +/- 3V. The output should match the ADC's range, which is Vcm (1.5 V) +/- 0.5 V for each input, or 2 Vpp differential swing.

Thanks,

Thomas

Hi Gilbeys,

thank you for your reply. The circuit is from a legacy design we're working on, where the original designer is not available anymore. I'd like to understand the implications of the resistor circuits for a possible redesign.

The The C1ROH input range is supposedly +/- 3V. The output should match the ADC's range, which is Vcm (1.5 V) +/- 0.5 V for each input, or 2 Vpp differential swing.

Thanks,

Thomas

Hi tgbe ,

Good day. The resistors at the input should be symmetrical to avoid mismatch errors. You might want to use ADI's DiffAmpCalc to redesign your circuit. Here's the link for download: https://www.analog.com/en/resources/interactive-design-tools/adi-diffampcalc.html. I hope this helps.

Regards,
Gilbeys

Hi Gilbeys,

thanks, that is what I thought. We'll have to redesign this circuit.

Thank you,

Thomas

Hi,

I believe that the question has been answered already so I am closing this thread. In case there will be additional questions, feel free to reply to this thread. Thank you!

Regards,
Paul