Hello to all ADAU1701 fans,

I would like to share a very simple circuit for expanding the standard audio ADC input

to a fully differential input path. It works very well and rises the SNR (in my hardware)

to 102dBA.

You have to select a low noise OpAmp with RRO for best performance. PLS note that

the full scale input is R1 * 100uA (eff). The buildtin ADCX-resistor must not be taken

into account.

Best regards

Ulli

Hello Ulli,

This is quite an elegant solution! I could not figure out how it works until actually writing out and solving its node equations. Once everything cancels out, we're left with your full-scale input formula,

Vfs = Ifs * R1. Your circuit is uniquely simple (compared to a differential amplifier feeding the ADC), as well as saving a valuable ADC (compared to subtraction within SigmaStudio). And it actually improves performance, because the ADC input sees a true current source instead of a voltage source and resistor. I love it!Best regards,

Bob