Hi,
I'm using the ADA4938-2 to drive an AD9653 ADC. I am observing marginal stability in the ADA4938-2 circuit when I include C121 and C127 in the design. However, if I remove these components, the circuit is stable. I cannot reproduce this issue in simulation. Could you explain to me why this is happening? I would like to include active differential lowpass filtering in this design to limit the noise bandwidth from this amplifier. Is there a way to modify this circuit to limit the bandwidth while keeping the circuit stable?
Please review the following images:
The schematic of the ADA4938-2 driver:
The noise measured with C121 and C127 populated (time domain [top], frequency domain [bottom], there are two channels with identical circuits [red and blue]):
The noise measured with C121 and C127 removed (time domain [top], frequency domain [bottom], there are two channels with identical circuits [red and blue]):
Thanks,
Peter