I am developing an Audio project which is required to output a signal between 10kHz - 40kHz at ±1V.
The sound is produced from an AD9106 chip which is interfaced to the following circuit:
When viewed on the picoscope I can see the following with the blue line (ignore the 'check USB'...). There is a relative alot of noise.
When I looked at the frequency spectrum I saw some significant noise coming from other sources - namely at 45kHz (unknown) 2MHz (Audio clock) and 4.5MHz (Unknown and very high)
I have a dedicated supply plane with splits and dedicated regulators for analog, digital and clock. There is one solid ground plane under everything. The digital section of the circuit is kept on one side and the analog on another. I did not implement a split analog plane due potential for more problems than solutions.
I have therefore decided to implement a bandpass filter for the required frequencies above - however I am unsure of what configuration to go for. The black plotted is with a digital bandpass filter of 10kHz to 40kHz in picoscope.
I plan on changing my differential amplifier to the following configuration from the following resource http://www.ti.com/lit/ug/tiducc9a/tiducc9a.pdf.