The AD7606 (and all variants thereof) is an excellent simultaneous-sampling ADC. Simultaneous sampling is necessary for my application. However, this ADC, unlike many others, does not have separate analog and digital power/ground pins. I'm seeing some crosstalk from the digital lines on the analog signals. I'm wondering what the best way to isolate the analog and digital signals is for this chip. Currently I just have one ground plane for the whole system, including the sensors that interface to the ADC.
The sensors are electret microphones amplified by AD8429 In-Amps. The microphones are always powered and so are always gathering, and they're not triggered in any way by the system.
Here's the datasheet: https://www.analog.com/media/en/technical-documentation/data-sheets/ad7606_7606-6_7606-4.pdf
And here's the pinout:
The analog inputs are on the north side of the IC, and the digital lines are on the south and west sides. Should I split the ground planes under the IC and star ground them at pin 2? Pin 26? Pin 47? The datasheet reads as if pin 23, Vdrive, is the digital power supply, but there's no dedicated digital ground. Any guidance is helpful.
Best Answer
Do NOT split the grounds underneath the IC. A single ground plane is fine. Instead, keep all analog components to the North and all digital components to the south west. That way, digital return currents are less likely to stray into the area where the analog return currents are circulating.
Is your issue cross talk with your ADC's own digital communications? Or cross talk from communications other devices sharing the same bus as the ADC?
If the problem is the latter, then the solution to this is to buffer the ADC from the rest of the digital bus with a transparent latch (sometimes even with two in cascade). The latch disconnects the ADC from the bus when the ADC is not communicating and thereby reduces crosstalk from the other devices on the bus.
You should check out everything else in that link too.