Bipolar supply vs single supply grounding scheme

[poorchava]

I'm designing a thing that has somewhat sizable analog front end, multiple opamps etc. Bipoalr supply like +/-2.5V makes the design more straightforward, but takes more space, digital control signals need levelshifting, there is additional +/- power supply needed. Conversion with single-supply is quite easy (virtual ground potential to some opamp inputs, etc) since the signal path is mostly ac coupled anyway. The decice will be handheld, so I need to go with single supply to dut the component count down.

So i have my 5V supply, and will have a 2.5V VGND powered by some push-pull stage (opamp and BJTs?). Easy enough. But the question is: things like RC filters, would you replace GND connection with VGND potantial? How about ground planes? Obviously in this case GND potential is essentially the negative rail, the signal common mode is generally +2.5V from that. Would you connect the internal planes and copepr pours to GND or VGND?

I was thinking of the latter. So then VGND will essentially be what used to be GND, GND will be what used to be -2.5V. So also connect all filters to VGND instead of GND. All shields would also be at VGND, not GND.

What are your thoughts on this? I'm leaning on making the copper pours and everything VGND potential, but not sure how to design voltage regulators for that, since those would be referenced to actual GND, not VGND.

I'm by no means new to the field, almost 20y of experience, almost 10 of which in T&M industry, but somehow it's the first time I have to make a shift like this. Up to now I've almost always been able to use bipolar supplies anytime I has any major analog processing.

[Salitronic]

To answer that question you need to ask yourself: what is the reference for the signal at the point of interest?
If your split DC supply was ideal, its ac-equivalent circuit would be a short circuit. Therefore with ideal DC supplies you could 'ground' the RC filter to either of the 'real' rails or the virtual ground, it wouldn't make any difference. In practice each of your supply rails comes with its equivalent noise source. If you are dealing with an input or intermediate signal that is referenced to the virtual ground you'd want to 'ground' your RC filter to the virtual ground. On the other hand if you are feeding the output signal to an ADC referenced to the 'real' ground, the RC filter should be connected to that ground to include the noise source from the split supply.

The ground planes in general should as much as possible always be the system ground, particularly for purposes of EMI/EMC.

[Terry Bites]

Signal gnd is Vref.
The emitter follower in the splitter can become unstable if not designed correctly.