Virtual Earth and AGND, impact on low noise front end electronics

[riscy00]

I have two design solution for low frequency (<1KHz) voltage signal amplifier, where instrument amp has fixed gain of x10 and x20 for low noise performance. The source impedance is quite low.

I have one design than work on +/-5V PSU where AGND is common/analogue ground plane, which attached to -VE of the instrument amp. It would requires +/-5V PSU.

The other design I could consider is to have single +10V PSU (which remove flyback transformer and use buck inductor) and have +5V virtual earth. The virtual earth would connects to -ve of the instrument amp.

The output signals goes to 12bit ADC (differential) that run on 0V to +5V.

My concern in understanding the behavior of the noise floor between two circuits, can any one advise or point to useful link, which measure the difference between these circuits.

Also should I modify the ground plane to virtual common (VIRCOM) plane for the analogue front end circuit, for example treating AGND as power track, VIRCOM as sheet plane, +10V as power track (4 layer PCB)

Thanks

 

[crutschow]

In general a switching regulator (either flyback or buck) will have higher noise than a linear regulator and likely will increase the noise floor, unless you take great pains to filter and isolate the switching regulator. Otherwise a properly designed virtual ground (well decoupled to the analog ground) will have little effect on the noise as compared to a standard analog ground.

I would make both AGND and VIRCOM separate (or split) planes on the PCB, if possible.