An interesting question which it seems it's hard to find any good answers. Analog switch noise may be negligable foir most applications but inevitably there comes a point where it becomes an issue.
The most obvious noise source is the thermal noise of the channel resistance of the switch, so the lower resistance the switch the better. But lower resistance switches wil be physically bigger and suffer higher leakage currents which I assume will contribute shot noise. I have no idea if this is significant but this paper might help:
https://www.nikhef.nl/~jds/vlsi/noise/sansen.pdfAnother important factor is flicker noise. This might not be a problem for your application, depending on your operating frequency, but generally the 1/f noise of a resistor is:
1) A function of the resistor type - wirewound/bulk metal foil have almost no flicker noise, unlike silicon diffused resistors.
2) Inversely proportional to the physical size of the resistor
3) Proportional (approximately) to the square root of the resistor value (according to Doug Self)
4) Proportional to the applied voltage.
Unfortunately almost no analog switch datasheets have anything to say about noise; I did once find one which did, but maddeningly I can't find it now. It was a pretty mundane cmos switch, something like a 4061.
This might be of some (small) interest:
https://ez.analog.com/switches_multiplexers/f/q-a/77163/is-spectral-noise-density-nv-rthz-information-available-for-adi-analog-switches-muxesIn particular the bit:
Hi dananderson75,
I have spoken with our device modellers and I have been assured that the 1/f corner frequency for the devices in the ADG16xx switches is below 100Hz.
Regards,
Joe
I guess you're essentially on your own here. It would be great if you would share any noise measurements you make should you investigate the issue further.