I am working on a 24 bit ADC and would like to eliminate noise as much as possible in order to maximize the performance of the 24 bit ADC.
There are two main areas where I am concerned where noise can come from:
- Internal noise where the noise from the circuit itself.
- External noises where noise from the environment can affect the reading.
I have a general idea of how to protect from these noises but I lack specifics if my counter measures are enough.
Internal noise from traces and power supply can affect the reading so I have used digital isolator to isolate the ADCs both power, ground, and data lines from the rest of the system. The power supply can either come from a power over rthernet module or a simple 5V USB cable.
Taking an advice from an answer to a previous question, the power supply is filtered by a series of low - pass RC filters. Should I place low pass filters on the AVDD of the ADC, too?
Another solution I found is using a multi-layered PCB with the signal traces be like this. According to an article I read, it helps reduce noise. With the top and bottom layers are either GND or Vcc.
This can be a bit tricky since the device will be in close proximity (less than 1 meter) of 50Hz AC mains lines. Those lines carry a maximum 50-75A of AC current (beyond this master breaker would trip.) My first idea is to use some of this shielding material which can be tediously cut and soldered to the board. Just like one of those wifi/bluetooth modules that has a metal covering the IC. Would that be sufficient? Also does shielding need to be connected to the ground of the circuit? If so which ground (digital or analog?)
If that is not enough I might go as far as placing the whole module into a solid metal container with holes just enough for the wires to go through. This should block those low frequency noises. Does it block the high frequency noise too? If so then the shielding above may be redundunt, but how thick would that need to be for it to be effective? What metal should it be?
Since its metal near power lines, I assumed this solid metal should be connected to earth. Should this metal also be connected to the circuit's ground? Would that affect the reading?
Although I may not need this many bits, I may as well go all out. Even modern oscilloscopes do not need this much of bit accuracy. Noise can still be induced by the probing. But since this project allows me to go a bit further I might as well go ahead and learn as much as I can.