I’m planning to use the Photon in a an environment that require high precision A to D. How good is the onboard SMPS at providing a stable power supply. I’m normally more inclined to use a linear power regulator, but things may have moved on in recent times.
In case I want to add a 3.3V external power supply to the Photon and I want to keep the Ground points separated between the Analogue and Digital side, which Ground should I use for my power supply, the Left side or RIght?
I may be wrong , but as few as I know both ground rails or common .
@bruce_miranda, as @peter_a pointed out, the Photon does not have a separate analog ground. You may want to do some research into the operation of the STM32F205 ADC design. For one, the STM32 uses the supply voltage as Vref, making it susceptible to supply noise and variability. The impedance of the ADC input also varies somewhat with the sampling frequency. If you search the forum, you will find a substantial volume of posts regarding the ADC accuracy and characteristics.
The onboard SMPS is good but like any switching supply, there is ripple. An external 3.3v linear supply may help though having a common analog and digital ground is not ideal for “high precision”.
If you require “high precision”, you may want to consider an external SPI ADC with its own high precision Vref. 