How to capture 8 bipolar analog inputs simultaneously using STM32MP157D device

[Ma.2]

Since STM32MP157D requires positive analog input, I have added a fully differential amplifier to capture the negative inputs. STM32MP157D devices embed two analog-to-digital converters.

I have attached a diagram that explains my problem. I need to capture the 8 bipolar analog inputs simultaneously to get accurate phase information.

What is the best and optimal way of achieving this? 

[PatrickF]

Hi @Ma.2​ ,

there is only one single sample&hold in each ADC, so you can't capture 8 analog inputs 'simultaneously'.

Only sequential sample+conversion is possible.

Nevertheless, it depend on how much sampling time error 'simultaneously' allow in your application.

At 3MSPS sampling rate, there will be only about 3us between the 1st and the 8th channel data conversion.

(sampling rate depend on chosen ADC resolution as well as sampling time. Sampling time depend on channel and your source impedance. Please refer to product reference manual as well as product datasheet for details)

Otherwise, you should have to implement an external sample&hold controlled by e.g. a timer output.

Same timer (using another channel) could also start the ADC conversions on the 8 channels sequentially.

Additional reading: AN2834 and AN3116 (this latest is rather old, but still relevant for most aspects)

Regards.

[Ma.2]

Thanks a lot. Like you said, a few microsec delay won't have a significant effect on the phase. 

I was thinking of starting from the sample design I attached and then go for other solutions like external sample and hold , ADC etc like you suggested. 

I am using the differential amplifier to increase the input signal capture range.

Is there any problem with my design? If so, how can I make it better? 

Any other simple and cost effective way to do this? Thank you again.

[Tesla DeLorean]

Or use an external multi-channel ADC?

What kind of sample rates are you looking for?