Confusion on using ESP32-S3 ADC

[robzy]

I want to use the ESP32-S3 ADC which proudly boasts that it can do 100ksp but I can't seem to work out how to practically use that because of bandwidth limitations.

The docs say you should ideally connect a 100nF ceramic capacitor to the ADC pin (source).

However, its also well known that the ADC pins will glitch low for 60uS on startup (source).

That low glitch would require an impedance of roughly 500ohms to avoid a significant over-current situations.

But an impedance of roughly 500ohms would make a low-pass filter with the 100nF capacitor for a bandwidth of roughly 3kHz.

What gives? Can I drop the capacitor to get more bandwidth at the expense of noise?

[Smokey]

At least there isn't a 0-250mV dead zone like in the original ESP32 ADC.  Who knows how that ended up being the case.  So they have a history of crappy ADCs.

The plot shows a decrease in noise between no cap and 100nF.  Interpolate between those and pick a cap that works with your series resistance maybe?
https://docs.espressif.com/projects/esp-idf/en/stable/esp32/api-reference/peripherals/adc_calibration.html


You could also buffer the ADC with an opamp that has an enable pin.

[robzy]

Thank you for confirming that I'm not losing my mind.

Its great that it has an ADC, but it definitely doesn't give practical 100ksps performance.

I'll drop an MCP3201 SPI ADC in there and be done with it. Should be able to do 50ksps easy with 3.3V.