ESP32:ADC1 Accuracy

[tekguy49]

I have been characterizing the ESP32 data converters. Measurements on Espressif DevC card(WROOM32)The DAC's look exactly as expected for resistor string dacs. However, ADC1 looks strange. For the record the test are done with the wifi "off" and no application other than the test code running. Setup Below;

1. DAC1 pin connected to ADC1:5 with a .1uf bypass capacitor to nearest ground pin.
Input voltage verified with 5 1/2 digit dvm
2. ADC1 configured to 10 bits with att0(1->1), 0.1 < vAdc < .950v
Each input sample allowed to settle ~5seconds
3. Each ADC1 sample is averaged 20 times
4. No ADC1 calibration, vref does not appear to be trimmed(1.1 volt is assumed)
AdcVal=vref*code/1023

Measured Data
vIn adcVal
0.077 0.008 <- Datasheet shows min. conversion = 0.1v
0.134 0.073
0.195 0.144
0.311 0.277
0.429 0.413
0.547 0.547
0.684 0.684
0.817 0.817
0.962 0.962
1.097 1.097

Can anyone explain the difference error vs input voltage?
Thanks,
tekguy49@gmail.com

[jgustavoam]

Hi,
ESP32 has a HW bug!
https://github.com/espressif/esp-idf/issues/164