Other Parts Discussed in Thread: ADC128S102
I am using the ADC128S102EVM to evaluate the ADC128S102 and I am experiencing crosstalk between channels.
My test setup is fairly simple.
I have connected the EVM board to an STM32F7 uC and I am simply alternating scans between channel 0 and channel 1 and I am injecting DC voltages on each channel and measuring the effect on the alternate channel. The DC sources are buffered, low impedance sources. I am running SCLK at 16MHz, and I am pulling CS high for 1us between samples. Vdd = 3V3 and VA = 5.148V which is well filtered and clean
When I inject 0V on Ch0 and Ch the output reading on both channels is 0 as expected.
However, when I inject 3V3 on Ch1 and 0V on Ch0 the readings are as follows: Ch = 2624 (3.298V) and Ch0 = 0009 (11.3mv) The analog inputs are reading 0.000V on a Fluke 179.
I thought that this might be due to the kick back filter (I am using the default on the EVM board which is a 48kHz cut-off, [200R and 10nF RC Lowpass]).
In order to test this I lowered the SCLK frequency 8MHz to increase the acquisition time, this has had little to no effect, I read 0008 instead of 0009 which I am putting down to an expected variation of 1 bit.
After lowering SCLK, I am now doing a dummy scan on each channel and discarding the result. Eg, I scan Ch0 throw away the result, then scan again and keep the value. Then I scan Ch1, throw away the result and scan it again to store the value. I repeat this cycle. I would expect this to remove the possibility of charge transfer from the sampling capacitor when switching channels affecting the readings. There has been no improvement after this change. As I lower Ch1 to 1V Ch0 reads 0003 and when Ch1 = 500mV, Ch0 reads 0001 so the readings on Ch0 seem to be related to Ch1.
Things to note, As the EVM board is connected to an STM evaluation board the layout is not ideal. There is some noise present, however, if that was causing the readings I would expect to have a reading when both inputs are 0V, is this an incorrect assumption?
Any assistance will be greatly appreciated.
Thanks in advance!