Hello there,
I would appreciate if someone could help me with an issue I have. I am using ADS8344 to sense several signals from photodiodes. The signal is coming from a standard photodiode amplifier based on an OPAMP. At the OPAMP output I have a voltage divider (1000 and 220 Ohm) and a capacitor (10 nF) to ground for filtering. I use ADC in single-ended scenario and read-out channels one by one in a for loop. ADC is powered by 3.3 V and receives 2.5 V reference from MAX6102EUR+T IC.
The issue is that all successive channels are affected by signal of the previously read ones. For example if I read channel 1 then 2 then 3 and then 4 I see that output of channel 2 to some extend depends on the signal I have on channel 1. Channel 3 is affected by signal of channel 2 etc. If I flip the read out sequence and read channel 4, then 3, 2 and 1, then channel 3 is affected by 4 and channel 2 is affected by 3 in turn.
I have googled for the problem and found that the reason is probably a ghosting effect that appears due to the fact that ADS8344 muxes 8 channels to 1 converter and there is 25pF capacitor in this converter that apparently does not have enough time to discharge. To solve this I tried to decrease SPI frequency and to introduce a delay after read outs, but it did not help. The only way I could remove (but not fully) this effect is to read out the same channel 10 times in a row. If I read it less than 10 times i see the ghosting. I think I am missing something here and would appreciate any help.
Another small and not related question is: this is 16 bit ADC, but the maximum readout counts that I get is 32 800 so 15 bit. I did not do research on this so far, but what am I doing wrong here? 
Many thanks for your help!
Rinat.
