STM32F205zc ADC scan mode singel crosstalk problem

Barbie · ‎2014-12-16

Posted on December 16, 2014 at 14:16

I have a problem of crosstalk between sequence channels scan automaticly on the ADC3,2 of the MCU. It is look like it is depend on the sequnce of the sample becase the voltage changes on the first scan channel influence the second one scan but not vice versa. So it is look like the internal sample cap didn't discharge between the sampling. So I prolong the sampling time for each of them from 3cycles to the maximum of 480cycles and also lower the ADC clk from dev2 to div8 but didn't help.

1. Is someone see that phenomena and get to solve it?

2. Is there anther setting can reduce this influence?

Thanks

Bar.

#crosstalk-stm32f205-adc

AvaTar · ‎2014-12-16

Posted on December 16, 2014 at 14:31

So it is look like the internal sample cap didn't discharge between the sampling.

Quite possible. But this is no crosstalk, but a common component - there is one S&H capacitor for all channels of one ADC.

So I prolong the sampling time for each of them from 3cycles to the maximum of 480cycles and also lower the ADC clk from dev2 to div8 but didn't help.

If longer sample times do not help, your input impedance is far too high, at least for the affected channels. Use buffer amplifiers (e.g. opamp in voltage follower mode).

Barbie · ‎2014-12-16

Posted on December 16, 2014 at 15:40

Hi,

thanks argentum. You are right- it's not really cross talk- because even when the sampled data is DC and not AC- we get a constant error in the following channel.

Our inputs are buffered and filtered in a standard way (i.e. the analog input is buffered- and enters the ADC port via 33ohm+100pF LPF).

We also did the following test: we are sampling each channel on a different (internal) ADC: the first channel on ADC2, and the following channel on ADC3. In this way the error on the second channel does not appear.

Tesla DeLorean · ‎2014-12-16

Posted on December 16, 2014 at 16:42

Can the source in question supply enough current to charge/discharge the capacitor? Do you need a buffer?

Nevermind, missed the earlier responses...

Tips, Buy me a coffee, or three.. PayPal Venmo
Up vote any posts that you find helpful, it shows what's working..