ADS1220EVM: interchannel singal mixing

Hi Arjun,

What channels are the signals being applied to?

Are the signals single-ended?

Best Regards,

Angel

When testing with one single-ended and one differential, as well as two single-ended we are facing this issue. In two differential we haven't faced this problem.

Hi Arjun, 

What is the signal source being used for the analog inputs of the EVM?

Can you share a picture or a wiring diagram?

Do your input signals establish a common-mode or share a GND with the ADS1220, or are they floating?

-Angel

AIN0 and AIN1 was connected to a bridge-type sensor which was driven by iDAC (return path to ground), and AN2 and AIN3 connected to single end sensor where it was configured to work as single end by grounding AIN3.

Hi Arjun,

Is this the full schematic? 

Earlier you mentioned you were applying a 5 and 10Hz signal to the ADC, but now you mention you are measuring the output of a bridge using the ADC's IDAC as an excitation current. 

You also claim AIN3 is grounded but the schematic shows a connection to the ADC power supply and to a capacitor. 

Can you please help clarify the setup and issue as this description is somewhat confusing.

Best Regards,

Angel

Hi,

The 5 and 10Hz signals were tested on EVM board tapping SPI lines to a STM32 controller. These were single ended outputs from function generator. Sensors mentioned before were also tested with the same EVM board. The problem came to notice while we were testing our design where the same issue was faced. But when two differential sensors were connected, we didn't observe this.

Correction: Instead of AIN3, AIN2 is grounded.

For clarity given cased when tested with EVM board (connected to STM32 controller) as well as our design:

• interchannel mixing happening when 2 single-ended sources given.
• interchannel mixing happening when 1 single-end and 1 differential source given.
• no interchannel mixing when connecting 2 differential sources.

Regards,

Arjun

Hi Arjun,

Is this mixing of signals in different channels happening as well for your sensor measurements, or just the 5-10Hz input test signals?

I suspect that this may be caused be the input tests signals not establishing a common-mode with the ADC or share a same ground i.e. are "floating".

Can you confirm if this is the case?

This is unusual behavior.

Is the plot shown earlier a result of the ADC reading, or is this measured with a scope at the analog input pins of the ADC?

-Angel

It is seen for both sensor measurement as well as test signals.

• interchannel mixing happening when 2 single-ended sources given.
• interchannel mixing happening when 1 single-end and 1 differential source given.
• no interchannel mixing when connecting 2 differential sources.

The sensors have common return path to ground, both single end sensor as well as differential sensor (bridge-based).

The plot is from acquisition using STM32 microcontroller, where the controller acquires the data and send the data via USB.

Hi Arjun R K,

Angel is out of the office today, he will get back to you in the next 1-2 days

-Bryan