How to resolve the analog multiplexer cross talk for 16 bit ADC ?

Ekko · ‎Jun 16, 2021

Hi

I encountered a problem while using AMUX to switch channel for 16 bit or higher resolution Delsig ADC.

I verify that in CY8CKIT-050 board and run the example project as below show, it can works as expected.

but when I change the ADC resolution to 16 bit, and input fixed voltage like half of power, the readout is abnormal of which jitter is serious, I think the Amux cause that, so I increase the delay time before start ADC to keep enough time after change channel, no matter what long I delay, the problem is still exist. I am confused about this problem.

I hope someone can help me solve this problem, thanks very much!

Best Regards,

Ekko

Len_CONSULTRON · ‎Jun 23, 2021

Ekko,

I've modified your project and simplified it to prove if the the Amux and ADC_DelSig is working at 16bit resolution.

I've attached my modified version of your project.

Here are a list of modifications:

Disabled all DMA. The DMA could be a factor in the 'wonky' conversion issues.
Disabled the DMA_done isr. This is because I disabled the DMA chain. I use the ADC_DelSig_IsEndConversion(ADC_DelSig_WAIT_FOR_RESULT).
I synchronize which channel is being sampled by reading the LUT output through a contiguous port pin assignment.
Added a UART Terminal debug output for the ADC counts and Converted mV for Vin0, Vin1, and Vin2 inputs. (115.2Kbps 8N1)
Added a systick ISR to allow for debugging output every 1 second.
Added 3 VDAC8s to generate static voltages from the CY8CKIT-059 board pins to be routed to the Vin0, Vin1 and Vin2 pins. This is used as input stimulus without external equipment.
Changed the VDD values (VDDA, VDDD, VDDIOx etc) in the DWR/System tab to the measured value of 4.8V. I did this because you chose to use the vref to the ADC_DelSig to be VDDA/4. Therefore by setting the VDDA value in the DWR/System tab to a more accurate value, allows the ADC_DelSig_CountsTo_mVolts() to better compensate to a more accurate value. Note: As /odissey1 pointed out, if you use change the ADC Input range: to "Vssa to 1.25V" and the Reference: Internal 1.024V, this setting is not needed.
Some pin assignments. Change if you need.

In the debug output to the terminal, I display Vin0, Vin1 and Vin2 values as ADC counts and converted mV values.

The results are very close to the expected values of Vin0 = 400mV, Vin1 = 100mV and Vin2 = 900mV.

Vin0 = 157C cnts   Vin1 = 592 cnts  Vin2 = 3152 cnts    Vin0 = 402mV  Vin1 = 104mV  Vin2 = 924mV
Vin0 = 1579 cnts   Vin1 = 593 cnts  Vin2 = 312F cnts    Vin0 = 402mV  Vin1 = 104mV  Vin2 = 922mV
Vin0 = 157B cnts   Vin1 = 591 cnts  Vin2 = 3108 cnts    Vin0 = 402mV  Vin1 = 104mV  Vin2 = 919mV
Vin0 = 1578 cnts   Vin1 = 592 cnts  Vin2 = 310A cnts    Vin0 = 402mV  Vin1 = 104mV  Vin2 = 919mV
Vin0 = 157A cnts   Vin1 = 596 cnts  Vin2 = 310C cnts    Vin0 = 402mV  Vin1 = 104mV  Vin2 = 919mV
Vin0 = 1571 cnts   Vin1 = 593 cnts  Vin2 = 3111 cnts    Vin0 = 402mV  Vin1 = 104mV  Vin2 = 920mV
Vin0 = 1571 cnts   Vin1 = 593 cnts  Vin2 = 310B cnts    Vin0 = 402mV  Vin1 = 104mV  Vin2 = 919mV
Vin0 = 156D cnts   Vin1 = 593 cnts  Vin2 = 3113 cnts    Vin0 = 401mV  Vin1 = 104mV  Vin2 = 920mV
Vin0 = 1563 cnts   Vin1 = 599 cnts  Vin2 = 3106 cnts    Vin0 = 401mV  Vin1 = 104mV  Vin2 = 919mV

Summary: In this modified project, I can say the ADC_DelSig with front-end AMUX is working.

Check your DMA.

I recommend simplifying the DMA chain first to replace the ADC_DelSig_IsEndConversion(ADC_DelSig_WAIT_FOR_RESULT) and move the results into the vin_adc array and use the debug terminal output as a verification of solid results.

Len
"Engineering is an Art. The Art of Compromise."

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How to resolve the analog multiplexer cross talk for 16 bit ADC ?

How to resolve the analog multiplexer cross talk for 16 bit ADC ?

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