One of the ADC channel is noisy

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Anonymous
Not applicable

Greetings,

I have a delta sigma ADC connected to mux for sampling three signals. I get two signals correctly but the third signal channel seems to be quite noisy. Below i have attached an image showing the ADC reading. The reading in red color is third channel and is more noisy than others. All channels are differential and connected to  pins from 4[2] to 4[7].  ADC conversion rate is 42000sps.

Is there any suggestion how to reduce the noise in third channel? Why there is noise more in one channel compare to other channels?

Also some times i get glitch in all the channels. What could be the reason for it? An image of glitches is also attached below.

Thank you.

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15 Replies
rola_264706
Level 8
Level 8
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How about posting your project by clicking on File then Create_WorkSpace_bundle and attaching it to a new comment.  Also lets see your schematic.

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odissey1
Level 9
Level 9
First comment on KBA 1000 replies posted 750 replies posted

I suspect a crosstalk to some adjacent digital pin. Try to move to another set of pins and see the result.

/odissey1

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Anonymous
Not applicable

hi,

i tried with other set of pins but it dint help much. One more thing i observed that when i connect the adc pins to sensor,  debugger led on PSoC board lights up even without powering PSoC. Why is it so? How can i avoid this? I suspect it can potentially damage my PSoC.

Thank you.

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Yes you can damage PSoC. You probably have a ground loop.

Disconnect all sensors from PSoC board and make sure that blue LED is not active.

Then short ADC inputs 1-3 ( with resistors) and check that no ADC noise observed.

Also post the schematic of the sensor, that will help (png/jpg, not full project).

/odissey1

Anonymous
Not applicable

hello,

The sensor what i am connecting is a quadcell (https://www.thorlabs.com/drawings/338563b2dc83dd4f-A4CD8DA6-EA77-8E3D-FE2D31014DC1B8F8/PDQ80A-SpecSh... ). It gives analog output voltage which i am trying to read through ADC.

I tried shorting adc inputs but i get spikes in output instead of zero reading as shown below.Spikes.PNG

Thank you.

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Your link has an error and I was unable to view the information on the sensor.  Also have you tried other Analog mux components?

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What version of Psoc Creator are you using?

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Anonymous
Not applicable

Here it is  https://www.thorlabs.com/thorproduct.cfm?partnumber=PDQ80A

Other mux i haven't tried, but i still couldnot figure out the problem. I am using PSoC creator 4.1.

Thank you.

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rola_264706
Level 8
Level 8
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One other thing you should be using a Star Ground.  That means all of the grounds are connected to same place.without any distance from each other.

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rola_264706
Level 8
Level 8
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Channel Ch_EXm is open it has no assigned pin.

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Anonymous
Not applicable

Yes, all grounds were connected to same place. The Ch_EXm is unconnected, but i think that should not affect other channels reading. Also i just read that channel and discard it.

Thank you.

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The PDQ80A has an Output Voltage Range of ± 2 Vmin

You must have a level matching scheme.

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StFa_285751
Level 3
Level 3
25 replies posted 10 replies posted 5 replies posted

This most likely doesn't apply because the pins you've assigned are different, but the symptoms are similar to an issue I had. So for the record:

If you're using the CY8C58LP processor module, when using pin P15[7] as an ADC input I saw a lot of noise. I then found in the documentation that R18 on the back of the module is to be removed when not using P15[7] for cap sense. Noise gone.

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rola_264706
Level 8
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Are you using this kit

CY8CKIT-050 PSoC® 5LP Development Kit 

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Anonymous
Not applicable

No i am using freesoc2, CY8C5888AXI-lp096 device.

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