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ADC problems | Cypress Semiconductor

ADC problems

Summary: 3 Replies, Latest post by dspGuru on 24 Feb 2011 09:03 AM PST
Verified Answers: 0
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user_74911844's picture
7 posts

I'm using the FirstTouch PSoC 3 kit. I have a 1.5V peak - to - peak 40kHz signal coming into my ADC, and i've offset this signal by 1.5V so that it lies between 0 and 3 V. I'm sampling this signal at 30kHz (subsampling). I've set up the ADC in 8 bit Single mode, running between Vssa and Vdda.

My problem is that the received ADC value should be varying between 0 and somewhere close to 255, but actually varies between 125 and 126 ( the centre line). What could the problem be?

user_74911844's picture
7 posts

Ah. It seems the internal filter of the ADC is preventing me from subsampling.

Is there any way to switch off the internal filters of the Delta Sigma ADC?


(Time critical solution needed)

uday's picture
Cypress Employee
569 posts


Can you provide some more information about your input signal. You said its 1.5 Volts peak to peak? that means if you add a 1.5 Volts offset, the signal will vary between 0.75 Volts and 2.25 Volts. 

Also how have configured the ADC, which mode. How are you reading the values from ADC.


user_156863's picture
9 posts

 Hi MechatronicsMan,

I don't believe that you cannot use the Sigma-Delta converter to sub-sample. The principle of operation is to highly oversample the input and then use dynamic correction and digital filters to reduce to the final sample rate. For your application, you may be better off with the PSoC5. It has a SAR ADC, where the sub-sampling should work just fine. Alternatively, you can use the mixers.

Try the new Kit-050 for analog designs.

Kelly C.

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