Does input(+) of ADC DelSig can receive minus voltage?

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Does input(+) of ADC DelSig can receive minus voltage?

Postby sbonylean » Wed Nov 27, 2013 3:13 am

Hi, Guys. I'm trying to receive a signal by using PSoC and send the data to my PC.
What I want to know is that input(+) of ADC DelSig can sense minus voltage.
For example, at the input mode of differential, +/- 2.408V range and input(-) of ADC is connected to VSSA, is it possible to convert input(+) = -1.5V to digital value?
input(+) = -1.5V, input(-) = Vssa(GND) -> converted data = -1.5V ??
Any help will be appreciated.
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Re: Does input(+) of ADC DelSig can receive minus voltage?

Postby danadak » Wed Nov 27, 2013 3:47 am

If you use mode w/o buffer the CM range extends below ground by ~ 100 mV.

If you need a larger CM range you can do this simple trick with R's, to effect
a DC level shift, see attached.

Regards, Dana.
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ADinput negative inputs.zip
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Re: Does input(+) of ADC DelSig can receive minus voltage?

Postby sbonylean » Wed Nov 27, 2013 5:06 am

I appreciate for your reply, Dana.

Do you mean that it is impossible to connect input(+) of ADC_DelSig to minus voltage and therefore I should use level shift circuit?
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Re: Does input(+) of ADC DelSig can receive minus voltage?

Postby danadak » Fri Nov 29, 2013 5:18 pm

Yes, you have to level shift into the CM range of the Analog System on chip.

Outside that range you turn on protection diodes and other parasitic elements
in CMOS process.

As pointed out earlier there are settings that allow you to go 100 mV out of CM range,
but that's it.

Regards, Dana.
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Re: Does input(+) of ADC DelSig can receive minus voltage?

Postby sbonylean » Sun Dec 01, 2013 6:18 am

Thank you for your reply, Dana :)
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