adc measurement

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Anonymous
Not applicable

Hello i'm am a newbie on using psoc and we are trying to use the delta sigma adc of the psoc5 dev board. But the problem ee are facing is the voltage reading we get from the circuit drops when we are reading it using psoc. The signal rates at 0 to 5 volts. Can someonr tell us what is thr reason for the voltage drop??

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ETRO_SSN583
Level 9
Level 9
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Can you post schematic and project, so we don't have to guess

   

how you have configured and what external interface looks like.

   

 

   

    

   

          

   

“File”                                                             Creator

   

“Create Workspace Bundle”

   

Use Firefox or IE or chrome to post.

   

 

   

 

   

Regards, Dana.

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HeLi_263931
Level 8
Level 8
100 solutions authored 50 solutions authored 25 solutions authored

What do you mean by "the voltage readings drop"? Does the signal you measure change? Do you just measure aa voltage that is too low? For signals that span from GND to Vdd you need to configure the ADC input buffer proeprly - look at the data sheet for that.

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Anonymous
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 the configuration of the ADC where given by our professor so we only know a little bit on it. the level shifter compresses the voltage from the main circuit from -14 volts to 14 volts into a 0 to 5 volts ratio. i posted the schematic of the circuit an the configuration of the adc.

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Anonymous
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here is the configuration

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ETRO_SSN583
Level 9
Level 9
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There are several considerations here -

   

 

   

1) With A/D configed with input buffer on you can see by graphic it cannot

   

range from gnd to Vdd, eg. its common mode range is NOT rail to rail.

   

 

   

2) You can config input buffer off, then input CM range exceeds 0 - Vdd,

   

however A/D input Z drops to 74 K (for 16 bits) which then upsets the

   

level shifter / divider in schematic, R11/12/13. So you would have to calc

   

new values for them.

   

 

   

3) The actual V at input to PSOC is level shifted and attenuated by R11/12/13.

   

That is reason voltage drops when referred to OP27's output.

   

 

   

Regards, Dana.

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Anonymous
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thank you for your help i'll try to do all of your suggestions

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