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Need suggestion on schematic of AD7682

Question asked by richiechen on Jan 9, 2013
Latest reply on Jan 14, 2013 by KarenNE

Hi all

 

I am trying to design an ADC circuit based on AD7682 and ADA4841-2.

 

Three channels of the ADC will be used. Two of them will be connected with bipolar signals ranging from -2V to +2V. These signals are basically DC signals, since they are outputs of a Lock-in Amplifier. However, since ADC can only measure positive voltages, they should be shifted up by +2V.

Here comes my question:

 

1.

For INCC=010, Bipolar, referenced to COM, 0.5VREF+-0.1

For INCC=110, Unipolar, referenced to COM, GND+-0.1

What are the differences of these two modes when my application is concerned? What I do not understand is that why does the ADC need to know whether COM is connected with 0.5REF or GND, since the results can be easily calculated by minus 0x8000??

Furthermore, if COM=0.5VREF is chosen, the COM pin needs to be connected further with 0.5VREF, which increases the current need a little bit.... 

 

2. I am not experienced with ADC design AT ALL. Could you please help to look at my schematic? It would be really appreciated.

Current setting is :

Internal voltage reference,

IN1 and IN2 level shifted by 2V,

Every channel is referenced to GND

 

 

Regards

Richie CHEN

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