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Role of Dummy capacitors in SAR ADC (Read 4793 times)
eternity
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Role of Dummy capacitors in SAR ADC
Jul 07th, 2014, 9:37am
 
Dear all,
           I just want to get clarified about the role of dummy capacitors in SAR ADCs. The dummy capacitor in the DAC array is used only for realising  Vref quantities in terms of base-2 radix. or is it also used to realise some other functions too?

Thanks to all

Eternity
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loose-electron
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Re: Role of Dummy capacitors in SAR ADC
Reply #1 - Jul 7th, 2014, 5:32pm
 
Dummy devices are often used to serve as a similar perimeter device so all active devices exist in an identical environment. This often helps with component matching
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eternity
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Re: Role of Dummy capacitors in SAR ADC
Reply #2 - Jul 8th, 2014, 2:51am
 
Hi there
thanks for the reply.
I guess you interepreted my question in terms of layout

I meant in terms of schematic. There is usually an extra unit cap placed in the DAC of SAR ADC to get binary weighed Vref levels(Vref/2, Vref/4..etc.,). I recently spotted in a journal seeing that extra cap connected to input voltage rather than to vref. So I want to get cleared on this.

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Eternity
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Re: Role of Dummy capacitors in SAR ADC
Reply #3 - Jul 8th, 2014, 12:03pm
 
If it is on a reference voltage it could be for high frequency stability or reduction of coupling noise.
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RobG
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Re: Role of Dummy capacitors in SAR ADC
Reply #4 - Jul 10th, 2014, 5:30pm
 
eternity wrote on Jul 8th, 2014, 2:51am:
Hi there
thanks for the reply.
I guess you interepreted my question in terms of layout

I meant in terms of schematic. There is usually an extra unit cap placed in the DAC of SAR ADC to get binary weighed Vref levels(Vref/2, Vref/4..etc.,). I recently spotted in a journal seeing that extra cap connected to input voltage rather than to vref. So I want to get cleared on this.

Thanks
Eternity

Interesting... which article had that?
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