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Values for Input RC Filter for ADC
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sakthivel.eee



Joined: 19 Jun 2009
Posts: 14
Location: Pune
Post24 Oct 2009 4:37   

Reg:Input Filter for ADC
Dear All,
How to decide R and c values of input filter to ADC. I know that it is depends on the cutoff frequency which is maximum frequency of input signal. But what is maximum value of resistance and capacitance should be used at the input of ADC. Is there any other factors which decides these values like input impedence of ADC, Internal Capacitor of ADC etc.,?

I have used Op-amp for signal condtioning, Before opamp i have low pass filter. Is it necessary to use one more filter or capacitor after op-amp?


Thanks in advance,

Thanks & Regards,
Sakthivel.S
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FvM



Joined: 22 Jan 2008
Posts: 5162
Helped: 767
Location: Bochum, Germany
Post24 Oct 2009 18:29   

Re: Reg:Input Filter for ADC
Generally, it's a good idea to follow the ADC vendors reference design, at least if you don't have an exact understanding of the requirements.

Quote:
Is it necessary to use one more filter or capacitor after op-amp?
May be, depending on the (unsaid) ADC type. It can be required to isolate ADC switching input currents from the OP or to reduce the noise bandwidth. Also in this regard, check the reference designs.
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sakthivel.eee



Joined: 19 Jun 2009
Posts: 14
Location: Pune
Post25 Oct 2009 5:41   

Re: Reg:Input Filter for ADC
Dear Sir,
My ADC is SAR only

Sakthi
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FvM



Joined: 22 Jan 2008
Posts: 5162
Helped: 767
Location: Bochum, Germany
Post25 Oct 2009 11:07   

Reg:Input Filter for ADC
A SAR ADC needs a S/H-circuit, but not necessarily an input filter.
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sakthivel.eee



Joined: 19 Jun 2009
Posts: 14
Location: Pune
Post26 Oct 2009 4:19   

Re: Reg:Input Filter for ADC
Dear Sir,
I am using the ADC in the microcontroller.. Does this not require input filter for anti-alising?


Sakthi
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