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How to decide on the values for filtering supply noise?

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santhoshv78

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filtering supply noise

While testing a chip( high resolution ADC), the Analog Supply voltages are filtered externally. A large inductor, resistor and capacitor are placed to filter the noise. Can anybody tell me how to decide on the filter values.
what is the basic idea. If anybody has some reference please mention.
The speed of ADC is 50Khz. Analog supply voltage is 3.3V. resolution is 10 bits.
thanks
 

Re: filtering supply noise

The external LC networks act like low pass filters. The cutoff frequency should be low enough to attenuate the noise on the supply so that there is less than 1 LSB error on your measurements.

One easy test is to put a DC signal into the ADC and slowly vary it to see if there are voltages where the output toggles between two adjacent numbers. The range of the input signal that causes this is the equivalent input noise.
 

filtering supply noise

What if I want to filter/reduce the power noise inside of a mixed-mode IC?
 

Re: filtering supply noise

see Decoupling, Bypassing and Layout topics in the attachment.
 

filtering supply noise

decoupling cap inchip maybe help!
but area is a big problem
 

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