Do I Need a Buffer for My ADC When Sharing a Bus with NAND Flash?

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quantum8000
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somebody says put a buffer between a bus and an ADC .even if the ADC has an internal buffer. it iminimises the noise feed through,and may improve ADC accuracy by lowering power dissipation.
in the project i am working on,the ADC must share 16bit BUS with a nand flash.the bufer is necessary? and what is the meaning of the buffer?
 
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Buffers are primarily used to match inpedance whether from voltage, current or RF.

http://en.m.wikipedia.org/wiki/Buffer_amplifier

an impedance mismatch in the case of signals and RF can cause damage to sensitive circuitry such as ADC's. A mismatch in RF for example creates reflective waves and inducing reflective voltages.
There are two main types of buffers. Current or voltage.
 
Mordred has answered the question for the analogue side. But the digital side can also be important.

A digital buffer can help isolate digital bus noise from the ADC chip. However, there should be separate ground planes for the analogue and digital sides of the chip. The ADC chip should have some form of differential analogue input that will minimise digital noise coupling into the analogue and reference inputs.

The manufacturer will provide a recommended PCB layout for operation, and will specify conditions for measurement of conversion noise. You will need to consult those details before you can decide on an acceptable noise environment for the ADC chip in your application.