instrumentation amplifier & anti-aliasing

[Ponkan]

Hi,
I was wondering if I could "integrate" easily a low-pass filter (for
ADC anti-aliasing purpose) in an instrumentation amplifier.
I would not want to include an active filter between the
instrumentation amplifier (the ADC buffer) and the ADC itself. Just
wanted to use to the instrumentation amplifier to do the job. Any
idea? For the instrumentation amplifier I was thinking of the
Burr-Brown INA128 and for the ADC the Burr-Brown ADS7813. The ADC can
work at up to 40kHz and I would like to limit the input bandwidth to
10kHz. Maybe a simple RC between them is enough... I would like to see
your points of view.

 

[Bob Masta]

On 23 Jul 2003 22:53:24 -0700, amizadefriend131@hotmail.com (Ponkan)
wrote:

Hi,
I was wondering if I could "integrate" easily a low-pass filter (for
ADC anti-aliasing purpose) in an instrumentation amplifier.
I would not want to include an active filter between the
instrumentation amplifier (the ADC buffer) and the ADC itself. Just
wanted to use to the instrumentation amplifier to do the job. Any
idea? For the instrumentation amplifier I was thinking of the
Burr-Brown INA128 and for the ADC the Burr-Brown ADS7813. The ADC can
work at up to 40kHz and I would like to limit the input bandwidth to
10kHz. Maybe a simple RC between them is enough... I would like to see
your points of view.

The main point of using an instrumentation amplifier is that it
has differential inputs with good common mode rejection.
If you try to turn a differential input into part of a filter, you
will almost certainly mess up the common mode rejection,
not to mention needing extra parts for each input. Why not
just use a separate op-amp filter stage?

Also, depending on exactly what you are using the ADC
for, you may be better off not using any filter at all.
You need a filter if you want to be able to handle any
arbitrary input without aliasing, but I have found that
there are huge numbers of applications where this
isn't really needed. And if it *is* really needed, it
usually needs something a whole lot beefier that
the simple few poles you are likely to want to build
yourself.

Tell us about your application and we may be able
to give specific advice.


Bob Masta
dqatechATdaqartaDOTcom

D A Q A R T A
Data AcQuisition And Real-Time Analysis
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