Low pass filter with chopper stabilized opamp

Feb 08, 2005 3 Replies
M

I'm looking for a anti-alias filter for my sub-hertz filter discussed previously. (thanks for the responses)



For this I need at least 2nd order to prevent aliasing down to the frequencies of interest to me. Looks like I wont be able to avoid an OP-amp in the signal chain so I'm looking for one with as little DC drift as possible.



Chopper stabilized (like the linear tech "zero drift") appear to to be some of the betterones for low drift with temeprature. With the current non-chopper precision Analog Devices amps there is considerable drift with temperature.



My question is if there are any special considerations for a chopper amplifier when configuring it as a low pass filter?


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L

previously. (thanks for the responses)

of interest to me. Looks like I wont be able to

drift as possible.

the betterones for low drift with temeprature.

considerable drift with temperature.

when configuring it as a low pass filter?

You need to be careful that the amplifier is not asked to process signals near the chopping frequency. This means getting at least that part of the input spectrum reduced passively.

--Larry Brasfield email: donotspam_larry_brasfield@hotmail.com Above views may belong only to me.
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L

Hi,

The ciruits for low pass filters using op-amps have very little drift or offset due to massive amounts of negative feedback (i.e. the op-amp is run at gain of 1 or 2.

Luhan Monat (luhanis 'at' yahoo 'dot' com) "The future is not what it used to be..." http://members.cox.net/berniekm
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T

(a) As Larry said, choppers do odd things around their switching frequencies. Last time I looked (years ago) Linear claimed that they had significantly reduced the effect. I'd still treat it as something that's going to alias.

(b) You can always sample faster and use an RC filter, assuming you can stand the series R between your signal and your ADC.

Tim Wescott Wescott Design Services http://www.wescottdesign.com
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