Low pass filter with chopper stabilized opamp
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Low pass filter with chopper stabilized opamp

 
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Mook Johnson
Guest
Posted: Tue Feb 08, 2005 8:40 am    Post subject: Low pass filter with chopper stabilized opamp Reply with quote
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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Larry Brasfield
Guest
Posted: Tue Feb 08, 2005 7:06 pm    Post subject: Re: Low pass filter with chopper stabilized opamp Reply with quote
"Mook Johnson" <mook@mook.net> wrote in message
news:S7WNd.19649$sr1.8331@fe2.texas.rr.com...
Quote:
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?


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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Luhan Monat
Guest
Posted: Tue Feb 08, 2005 9:22 pm    Post subject: Re: Low pass filter with chopper stabilized opamp Reply with quote
Mook Johnson wrote:
Quote:
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?





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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Tim Wescott
Guest
Posted: Tue Feb 08, 2005 9:23 pm    Post subject: Re: Low pass filter with chopper stabilized opamp Reply with quote
Mook Johnson wrote:

Quote:
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?

(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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