PSN-L Email List Message
Subject: Re: Filter input
From: ChrisAtUpw@.......
Date: Wed, 10 Mar 2010 06:52:41 EST
In a message dated 10/03/2010, barry_lotz@............. writes:
Hi All
I was using multipole LP filters with my seismographs. They use the opamp
non-inverting input. The note with the filter design says that the input "
must return to ground via a low-impedance dc path". I wanted to reduce in
half the input to the filter. I know the output of an opamp buffer would work
but if I used a voltage divider w/o the buffer how low of resistor would
be considered "low impedance".
Hi Barry,
You can download a FREE filter design program from _www.ti.com_
(http://www.ti.com) called FILTERPRO.
The 'return to ground' is either the earth end of the coil or the zero
level of the previous opamp. If you are using a Sallen&Key filter and want
to reduce the input sensitivity, you can connect a resistor 1/10 the input
filter resistor value to earth and put a >x10 resistor onto the junction.
Regards,
Chris Chapman
In a message dated 10/03/2010, barry_lotz@............. writes:
Hi=20
All
I was using multipole LP filters with my seismographs. They use=
the=20
opamp non-inverting input. The note with the filter design says that the=
input=20
" must return to ground via a low-impedance dc path". I wanted to reduce=
in=20
half the input to the filter. I know the output of an opamp buffer would=
work=20
but if I used a voltage divider w/o the buffer how low of resistor would=
be=20
considered "low impedance".
Hi Barry,
You can download a FREE filter design program=
from=20
www.ti.com called FILTERPRO.
The 'return to ground' is either the earth en=
d of=20
the coil or the zero level of the previous opamp. If you are using a=20
Sallen&Key filter and want to reduce the input sensitivity, you can co=
nnect=20
a resistor 1/10 the input filter resistor value to earth and put a >x10=
=20
resistor onto the junction.
Regards,
Chris Chapman
[ Top ]
[ Back ]
[ Home Page ]