op-amps

[kv at us.ibm.com]

Also-

By definition- the Ideal op-amp has high impedance inputs... there is
another class of op-amps called "current feedback" opamps that change the
rules a bit though...  these are quite neat and can be read about in
various databooks.  Primary advantage is that they have a constant
bandwidth regardless of gain.

________________________________________________
  Kevin Vannorsdel     IBM Arm Electronics Development
   408-256-6492                Tie 276-6492     kv at us.ibm.com



Frederic Breitwieser <frederic at xephic.dynip.com> on 04/21/99 01:49:46 PM

Please respond to diy_efi at efi332.eng.ohio-state.edu

To:   diy_efi at efi332.eng.ohio-state.edu
cc:    (bcc: Kevin Vannorsdel/San Jose/IBM)
Subject:  Re: op-amps





> What is an op-amp and what does it do?  I have an LM2904N 8-pin chip and
> I understand it it a dual low power op-amp and I'd like to understand
> it's function.

OP-AMP stands for "Operational Amplifier".  By setting the gain with two
resistors, you can amplify or deamplfy a signal easily.  Say you have a
sensor, like an 02 sensor, that produces 0-1V.  You can use an OP-AMP to
change the output range to 0-5V for your microprocessor or other device.
This is the most common use actually.  Also, most stereo pre-amplifiers use
variations of the op-amp.  Remember the turntables used to have a
pre-amplifier installed before your tuner?  These converted the 0-350mv
signal to 0-1.5V typically required by stereo systems, as well as the
impedance, which is another use for an Operational Amplifier.

"Operational" comes into play as you can add signals (mix), subtract
signals, invert, and do other neat stuff.  So, you can take your 0-5V input
and reverse the range (5v - 0V), etc.

They are many variations, some are temperature compensated, so that their
output is consistant with a wide temperature range - most analog
semiconductors will drift with temperature shifts.  Some Op-Amps also have
high impedance inputs, good for high sensitivity applications.

Hope that wasn't too convoluted.

--

Frederic Breitwieser
Bridgeport CT 06606

1993 Supercharged Lincoln Continental
1989 HWMMV w/turbocharged 500cid Caddy
1975 Dodge D200 Club Cab soon to have 431 stroker + turbos
2000 (I hope) Buick GTP (Mid-Engined Sports Car)