PSN-L Email List Message
Subject: Re: Op-Amps
Date: Thu, 10 Mar 2005 16:54:56 -0800 (PST)
Doug and all -
The OP-80 was PMI's first attempt at a CMOS op amp - hence the high input
impedance. Other than that its spec's weren't that great compared to the
other PMI op amps so those of us in marketing didn't think too much of it
- we had a hard time getting our sales force to sell it because we
couldn't give them too much guidance on how to sell it.
More on the OP-400 - it wasn't meant to have the lowest noise because it
was also a low power quad amp (op map voltage noise is directly related to
the collector current in the input differential pair). The OP-470 was
designed as a quad OP-27 and runs at several ma per device - everything in
life is a tradeoff.
> Douglas Gavilanes wrote:
>> You might try the OP80A, which is very low noise and has a high input
>> impedance. A decent second could be the LF356, unless you're locked
>> into another package. Just a thought. Of course, the OP80 is out of
>> production now, I believe, but if you can find some, let me know!
> Not only can't I find a source for the OP80A, I can't locate a data
> sheet. If you have a PDF datasheet file, you are welcome to email it
> to me.
> I will include the LF356 in the survey, because it is well suited for
> second and later filter stages where high value input resistors (low
> bias current and low current noise) may be involved and its fairly
> large offset voltage is not so important. It really needs nearly a
> full +-15 volt supply to produce a perfect +-10 volt output, though.
> There are others that do as well with a +-12 volt supply.
> I hope to produce a graphical comparison of many types that are
> optimum choices for various source impedances, at around 1 hertz
> (lower than the frequency considered in many comparison charts I have
> seen). That 1/f corner frequency where the noise starts to rise as
> frequency falls makes all the difference.
> Looks like I may have to build a web page.
> John Popelish
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