LM4250 Programmable OP-AMP.

I

ian field

Guest
Is this device suitable for use as a variable gain amplifier like the
discontinued LM3080?

TIA.
 
ian field wrote:
Is this device suitable for use as a variable gain amplifier like the
discontinued LM3080?

TIA.


It is not a direct replacement.
Click to expand...

pin lay out is different, bias voltage is different how ever,
if you're in the engineering mood, then I guess you could make it
work.
 
"Jamie" <jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote in message
news:gAifm.109681$FP2.71774@newsfe05.iad...
ian field wrote:
Is this device suitable for use as a variable gain amplifier like the
discontinued LM3080?

TIA.
It is not a direct replacement.

pin lay out is different, bias voltage is different how ever,
if you're in the engineering mood, then I guess you could make it
work.
Click to expand...
It appears the programming pin is the other way up so it has to be driven by
a current sink rather than a current source, other than that how much
difference do the internal differences make?
 
"whit3rd" <whit3rd@gmail.com> wrote in message
news:b5d35e4c-93ad-4879-be2b-23f608f5b4da@r36g2000vbn.googlegroups.com...
On Aug 7, 2:49 pm, "ian field" <gangprobing.al...@ntlworld.com> wrote:
Is this device suitable for use as a variable gain amplifier like the
discontinued LM3080?
Click to expand...
Not really; the program pin changes the slew rate, but the gain
is high and uncontrolled. If you really want something 'like the
CA3080',
there's LM13700 and JRC13700 (dual, with some accessories, but
very similar to CA3080). They're terrible amplifiers, though,
with high input currents, and low output current. The Darlington
followers (see the pinout) help.

--------------------------

The NS web page lists the LM13700 as 1998 last time buy - is the JRC part
still in production?
 
On Aug 7, 2:49 pm, "ian field" <gangprobing.al...@ntlworld.com> wrote:
Is this device suitable for use as a variable gain amplifier like the
discontinued LM3080?
Click to expand...
Not really; the program pin changes the slew rate, but the gain
is high and uncontrolled. If you really want something 'like the
CA3080',
there's LM13700 and JRC13700 (dual, with some accessories, but
very similar to CA3080). They're terrible amplifiers, though,
with high input currents, and low output current. The Darlington
followers (see the pinout) help.

For something with gain control, I'd consider THAT2181 or other
more modern transconductance amp designs. Single-source
and pricey, alas.
 
On Aug 8, 2:15 pm, "ian field" <gangprobing.al...@ntlworld.com> wrote:
"whit3rd" <whit...@gmail.com> wrote in message
... If you really want something 'like the
CA3080',
there's LM13700 and JRC13700 (dual, with some accessories, but
very similar to CA3080).

The NS web page lists the LM13700 as 1998 last time buy - is the JRC part
still in production?
Click to expand...
Checking, the actual part number is NJM13700, from JRC's NJR (?)
division...
and it shows as in-stock at distributors. The JRC web site doesn't
have any
end-of-life warnings I can see. I bought some this year.
 
On Fri, 7 Aug 2009, ian field wrote:

Is this device suitable for use as a variable gain amplifier like the
discontinued LM3080?

Walter Jung's "IC Op-Amp Cookbook" has a section on programmable opamps,
Click to expand...
but it has nothing about using them as variable gain amplifiers. A bit
later in the book, he does cover the CA3080, which isn't really an opamp,
but is useful as a variable gain element.

The odd thing is, the schematic for the 4250 does have a resemblance
to a variable gain amplifier, a current source feeding a differential
amplifier. So if one had one, one ought to play with it and see
what happens.

On the other hand, you didn't really tell us what you want. Lots
of things will provide voltage controlled gain, some being better
than others. Any four-quadrant multiplier will work, any 3
transistor differential amplifier will work (changing the voltage
on the common transistor to ground will change the gain), though
not as "perfectly" as the four-quadrant multiplier. Something like
the MC1350p, which may be out of production I don't know, is a variable
gain stage intended for radio work, but it works at audio. Lots of
other devices one could pull off consumer electronic equipment.

But until the end need is described, everyone is going to go after
"more modern" transconductance amplifiers to replace the 3080 rather
than devices that will accept a control voltage to vary gain.

Michael
 
"Michael Black" <et472@ncf.ca> wrote in message
news:pine.LNX.4.64.0908082043230.24767@darkstar.example.net...
On Fri, 7 Aug 2009, ian field wrote:

Is this device suitable for use as a variable gain amplifier like the
discontinued LM3080?

Walter Jung's "IC Op-Amp Cookbook" has a section on programmable opamps,
but it has nothing about using them as variable gain amplifiers. A bit
later in the book, he does cover the CA3080, which isn't really an opamp,
but is useful as a variable gain element.

The odd thing is, the schematic for the 4250 does have a resemblance
to a variable gain amplifier, a current source feeding a differential
amplifier. So if one had one, one ought to play with it and see
what happens.

On the other hand, you didn't really tell us what you want. Lots
of things will provide voltage controlled gain, some being better
than others. Any four-quadrant multiplier will work, any 3
transistor differential amplifier will work (changing the voltage
on the common transistor to ground will change the gain), though
not as "perfectly" as the four-quadrant multiplier. Something like
the MC1350p, which may be out of production I don't know, is a variable
gain stage intended for radio work, but it works at audio. Lots of
other devices one could pull off consumer electronic equipment.

But until the end need is described, everyone is going to go after
"more modern" transconductance amplifiers to replace the 3080 rather
than devices that will accept a control voltage to vary gain.
Click to expand...
Its for an audio compressor, all the chips mentioned so far are announced
last buy date or well and truly discontinued, I have some MC1496 in the
parts drawer but I thought they would have too limited dynamic range.
 
On Aug 9, 11:25 am, "ian field" <gangprobing.al...@ntlworld.com>
wrote:

Its for an audio compressor, all the chips mentioned so far are announced
last buy date or well and truly discontinued,
Click to expand...
NJM13700 and THAT2181 are still current, as far as I know.
Analog Devices has the SSM2166, if price is no object...
 
On Aug 9, 11:25 am, "ian field" <gangprobing.al...@ntlworld.com>
wrote:
Its for an audio compressor, all the chips mentioned so far are announced
last buy date or well and truly discontinued,
Click to expand...
NJM13700 and THAT2181 are still current, as far as I know.
Analog Devices has the SSM2018 and SSM2164 as well.
 
On Aug 9, 1:37 pm, whit3rd <whit...@gmail.com> wrote:
On Aug 9, 11:25 am, "ian field" <gangprobing.al...@ntlworld.com
wrote:

Its for an audio compressor, all the chips mentioned so far are announced
last buy date or well and truly discontinued,

NJM13700 and THAT2181 are still current, as far as I know.
Analog Devices has the SSM2018 and SSM2164 as well.
Click to expand...
I just looked at National Semiconductor's site; they still make
LM13700
as always. Maybe a non-leadfree variant was end-of-life, but
the base part is still showing as in production and in stock.
 
"whit3rd" <whit3rd@gmail.com> wrote in message
news:c0b81a8f-8b5b-4178-bff1-449758e69324@33g2000vbe.googlegroups.com...
On Aug 9, 1:37 pm, whit3rd <whit...@gmail.com> wrote:
On Aug 9, 11:25 am, "ian field" <gangprobing.al...@ntlworld.com
wrote:

Its for an audio compressor, all the chips mentioned so far are
announced
last buy date or well and truly discontinued,

NJM13700 and THAT2181 are still current, as far as I know.
Analog Devices has the SSM2018 and SSM2164 as well.
Click to expand...
I just looked at National Semiconductor's site; they still make
LM13700
as always. Maybe a non-leadfree variant was end-of-life, but
the base part is still showing as in production and in stock.

That could be it - thanks.
 
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