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op amp question

A

Albre

Jan 1, 1970
0
What gain-bandwidth do I need for a 90 degree phase shift op amp that
will operate at less than 3000 Hz?

I found a diagram on the internet, but it specifies a 6 Mhz
gain-bandwidth op amp that uses alot of power. Since I hope to use it
in a battery powered and portable environment, I'd like to use the
lower power part. The original designer wasn't after low power as a
design parameter, I'm hoping that the lower power part will work just
as well.

I was able to find a part that has the same noise rating (actually
better), but the main difference is the gain-bandwidth and the supply
current.

Do I really need to use the 6 Mhz (1.5 ma) gain-bandwidth part, or
will the 400 Khz (60 ua) gain bandwidth part work just as well?

TIA

Albre
 
J

John Woodgate

Jan 1, 1970
0
<[email protected]>) about 'op amp question',
Do I really need to use the 6 Mhz (1.5 ma) gain-bandwidth part, or
will the 400 Khz (60 ua) gain bandwidth part work just as well?

What do you mean by a '90 degree phase-shift op-amp'? Bear in mind that
the open-loop response of many op-amps is only a few tens of Hz at most,
so you get quite a lot of closed-loop phase-shift at audio frequencies
unless the closed-loop gain is very low.

You probably don't need the 6 MHz part, but without knowing exactly what
you are trying to do, it isn't possible to advise you properly.
 
P

Pooh Bear

Jan 1, 1970
0
Albre said:
What gain-bandwidth do I need for a 90 degree phase shift op amp that
will operate at less than 3000 Hz?

You mean you *want* to create a 90 degree phase shift ? Like one of those
all pass filters ?
I found a diagram on the internet, but it specifies a 6 Mhz
gain-bandwidth op amp that uses alot of power. Since I hope to use it
in a battery powered and portable environment, I'd like to use the
lower power part. The original designer wasn't after low power as a
design parameter, I'm hoping that the lower power part will work just
as well.

I was able to find a part that has the same noise rating (actually
better), but the main difference is the gain-bandwidth and the supply
current.

Do I really need to use the 6 Mhz (1.5 ma) gain-bandwidth part, or
will the 400 Khz (60 ua) gain bandwidth part work just as well?

Oh - you consider 1.5mA to be high power - lol !

If it's the configuration I think you mean, the 400kHz GBW part will be
just fine.


Graham
 
A

Albre

Jan 1, 1970
0
OK, thanks for the comments. I'll get a copy of it and post the
circuit in abse.

It's the 90 degree phase shift circuit that is usually done by a
polyphase rc network. In this case, it's done for cw only, so it's a
relatively narrow band shifting circuit instead of the typical ssb
bandwidth filter. An active circuit overcomes the high loss in
associated with polyphase filters, plus it eliminates one gain stage
because you don't have to re-amplify after the polyphase filter.

The gain appears to be one, so I'm not sure whether it needs such high
gain-bandwidth IC's.

And, yes....1.5 ma is high power IF the job can be done with 50 or 100
ua....

Thanks, will post another message when I can get the schematic posted.

Albre
 
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