op amp question

Apr 12, 2005 3 Replies
A

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



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A

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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J

I read in sci.electronics.design that Albre

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P

You mean you *want* to create a 90 degree phase shift ? Like one of those all pass filters ?

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

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