Re: gEDA-user: opamp slew rate limiting

[Peter TB Brett <peter@xxxxxxxxxxxxx>]

On Tue, 10 Nov 2009 01:58:26 +0000 (GMT), carzrgr8@xxxxxxxxxxxxx wrote:
> I have a problem with an opamp at work and was hoping someone may have
some
> insight.
> 
> This particular opamp is opa2132 from TI, and has slew rate of about 20
> V/us.  It's driven by a sine wave at 5 kHz.  The gain is sufficiently
large
> that the opamp is driven into saturation by the sine wave and the slew
rate
> limited edges are very obvious.  The rails are +/- 7.5V and it is able to
> drive to about +/- 6V.  It is connected to an old CD40106 schmitt trigger
> inverter.  
> 
> Here's the rub.  The opa2132 doesn't run anywhere near the advertised
> 20V/uS spec.  I see, at best, around 15V / 12 uS, or about 1 or 2 V/ uS. 
> Not even close to spec.  I am fairly certain that the schmitt trigger
> responds poorly to the very slow edges from the opamp.  I happen to use 2
> channels of this, and the phase relationship is very important - but it
> gets destroyed through the schmitt trigger.
> 
> I've gone as far as removing all loads from the opa2132, and it doesn't
> change the slew rate.  The data sheet has a drawing with 'large signal
step
> response', and it shows the part slewing around 15 or 20V in 1 uS.  Not
> bad.  So what have I done wrong?  They do claim it's with a gain of -1,
but
> I don't see how that has anything to do with it.

What's the op-amp's gain-bandwidth product?

Peter

-- 
Peter Brett <peter@xxxxxxxxxxxxx>
Remote Sensing Research Group
Surrey Space Centre


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