gEDA-user: opamp slew rate limiting

[carzrgr8@xxxxxxxxxxxxx]

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.

Any help?

gene


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