Two thoughts: First, if you are saturating your op-amp, then why not using a comparator instead? Even the humble LM339 has a large signal response time of 300ns, which at your voltage is equivalent to a slew rate of 50V/us
Secondly, the opamp's datasheet specified the slew rate using an inverting amplifier for the test circuit. The inverting configuration guarantees that the input common-mode voltage is always very close to 0. Not sure if this affects the slew rate, but it might. -Alan On Mon, Nov 9, 2009 at 6:58 PM, <carzr...@optonline.net> 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. > > Any help? > > gene > > > _______________________________________________ > geda-user mailing list > geda-user@moria.seul.org > http://www.seul.org/cgi-bin/mailman/listinfo/geda-user > _______________________________________________ geda-user mailing list geda-user@moria.seul.org http://www.seul.org/cgi-bin/mailman/listinfo/geda-user
