OT: instrument amp (with variable offset), low-loss rectifier and integrator (?)

[brett]

Hi
I would like to build a small signal amplifier (with variable offset), low-loss rectifier and integrator.

Can I do it all with one op-amp like this? (please ignore the meter polarity being wrong)



Does the integration time/frequency follow the same roll-off frequency rule as if the 1nF cap and 470k were in a 1 fole low-pass filter?  ie. -3dB is at the frequency where Zcap = Zresistor.  ??

thanks for any advice 

[brett]

Anyone?

[R.G.]

I would normally dump it into a simulator and see if it acted the way I thought it did.

In fact I'd do that for you but I'm in a rush right now.

[brett]

Thanks RG
I'll build it and let you know how it goes.
(I haven't learned to use electronic simulators, which is kinda strange because my day job is bio-physical simulation).

[Cliff Schecht]

The thing that worries me with this circuit is the feedback, I'm not sure if the op amp will filter like you think it will with the diode in the feedback path. My simulations tell me that the circuit is only active for a small portion of a signal swing, 0V to 1.25V in gives a comparator like response at 0V to 12V out (I think my rails were 15V but meh). Definitely no filtering going on here, just a "perfect" diode type response. Why not put a passive filter after the diode output? You can easily make up for losses with moree gain. Some more specifications of what you are designing would of course help as well .

Also, R10 serves no purpose here. It isn't going to help balance impedance, it's just current limiting something that draws negligible current. In other words, you and the op amp won't notice even the slightest difference in performance (unless you have an unusually low input impedance!!).