circuit identification

[megs]

Hi,
I need help identifying this ckt..and find out the gain vo/vin
its and opamp with double feedback with limiting diodes..


Any hints or help is greatly appreciated.....


Thanks,
Meg

 

[FvM]

Nice homework

 

[ZASto]

It was Llloooooooong ago when I was solving similar homeworks

Don't skip classes, you may LEARN something. You will need knowledge, or you can be one of gazillion beggars.

 

[BradtheRad]

Since there is both positive and negative feedback, it's a lot to expect for anyone to predict the shape of the resulting waveform, and its amplitude. The different feedback loops interact to some extent, depending on the ratios of the resistors.

If there were only negative feedback it would be relatively easy to calculate the result.

Or if there were only positive feedback, it would create hysteresis action. The range of the hysteresis loop would take some effort to calculate.

If those are limiting diodes at the output, then I think they are zener diodes.

By experimenting with a variety of feedback resistances, it is possible to obtain a sinewave, or square wave, or clamped sinewave.

 

[megs]

Since there is both positive and negative feedback, it's a lot to expect for anyone to predict the shape of the resulting waveform, and its amplitude. The different feedback loops interact to some extent, depending on the ratios of the resistors.

If there were only negative feedback it would be relatively easy to calculate the result.

Or if there were only positive feedback, it would create hysteresis action. The range of the hysteresis loop would take some effort to calculate.

If those are limiting diodes at the output, then I think they are zener diodes.

By experimenting with a variety of feedback resistances, it is possible to obtain a sinewave, or square wave, or clamped sinewave.

Hi BradtheRad,

Thanks for your response. Could you please shed some light on how I can find out what decides the shape of the wave and how I go about it? I found the Av-voltage gain (1.2) ie vo/vin by doing the circuit analysis.
Any good reference?

Thanks,
Meghana

 

[godfreyl]

If R1 > 10K, then negative feedback is greater than positive feedback, so the circuit is a linear amplifier and you can calculate the gain as Vo/Vi.

If R1 < 10K, then positive feedback is greater than negative feedback, so the circuit is a Schmitt trigger, and you can calculate the input voltages required at the input to switch the output high and low.

 

[megs]

If R1 > 10K, then negative feedback is greater than positive feedback, so the circuit is a linear amplifier and you can calculate the gain as Vo/Vi.

If R1 < 10K, then positive feedback is greater than negative feedback, so the circuit is a Schmitt trigger, and you can calculate the input voltages required at the input to switch the output high and low.

Thanks a lot!

 

[BradtheRad]

Hi BradtheRad,

Thanks for your response. Could you please shed some light on how I can find out what decides the shape of the wave and how I go about it? I found the Av-voltage gain (1.2) ie vo/vin by doing the circuit analysis.
Any good reference?

Thanks,
Meghana

Perhaps you are thinking of books or articles? Because, in addition there are also simulators to educate us.

I used Falstad's interactive animated simulator to find out how your circuit works. (A free download at www.falstad.com/circuit.)

In the 'old days' we only had books and human teachers and hands-on experience. Simulators have been made more sophisticated, and they are a big help...

however experimentation with real components trumps everything else. I should go and set up your circuit on my breadboard, but I'll leave that for someone else.

There is a benefit to figuring out such problems by mental analysis, because we need to develop our analytical skills. We are bound to meet up with harder problems than the circuit you are considering, and not all can be solved with a simulator, since a simulator does not always duplicate real life.