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# Electronics/Analogue Electronics - OP amp circuits

Question

Amplifier Circuit Diag
I have some questions about OP amp circuits in my coursework that I am having problems with and I would like your help in answering them.

In the attachment, I am including an image of two amplifier stages, one inverting and one non-inverting, with resistors Rf and Ri (also Rin in the non-inverting stage) and Capacitors Cf and Ci.

I am having trouble with the following concepts:

Deriving the transfer function for the non-inverting stage as well as drawing a Bode plot for such an amplifier.

The effect of Cf on circuit stability in each stage (Also, why is the inverting stage more stable?)

Calculating the input impedance of each stage within its passband.

The minimum load resistance for each stage so that the load is double the output resistance of the amps - (37 Ohms) and finding Rf and Ri for both stages.

Best Regards,
Marek

Maybe this will help:

http://www.technologystudent.com/elec1/opamp2.htm

and

http://www.researchgate.net/post/Why_are_inverting_op_amp_amplifiers_used_in_mos

The purpose of the cap across the feedback resistor is to control the high frequency stability. Did you have nyquist theory in your course work yet?  In any event, as the upper bandwidth of the opamp is approached there becomes a phase shift due to stray capacities and the internal elements of the opamp; if that shift become sufficient as the frequency goes higher and higher the feedback signal becomes positive and the amp goes into high frequency oscillation or instability thus the need for the cap to swamp it out.

Hope this gets you started in a more deep understanding of what goes on......

Cheers

Electronics

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#### ZZ

##### Expertise

Electronics questions about AC, DC and digital theory.

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Graduate electrical engineer with over 40 years in electronic design, manufacturing, project organization and patent review. Experience in fields of industrial and consumer electronics (audio, video, acoustics, etc.)

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BSEE University of North Dakota