Variable Capacitance Multiplier Design with Op Amp

[@mr1enrollment]

So prof,... this is a ground connected C on one side. If + input of Amp2 were un:grounded - could the circuit topology support a floating G*Cap1? Imagine using two of these circuits in a Wien Bridge Oscillator. I suspect so, but also imagine some challenges with the result. Comment?

[@STEMprof]

Thanks for watching and sharing your thoughts. I am afraid we can't un-ground the positive (non-inverting) input terminal of the second Op Amp as it destabilizes the circuit. But to your point, simulated floating impedance (capacitor or inductor) has practical applications. Few examples of such circuits and applications are: Simulated floating inductor realized by converting a Capacitance to inductance kzbin.info/www/bejne/rZaseXpqaqxphsk and Butterworth Filter Design with Capacitor Multiplier, Op Amp and Transistor kzbin.info/www/bejne/b3SpgZhta9t0qsk I hope these videos are helpful and interesting.

[@mr1enrollment]

I believe then, in principal using a transformer at the input will provide a "floating" capacitive reactance --- at least over a useful frequency range. @@STEMprof ??? It works in Spice but yeah spice is spice, not real circuits.

[@STEMprof]

Implementation and analysis of a variable capacitance multiplier circuit are presented in this video. This circuit is useful in applications where a large adjustable capacitance is needed. This Analog circuit is implemented with two operational amplifiers and one potentiometer. For more circuit design videos please see the analog circuit and signal processing video playlist kzbin.info/aero/PLrwXF7N522y4c7c-8KBjrwd7IyaZfWxyt And Digital Circuits and DSP playlist kzbin.info/aero/PLrwXF7N522y6cSKr0FmEPP_zQl011VvLr Thanks for watching.

[@TomLeg]

What is "S"?

[@STEMprof]

In S domain circuit Analysis, the circuit is transformed from time domain to Laplace domain where derivativative of variable is represented by multiplying variable with S and integrating a variable is represented by dividing it by S. I hope this is helpful.

[@TomLeg]

@@STEMprof I'm afraid you might as well have been speaking Chinese. Is there somewhere I can learn about this?

[@STEMprof]

@@TomLeg Please watch the video: Analog Computer that solves Differential Equation kzbin.info/www/bejne/e3_UZGx7mtiZhtk . I hope it helps with explaining what I meant by S domain circuit analysis.