dear friends,

can any one tell me how to change active impedance of opamp from let say 0.005 to 200 ohms.

 

What circuit are you considering?

(Quick answer: put a 200 ohm resistor in series with the output, but without a picture I don't know whether I understand your question.)

 

Many years ago, RTS invented a multi-station intercom for TV production. It was based on a power supply regulator that synthesized a 200 ohm output impedance without needing a big fat power resistor. The circuit was based on an opamp with both positive and negative feedback, sorta like a Howland current pump but with non-equal resistor ratios.

The theoretical output impedance of an opamp circuit is based on both the positive and negative feedback loops. For a linear amplifier stage there usually is no positive feedback, and the circuit gain and output impedance equations reduce to the familiar forms we all use. But they come from a more complex form that defines the output impedance in terms of four circuit impedances. This is how things like gyrators and synthetic inductors are designed and analyzed.

ak

 

Ring Tip Sleeve they owned that business. Bet they have since moved on to wireless.