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I/o Impedences

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andrebc

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Would you guys please tell me how to measure in I/o impedences of a CE amplifier. I found out about a way how to do it using a potentiometer. But since I dont have a potentiometer, is there an alternative way to it? If i just use the DMM across the input or ourput and tge ground will I get the right value of resistance. how about measuring the internal resistance of the frequency generator, How can I do that? sorry for asking these very basic questions!
 

Hero999

Banned
Measure the input impedance by setting the input to a known peak voltage and measure the input current.

The output impedance can be obtained by measuring the output voltage off load, connecting a load and measuring the voltage again and using Norton's theorem to work out the internal resistance.

All measurements should me made using a scope, you might need to use the differential setting to get accurate results.
 

audioguru

Well-Known Member
Most Helpful Member
It is simple to calculate the input and output impedances of a CE transistor amplifier.
The input impedance is shown on a graph on the datasheet for the 2n3904 transistror. Then it is in parallel with the biasing resistors and the beta-amplified emitter resistor.
The output impedance is the collector resistor.
 
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