Input Impedance and output Impedance

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Neo_Star

Joined Jan 23, 2009
1
wat is the practical use of having high input impedance and low output impedanace in an op-amp or in a transistor :)
 

Papabravo

Joined Feb 24, 2006
21,159
A high input impedance doesnt load the source.
Think about the low output impedance for a moment. It will come to you.
 

steveb

Joined Jul 3, 2008
2,436
wat is the practical use of having high input impedance and low output impedanace in an op-amp or in a transistor :)
This type of impedance matching maximizes voltage gain when input sources, voltage amplifiers and output loads are connected.

See attached PDF for diagram and formula.

You will see that the source impedance (\( R_s\) or \( R_{out}\) ) of a prior stage and the input impedance of the following stage (\( R_{in} \) or \( R_L\) ) form a voltage divider network that reduces the effective gain of the amplifiers (\( A_1, A_2 ... A_N\) ).

Note that different rules apply when you want to maximize power gain (transfer) and not voltage gain, as discussed here.
 

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