# Input Impedance and output Impedance

Discussion in 'General Electronics Chat' started by Neo_Star, Mar 2, 2009.

1. ### Neo_Star Thread Starter New Member

Jan 23, 2009
1
0
wat is the practical use of having high input impedance and low output impedanace in an op-amp or in a transistor

2. ### Papabravo Expert

Feb 24, 2006
11,542
2,386
A high input impedance doesnt load the source.
Think about the low output impedance for a moment. It will come to you.

3. ### steveb Senior Member

Jul 3, 2008
2,433
469
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.

File size:
17.5 KB
Views:
33