thank you .... can you be more specific by citing an example.....Normally you want a relatively high input impedance to minimize any loading of the signal source.
Generally you want the output impedance to be low so the signal is not attenuated by any load.
One exception is if you are driving a high frequency signal into a transmission line and need to match its characteristic impedance, such as 50 or 75 ohms, then you want the output impedance to be the same.
Yesvijaytej
Do you know what a potential divider is?
Thank you ,what are you referring to in the 1st para.is that a transistor or a cascade combination??OK,
Well the output impedence of the previous stage (Zo or Ro) or input device and the input impedence of the following stage or device (Zi or Ri) form a potential divider.
The following device (amplifier) sees the voltage across Zi as its input. That is it sees Zi/(Zi+Zo) times the source voltage.
If Zi > Zo then more of the source voltage appears across Zi (the input signal is bigger) If Zi>>Zo then most of the source voltage appears across Zi
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