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I have come across this term many times while studying amplifiers. How does this effect affect an amplifier circuit(or any other circuit in which it plays a role) and why is the input impedance kept as high as possible to negate it?

Infusion of Wormwood n Asfodel
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    Can you give us some more context, or perhaps a schematic? –  Apr 07 '13 at 18:01
  • don't have a schematic but i know that input impedance in an amplifier is kept as high as possible to reduce the effects of this phenomenon. – Infusion of Wormwood n Asfodel Apr 07 '13 at 18:04
  • ... i know that input impedance in an amplifier is kept as high as possible to reduce the effects of this phenomenon - That is not constructive. "I know" isn't a scientific basis for pretty much anything, regardless of whether the statement is valid or not. – Anindo Ghosh Apr 07 '13 at 19:55
  • I get the impression that you may have formed an opinion that a circuit with high input impedance will cope better with "loads" on its output. This is incorrect if that is what you believe. A circuit with high input impedance will not "significantly" form a load or "burden" to the output of another circuit it connects to. That's why, in a lot of electronic circuits inputs are kept high-impedance. – Andy aka Apr 07 '13 at 21:53

2 Answers2

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Loading refers to how your measurement circuit affects the attached device. If e.g. you want to read a sensor that has a big internal resistance Ro any current drawn will create you additional voltage error equal to io*Ro. Drawing as little current as possible lowers the sensor loading thus providing more accurate readout.

Szymon Bęczkowski
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If two transistor were added then 2nd transistor will be parallel to the load of 1st transistor.so effective load resistance will decrease of 1st transistor due to this effective gain will also decrease. Thus 2nd stage will load 1 st stage this is called loading effect

Jai
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    Welcome to EE.SE, Jai. Since there are so many variations of transistor connections for amplifiers and logic circuits your answer would need a schematic diagram to understand what you are talking about. There is a CircuitLab schematic button on the editor toolbar so you can add one in if you wish to improve your answer. I suspect that you are a little confused on the topic and may need some more study. Have a look at Szymon's answer and the others that will probably follow. – Transistor Sep 19 '18 at 12:37