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What is the needed for a very high input impedance and a very low output impedance?

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deepabhargavi

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What is the need for very high input impedance and very low output impedance ?
 

elementary question

for acting as voltage amplifiers , to take the majour part of the input voltage and deliver the most part of the output voltage
consider a voltage divider , the voltage signal is mostly delivered to the high resistance , so if u deliver voltage u need to have a very small output resistance to give any small load most of the voltage signal , on the other hand if u accept voltage signal u have to have a large input resistance to accept most of the sources voltage (i.e. lower drop on the source resistance)
 

Re: elementary question

we need that for the (voltage gain) amplifier configuration where the input signal is a voltage and the output signal is voltage too ...

we need the input impedance to be very high (ideally =infinity) so that large portion of the input signal is amplified (Vs*Rin/(Rin+rs)) and the voltage drop across internal source resistance (rs) is negligible

we need the output impedance to be very small (ideally = 0) so that all oor most of the output voltage is taken on the load impedance (Av*Vin*Rload/(Rload+Rout)) and the voltage drop across the output impedance is negligible

**broken link removed**
 
Re: elementary question

simply by increasing the input impedance, you will take as much voltage as you can into your circuits, since you will have a negligible drop on source resistance

and by decreasing the output impedance, you will deliver as much voltage as you can out of your circuit to your load, since you will have a negligible drop on output impedance
 
Re: elementary question

All good answers. It would help if the o.p. would clarify what application he is talking about.
 

Re: elementary question

for voltage amplofiers, the next stage would be connected in parallel with the first stage's output.
assume 1st stage output taken across a resistor. then only a large resistor connected in parallel would make its effect negligible on the 1st resistor's value.
hence a large input impedance is needed to make the effect of the 2nd stage negligible on the first stage.
the reverse applies for the output impedance.

hope you get my idea.
AMRITH.S.
 

Re: elementary question

the efficiency of any amplifier depends on the input and output impedances, so your design goal to achieve a very high input impedance and a very low output impedance , the ideal opamp has infinity input impedance and zero output impedance to get 100% efficiency, hope it will help
 

elementary question

sothat your appliance need less power from input power source and less o/p impedance mean other circuit added to your device takes more power from it.
 

Re: elementary question

High input impedance => no loading on the source to which the component is connected

low outpu impedance => component maintains sufficient voltage levels to be in compliance with noise margins
 

Re: elementary question

hello,
input impedance should be high so as it will not load th source
output impedance should be low so as to source the next stage amount of current required.

regards
JSPS
 

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