[SOLVED] Reducing Input Impedance

[rahdirs]

Hi all,

Consider a scenario in which the input to a system is coming from a previous stage with short circuit current of 'x' A (x is large).But the system having high input impedance allows small current to flow through.Is there a way to reduce to input impedance of system to allow large currents to pass through.

I am asking for a general way,like if my system is op-amp i can change impedance by designing a custom op-amp by changing size of transistors.But is there a way to change impedance externally without changing system internal properties (or am I wasting time thinking there is a way to do this).

Thanks,
rahdirs

 

[ZekeR]

You can reduce your input impedance by simply adding a parallel resistor to ground. This approach is often taken to ensure a transmission line is terminated by a matching impedance.

You can also reduce input impedance (to near zero) using feedback, such as in a transimpedance amplifier.

It really depends on what your objective is.

 

[rahdirs]

@Zeker: Obviously you can reduce impedance by adding a resistance in parallel,but that resistance would take in part of the current.I was asking for a way in which you can reduce impedance but that extra circuitry take in no current(maybe i sound selfish).

 

[ZekeR]

Umm, what exactly do you want? Is there a reason you would like to reduce your circuit's input impedance, besides impedance matching? In general, we don't make circuits draw more current from their input unless it actually gives us some benefit...

 

[rahdirs]

@Zeker:In my circuit my input is capable of providing current,but high input impedance of Power amplifier makes input to supply less current.If i could decrease input impedance of amplifier then i could increase the current supplied by the input.

I had a way to increase beta of my transistors in my amplifier but that produced nothing,so am trying to reduce its input-impedance so that more current flows from input & i get an even higher current gain from Power amplifier

 

[ZekeR]

Okay, so one obvious way to increase the input current (decrease input impedance) is to run the input stage of your amplifier at a higher quiescent current. For a fixed beta, since the tail current is higher, the input current will also be higher. By running your input stage at higher current, you will need less gain stages to get the same output current.