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It is generally desired that a transistor should have _____ input impedance.
Low
Very low
High
Very high
High
A transistor amplifier should generally have a high input impedance to avoid loading the preceding signal source. High input impedance ensures that maximum signal voltage is dropped across the transistor's input terminals rather than being lost across the internal impedance of the signal source. In practical multistage amplifiers, configurations like Common Collector (Emitter Follower) or FETs are used to achieve very high input impedance.
A transistor amplifier should generally have a high input impedance to avoid loading the preceding signal source. High input impedance ensures that maximum signal voltage is dropped across the transistor's input terminals rather than being lost across the internal impedance of the signal source. In practical multistage amplifiers, configurations like Common Collector (Emitter Follower) or FETs are used to achieve very high input impedance.
VinтАЛ=VsтАЛ├ЧZinтАЛ+ZsтАЛZinтАЛтАЛ тАФ Input voltage transfer equation showing loading effect
ZinтАЛ=RBтАЛтИе(1+╬▓)reтАЛ тАФ Input impedance of Common Emitter configuration
When an AC signal source with internal impedance ZsтАЛ is connected to an amplifier, they form a voltage divider network with the input impedance ZinтАЛ. The voltage available at the input terminals of the amplifier is VinтАЛ=VsтАЛ├ЧZinтАЛ+ZsтАЛZinтАЛтАЛ. If ZinтАЛ is much larger than ZsтАЛ, then VinтАЛтЙИVsтАЛ, ensuring efficient voltage transfer without loading the source.
High input impedance minimizes current drawn from the signal source, preventing voltage drop across source resistance.
Common Collector (Emitter Follower) provides high input impedance, while Common Base provides very low input impedance.
Field Effect Transistors (FETs/MOSFETs) offer much higher input impedance (108 to 1012┬а╬й) compared to BJTs.
Prevents loading down of the input signal source.
Allows efficient voltage amplification in multi-stage systems.
Higher input impedance can make the circuit more susceptible to pick-up noise.
Design adjustments may reduce overall stage voltage gain.
Impedance matching buffer stages using Emitter Followers.
Preamplifiers for sensitive transducers and sensors.
Option A and B are incorrect because low input impedance causes significant signal loss across the source's internal resistance (loading effect).
Option D is generally characteristic of FETs or specialized circuits, but for general bipolar transistors, high input impedance (Option C) is the primary requirement for efficient voltage transfer.
C is correct тАФ High input impedance prevents loading of the preceding signal source and ensures maximum voltage transfer.
In voltage amplifiers, aim for High Input Impedance and Low Output Impedance; for current amplifiers, aim for Low Input Impedance and High Output Impedance.