Why the input resistance of transistor is low?

Why the input resistance of transistor is low?

While using a transister, the emitter-base junction is always forward biased and collectorbase junction is always reverse-biased. This means that a small signal voltage variation at the input of the transistor produces a large emitter current variation. This shown that the input resistance of a transistor is low.

Why the input impedance of CB configuration is lower than CE configuration?

So, there is no phase reversal between input and output in a CB amplifier. If CB configuration is considered for amplification, it has low input impedance and high output impedance. The voltage gain is also low compared to CE configuration.

Why is output resistance important in a BJT?

There are BJT circuits which should have a large output resistance (current sources) and there are other circuits (voltage amplifiers) which should have a small output resistance. This is desired because we do not want that any load drastically will change the resistance that determines the gain.

Which is the current source of a BJT?

An analog voltage signal applied to the base of a BJT through a resistor creates a varying base CURRENT which is amplified by a factor of BETA and appears as varying collector current with a magnitude of Ib times BETA. However, the term “current source” usually refers to a circuit that supplies a constant (or adjustable) current.

Why do we need resistor connected to the base of the transistor?

You only need a base resistor when you operate a transistor in the common emitter mode, and that, as has been said is to limit the base current to protect both the transistor and the arduino output. However, you do not need a base resistor if you operate the transistor in the common collector configuration sometimes called an emitter follower.

Why do we need a high input resistance?

This is desired because we do not want that any load drastically will change the resistance that determines the gain. Remember the opamp principle: High input resistance (MegOhm range) because the amplifier should not draw a large current (and cause unwanted voltage drops across the internal resistance of the signal source).