Common Emitter Configuration Input Characteristics in English

COMMON EMITTER CONFIGUATION INPUT CHARACTERISTICS
We study input characteristics during Active mode of operation
Input characteristics:
It is the curve between input current and input voltage keeping output voltage constant.
In case of common emitter, it is the curve between base current, IB and base to emitter voltage, VBE at constant collector to emitter voltage, VCE
These characteristics can be used to determine input resistance Ri
For drawing these characteristics, the input voltage VBE is increased in small steps of 0.1 V and the output voltage, VCE is kept constant at 1V.
Knee voltage
Below knee voltage the base current is approximately equal to zero. Because the barrier potential at the emitter base junction does not allow the majority carriers to flow through the junction and thus emitter current is zero making base recombination current IB = 0.
Therefore, input resistance in C-E configuration is higher than in C-B connection.
When VCE is increased above 1V as shown in figure, the curve shifts downwards.
Because as VCE increases, depletion layer width increases which decreases effective base width, in turn reduces base recombination current IB.
Input resistance
It is the ratio of change in VBE to change in IB keeping VCE constant
Since with increase in base to emitter voltage the base current increase less rapidly, input resistance in CE connection is higher than input resistance in CB connection.