Objective:

Objective:

The objective of this experiment is to simulate:

1. DC characteristics of BJT in Common Emitter and Common Base configuration

2. Biasing of BJT

3. Small signal Analysis using BJT

We can also analyze temperature effect and the working way of BJT as amplifier.

Part 1: DC characteristic of BJT Q2N2222

(a) Common Emitter configuration:

Schematic for DC analysis of BJT in CE configuration

Output characteristic curve:

DC current gain (Ic/Ib) vs. Ib curve: DC current gain (Ic/Ib) vs. Ic curve:

From the above curve:

Maximum current gain=186.790

Corresponding Ic=20.960

Common Base current gain = /(+1)= 0.995DC current gain vs. Temperature curve:

(b) Common Base configuration:

Schematic for DC analysis of BJT in CB configurationOutput characteristic curve:

DC current gain (Ic/Ib) vs. Ib curve:

DC current gain (Ic/Ib) vs. Ic curve:

Part 2: Biasing of BJT

Schematic for biasing of BJT

Table: (Model: Q2N3904)VccVbVeVcVceIbIeIc

102.9432.2776.6084.3317.3931.035m1.028m139.05

To make Vce=0.5 Vcc the value of R1 was changed to 57.3 k

When the temperature is increased, value of Vce is reduced to 4.878 V

Table: (Model: Q2N2222)

VccVbVeVcVceIbIeIc

102.9532.3076.5624.2556.7271.049m1.042m154.9

Model is changed again with Q2N3904. RE is removed and the emitter is short circuited to ground. The value of R1 will be 227.40 k (Determined manually) to keep Vce=0.5Vcc.

Table: (Model: Q2N3904 and RE removed)

VccVbVeVcVceIbIeIc

10675.25m05.0025.00210.311.525m1.515m146.94

Effect of temperature on the stability of the biasing circuits:

When the temperature is changed, resistivity of the transistor changes. As a result the change in voltage and current occur. Current through the collector changes more than that of the base. So, the ratio Ic/Ib or current gain increases.Effect of Device model on the stability of the biasing circuits:

Different models of BJT consist of diodes of various junction areas. We know current through any material depends on its cross-sectional area. That is why different amount of current pass through the BJT though other factors remain same. Thus resistivity and voltage drop also change with model.

Part 3: Small signal analysis of BJT

Schematic for small signal analysis using BJT

Gain vs. frequency curve:

Avmax=53.617

Phase vs. frequency curve:

Normalized curve: Avn=Av/Avmax

Voltage gain (in dB) vs. frequency curve:

From the curve: cutoff frequencies: 6.918 MHz and 113.066 Hz

Input resistance=Vin/IinCurve:

Output resistance:

Curve:

Discussion:(I) BJT is an important device in electronic circuit. In this experiment we knew about the current-voltage characteristics of BJT circuits.(II) In small signal analysis of BJT, the circuit acts as an amplifier that can magnify input signal.