Electronic Circuit Design Lab Manual
Experiment No. 10
BJT Differential Amplifier
OBJECTIVE
Construct and analyze performance of a differential amplifier in terms of Common Mode
and Differential gain and to evaluate its Common Mode RejectionRatio.
EQUIPMENT
Instruments Components
• Digital Multimeter(DMM)
•Oscilloscope.
•Functiongenerator.
• Transistors: 2N3904(02)
• Resistors: 10kΩ Ω (3), 100kΩ Ω (02), 330 Ω(1)
• Capacitors: 1F(02)
THEORY
The electronic amplifierused for amplifying the difference between two input signals can be
called as a differential amplifier. In general, these differential amplifiersconsistoftwoterminals namely
inverting terminal and non-inverting terminal. These inverting and non-inverting terminals are
represented with – and +respectively.
The output voltage of a differential amplifier is proportional to the difference between the two
input voltages. The differential amplifier circuit using transistors can be designed as shown in the
figure below which consists of two transistors T1 and T2. These transistors and resistors are
connected as shown in the circuit diagram. There are two inputs Vin+&Vin-andtwooutputs Vo- &
Vo+ in the differential amplifier circuit. The input Vin+ is applied to the transistor T1 base
terminal input Vin- is applied to the transistor T2 base terminal. The emitter terminals of transistor T1
and transistor T2 are connected to a common emitter resistor. Thus, the two input
signalswillaffecttheoutputs.The differential amplifier circuit consistsoftwosupplyvoltages but there is no
ground terminal. Even with single voltage supply also circuit can be operated fine as it is
intended (similarly while using two supply voltages). Hence, the opposite points of positive
voltage supply & negative voltage supplyare connected to theground.
