Configurations of Differential Amplifier

Configurations of Differential Amplifier

• The differential amplifier, in the difference amplifier stage in the op-amp, can be used in four configurations :

i) Dual input, balanced output differential amplifier.

ii) Dual input, unbalanced output differential amplifier.

iii) Single input, balanced output differential amplifier.

iv) Single input, imbalanced output differential amplifier.

• The differential amplifier uses two transistors in common emitter configuration. If output is taken between the two collectors it is called balanced output or double ended output. While if the output is taken between one collector with respect to ground it is called unbalanced output or single ended output. If the signal is given to both the input terminals it is called dual input, while if the signal is given to only one input terminal and other terminal is grounded it is called single input or single ended input.

• Out of these four configurations the dual input, balanced output is the basic differential amplifier configuration. This is shown in the Fig. 8.6.1 (a). The dual input, unbalanced output differential amplifier is shown in the Fig. 8.6.1 (b). The single input, balanced output differential amplifier is shown in the Fig. 8.6.1 (c) and the single input, imbalanced output differential amplifier is shown in the Fig. 8.6.1 (d).

• The operation of dual input balanced output differential amplifier in differential mode and common mode is already discussed in the last section. This configuration is also called symmetrical differential amplifier.

Review Question

1. What are the configurations of differential amplifier ? Draw and explain them.