Differential Amplifier
A differential amplifier serves to amplify the difference
between tow signals. A differential amplifiers forms the basic stage of an integrated
op-amp with differential inputs.
The circuit diagram of the emitter coupled differential
amplifier is shown in the below fig. it uses two identical npn transistors. The
transistors are connected in CE mode. The emitter bias is used here. The two
inputs V1 and V2 and the output is Vo. The
output is derived from the two collector points.
If the inputs are similar, the output of the amplifier is
zero. The amplifier outputs V1 and V2. Therefore it is
called as differential amplifier. The emitter coupled differential amplifier of
the below fig possess the following properties.
Emitter Coupled Differential Amplifier
1. Low drift.
2. Very high input resistance.
3. Cancels the effects of supply
voltages.
4. High CMRR.
5. Very high stability.
CMRR is defined as the ratio of difference gain to the common
gain of a difference amplifier.
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