The negative current feedback has the following effects on the performance of amplifiers :

**Effects of Negative Current Feedback**

The negative current feedback has the following
effects on the performance of amplifiers :

**(i)
Decreases the input impedance. **The negative current feedback decreases the input impedance of** **most amplifiers.

Let

Z_{in} = Input impedance of the
amplifier without feedback

Z ′_{in} = Input impedance of the
amplifier with negative current feedback

Thus the input impedance of the amplifier is
decreased by the factor (1 + m_{i} A_{i}). Note the primary
difference between negative current feedback and negative voltage feedback.
Negative current feedback decreases the input impedance of the amplifier while
negative voltage feedback increases the input impedance of the amplifier.

**Increases
the output impedance. **It can
be proved that with negative current feedback, the output** **impedance of the amplifier is increased by a factor (1 + m_{i}
A_{i}).

Z ′_{out} = Z_{out} (1 + m_{i}
A_{i})

where

Z_{out} = output impedance of the
amplifier without feedback

Z ′_{out} = output impedance of the
amplifier with negative current feedback

The reader may recall that with negative
voltage feedback, the output impedance of the amplifier is decreased.

**Increases
bandwidth. **It can
be shown that with negative current feedback, the bandwidth of the** **amplifier is increased by the factor
(1 + m_{i} A_{i}).

BW′ = BW (1 + m_{i} A_{i})

where

BW = Bandwidth of the amplifier without
feedback

BW′ = Bandwidth of the amplifier with negative
current feedback

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