Signal Variation

SIGNAL VARIATION

>>  It is the maximum or peak change in the value of voltage and current with respect to DC value.

>>  Based upon the value of signal variation, amplifier can be divided into two types.

(i). Small Signal Amplifier                             (ii). Large Signal Amplifier

SMALL SIGNAL AMPLIFIER

>>  An amplifier in which signal variation is much smaller than DC value.

bjt26

Let DC value (IB) = 20 μA

And ib = 2 Sin (ωt) μA

iB = IB + ib

⇒  ΔiB = ± 2 μA (Signal variation)
Signal Variation is very small in comparison to DC value.
>>  In small signal amplifier, BJT exhibits piecewise linearity or behaves as a linear
      element, due to which output signal will be distortion less.
>>  Small Signal amplifier is used as a voltage amplifier.
LARGE SIGNAL AMPLIFIER
  •   An amplifier in which signal variation is large or close to DC value.
Let DC value (IB) = 20 μA
And ib = 18 Sin (ωt) μA
⇒ iB = IB + ib
⇒  ΔiB = ± 18 μA (Signal variation)
Signal Variation is very close to DC value.
  •  BJT behaves as a non-linear element because β does not remain fixed for large input signal.
  •  Due to which equal change in base current does not produce proportionally equal change in collector current.
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