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.

Let DC value (I_B) = 20 μA

And i_b = 2 Sin (ωt) μA

⇒ i_B = I_B + i_b

⇒  Δi_B = ± 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 (I_B) = 20 μA

And i_b = 18 Sin (ωt) μA

⇒ i_B = I_B + i_b

⇒  Δi_B = ± 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.