Explain miller effect in transistor amplifier.
Answers
In electronics, the Miller effect accounts for the increase in the equivalent input capacitance of an inverting voltage amplifier due to amplification of the effect of capacitance between the input and output terminals. The virtually increased input capacitance due to the Miller effect is given by
{\displaystyle C_{M}=C(1+A_{v})\,} C_{{M}}=C(1+A_{v})\,
where {\displaystyle -A_{v}} -A_{v} is the voltage gain of the inverting amplifier ( {\displaystyle A_{v}} A_{v} positive) and {\displaystyle C} C is the feedback capacitance.
Although the term Miller effect normally refers to capacitance, any impedance connected between the input and another node exhibiting gain can modify the amplifier input impedance via this effect. These properties of the Miller effect are generalized in the Miller theorem. The Miller capacitance due to parasitic capacitance between the output and input of active devices like transistors and vacuum tubes is a major factor limiting their gain at high frequencies. Miller capacitance was identified in 1920 in triode vacuum tubes by John Milton Miller.