Electronic Circuit Analysis

190 Electronic Circuit Analysis
5.1 Introduction
A tuned amplifier is one, which uses a parallel tuned circuit, as its load impedance. A parallel tuned
circuit, is also known as anti resonant circuit. The characteristics of such an anti resonant circuit is
that its IZI is high, at the resonant frequency, and falls off sharply as the frequency departs from the
resonant frequency. So the gain versus frequency characteristics of a tuned amplifier will also be
similar to the IZI characterisr~s of the resonant circuit. When IZI is maximum, V (} will also be
maximum. This is for AC. IZI ~S\considered.
;~:J\~" "
(load)
jZj
i
5.1.1 Applications
~f ~f
Fig. 5.1 Tuned amplifier characteristics
Tuned amplifiers are used to amplify a single radio frequency or narrow band of frequencies ..
So basically they are used in 1. RF amplifiers 2. Communication receivers
Tuned amplifiers use variable Inductance (L) or variable Capacitance (C) to vary the resonant
frequency.
In tuned amplifiers, harmonic distortion is very small, because the gain of the amplifiers is
negligibly small for frequencies other than to (the resonant frequency). So Harmonics which on
of higher frequencies will have very low gain and hence harmonic distortion will be less for
tuned amplifiers.
5.1.2 Classification
I
Small Signal
* To amplify low RF signals
* Power output is low
* Operated in class A
I
Tuned Amplifiers
I
Single tuned Double tuned Staggered tuned
j
Large Signal
* To amplify large RF signals
* Power output is more
* Operated in class B, class C or
class AB modes.
* Pushpull configuration used to
further reduce harmonic
distortion.
This classification is similar to the classification of power amplifiers.