shown in B of figure 1-11.
The schematic of the same amplifier is
shown in C of that figure.
The varying input signal results in a
varying output voltage across the load resistor. The amplitude of the
output signal is greater than that of the input signal; therefore,
amplification has been accomplished.
Assume that an amplifier is designed to amplify a given
frequency, or band of frequencies, as shown in A of figure 1-12.
If the output
signal is fed back to the input circuit, in phase with the input signal (B of fig.
1-12), the amplifier will oscillate as long as the in-phase feedback continues. In
this circuit, the oscillating frequency is determined by the values
of inductor L and capacitor C.
In another circuit it may be determined by a
resistor and capacitor, or by a crystal. The requirements for any oscillator