Any of the three basic amplifier configurations (common collector, common base, or common emitter) described in NEETS, Module 7, Introduction to Solid-State Devices and Power Supplies, Chapter 2, may be used for the oscillator circuit.
However, certain considerations in the application of the circuit, such as the operating frequency and output power required, usually determine which of the three configurations is to be used. The three basic configurations of oscillators are shown in the figure below, views (A), (B), and (C).
Basic configurations COMMON-COLLECTOR-CONFIGURATION.
Basic configurations COMMON-BASE-CONFIGURATION.
Basic configurations COMMON-EMITTER-CONFIGURATION.
there is no phase reversal between the input and output circuits of a
common-collector configuration, the feedback network does not need to
provide a phase shift. However, since the voltage gain is less than
unity and the power gain is low, the common-collector configuration is
very seldom used in oscillator circuits.
The power gain and
voltage gain of the common-base configuration are high enough to give
satisfactory operation in an oscillator circuit. The wide range between
the input resistance and the output resistance make impedance matching
slightly harder to achieve in the common-base circuit than in the
common-emitter circuit. An advantage of the common-base configuration is
that it exhibits better high- frequency response than does the
The common-emitter configuration has high power gain and is used in low-frequency applications. For the energy which is fed back from the output to be in phase with the energy at the input, the feedback network of a common-emitter oscillator must provide a phase shift of approximately 180 degrees. An advantage of the common-emitter configuration is that the medium resistance range of the input and output simplifies the job of impedance matching.