Oscillators

Introduction to Oscillators

WAVE GENERATORS play a prominent role in the field of electronics. They generate signals from a few hertz to several gigahertz (10 to the 9th hertz). Modern wave generators use many different circuits and generate such outputs as SINUSOIDAL, SQUARE, RECTANGULAR, SAWTOOTH, and TRAPEZOIDAL wave shapes.

These wave shapes serve many useful purposes in the electronic circuits you will be studying. For example, they are used extensively throughout the television receiver to produce both picture and sound.

One type of wave generator is known as an OSCILLATOR. This device can be regarded as an amplifier which provides its own input signal. these amplifier devices are classified according to the wave shapes they produce and the requirements needed for them to produce oscillations.

CLASSIFICATION (GENERATORS)

Wave generators can be classified into two broad categories according to their output wave shapes, SINUSOIDAL and NONSINUSOIDAL.

Sinusoidal

A sinusoidal type produces a sine-wave output signal. Ideally, the output signal is of constant amplitude with no variation in frequency. Actually, something less than this is usually obtained. The degree to which the ideal is approached depends upon such factors as class of amplifier operation,amplifier characteristics, frequency stability, and amplitude stability.

Sine-wave generators produce signals ranging from low audio frequencies to ultrahigh radio and microwave frequencies. Many low-frequency generators use resistors and capacitors to form their frequency-determining networks and are referred to as RC types. They are widely used in the audio-frequency range.

Another type of sine-wave generator uses inductors and capacitors for its frequency-determining network. This type is known as the LC types. LC types, which use tank circuits, are commonly used for the higher radio frequencies. They are not suitable for use as extremely low-frequency devices because the inductors and capacitors would be large in size, heavy, and costly to manufacture.

A third type of sine-wave generator is the CRYSTAL-CONTROLLED type. The crystal controlled type provides excellent frequency stability and is used from the middle of the audio range through the radio frequency range.

Nonsinusoidal

Nonsinusoidal types generate complex waveforms, such as square, rectangular, trigger, sawtooth, or trapezoidal. Because their outputs are generally characterized by a sudden change, orrelaxation, they are often referred to as RELAXATION types. The signal frequency of these devices are usually governed by the charge or discharge time of a capacitor in series with a resistor.

Some types, however, contain inductors that affect the output frequency. Thus, like sinusoidal types, both RC and LC networks are used for determining the frequency of oscillation. Within this category of nonsinusoidal types are MULTIVIBRATORS, BLOCKING, SAWTOOTH GENERATORS, and TRAPEZOIDAL GENERATORS.

Basic Oscillators

Sine-Wave and the LC and RC network

Crystals, solid-state LC and types of feedback

Configuration: common-emitter, collector, and base configurations

Circuits, frequency stability, and amplitude stability

Armstrong

Hartley and the Shunt-fed Hartley

Colpitts and the resistive-capacitive (RC) feedback network

Phase Shift

Crystals and crystals as tuned circuits

Crystal-Controlled Armstrong and Pierce

Pulsed types and Frequency

Harmonics, frequency multiplication, and the buffer amplifier

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