Types of Transistor Oscillators

A transistor can be operated as an oscillator for producing continuous undamped oscillations of any desired frequency if tank and feedback circuits are properly connected to it.All oscillators under different names have similar function i.e.they generate continuous undamped output.However,they differ in methods of supplying energy to the tank or oscillatory circuit to meet the losses and the frequency ranges over which they are used.

The frequency spectrum over which oscillators are employed to produce sinusoidal signals is extremely wide (from less than 1 Hz to many GHz).However,no signal oscillator design is practical for generating signals over this entire range.Instead,a variety of designs are employed,each of which generates sinusoidal outputs most advantageously over various portions of the frequency spectrum.

Oscillators,which use inductance-capacitance(L-C)circuits as their tank or oscillatory circuits,are very popular for generating high frequency (e.g.10 kHZ to 100 MHz) outputs.The most widely used LC oscillators.Although they slightly differ from one another in their electronic circuitry but they have virtually identical frequency ranges and frequency and frequency-stability characteristics,However,such oscillators are not suitable for generating low-frequency sinusoidal outputs.This is due to the fact that the components required in construction of low-frequency L-C resonant circuits are too bulky and heavy. So resistor-capacitor(R-C) oscillators are generally employed for generating low-frequency sinusoidal signals.Two most common R-C oscillators are the Wien bridge and phase and phase shift types.

Type of oscillator                                                                          Frequency Ranges 

Wien bridge oscillator                                                                1 Hz-1 MHz

phase shift oscillator                                                                   1Hz-10 MHz

Hartly oscillator                                                                           10 kHz-100 MHz

Colpitt's oscillator                                                                       10 kHz-100 MHz

Negative resistance oscillator                                                        > 100 MHz

Crystal oscillator                                                                          Fixed frequency