Explanation of Function Generator

Function Generators

The function generator is a versatile instrument that gives a number of different waveforms at the output with their frequencies that can be adjusted over a wide range. The most commonly used waveforms are sine wave, square wave, triangular wave and the sawtooth wave. Different output signals from the function generator may be available simultaneously.

Pic 1

The fig shows the block diagram of a function generator. Here two constant current sources are used to feed the integrator circuit. When the circuit is switched ON, the upper constant current source sends a constant current into the integrator and the output of the integrator is connected to comparator. When the integrator output reaches a predetermined level, the comparator changes the state i.e. the upper constant current source is cut OFF while the lower source is switched ON. This current source passes a current in the reverse direction and the voltage at the integrator output decreases to a pre-determined level, again the comparator switches ON, the lower current source is switched OFF and the upper is switched ON and the cycle repeats.

The rate of rise/fall of the integrator output depends upon the magnitude of the current supplied by the upper/lower constant current sources. This change in the magnitudes of these currents would change the integrator output. Frequency control network controls the magnitudes of the current sources and hence the frequency of the output.

The integrator output is of triangular waveform which may be amplified by the output amplifier and obtained at the output which is shown in fig. the comparator output which is used to switch over function of the current source is of square wave shape. This square wave output may be amplified and used as a square wave output. Lastly the triangular diode wave shaping circuit which converts this triangular signal into a sinusoidal signal.