Introduction to Signal Generators

The function of a signal generator is to produce time a dependent signal with some special characteristics of frequency, amplitude and shape. Sometimes these features are controlled externally throughout control signals.  The voltage-controlled oscillator or VCO is a clear example.

To ensure that the signal generator acheives its function, some kind of feedback devices are used. These devices have features that are time-dependent (usually capacitors). There are two types of signal generator: Tuned or Sinusoidal oscillators and Relaxation oscilators

• The tuned oscillators use a system that theorycally creates pairs of conjugated poles exactly in the imaginary axis in order to maintain a sustained sinusoidal oscillation.
• The relaxation oscillators use bistable devices such as switches, Schmitt triggers, logic gates, comparators and flip-flops that repeatedly charge and discharge capacitors.

Typical waveforms that are obtained with relaxation oscillators are triangular, square, exponential or pulse.