Frequency synthesis: a comparison of techniques

All clocked synchronous circuits and waveform generation circuits require the manipulation of a periodic pulsed signal for commonality. The clocked circuits are required to perform logic operation in unison. Waveform generation circuitry such as modulators and local oscillators must adhere to strict tolerances to permit the production of desired signals. These types of circuits are very dependant upon a single input waveform or signal. There are several basic types of frequency synthesizers which may be used to generate these periodic signals. Such types range from employing a vast quantity of crystals each resonating at different frequencies to those which operate solely from a single crystal. All frequency synthesizers may be classed as direct, indirect, analog, digital or a combination of these