Clock Sources for Synchronized Communication Systems

The ideal clock source will have start-stop capability, maintain known phase with respect to a start signal and combine high-frequency stability with voltage tuning to permit phase lock and Doppler correction. These properties define a clock source suitable for synchronized communication systems in which a remote unit must be started in synchronism with the signal received from a local unit. For some space applications clock stabilities of the order of one part in 10⁷ may be required. The two approaches to the problem considered are the gated crystal oscillator and the gated divider chain. The first requires that a high Q crystal oscillator be turned on in essentially steady state with insignificant transients of amplitude and phase. In the second a continuously running crystal oscillator is gated into a series of count-down dividers to obtain the clock output. Both of these approaches will produce circuits that have the required properties.