U.S. Philips Corporation

Dieter J Kunze

Jorg Wolber

Gerd Onken

Walter H Demmer

Friedrich E Hahn

Ulrich Mohlmann

A digital phase-locked loop (PLL) which responds to a square-wave input signal of on expected frequency f.sub.E and comprises a change-over switch which is switched in response to square-wave signals or different frequencies and precedes a main divider operating with a divisor D and which produces the output signal of the phase-locked loop. The change-over switch is activated as a function of the output signal and the input signal. In order to provide symmetrical locking in of the phase-locked loop and a small capture-and-hold range, the change-over switch is switched between a first square-wave signal of the frequency f.sub.1, a second square-wave signal of the second frequency f.sub.2 and a third square-wave signal of the frequency f.sub.3, in which:

Digital phase-locked loop

A circuit arrangement for transferring a d.c. voltage via a smoothing network including a capacitor which can be switched to prevent a surge in the transferred signal from occurring. The voltage from the output terminal is applied to the capacitor in the changed-over state via an amplifier having a high input impedance and a gain factor of substantially 1.

Switchable smoothing network

A charging current source and a discharging current source are alternately connected to an input capacitor. By choosing the current ratios it is possible to switch a reference level located in the signal range, for example the black level in a television signal, in the circuit, without the necessity for interval keying.

Circuit arrangement for adjusting the direct current level of a video

Circuit arrangement for generating a sawtooth voltage which has a substantially nominal frequency in the absence of synchronization pulses, whereby the changeover to direct synchronizability takes place as soon as a synchronization pulse comes into coincidence with the sawtooth flyback. In this way a phase change is avoided when the changeover is made. The changeover to nominal frequency occurs as soon as a pulse fails to occur within the natural period effective in case of direct synchronization. A threshold value circuit has an intermediate value which prevents synchronization by interference pulses occurring prematurely.

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Kaltenkirchen, Germany

Dieter J Kunze