GB1307916A - Phase comparison circuit - Google Patents

Abstract

1307916 Phase comparators in automatic phase control systems ITT INDUSTRIES Inc 21 April 1970 [25 April 1969 26 March 1970] 18973/70 Heading H3A A phase comparator for comparing the phases of a triangular and a rectangular pulse signal comprises: a first circuit T1, T2, T3 which inverts the portion of the rectangular pulse occurring during the time when the triangular pulse amplitude lies on one side of a reference level, and passes un-inverted that portion of the rectangular pulse occurring during the time when the triangular pulse amplitude lies on the other side of the reference level; a second circuit T4, T5, T6 for combining the inverted and non- inverted outputs from the first circuit; and an integrator C1, R1 for integrating the combined signal. The triangular signal is applied to one side A of a long-tailed pair. The reference level D is applied to the other side and, during the time that a pulse is present at B, either T1 or T2 will conduct depending on the amplitude of the signal at A relative to that at D. The comparator is used in an A.P.C. system in a television receiver, and when the two phases are synchronized, the time constant of the integrator C1, R1 may be increased by switching in a second capacitor C2, by means of a further circuit T7 ... T11. The pulse signal applied at B and a further rectangular pulse signal derived from the triangular signal are applied at inputs E, F of a coincidence gate T8, T9, so that when the pulses in the two trains coincide transistor T7 is switched on to connect capacitor C2 across capacitor C1