Programmable frequency divider for a television receiver frequency

Abstract

A phase locked local oscillator loop of a frequency synthesizer tuning system for a television receiver includes a programmable frequency divider for deriving an output signal having a period which is N times the period of its input signal, N being the number in MHz of the local oscillator frequency required for tuning the receiver to a selected channel (e.g., N = 101 for U.S. channel 2). The 'divide by' number N is controlled by first counting the input signal pulses in groups of (S) pulses, where (S) is a factor equal to the channel separation in MHz (6 in the U.S.). Counting by groups of S continues until the number of such groups equals the channel number, e.g., 2 for channel 2, 83 for channel 83, and then continues for an additional predetermined number of groups of S dependent on the band in which the selected channel resides. The counting then continues in groups of T (T = S-1 is usual) for another predetermined number of groups, likewise dependent on the channel band, until the correct number N of input pulses have been counted, in groups of S and T counts. When the correct N is reached, an output signal is generated and the process is repeated.