Frequency synthesizer.

摘要

It is required to generate a constant frequency 1 MHz signal from a higher frequency signal 02 which may have any one of a plurality of higher frequencies which are non-integral multiples of 1 MHz. Groups of 02 pulses are counted off in a counter (85) and the group counts follow a recurrent pattern such that the mean frequency of the output pulses is 1 MHz. A latch (80) stores a signal identifying which frequency 02 is being employed and ROMs (80, 81, 82 and 83) determine the recurrent pattern by selecting two different numbers for the group counts, the total number of groups in the recurrent cycle and which of these groups employ the high count and which employ the low count. For example, a signal 02 with a period of 350 ns is counted down to 1 MHz using 3 counts of 3 pulses followed by 1 count of 2 pulses followed by 3 more counts of 3 pulses.