Programmable frequency following device

摘要

A programmable frequency following device is provided. The programmable frequency following device includes a frequency divider for dividing the input frequency by a predetermined divisor. A frequency counter is used to count the output frequency of the programmable frequency following device, the frequency counter being reset to 0 after reaching a cycle time of the output frequency from the frequency divider. A programmable frequency comparator is used to compare the output count from the frequency counter with a user-programmable reference value at the time before the frequency counter is reset to 0. An up-down counter is under control by the programmable frequency comparator to count either in the upward or downward direction, and the count is locked when the output frequency reaches an intended value. A digitally controlled oscillator (DCO) is coupled to the up-down counter, and whose output frequency is inversely proportional to the output count from the up-down counter, and whose output frequency serves as the output frequency of the programmable frequency following device. The output frequency from this programmable frequency following device is programmable through firmware or software means and can be varied in a real-time manner through microprocessor control without having to replace the external oscillator that serves as clock generator.