PHASE-LOCKED LOOP FREQUENCY MODULATION CIRCUIT FOR INPUT MODULATION SIGNALS HAVING LOW-FREQUENCY CONTENT

摘要

A phase-locked loop frequency modulation circuit that compensates for the inability of a phase-locked loop to pass low-frequency content of an input modulation signal, and that may be utilized with existing communication apparatus, such as a cellular telephone voice radio, for accurate data transmission without having to modify such apparatus, includes a compensation circuit (50) for processing an input modulation signal (72) to provide a compensation signal (78) that is added to a loop filter output signal (70) by processing the input modulation signal to provide the same effect as adding the input modulation signal to an integrated input modulation signal (74) that is filtered by a filter (54) having the same transfer function as the loop filter (46) to provide the compensation signal.