Digital Technique for FM Modulation of Infrared Headphone Interface Signals

摘要

A method of modulating an infrared headphone interface signal includes providing a first audio signal having an analog audio value. A memory is provided having a plurality of locations and containing digital phase offset values. A clock signal having a clock frequency is provided. A second audio signal having a center carrier frequency that deviates with the analog audio value of the first audio signal is provided. An instantaneous value of the center carrier frequency is determined. The clock frequency is divided by the instantaneous carrier frequency value to calculate a number of samples per cycle. A number of location addresses in the memory is divided by the number of samples per cycle to calculate a memory access interval. The memory is accessed at addresses separated by the memory access interval. The digital phase offset values at the accessed memory addresses are used to reproduce the first audio signal.