| 摘要 |
Digital frequency demodulation is accomplished by monitoring similar transitions in an FM radio signal to determine frequency. Time intervals between similar transitions in the FM signal are established by selecting anticipated transition times and accumulating error values relative to actual transition times. Accumulated error values provide a basis for further selecting anticipated transition times in such manner that a reported sequence of anticipated transition times provides a basis for inferring signal frequency. In one illustrated embodiment, the chosen transition times are positive transitions in the FM signal and the anticipated times of transition are taken from a set of two time periods, an early transition and a late transition relative to a valid transition window. In one embodiment of the invention, accumulated error is stored in an integrator device while in another embodiment accumulated error is stored in the phase of a bi-frequency oscillator. By reporting the selected anticipation times by associated values in a digital bit stream, frequency may be inferred by computing a ratio of given digital values in the bit stream relative to the total number of samples in the bit stream. |
