| 摘要 |
An RF receiver (120) receives FSK-modulated bit streams on a carrier frequency, and adjusts its local oscillator (122) frequency to the carrier frequency by comparing the accumulated spread between the higher tone of the FSK signal and the frequency of the local oscillator to the accumulated spread of the lower tone of the FSK signal and the frequency of the local oscillator. In certain embodiments, this involves detecting zero- crossings (132) for I and Q signal pairs of the received FSK-modulated bit stream, and determining (218) positive occurrences of each zero-crossing of the I and Q signal pairs in one direction, and negative occurrences for each zero-crossing of the I and Q signal pairs in the opposite direction. Over a plurality of positive and negative occurrences, the total time elapsed between consecutive positive occurrences is measured and accumulated (134, 234) along with the total time elapsed between consecutive negative occurrences. The total time elapsed between consecutive positive occurrences is divided by the total positive occurrences to develop a positive occurrence ratio. Similarly, a negative occurrence ratio is developed. The positive and negative occurrence ratios are then compared, and the result of the comparison is used to adjust (134, 234) the local oscillator frequency of the RF receiver. |
