| 摘要 |
Apparatus and methods for automatically determining the bit rate of an incoming signal are provided. The apparatus includes a counter, a logic circuit, and a histogram generating circuit. The counter counts the number of fast reference clock cycles which fit within each pulse of the incoming signal for a statistically significant number of pulses and provides indications thereof to the logic circuit. The logic circuit associates each of the indications with one of a plurality of allowable bit rates. The histogram generating circuit tracks the numbers of times the counts are associated with each allowable bit rate. In one embodiment, the allowable bit rate most often chosen is determined to be the bit rate of the incoming signal. In another embodiment, if a DDS1 line rate is determined to be the bit rate most often chosen, the DDS2 rate associated with the DDS1 line rate is provisionally selected. Also, if a DDS2 line is determined to be the bit rate most often chosen, that DDS2 line rate is provisionally selected. Then a frame pattern detector is used to detect the DDS/SC frame pattern. If a frame pattern is detected, the DDS2 rate provisionally selected is determined to be the bit rate of the incoming signal; if not, the DDS1 line rate associated with the DDS2 provisionally selected is chosen. |
