Variable data rate receiver

Abstract

A clock signal and data is recovered from a variable rate signal including biphase mark encoded digital audio data. Such recovery involves regularly determining a minimum or maximum pulse width in the biphase mark encoded digital audio data using a high frequency clock. This pulse width is used to define a window in which a transition in the biphase mark encoded digital audio data may be detected. If a transition occurs in the defined window, a data one is output; if a transition does not occur in the defined window, a data zero is output. The recovered clock has a period of twice the minimum pulse width. A minimum or maximum pulse width can be tracked with an accumulator with decay. In particular, if the data rate of the input signal becomes faster, the shortest pulse will become shorter and a minimum value stored by the accumulator will become shorter. If the data rate of the input signal becomes slower, the longest pulse will become longer and any maximum value stored by the accumulator will become longer. However, if a minimum is stored and the input signal becomes slower, or if a maximum is stored and the input signal becomes faster, the stored minimum or maximum values would not otherwise change. By incorporating decay, the stored value changes over time towards a larger value (if a minimum is stored) or a smaller value (if a maximum is stored) to a limit. By regularly updating the determined minimum or maximum pulse width, the rate of the input signal may vary over time and still permit recovery of the clock and data signals. By using a window in which a transition is detected, jitter in the input signal is tolerated and gradual changes in input rate may be tracked.