A Circuit That Changes the Word Rate of Pulse Code Modulated Signals

It often is impractical to synchronize all of the clocks of an extensive digital network. Consequently, data will arrive at connections out of synchronism and special circuits are needed to bring them into time with the local clock. For irregular bursts of data, synchronism can be easily obtained using buffer memories, but for continuous streams of data, such methods are useful only for very small discrepancies in clock frequencies. A case of particular interest in telephone networks is the transmission and processing of pulse code modulation (PCM). Changing the word rate of such data can introduce objectionable noise into the signal. We describe a circuit that uses digital filters to contain this noise.