Clock synchronizer and clock and data recovery apparatus and method

Abstract

A clock synchroniser, and clock and data recovery apparatus incorporating the clock synchroniser, are described, together with corresponding clock synchronisation methods. The clock synchroniser incorporates an elastic buffer. A received clock signal RCK is used to clock data into the buffer, and a locally generated clock LCK is used to clock data out of the buffer. The local clock is synthesised using a PLL, and a fill-level signal from the elastic buffer is used to control to local clock frequency to maintain a desired average quantity of data in the buffer, thereby achieving synchronisation of the received and local clocks. In preferred embodiments the fill-level signal is used to control a variable divider in the feedback path of the PLL, which is supplied with a highly stable reference signal. A synchronised, and low-jitter local clock is thus produced. Preferably, the elastic buffer employs counters of relatively wide word width, and a storage array of much reduced depth, read and write pointers being provided by just a few of the least significant bits of the words.

Description

technical field [0001] The present invention relates to a clock synchronizer and to a clock and data recovery device and method. Certain embodiments relate to methods and circuits for recovering a low-jitter clock and data (eg, a jittered data stream) from jittered data. Background technique [0002] figure 1 A data link is shown comprising two systems, each clocked by a respective PLL. The transmitter transmits data at a given rate and the receiver clocks the data using its local clock. However the two clock frequencies may not be exactly the same, either short term or long term. [0003] Short-term variations in frequency will be induced in each clock due to thermal noise or external interference and can be considered as jitter in the corresponding clock. Additional jitter in the data stream can be introduced through intersymbol interference due to the limited bandwidth of the transmit channel or through crosstalk between adjacent cables. [0004] For general purpose ...

AI Technical Summary

Problems solved by technology

The low-bandwidth loop still receives a signal with a large amount of jitter from the high-bandwidth loop, which may occasionally lose lock unless design tradeoffs are made with its performance

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