Method and apparatus for multiphase, fast-locking clock and data recovery
View Patent ↗A method and apparatus for clock and data recovery that is advantageous in burst-mode systems is disclosed. This clock and data recovery method allows a) fast locking to a rapidly changed phase of the transmission clock, and b) stable tracking of a slowly changing phase of the transmission clock. Such fast locking minimizes the “guard band” between consecutive transmission bursts, while stable tracking provides reliable data tracking, resulting in the efficient use of bandwidth. A plurality of clock signals, is generated, each having a different phase. The phase of an input signal data stream is determined and a desired clock signal in the plurality that corresponds to the phase of the input data stream is selected and used to sample the input signal data stream.
1. A method for clock and data recovery comprising:
generating a plurality of input clock signals in said plurality having a different phase;
determining the phase of an input signal data stream;
selecting at least one of said plurality of input clock signals, said selection based on said phase of an input signal data stream, to sample said input signal data stream, wherein the step of determining the phase of an input signal data stream comprises:
generating a plurality of gated clock signals from said plurality of input clock signals;
retiming samples from said input data stream in a way such that a digital representation of at least one period of said input data signal is generated; and
detecting the position of a desired bit in said at least one period of said input data signal.
2. The method of claim 1 wherein the step of selecting at least one of said plurality of input clock signals comprises:
comparing each clock signal in said plurality of input clock signals to the phase of said input signal data stream; and
determining which of said plurality of input clock signals has a rising or falling edge that is closer in time to the middle of a bit interval of said input data signal than a rising or falling edge of any other clock signal in said plurality.
3. Apparatus for clock and data recovery comprising:
means for generating a plurality of input clock signals, each of said input clock signals in said plurality having a different phase;
means for determining the phase of an input signal data stream;
means for selecting at least one of said plurality of input clock signals, based on said phase of an input signal data stream, to sample said input signal data stream, wherein said means for determining the phase of an input signal data stream comprises:
means for generating a plurality of gated clock signals from said plurality of input clock signals;
means for retiming samples from said input data stream in a way such that a digital representation of at least one period of said input data signal is generated; and
means for detecting the position of a desired bit in said at least one period of said input data signal.
4. The apparatus of claim 3 wherein said means for selecting at least one of said plurality of input clock signals comprises:
means for comparing each clock signal in said plurality of input clock signals to the phase of said input signal data stream; and
means for determining which of said plurality of input clock signals has a rising or falling edge that is closer in time to the middle of a bit interval of said input data signal than a rising or falling edge of any other clock signal in said plurality.