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Hybrid Analog/Digital Clock Recovery for Burst-Mode Data

IP.com Disclosure Number: IPCOM000112234D
Original Publication Date: 1994-Apr-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 2 page(s) / 60K

Publishing Venue

IBM

Related People

Gill, DE: AUTHOR [+3]

Abstract

Described is a Quick Phase Lock Analog/Digital Phase Lock Loop (PLL). The PLL allows the use of a narrow band control loop for controlling the ring-oscillator free-running frequency (Fo). At the same time fast acquisition of burst mode data is possible (which requires a wide band control loop). Thus, this general topology allows the optimization of two conflicting requirements.

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Hybrid Analog/Digital Clock Recovery for Burst-Mode Data

      Described is a Quick Phase Lock Analog/Digital Phase Lock Loop
(PLL).  The PLL allows the use of a narrow band control loop for
controlling the ring-oscillator free-running frequency (Fo).  At the
same time fast acquisition of burst mode data is possible (which
requires a wide band control loop).  Thus, this general topology
allows the optimization of two conflicting requirements.

      PLL's of this type consist of three major blocks.  The first
block is a Frequency-Locked Loop (FLL) which sets Fo of the ring
oscillator.  The second block is the Phase-Acquisition (PA) logic.
The third block is a state machine which provides control for the PA
logic.  The Figure shows the block diagram of the PLL.  The PLL is
composed of the four topmost blocks.  The state machine is labeled as
"digital control".  The rest of the blocks comprise the PA logic.

      The basic function of the PA logic is to select the correct
output stage of the ring oscillator such that the optimum data
sampling time is obtained.  The selection is made by comparing the
data (RDATA) transitions with the transitions of the ring oscillator.
For each data transition the logic determines which inverter in the
ring oscillator is transitioning.  A long term average is kept of the
RDATA crossings as compared to the inverter transitions.  The average
is used to select the best inverter output for the recovered clock.
The followin...