Multiple-mode clock distribution apparatus and method with adaptive skew compensation

Abstract

An apparatus and method for distributing a clock signal within circuitry disposed on a number of separate system cards includes a first system card that generates a reference clock signal representative of a fixed delay of a system clock signal. A number of variable clock signals are produced using the system clock signal. Each of a number of system cards separate from the first system card receive one of the variable clock signals. A delay associated with the reference clock signal is typically longer than a delay associated with each of the variable clock signals. The phase of each of the variable clock signals is adjusted to a substantially in-phase relationship with respect to the reference clock signal in response to a phase difference between the reference clock signal an output signal received from each of the separate system cards. Producing each of the variable clock signals may involve selecting between a first delay line and a second delay line, and then producing the variable delay signal using the selected first or second delay line. A delay factor of the non-selected first or second delay line may be changed by varying a resistance and a current of one or more delay elements of the non-selected first or second delay lines. The circuitry is selectably operable in a slave or buffer-type clock repowering mode or an adaptive mode. The variable clock signals and the output signals may respectively comprise low voltage differential signals (LVDS) or CMOS level signals.