A circuit and method is shown for digital control of delay lines in a delay locked
loop (DLL) system. A pair of multiplexors (MUXes) is used to select output taps
from a pair of complementary delay lines that delay a reference clock signal in
order to lock onto a received clock signal. An output tap from one delay line is
used to produce a rising edge in an output clock signal while a corresponding tap
in the complementary delay line is used to produce a falling edge in the output
signal in order to correct for distortion. The MUXes are controlled based on a
phase difference detected between the received clock signal and a feedback clock
corresponding to the output clock signal. Another aspect of the present invention
provides for generation of a quadrature clock by interpolating between the rising
and falling edges selected for the output clock signal. Still another aspect of
the present invention provides for selectively disabling unused elements of the
delay lines to reduce power consumption.
