A low-speed DLL facilitates a deskewed interface between a high-speed RX
data demultiplexer circuit directly to an Application Specific Integrated
Circuit (ASIC) with which it is integrated by locking a 156 MHz ASIC
clock to a 156 MHz reference derived from a high speed 2.5 GHz clock. The
DLL employs a digital interpolator to generate 32 phases of the 156 MHz
clock. The digital interpolator supplies the phases using a double
clocked shift register with recirculating feedback. The shift register is
double clocked using the 2.5 GHz clock. The register outputs are tapped
and fed to a 32:1 multiplexer having a phase select input that is
controlled by the phase difference signal generated by the DLL. The phase
difference control signal is converted to a digital representation of its
magnitude by which the requisite number of phase shift increments may be
selected. The phase chosen is that which eliminates any difference in the
phases of the 156 MHz clock that clocks the data transmitted to the ASIC
domain and the clock that is used in the ASIC domain to latch the data.
Thus, the interpolator takes advantage of the availability of the
high-speed clock to generate a sufficient number of phases for a low
speed DLL.