Delay locked loop circuitry for generating a predetermined
phase relationship between a pair of clocks. A first
delay-locked loop includes a
delay elements arranged in a chain, the chain receiving an input
clock and generating, from each
delay element, a set of phase vectors, each shifted a
unit delay from the adjacent vector. The first delay-locked loop adjusts the unit delays in the delay chain using a delay adjustment
signal so that the phase vectors span a predetermined phase shift of the input
clock. A second delay-locked loop selects, from the first delay-locked loop, a pair of phase vectors which brackets the phase of an input
clock. A phase interpolator receives the selected pair of vectors and generates an output clock and a delayed output clock, the amount of the delay being controlled by the delay adjustment
signal of the first delay-locked loop circuitry. A
phase detector compares the delayed output clock with the input clock and adjusts the phase interpolator, based on the phase comparison, so that the phase of the delayed output clock is in phase with the input clock. As a result, there is a predetermined
phase relationship between the output clock and the input clock, the
phase relationship being the amount of delay between the output clock and the delayed output clock. Different phase relationships between the input and output clock are possible depending on the number of unit delays used in the path of the, delayed output clock or the output clock.