Method and apparatus for adjusting the timing of signals over fine and coarse ranges

摘要

A variable delay circuit is formed by a fine delay circuit and a coarse delay circuit. The fine delay circuit adjusts the delay of a delayed clock signal in relatively small phase increments with respect to an input clock signal. The coarse delay circuit adjusts the timing of a digital signal in relatively large phase increments. The delayed clock signal is used to clock a register to which the digital signal is applied to control the timing a the digital signal clocked through the register responsive to adjusting the timing of the fine delay circuit and the coarse delay circuit. The timing relationship is initially adjusted by altering the delay of the fine delay circuit. Whenever the maximum or minimum delay of the fine delay circuit is reached, the coarse delay circuit is adjusted. The variable delay circuit may be used in a memory device to control the timing at which read data is applied to the data bus of the memory device. The fine delay circuit includes a multi-tapped delay line coupled to a multiplexer that selects one of the taps for use in generating the delayed clock. When the first or last tap is selected, the timing of the coarse delay circuit is adjusted. The coarse delay circuit includes a counter that generates the digital signal upon counting from an initial count to the terminal count. The coarse delay circuit is adjusted by adjusting the initial count of the counter.