Programmable digital delay

Abstract

A method of delaying successive first and second input signals by first and second different selectable time periods using a programmable delay line comprising a sequence of delay elements, each introducing a delay, the method comprising the steps of: providing a control signal to each delay element, the control signal selectively being in a first logic state or a second logic state wherein in a first logic state the delay element selects an input from an adjacent delay element thereby to select the delay elements as part of a set of delay elements introducing said selectable time period and in a second logic state the delay element is not selected in the set; setting the control signals for a first number of adjacent delay elements to the first logic state to introduce the first selectable time period wherein the control signals for the delay elements in the sequence not in the first number are set to the second logic state; and setting the control signals of a second number of adjacent delay elements to the first logic state to introduce a second selectable time period, wherein the control signals for the delay elements in the sequence not in the second number are set to the second logic state; whereby the reconfiguration time between the first and second input signals is less than the maximum delay introduced by the sequence of delay elements.