Abstract: Method and apparatus for detecting clock loss in clock circuit. An example of the invention relates to detecting loss of a feedback clock signal input to a digital clock manager, where the feedback clock signal is derived from the reference clock signal. A clock divider is provided to produce a divided feedback clock signal from the feedback clock signal. A first pair of flip-flops is configured to store samples of the divided feedback clock signal on consecutive edges of the reference clock signal. A second pair of flip-flops is configured to store samples of the divided feedback clock signal on consecutive edges of an inversion of the reference clock signal. Detection logic is configured to detect whether each of the first pair of flip-flops and each of the second pair of flip-flops store the same value.

Abstract: Method and apparatus for reducing power dissipation and jitter in a delay line is described. The delay line includes a plurality of delay elements. At least one of the plurality of delay elements includes a gate terminal configured to receive gate control signals for activating or deactivating one or more of the delay elements. The delay line further includes gate control circuitry for providing gate control signals to the gate terminal of at least one of the plurality of delay elements.

Abstract: Delay lock loops (DLLs) that include delay line circuits with an optional clock pulse width restoration feature, and programmable delay circuits that enable the DLLs. A DLL can include optional inversions before and after at least one of the delay lines included in the DLL. Because two inversions are provided, the overall logic of the delay line is preserved. A DLL typically includes several different delay lines. Therefore, by selectively inverting the clock signal between the delay lines, the effect of each delay line on the clock pulse width can be balanced to provide an output clock signal having a pulse width closer to that of the input clock than would be achievable without the use of such selective inversion. In embodiments where the DLL forms a portion of a programmable logic device (PLD), the optional inversions can be controlled, for example, by configuration memory cells of the PLD.