Abstract: A programmable logic fabric includes configurable logic block (CLB) containing registers and combinatorial logic elements. An input switch matrix distributes incoming signals to CLB inputs or inputs of embedded logic elements including a register clock. A routing network allows a variety of routing paths with distinct delays to be selected to route the CLB outputs to the input switch matrices. Presented clock delay insertion architectures allow a leaf node of dedicated clock network and a register clock input can be alternatively routed through the routing network, thereby allowing for the generation of a variable amount of clock delay. Required clock delay for each register minimizing the clock period is computed by clock skew optimization program. A set of alternative clock routes is generated for each register clock where each route delay is close to the corresponding required delay while satisfying the monotone increasing conditions.