Estimating propagation delays in a programmable device

A method of estimating a propagation delay, comprising:

• storing a second representation of a circuit by replacing a capacitor in a first representation of said circuit with a resistance Ri and a voltage source Vi, said second representation having a plurality of nodes, said resistance Ri having a first value R1 at a first point in time and said voltage source having a first value V1 at said first point in time;
• using R1 and V1 to estimate voltages on said plurality of nodes in said second representation at a second point in time;
• determining a second value R2 of said resistance Ri and a second value V2 of said voltage source Vi;
• and
• using R2 and V2 to estimate voltages on said plurality of nodes in said second representation at a third point in time;
• and
• using at least one of the estimated voltage values V1 and V2 to estimate said propagation delay, wherein said propagation delay is estimated based in part on the time at which the voltage on a node is estimated to reach a predetermined voltage.

A computer implemented method, comprising:

• storing in a computer a representation of a circuit having a net;
• and
• using said computer to estimate a propagation delay through said net using a backward stepping rule without solving a set of simultaneous equations, involving:
• (a) generating a model for said net, said model having nodes;
• (b) determining voltages on said nodes at a second point in time given voltages on said nodes at a previous point in time using said backward stepping rule;
• and
• (c) repeating step (b) from point in time to point in time to estimate said propagation delay.