Re: Dependence of propogation delay of a gate on the feature
To constitute the propagation delay THROUGH a logic gate, consider the following factors:
A logic gate is made up of several transistors, so the gate-bulk capacitance, gate-source capacitance and gate-drain capacitance per transistor are parasitic capacitances that constitute propagation delay.
The poly-Si and metal layers that interconnect the gates and drains between transistors, inside a logic gate, exhibit load capacitance (inclusive of fringing capacitance) that constitute propagation delay.
The magnitude of the threshold voltage (Vth) and the supply voltage (Vdd) used can affect the switching speed, thus propagation delay.
The fan-out or the load capacitance perceived at the output of the logic can also constitute propagation delay.
The smaller the transistors, the higher the switching speed, at lower Vdd and Vth, with leakage becoming more significant in percentage. The propagation delay is also relatively shorter. All these are scaled carefully.