CMOS VLSI Physical Layout & Delay Analysis
Overview
I built a CMOS cell library from scratch in Tanner EDA on a generic 250 nm process (W/L = 1.5 μm / 250 nm). Each lab added cells, starting from single-transistor layouts, and the final design reused all of them in a 2-bit parallel adder placed inside a pad frame.
Architecture
The CMOS inverter cell was laid out manually at 21.3 × 12.5 μm, confirmed with DRC, then re-generated via Schematic Driven Layout (SDL) from a T-Spice netlist export to cross-validate both flows. DC sweep produced a VTC with a switching threshold near 1.7 V, below the ideal 2.5V midpoint due to the NMOS electron mobility advantage over the matched-width PMOS. Transient simulation at 50 MHz (20ns period, 1ns rise/fall) confirmed clean inversion. Subsequent labs added NAND/NOR, transmission gate, and D flip-flop cells, all reused as subcomponents in the final design: a 2-bit parallel adder (2 FA, 8 DFF, 3 TG, 1 inverter) placed within a pad frame, with a WRITE-controlled transmission gate output buffer and synchronous CK/_CK control interface.