Introduction to CMOS VLSI Design Lecture 2: Standard Cell Design Layout

1. Introduction toCMOS VLSIDesignLecture 2: Standard Cell Design Layout SalmanZaffar IqraUniversity, Spring 2012 Slides from D. Harris, Harvey Mudd College USA

2. Gate Layout • Layout can be very time consuming • Design gates to fit together nicely • Build a library of standard cells • Standard cell design methodology • VDD and GND should abut (standard height) • Adjacent gates should satisfy design rules • nMOS at bottom and pMOS at top • All gates include well and substrate contacts Lecture 2

3. Example: Inverter Lecture 2

4. Example: NAND3 • Horizontal N-diffusion and p-diffusion strips • Vertical polysilicon gates • Metal1 VDD rail at top • Metal1 GND rail at bottom • 32 l by 40 l Lecture 2

5. Stick Diagrams • Stick diagrams help plan layout quickly • Need not be to scale • Draw with color pencils or dry-erase markers Lecture 2

6. Wiring Tracks • A wiring track is the space required for a wire • 4 l width, 4 l spacing from neighbor = 8 l pitch • Transistors also consume one wiring track Lecture 2

7. Well spacing • Wells must surround transistors by 6 l • Implies 12 l between opposite transistor flavors • Leaves room for one wire track Lecture 2

8. Area Estimation • Estimate area by counting wiring tracks • Multiply by 8 to express in l Lecture 2

9. Example: O3AI • Sketch a stick diagram for O3AI and estimate area Lecture 2

10. Example: O3AI • Sketch a stick diagram for O3AI and estimate area Lecture 2

11. Example: O3AI • Sketch a stick diagram for O3AI and estimate area Lecture 2

12. Standard Cells • Uniform cell height • Uniform well height • M1 VDD and GND rails • M2 Access to I/Os • Well / substrate taps • Exploits regularity Lecture 2

13. Layout through Synthesis • Synthesize HDL into gate-level netlist • Place & Route using standard cell library Lecture 2