Static CMOS Circuits

Static CMOS Circuits In Static CMOS circuits with n inputs, 2n transistors are needed. nMOS block is a dual of the pMOS block. What ever is in series in nMOS, appears in parallel in pMOS and vice versa. CMOS gates consume power only during the transition of inputs.

Static complementary gate structure Pull-up and pull-down networks VDD pull-up network out inputs Pull-down network VSS 7

Pull-up/pull-down network design Pull-up and pull-down networks are duals. To design one gate, first design one network, then compute dual to get other network. 13

Static CMOS Circuits Static CMOS Logic Structure Logic Gates – Inverter, NAND and NOR Complex Structures AOI/OAI Structures Stick Diagrams Layouts

Inverter 8

NAND Gate Va Vb Vout 1

NOR2 Gate Va Vb Vout 1

Static CMOS Circuits Static CMOS Logic Structure Logic Gates – Inverter, NAND and NOR Complex Structures AOI/OAI Structures Stick Diagrams Layouts

Complex CMOS Structures

Xor gate

Static CMOS Circuits Static CMOS Logic Structure Logic Gates – Inverter, NAND and NOR Complex Structures AOI/OAI Structures Stick Diagrams Layouts

AOI/OAI gates AOI = and/or/invert; OAI = or/and/invert. Implement larger functions. Pull-up and pull-down networks are compact: smaller area, higher speed than NAND/NOR network equivalents. 11

AOI example invert or and 12

Problems A C B D Y A B C D

Problems Design a CMOS circuit to implement the logic Y = A'B' + B'C + C'A Make a 2 input CMOS XOR gate to implement Y = A  B. CMOS XOR and XNOR gates are similar. Just one of the input pairs (A and A' are reversed).

Static CMOS Circuits Static CMOS Logic Structure Logic Gates – Inverter, NAND and NOR Complex Structures AOI/OAI Structures Stick Diagrams Layouts

Stick diagrams A stick diagram is a cartoon of a layout. Does show all components/vias (except possibly tub ties), relative placement. Does not show exact placement, transistor sizes, wire lengths, wire widths, tub boundaries.

Stick Diagram of NOR gate

Stores charge on inverter gate capacitance: Dynamic latch Stores charge on inverter gate capacitance:

Dynamic latch stick diagram VDD in out VSS phi phi’

Static CMOS Circuits Static CMOS Logic Structure Logic Gates – Inverter, NAND and NOR Complex Structures AOI/OAI Structures Stick Diagrams Layouts

Layout VDD D Q’ VSS f f’

Layout of NOR Gate

Stick Diagram of NAND gate