Integrated Circuit Technology

Tom Kelliher, CS 220

Sept. 24, 2003

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Assignment

Read 3.1--3.

From Last Time

NAND gates, two-level implementation, parity.

Outline

1. Terminology.

2. Transmission gates.

3. CMOS.

Coming Up

Combinational logic design process and simulation.

Terminology

1. Today's important logic families: TTL, CMOS, LVTTL.

   Voltage, current, power, speed.

2. Fan-in, fan-out.

3. Noise margin. Where does noise come from?

4. Power dissipation. Who cares? Extended battery, device life.

5. Propagation delay. Don't forget about wires: on-chip and off-chip.

   Delay may be asymmetric: , . Max of both: .

6. We'll only examine positive logic and transport delay.

Transmission Gates

An electronic switch:

Typically used to enable writes onto a bus. For examples, two CPUs sharing a memory bus. Bus arbitration.

Can be used in more crafty ways: viewing an EXOR as a ``conditional inverter:''

Eight transistors; two gate delays.

The standard NAND implementation requires four gates (16 transistors) and has a propagation delay of three gate delays.

CMOS

CMOS Transistors

1. N-type transistor:
   1. Passes GND well.

   2. Degrades Vdd.

   3. Normally open switch.

2. P-type transistor:
   1. Passes Vdd well.

   2. Degrades GND.

   3. Normally closed switch.

Diagrams:

1. Terminals: gate, drain, source.

2. High capacitance on the gate.

CMOS Logic Gates

A CMOS inverter:

A CMOS transmission gate:

A CMOS 2-input NAND gate:

What determines power dissipation? Switching frequency.

Why transport delay isn't a good model: It takes time to move the charge on the gate. This is correctly modeled with inertial delay.