Chapter 3 - Digital logic structures. This chapter includes contents: Transistor: building block of computers, simple switch circuit, n-type MOS transistor, logic gates, inverter (NOT Gate),.and other contents. | Chapter 3 Digital Logic Structures Transistor: Building Block of Computers Microprocessors contain millions of transistors Intel Pentium II: 7 million Compaq Alpha 21264: 15 million Intel Pentium III: 28 million Logically, each transistor acts as a switch Combined to implement logic functions AND, OR, NOT Combined to build higher-level structures Adder, multiplexor, decoder, register, Combined to build processor LC-2 3- Simple Switch Circuit Switch open: No current through circuit Light is off Vout is + Switch closed: Short circuit across switch Current flows Light is on Vout is 0V Switch-based circuits can easily represent two states: on/off, open/closed, voltage/no voltage. 3- N-type MOS Transistor MOS = Metal Oxide Semiconductor two types: N-type and P-type N-type when Gate has positive voltage, short circuit between #1 and #2 (switch closed) when Gate has zero voltage, open circuit between #1 and #2 (switch open) Gate = 1 Gate = 0 Terminal #2 must be connected to GND (0V). 3- P-type MOS Transistor P-type is complementary to N-type when Gate has positive voltage, open circuit between #1 and #2 (switch open) when Gate has zero voltage, short circuit between #1 and #2 (switch closed) Gate = 1 Gate = 0 Terminal #1 must be connected to +. 3- Logic Gates Use switch behavior of MOS transistors to implement logical functions: AND, OR, NOT. Digital symbols: recall that we assign a range of analog voltages to each digital (logic) symbol assignment of voltage ranges depends on electrical properties of transistors being used typical values for "1": +5V, +, + from now on we'll use + 3- CMOS Circuit Complementary MOS Uses both N-type and P-type MOS transistors P-type Attached to + voltage Pulls output voltage UP when input is zero N-type Attached to GND Pulls output voltage DOWN when input is one For all inputs, make sure that output is either connected to GND or to +, but not both! 3- Inverter (NOT Gate) In Out 0 V V V | Chapter 3 Digital Logic Structures Transistor: Building Block of Computers Microprocessors contain millions of transistors Intel Pentium II: 7 million Compaq Alpha 21264: 15 million Intel Pentium III: 28 million Logically, each transistor acts as a switch Combined to implement logic functions AND, OR, NOT Combined to build higher-level structures Adder, multiplexor, decoder, register, Combined to build processor LC-2 3- Simple Switch Circuit Switch open: No current through circuit Light is off Vout is + Switch closed: Short circuit across switch Current flows Light is on Vout is 0V Switch-based circuits can easily represent two states: on/off, open/closed, voltage/no voltage. 3- N-type MOS Transistor MOS = Metal Oxide Semiconductor two types: N-type and P-type N-type when Gate has positive voltage, short circuit between #1 and #2 (switch closed) when Gate has zero voltage, open circuit between #1 and #2 (switch open) Gate = 1 Gate = 0 Terminal #2 must be connected to GND
