ECE 275: Digital Design I

Class 1

Terms

i/p = Input o/p = Output

Signals

3 types of signal

1. Continuous (Analog)
2. Discrete
3. Digital - (Discrete in time and amplitude)

Sensors

• Proximity
• Motion
• Photosensor (Light)
• Microphone
• Temperature
• Gyroscopic
• Gas
• Pressure ...

Pressure Sensor

Analog -> ADC (to Digital) -> Process -> DAC (to Analog) -> Sound,Light,...

Transistors

Most basic component of digital circuits

Why are analog circuits not precise?

In Analog systems, noise is hard to filter

1.5V -> { +- 0.02V } -> 1.52V or 1.48V

In Digital systems, noise is hidden by reducing the amount of data stored by a signal

5V On On lv4 Off On lv3 On Off lv2 0v Off Off lv1 Sw1 Sw2

1.5 = Level 1 1.5 +- 0.02 is still Level 1

Basic Types of Circuits

• Combinational (current output depends on only current input)
• Sequential (current output depends on current input and past output)

Combinational circuits are typically the processing elements:

• Adders
• Multipliers
• Encoders
• Decoders

Sequential Circuits involve memory components:

• Latches
• Flip-Flops
• Registers
• Counters
• State Machines

Gates (Logic Gates)

Three main logic gates

• AND F = A * B -- Typically use this (like multiplication) F = A & B
• OR F = A + B -- Typically use this (like addition) F = A | B
• NOT F = ~A -- Typically use this in programming F = Ä€ } -- (A bar) F = A' } -- Typically use this in design

Circuit Examples

1. F = (A + B) * C

2. F = (A B C) + D' or F = ABC + D'