Analog vs Digital Signals (4a)

What is an analog signal?

is a continuous wave in both amplitude and time

Give an example of an analog signal.

A wave in the ocean

What is a digital signal?

A digital signal is composed of individual, identifiable steps.

Give an example of a digital signal.

The tick-tick-tick of the second hand on a clock is a digital signal.

What is “noise” in electronics?

is any unwanted interference with a signal.

What are some sources of electronic noise?

can be natural (from electromagnetic interactions) or man-made (from motors, fluorescent lights, radio or radar transmissions, and wireless signals

How does a digital signal perform compared to an analog signal in noisy environments?

is less likely to be affected by noise than the other signal.

What are the advantages of analog signals?

Can represent natural phenomena directly (e.g., speech, temperature, pressure).

Infinite resolution — no loss in quantisation.

Simple circuits can easily amplify or filter them.

What are the disadvantages of analog signals?

Noise-sensitive — any interference alters the signal (e.g., static noise in FM/AM radio).

Degradation — signal weakens over distance (attenuation), e.g., old analog phone lines.

Storage difficulty — hard to store precisely (e.g., tape, film).

Limited processing — harder to perform mathematical operations.

What are the advantages of digital signals?

Noise immunity — errors can be detected and corrected.

Easy storage and transmission — can be stored on memory chips, disks, etc.

High reliability — signal remains consistent after copying or amplification.

Easy processing — can be mathematically analyzed by computers.

What are the disadvantages of digital signals?

Quantisation error — loss of fine detail when converting from analog.

Bandwidth requirement — faster switching and higher frequency need more bandwidth.

Hardware complexity — requires ADCs, DACs, and logic circuits.

Power consumption — higher in high-speed circuits.

What are the basic Boolean logic gates and their functions?

• AND Gate: Output is 1 only if both inputs are 1.

• OR Gate: Output is 1 if either or both inputs are 1.

• NOT Gate: Also called Inverter — outputs the opposite of the input (1 → 0, 0 → 1).

• NAND Gate: Output is 0 only if both inputs are 1 (opposite of AND).

• NOR Gate: Output is 1 only if both inputs are 0 (opposite of OR).

• XOR Gate (Exclusive OR): Output is 1 only if one input is 1 (but not both).

• XNOR Gate (Exclusive NOR): Output is 1 only if both inputs are the same.

What is a truth table and how is it used in Boolean logic?

• An operand is a quantity that a mathematical or logical operation is performed on.

• A truth table shows all possible inputs and outputs for a Boolean operation.

• Columns represent one operand; rows represent the other.

• The result of each combination is shown in the intersecting box.

• Example: For “A ≠ B,”

  • 0 ≠ 1 → true (1)

  • 0 ≠ 0 → false (0)

• Truth tables do not represent real math operations like multiplication or division.

• They show the output of logical questions using binary digits (0 for false, 1 for true).

How do AND and OR operations work in Boolean logic truth tables?

• Operands: 0 = false, 1 = true.

• AND Operation: True only if both operands are true (1).

  • 0 AND 0 → 0 (false)

  • 1 AND 0 → 0 (false)

  • 0 AND 1 → 0 (false)

  • 1 AND 1 → 1 (true)

• OR Operation: False only if both operands are false (0).

  • 0 OR 0 → 0 (false)

  • 1 OR 0 → 1 (true)

  • 0 OR 1 → 1 (true)

  • 1 OR 1 → 1 (true)

What are binary numbers and how are they represented?

Binary numbers are distinct from Boolean numbers, but both use digits 0 and 1.

Binary numbers are real numbers that can represent values beyond just 0 and 1.

They can represent decimal numbers (base 10) using strings of 0s and 1s.

Binary-coded decimals (BCDs) can be sent in series (one digit at a time) or in parallel (group of bits at once).

• Bit: a single binary digit.

• Nibble: 4 bits.

• Byte: 8 bits.

How does the binary number system work and how do you convert binary to decimal?

• Binary is a base-2 system using only 0 and 1.

• Each digit is called a bit (binary digit).

• Each position has a place value based on powers of 2, just like decimal uses powers of 10.

• Example: Binary 1011 →

  • (1 × 2³) + (0 × 2²) + (1 × 2¹) + (1 × 2⁰)

  • = 8 + 0 + 2 + 1 = 11 in decimal

What are logic gates and what are some key points about them?

• Circuits that perform computations contain gates.

• In digital circuits, these are called logic gates.

• Each gate has one output but can have multiple inputs.

• NAND and NOR gates are universal gates — they can mimic any other logic gate if combined properly.

• NOT gate is also called an inverter because it reverses the input signal.

What are the differences between digital and analog systems, and why are analog-to-digital conversions used?

• Digital systems: Can correct errors, so output matches the input exactly.

• Analog systems: Always imperfect — output is never an exact replica of the input.

• Analog signals are essential for applications involving human senses (hearing, seeing).

• Logical approach: Convert analog → digital for transmission, then digital → analog at the output.

• Analog signals are also important in control systems and measurements, beyond sensory applications.

What are the differences between digital and analog systems, and why are analog-to-digital conversions used?

• Digital systems: Can correct errors, so output matches the input exactly.

• Analog systems: Always imperfect — output is never an exact replica of the input.

• Analog signals are essential for applications involving human senses (hearing, seeing).

• Logical approach: Convert analog → digital for transmission, then digital → analog at the output.

• Analog signals are also important in control systems and measurements, beyond sensory applications.

What is digital-to-analog (D/A) conversion and how does it work?

• Conversion: Converts a digital signal into an analog signal.

• Digital-to-Analog Converter.

• Digital signals are usually in binary code, analog signals are voltages or currents varying over a range.

• Example: A 4-bit DAC with inputs D, C, B, A can represent 16 different values (0–15).

• The output voltage can be directly proportional to the binary input:

  • 1011 (11) → 11 mV

  • 0110 (6) → 6 mV

• A proportionality factor can scale the output:

  • Factor 7 → 1011 (11) → 77 mV, 0110 (6) → 42 mV

What is an analog-to-digital (A/D) converter and what does it do?

Conversion: Converts an analog signal into a digital output code.

ADC: Analog-to-Digital Converter.

The digital output represents the original analog signal in binary form.

What is a key characteristic of A/D converters regarding timing?

• A significant feature of an A/D converter is the time delay between the input signal entering and the digital output being produced.

• This delay occurs due to the complexity of the conversion process.

Do we need to understand the internal circuitry of A/D and D/A converters?

• Over time, many methods for A/D conversion have been developed.

• Like D/A converters, the internal circuitry is rarely a concern for users.

• Converters are usually produced as complete units, ready to use.

Why do we need to consider circuits when studying A/D converters?

To understand the function of an A/D converter, it is necessary to consider the operation of the appropriate circuits.

This helps explain how the analog input is processed and converted into a digital output code.

What roles do the start command and clock play in A/D conversion?

Goes high to initiate the A/D conversion process.

Determines the rate at which data are sent by the control unit to the register.

What happens during the comparison stage of A/D conversion?

The register holds a binary number and passes it to the D/A converter.

The D/A converter outputs an analog signal to the comparator.

The input analog signal is also sent to the comparator.

The comparator compares the input signal with the D/A output to guide the conversion process.

How does a digital thermometer measure and display temperature?

Sensor: Produces an analog signal proportional to temperature (via e.m.f. or resistance change).

Amplifier: A linear amplifier boosts the small signal.

A/D Converter: Converts the analog signal into a digital (binary) signal.

Logic Controller: Samples the binary signal at regular intervals and formats it for the display.

Display: Shows the temperature in °C or °F depending on formatting.

How does a CD player produce analog sound from digital music?

• Music is stored as digital information on the disc.

• Laser Pick-up: Reads the digital data.

• Amplification: The signal is amplified (quality less critical for digital pulses).

• D/A Converter: Converts the digital signal into an analog signal.

• Final Amplification & Output: Analog signal is amplified and sent to loudspeakers to produce sound.