Digital signals and information

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Lesson notes

Signals and Codes

Signals are used to transmit information, and codes have been used throughout history to keep messages secret.
Example: George Washington used codes to send secret messages during the American Revolutionary War.
Fireflies communicate using patterns of light signals—each blinking pattern is a unique signal.

A coded alphabet where each letter is represented by a unique symbol.

Analog Signals

Analog signals are representations of actual images, sounds, or words, often using waves to transfer information.
Analog signals do not use mathematical codes.
Examples: conversations (sound waves), film cameras (light waves), vinyl records (grooves in plastic).
Analog instruments like alcohol thermometers and grandfather clocks measure continuously.

A clock tower (Big Ben), an example of an analog instrument.

Digital Signals

Digital signals are sent as mathematically coded waves and can travel long distances.
They are decoded back into understandable information at the receiving end.
Examples: computers, smartphones, digital cameras, digital thermometers, video game systems.

Analog vs. Digital Recording

Analog recording captures every part of the sound wave, including background noise, making it complex and prone to errors.
Digital recording takes samples of the wave at set intervals, not the whole wave.
The diagram below shows the difference: the analog wave is smooth and continuous, while the digital wave is stepped because it only records samples.
Digital waves are simpler and easier to copy or transmit without mistakes because they are not affected by outside sources.

A diagram comparing an analog wave to digital waves sampled at low and high rates.

Sampling and Storage

Low sampling records less often; high sampling records more often; analog records constantly.
Digital stores only a smaller number of values compared to analog's infinite values, making it easier to remember/copy accurately.
Example: Digital thermometers show set values (98.6 to 98.7) while alcohol thermometers show every tiny change.
Analog requires more storage space and is more likely to store flaws; digital takes less space and filters out interference.

A digital thermometer and an analog thermometer

Reliability and Examples

Vinyl records (analog) hold about 44 minutes of music; CDs (digital) hold 75-80 minutes.
Digital files on devices can hold 100-150 songs on a CD, or about 14,000 songs on 64 GB storage.
Digital signals are more reliable for storing and transmitting information because they are less affected by damage or interference.
However, digital signals must be converted back to analog for humans to hear or see.

A vinyl record, CDs, and a smartphone with earbuds.

Conclusion

The structure of digital signals (sampled, coded) makes them more reliable than analog signals for storage and transmission.
Digital technology reduces issues like static and physical damage, as seen in electronic music devices vs. vinyl records.

Slides

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Practice questions

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1.Analog signals use mathematical codes to transfer information.
Easy
True or false?
2.Which of the following is an example of an analog signal?
Easy
- AVinyl record
- BDigital song file
- CSmartphone text message
- DMP3 player
3.Which of the following are advantages of digital signals compared to analog signals? (Select all that apply)
Medium
- AThey are easier to copy without mistakes.
- BThey are unaffected by outside sources.
- CThey store every tiny piece of information.
- DThey take up less storage space.
- EThey are more reliable for storing information.
4.Digital signals record every part of the sound wave.
Easy
True or false?
5.Why is a digital signal more reliable for storing information than an analog signal?
Medium
- AIt records every part of the wave.
- BIt is simpler, so it is easier to copy without mistakes.
- CIt uses more storage space.
- DIt is affected by background noise.
6.Which of the following are examples of digital signals? (Select all that apply)
Medium
- AA digital camera storing a photo
- BA vinyl record playing music
- CA smartphone receiving a text
- DA film camera imprinting an image on film
- EA video game system sending data to a controller
7.An alcohol thermometer is an example of a digital signal.
Easy
True or false?
8.A digital thermometer shows temperatures in whole degrees. Which of the following readings would NOT be possible on this thermometer?
Medium
- A24 °C
- B24.5 °C
- C25 °C
- D26 °C

Revision notes

## Digital Signals and Information ### Analog vs. Digital Signals - **Analog signal**: continuous values; can be any real number within a range. Noise always degrades it. - **Digital signal**: discrete values; at any time it takes one of a finite number of values. Noise immunity: small changes do not affect the signal state. ### Binary Signals - Most common digital signal: **binary** (two states: 0 and 1, or low and high). - Represented by two voltage bands: near ground (0) and near supply voltage (1). - Each binary digit is a **bit**. ### Advantages of Digital Signals - **Noise immunity**: electronic noise, if not too great, is ignored by circuitry. - **Data compression**: reduces bandwidth needed for audio/video. - **Reliability**: more reliable than analog for encoding and transmitting information. ### Key Concepts - **Discrete values**: only specific levels are valid; levels within a band represent the same state. - **Logic signal**: another name for binary signal. - **Clock signal**: a special digital signal that synchronizes circuits; triggers on rising or falling edge. ### Applications - Used in all digital electronics: computers, data transmission, audio/video. - Physical quantity can be voltage, current, light pulses, magnetization, etc. ### Summary Digital signals use discrete values (often two) to represent information, providing noise immunity and reliability over analog signals.

Digital signal: A signal that represents data as a sequence of discrete values; at any given time it can only take on one of a finite number of values.
Analog signal: A signal that represents continuous values; at any given time it represents a real number within an infinite set of values.
Binary signal: A digital signal with two possible valid values (0 and 1, or low and high), representing one binary digit (bit).
Noise immunity: The property of digital signals that allows them to ignore small changes in signal level due to electronic noise, unlike analog signals.
Bit: A binary digit; the basic unit of information in digital systems, representing either 0 or 1.
Clock signal: A special digital signal used to synchronize digital circuits; logic changes are triggered by its rising or falling edge.

Flashcards

What is a digital signal?

A digital signal represents data as a sequence of discrete values, taking on only a finite number of values at any given time.

What is an analog signal?

An analog signal represents continuous values, taking on an infinite number of values within a range.

What is a binary signal?

A binary signal is a digital signal with only two possible valid values, typically 0 and 1 (or low and high).

What does 'bit' stand for?

Bit stands for binary digit, the basic unit of information in digital systems, representing a 0 or 1.

How are binary signals represented in electronics?

They are represented by two voltage bands: one near ground (0 volts) for 0, and one near the supply voltage for 1.

What is noise immunity?

Noise immunity is the ability of digital signals to ignore small changes in signal level, making them resistant to electronic noise.

Why are digital signals more reliable than analog signals?

Digital signals have noise immunity; small noise does not change the discrete value, whereas noise always degrades analog signals.

What is a logic signal?

A logic signal is another name for a binary signal, representing Boolean values (true/false or 0/1).

What is a clock signal?

A clock signal is a special digital signal that synchronizes digital circuits, with logic changes triggered by rising or falling edges.

What is the rising edge of a clock signal?

The rising edge is the transition from a low voltage to a high voltage.

What is the falling edge of a clock signal?

The falling edge is the transition from a high voltage to a low voltage.

What is a multivalued logic signal?

A multivalued logic signal has more than two discrete states, such as three-valued logic with three possible values.

What is pulse-code modulation (PCM)?

PCM is a method to digitally represent sampled analog signals by quantizing the amplitude into discrete levels.

What is data compression?

Data compression reduces the amount of data needed to represent information, often used in digital audio and video to decrease bandwidth.

How does a digital signal in communications handle noise?

Interference is minimized by filtering and using data redundancy, and digital signals have inherent noise immunity.

What is a bitstream?

A bitstream is a sequence of bits (0s and 1s) representing digital data, often transmitted as a digital signal.

What is the difference between baseband and passband transmission?

Baseband transmits digital signals directly as voltage pulses; passband modulates a carrier wave for long-distance or radio transmission.

What is a digital modulation scheme?

A digital modulation scheme encodes bits by varying a carrier wave's amplitude, frequency, or phase for passband transmission.

What is a line coding scheme?

A line coding scheme encodes bits into voltage levels for baseband transmission over wires.

Can a digital signal have more than two states?

Yes, multivalued logic signals have more than two states, but binary (two-state) signals are most common.

What physical quantities can represent a digital signal?

Digital signals can be represented by voltage, current, light intensity, phase, polarization, acoustic pressure, or magnetization.

What is the Boolean domain?

The Boolean domain consists of two values: false and true, often represented as 0 and 1 in digital circuits.

Why are digital signals used in computing?

Digital signals are reliable, noise-immune, and easy to process, making them ideal for computing and data transmission.

What does 'discrete' mean in the context of digital signals?

Discrete means the signal takes on only specific, separate values (e.g., 0 or 1) rather than a continuous range.

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