Understanding Signal Types: Analog, Digital, Periodic, and Aperiodic

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Understanding Signal Types

Continuous signals vary smoothly over time without discontinuities, like voice. Discrete signals maintain a constant value for a period, then change abruptly, such as binary signals (0 and 1).

Analog vs. Digital Signals

Analog signals have a continuous waveform, smoothly changing over time, passing through an infinite number of values. Digital signals are discrete, with a defined number of values, often zeros and ones. Transitions are instantaneous, like a light switch.

Signal Representation

Signals are illustrated on perpendicular axes: the vertical axis represents signal strength, and the horizontal axis represents time.

Periodic and Aperiodic Signals

Periodic signals complete a pattern within a measurable time frame (the period) and repeat it. A full pattern is a cycle. The period (T) is constant for a given periodic signal. Aperiodic signals change without a repeating pattern. However, Fourier transform can decompose any aperiodic signal into infinite periodic signals.

Analog Signal Classification

Analog signals can be simple (sine waves, not decomposable) or composite (multiple sine waves).

Signal Characteristics

Amplitude

The amplitude is the signal's value at any point, equal to the vertical distance from the wave to the horizontal axis. Maximum amplitude is the highest value on the vertical axis. It's measured in volts, amps, or watts.

Period and Frequency

The period is the time for a signal to complete a cycle. Frequency is the number of cycles per second.

Phase

Phase describes the wave's position at time 0, indicating its displacement along the time axis. It's measured in degrees or radians. A 360-degree phase shift is a full period, 180 degrees is half, and 90 degrees is a quarter.

Composite Signals

These periodic signals are not sine waves. They have irregularities, but if consistent, the signal remains periodic. Fourier analysis decomposes composite signals into components.

Digital Signal Representation

Digital signals can represent data. For example, 1 can be positive voltage, and 0 can be zero voltage.

Bit Interval and Bit Rate

Most digital signals are aperiodic. Bit interval is the time to send a single bit. Bit rate is the number of bits sent per second, usually in bits per second (bps).

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