Signal Modulation

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This material was developed with funding from the National Science Foundation under Grant # DUE 1601612

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Modulation is a process of mixing a signal with a sinusoid to produce a new signal. This new signal, conceivably, will have certain benefits over an un-modulated signal. Mixing of low frequency signal with high frequency carrier signal is called modulation.

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Frequency Modulation (FM)

Digital Modulation

Amplitude Modulation (AM)

Amplitude 

Frequency 

Digital signal modulation is the process of mixing a digital (discrete) signal with an analog carrier signal. The analog signal can then carry the digital information to analog receivers. Digital signal modulation is produced by a discrete signal being used to modify the amplitude, frequesncy or phase of the original analog signal.

Phase

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The amplitude of a signal is the strength of the signal. There are various definitions of amplitude.

Root Mean Square Amplitude (RMS) The RMS amplitude is used especially in electrical engineering: the RMS is defined as the square root of the mean over time of the square of the vertical distance of the graph from the rest state.

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Peak-to-peak amplitude    Peak-to-Peak Amplitude is the change between peaks (highest amplitude value) and trough (lowest amplitude value, which can be negative).

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Peak Amplitude Peak amplitude is used to measure the signal rise above and below a reference value.

Amplitude

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Frequency is the number of occurrences of a repeating signal pattern per unit of time. The period is the duration of time of one cycle in a repeating event, so the period is the reciprocal of the frequency. For example: if a persons heart beats at a frequency of 120 times a minute, its period—the time interval between beats—is half a second (60 seconds divided by 120 beats).

Frequency

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360°

Signal Phase

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180°

90°

In electronic signaling, phase is a definition of the position of a point in time (instant) on a waveform cycle. A complete cycle is defined as 360 degrees of phase as shown in Illustration A below. Phase can also be an expression of relative displacement between or among waves having the same frequency . Phase difference, also called phase angle , in degrees is conventionally defined as a number greater than -180, and less than or equal to +180. Leading phase refers to a wave that occurs "ahead" of another wave of the same frequency. Lagging phase refers to a wave that occurs "behind" another wave of the same frequency. When two signals differ in phase by -90 or +90 degrees, they are said to be in phase quadrature . When two waves differ in phase by 180 degrees (-180 is technically the same as +180), the waves are said to be in phase opposition . Illustration B shows two waves that are in phase quadrature. The wave depicted by the dashed line leads the wave represented by the solid line by 90 degrees.