Glossary of EE Terms
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Quadature Modulation
Quadrature Modulation is a technique for encoding 2-dimensional signals as the sum of in-phase and quadrature (90 degrees out of phase) signals.
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Quadrature Amplitude (QAM)
This communication scheme involves the modulation of a carrier by two different signals. One signal modulates the carrier (I) and the other signal modulates the carrier shifted by 90° (Q). The two modulated carriers are then summed and transmitted as a single I&Q modulated carrier. The receiver decodes the I&Q channels and demodulates them 90° apart. QAM lends itself to the transmission of data in a digital format by assigning discrete levels to the two signal inputs which creates a "constellation" of possible digital word combinations on the I&Q graph. The following illustrates a 16-QAM constellation (4 levels of input on the I channel/4 levels of input on the Q channel).
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Quadrature Phase Error
Quadrature Phase Error represents the amount to which that ideal phase deviates from 90 degrees, and will degrade the ability of the channel to transmit information.
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Quantization
The mathematical operation of truncating a decimal value of arbitrary precision to a fixed binary resolution.
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Quantization Noise
Noise generated in a DAC output due to errors created by the quantization process.
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