What is Phase Noise?

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Editorial Team - everything RF

Aug 13, 2019

Phase noise is defined as the noise arising from the rapid, short term, random phase fluctuations that occur in a signal. These random fluctuations are caused by time domain instabilities called as phase jitter.

Phase noise is the noise spectrum that is seen spreading out on either side of a signal as a result of the phase jitter. In most radio receiver applications the phase noise is quoted in terms of single sideband phase noise. The phase noise spreads out equally either side of the carrier but only one side is measured - hence the name single sideband phase noise.

While specifying phase noise, three elements need to be specified:

1. Phase Noise Amplitude: It is expressed in dB relative to the carrier. This is normally denoted in dBc, e.g. -70 dBc - 70 decibels down in level from the carrier.

2. The offset from the carrier: Ex. 1 kHz, 10 kHz, 100 kHz.

3. Measurement bandwidth: Noise power is proportional to the bandwidth so it should be always mentioned. Typically 1 Hz is taken as the bandwidth.

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