Phase noise isRF synthesizerswithRF oscillatorkey technical indicators. Phase noise is often referred to as phase jitter or frequency domain jitter. Jitter is phase noise simulated from the time domain to the frequency domain. The root cause of phase noise is frequency instability or phase instability in the frequency source. In most RF oscillators, there are design techniques and circuitry in place to minimize phase noise. However, phase noise cannot be completely eliminated and has a significant impact on the performance of RF communication and sensing applications that rely on frequency and phase fidelity.
SPI Phase-Locked Loop Frequency Synthesizer, 1 GHz - 64 GHz, 25 Hz steps, +15 dBm output power, 100 MHz reference frequency, +475 VDC and SMA output interfaces
An example of the effect of phase noise on wireless communications is the high-order quadrature amplitude modulation (QAM) scheme used in WiFi or 4G 5G cellular telecommunications. Phase noise is the limiting factor for the bit rate (BER) or symbol error rate (SER) of these communications. The higher-order modulation scheme has a low error vector magnitude (EVM) requirement, where the EVM is directly affected by excessive phase noise. In cases where the amplitude error will add a vertical error to the symbol, the phase error will cause the symbol to permeate in a circular pattern around the origin. This same phenomenon affects RF sensing applications, such as radar, where phase errors can lead to position or velocity sensing errors in the target. Another possibility is that due to the "blurring" of the characteristics of two nearby targets, the phase error may lead to the appearance of two targets as a single target.
In non-ideal oscillators or other frequency-generating components, phase noise is the tail of the frequency content of a given frequency around the center frequency of the signal. In the case of an oscillator, a single tone should be generated, but in reality, the result is a tone with an attenuated sideband that extends from the carrier frequency. In the time domain, this looks like several sine waves, almost overlapping the carrier frequency (tone) but slightly offset in time. The greater the severity of the phase noise, the higher the sideband energy compared to the center frequency, and the greater the temporal variation of the additional sine wave compared to the center frequency in the frequency and time domains.
During the mixing process, too much phase noise can cause the mixing products with phase noise to be distorted and diffuse, and may even overlap or spread to the desired frequency. In wideband signals, too much phase noise can cause spectral regeneration to be severe enough to result in an unacceptable level of adjacent channel power leak ratio (ACLR). ACLR refers to the leakage of energy from a signal in one band to another in a wireless communication band plan.
50 MHz Surface Mount (SMT) Reference Oscillator, Internal Reference, Phase Noise -150 dBc Hz, 09-inch package
Phase noise is typically measured as a small bandwidth difference on either side of the carrier frequency. For example, the phase noise of an oscillator can be measured from the carrier frequency of the tone or the center frequency at 1kHz bandwidth of 10kHz. Usually only the positive or upper sideband of the phase noise result is given, which is known as positive unilateral sideband phase noise. There are different contributing factors to phase noise and ways to describe them. One of the main considerations for phase noise is the phase noise added by other components in the signal path. One way to solve this problem is to use components specified for low-phase noise devices, such as low-phase noise amplifiers (LPNAs).