Phase noise and Jitter

      Phase noise refers to the random fluctuation of the phase of a system's output signal (such as various RF devices) under the influence of various types of noise. The three elements that describe radio waves are amplitude, frequency, and phase, and frequency and phase are interrelated. In an ideal situation, the period of a fixed-frequency wireless signal's waveform is fixed, just like the scheduled takeoff time of an airplane. A pulse signal in the frequency domain (with a spectrum width close to zero) is a sine wave of a certain frequency in the time domain. However, in reality, a signal always has a certain spectral width, and due to noise, the power of the signal is also present far away from the center frequency, just like a flight delayed for more than an hour. The signal that is far away from the center frequency is called a sideband signal, and the sideband signal may be squeezed into adjacent frequencies, just like a delayed flight may disrupt the scheduling of other flights. This sideband signal is called phase noise. How to describe the magnitude of phase noise? It is the ratio of the power within a certain offset from the center frequency to the total signal power in a unit bandwidth, expressed in dBc/Hz. If you want to evaluate the impact of weather on flights on a certain day, you can also use a similar approach, defining the ratio of flights delayed for more than an hour to the total number of flights. Of course, the smaller this ratio, the better.
      Thermal noise within RF devices may lead to the generation of phase noise. The magnitude of phase noise can reflect the quality of RF devices. When designing and using RF devices, attention should be paid to the device's ability to suppress phase noise.The smaller the phase noise, the better the RF device. Phase noise and jitter are two different quantitative ways to describe the same phenomenon. In an ideal situation, the duration of a fixed-frequency pulse signal (e.g., 1 MHz) should be exactly 1 microsecond, with a transition edge every 500 ns. Unfortunately, such a signal does not exist. The length of the signal period of an actual signal always varies to some extent, causing the arrival time of the next edge to be uncertain. This uncertainty is called phase noise or jitter.