What Is Tremulousness?

Jitter is one of the core contents of the signal integrity test of digital systems. It is the most important measurement parameter of clock and serial signals (Note: the most important measurement parameters of parallel buses are setup time and hold time). Jitter is generally defined as follows: "A short-term deviation of a particular moment in a signal from its ideal time position is jitter." ^[1]

The definition of jitter is "the short-term deviation of each valid instant of a digital signal from its ideal position at that time", which means that jitter is an unwanted phase modulation of a digital signal.

The frequency of phase deviation is called jitter frequency, and the second parameter closely related to jitter is called drift, which is defined as "the long-term deviation of each valid instant of a digital signal from its ideal position at that time". So far, the boundary between jitter and drift has not been clearly defined, and usually the part with a phase change at frequencies below 1 Hz to 10 Hz is called drift.

Because the signal regeneration point introduces errors into the digital bit stream and digital overflow or emptying in digital devices containing buffer memories, sliding can be introduced into digital signals, so jitter can reduce the transmission performance of digital circuits. Systematic jitter and jitter

There are two main types of jitter: deterministic jitter and

The characteristics of jitter can be determined through many basic measurement indicators. Basic jitter parameters include:

1. Period jitter

Measure the width of each clock and data cycle in a real-time waveform. This is the earliest and most direct way to measure jitter. This indicator illustrates

With the continuous improvement of signal rate and higher and higher requirements for accuracy, the separation of jitter components needs to be performed in order to characterize and find jitter characteristics in more depth.

Jitter communication field

In the past communication field, there is no clear definition of jitter, because in the previous communication network, only pure data services would be transmitted, and the impact of jitter is not very obvious. However, IP-based video and audio services are becoming mainstream in today's communication networks, so jitter has a clear definition:

Jitter: The absolute value of the difference between the forwarding delays of two adjacent frames transmitted in sequence, which is always a positive value.

Dithering computer operating system

The jitter in computer operating systems is also called bumps. If the number of memory blocks allocated to a process is less than the minimum required by the process, the running of the process will frequently generate page fault interrupts. This very frequent page replacement phenomenon is called jitter. In request paging storage management, this situation may occur, that is, the page that has just been replaced is immediately accessed again. It needs to be transferred in, because there is no free memory and another page needs to be replaced, and the latter is a page that is about to be accessed, which causes the system to spend a lot of time busy with this frequent page exchange, resulting in the actual efficiency of the system Very low, causing severe system paralysis. This phenomenon is called jitter.

Jitter frequency domain representation

Phase noise

Phase noise is another measure of the timing of a signal, and its time jitter is displayed in the frequency domain. Figure 2 uses an oscillator signal to explain phase noise.

Function: If there is no phase noise, the entire power of the oscillator should be concentrated at the frequency f = fo. However, the appearance of phase noise spreads a part of the power of the oscillator to adjacent frequencies, resulting in sidebands. It can be seen from Figure 2 that at an offset frequency with a reasonable distance from the center frequency, the sideband power rolls off to 1 / fm, where fm is the difference between the frequency and the center frequency.

Phase noise is usually defined as the dBc / Hz value at a given offset frequency, where dBc is the ratio of the power to the total power at that frequency in dB. The phase noise of an oscillator at a certain offset frequency is defined as the ratio of the signal power to the total power of the signal in a 1 Hz bandwidth at that frequency.