Jitter in Oscillators

Jitter in oscillators should arise only from random sources if they are correctly designed and the output frequency matches the natural resonant frequency of the crystal. The random jitter in the oscillators should be sufficiently small as to be measured in picoseconds. This should be the case for all oscillators even for those whose output is a squarewave signal derived from the sine-wave output of the crystal oscillator.

The jitter in programmable crystal oscillators is generally larger due to the way in which their output frequency is generated. They usually use a phase locked loop (PLL) method of frequency generation and this can increase their susceptibility to jitter, usually in the order of 100ps rms. It is useful to consider the jitter that may be induced into the system from external systems. If a low jitter signal is essential to the workings of the system then choosing a component with low jitter values isn’t enough and a decision should be made to design a circuit that minimises jitter. For example shielding the component and circuitry from interference may be sufficient or placing a simple RC-filter in the supply line may help attenuate all high voltage ripples from the power supply. The output signal from the oscillator may be pure and clean however the circuit in which it lies may be easily susceptible to noise and jitter.

由于大多數(shù)數(shù)字系統(tǒng)都依賴于通用時(shí)鐘總線關(guān)心電路是否能承受任何輕微的時(shí)鐘脈沖定時(shí)的變化。

Jitter Effects

As most digital systems rely on a universal clock bus, we are concerned in whether a circuit can tolerate any slight changes in clock pulse timing.

在數(shù)字通信系統(tǒng)中，編碼數(shù)據(jù)是通常通過(guò)長(zhǎng)距離發(fā)送，然后進(jìn)行解碼一旦收到。然而，需要有一個(gè)共同的時(shí)鐘，以允許對(duì)脈沖進(jìn)行解碼，并且如果時(shí)鐘中的任何一個(gè)受到抖動(dòng)的影響，數(shù)據(jù)可能會(huì)丟失從源頭上講誠(chéng)信。同樣值得考慮的是應(yīng)用程序，然后選擇合適的晶體振蕩器。

In digital communication systems, the encoded data is usually sent over long distances and it is then decoded once received. However there needs to be a common clock to allow for the pulse to be decoded and if the clock of either is affected by jitter there may be some loss in data integrity from the source. Again it is worth considering your application before choosing an appropriate crystal oscillator.