What is jitter in PCIe?
Jitter of the reference clock has a direct impact on the efficiency of the data transfer between two PCIe devices. The data recovery process is able to track a portion of the jitter frequencies that are within its bandwidth, but it is the jitter frequencies that it cannot track that must be limited.
What is PCIe reference clock?
PCIe Clocking Architectures The PCIe standard specifies a 100 MHz clock (Refclk) with at least ±300 ppm frequency stability for Gen 1, 2, 3 and 4, and at least ±100 ppm frequency stability for Gen 5, at both the transmitting and receiving devices.
What is a reference clock?
A master clock used as a timekeeping standard to regulate or compare the accuracy of other clocks. In electronics and computing, the clock signal used to synchronise and schedule operations.
What is reference clock frequency?
The most common frequency for a reference clock is 10 MHz because a clock of that frequency can generally be shared over a cable without much attenuation or loss. However, the frequency range of reference clocks can vary anywhere from 1 MHz to 20 MHz.
What is jitter transfer function?
The jitter transfer function gives the amount of jitter attenuation that will occur at a particular offset frequency. It is strongly affected by the loop bandwidth of the PLL, which is strongly affected by the PLL’s low-pass loop filter. Accordingly, a PLL’s response to jitter can be characterized as low-pass.
What is PCIe latency timer?
“PCI Latency Timer. Controls how long each PCI device can hold the bus before another takes over. When set to higher values, every PCI device can conduct transactions for a longer time and thus improve the effective PCI bandwidth.”
What is jitter clock signal?
1 Introduction. Jitter is the timing variations of a set of signal edges from their ideal values. Jitters in clock signals are typically caused by noise or other disturbances in the system.
What is NTP jitter?
Jitter: The jitter associated with a timing reference indicates the magnitude of variance, or dispersion, of the signal. Different timing references have different amounts of jitter. The more accurate a timing reference, the lower the jitter value. Jitter is usually measure in milliseconds.
Is PCIe source synchronous?
PCIe, fundamentally, is a short-reach, point-to-point-protocol that is typically synchronous.
What is spread spectrum PLL?
Spread spectrum clocking is a technique used in electronics design to intentionally modulate the ideal position of the clock edge such that the resulting signal’s spectrum is “spread”, around the ideal frequency of the clock.
What is an acceptable amount of jitter?
30ms
Ideally, jitter should be below 30ms. Packet loss should be no more than 1%, and network latency shouldn’t exceed 150 ms one-way (300 ms return).
How much jitter is too much?
Jitter is measured in milliseconds (ms). A delay of around 30 ms or more can result in distortion and disruption to a call. For video streaming to work efficiently, jitter should be below 30 ms. If the receiving jitter is higher than this, it can start to slack, resulting in packet loss and problems with audio quality.