ICS874001AGI-05LF Datasheet, PDF (12/18 Pages) Integrated Device Technology – PCI Express™ Jitter Attenuator

ICS74001I-05 Data Sheet
PCI EXPRESS™ JITTER ATTENUATOR
PCI Express Application Note
PCI Express jitter analysis methodology models the system response
to reference clock jitter. The block diagram below shows the most
frequently used Common Clock Architecture in which a copy of the
reference clock is provided to both ends of the PCI Express Link.
In the jitter analysis, the transmit (Tx) and receive (Rx) serdes PLLs
are modeled as well as the phase interpolator in the receiver. These
transfer functions are called H1, H2, and H3 respectively. The overall
system transfer function at the receiver is:
Ht(s) = H3(s) × [H1(s) – H2(s)]
The jitter spectrum seen by the receiver is the result of applying this
system transfer function to the clock spectrum X(s) and is:
Y(s) = X(s) × H3(s) × [H1(s) – H2(s)]
In order to generate time domain jitter numbers, an inverse Fourier
Transform is performed on X(s)*H3(s) * [H1(s) - H2(s)].
For PCI Express Gen 2, two transfer functions are defined with 2
evaluation ranges and the final jitter number is reported in rms. The
two evaluation ranges for PCI Express Gen 2 are 10kHz – 1.5MHz
(Low Band) and 1.5MHz – Nyquist (High Band). The plots show the
individual transfer functions as well as the overall transfer function Ht.
PCIe Gen 2A Magnitude of Transfer Function
PCI Express Common Clock Architecture
For PCI Express Gen 1, one transfer function is defined and the
evaluation is performed over the entire spectrum: DC to Nyquist (e.g
for a 100MHz reference clock: 0Hz – 50MHz) and the jitter result is
reported in peak-peak.
PCIe Gen 2B Magnitude of Transfer Function
For a more thorough overview of PCI Express jitter analysis
methodology, please refer to IDT Application Note PCI Express
Reference Clock Requirements.
PCIe Gen 1 Magnitude of Transfer Function
ICS874001AGI-05 REVISION A JANUARY 14, 2011
12
©2011 Integrated Device Technology, Inc.