XIO2000AI datasheet(147/165 Pages) TI

147 / 165 page

Electrical Characteristics

138

April 2007 Revised October 2008

SCPS155C

13. A TRX-EYE = 0.40 UI provides for a total sum of 0.60 UI deterministic and random jitter budget for the transmitter and interconnect

collected any 250 consecutive UIs. The TRX-EYE-MEDIAN-to-MAX-JITTER specification ensures a jitter distribution in which the median

and the maximum deviation from the median is less than half of the total UI jitter budget collected over any 250 consecutive TX UIs.

It must be noted that the median is not the same as the mean. The jitter median describes the point in time where the number of

jitter points on either side is approximately equal as opposed to the averaged time value. If the clocks to the RX and TX are not derived

from the same reference clock, then the TX UI recovered from 3500 consecutive UIs must be used as the reference for the eye

diagram.

14. The receiver input impedance results in a differential return loss greater than or equal to 15 dB with the P line biased to 300 mV and

the N line biased to −300 mV and a common mode return loss greater than or equal to 6 dB (no bias required) over a frequency range

of 50 MHz to 1.25 GHz. This input impedance requirement applies to all valid input levels. The reference impedance for return loss

measurements for is 50

Ω to ground for both the P and N line (i.e., as measured by a Vector Network Analyzer with 50-Ω probes).

The series capacitors CTX is optional for the return loss measurement.

15. Impedance during all link training status state machine (LTSSM) states. When transitioning from a PCI Express reset to the detect

state (the initial state of the LTSSM) there is a 5-ms transition time before receiver termination values must be met on the

unconfigured lane of a port.

16. The RX dc common mode impedance that exists when no power is present or PCI Express reset is asserted. This helps ensure that

the receiver detect circuit does not falsely assume a receiver is powered on when it is not. This term must be measured at 300 mV

above the RX ground.

XIO2000AI 数据表(PDF) 147 Page - Texas Instruments