XIO3130
www.ti.com
SLLS693F–MAY 2007–REVISED JANUARY 2010
6.3 PCI Express Differential Transmitter Output Ranges
PARAMETER
TERMINALS
MIN NOM
MAX UNIT
COMMENTS
UI
PETP,
PETN
Each UI is 400 ps ±300 ppm. UI does not account
for SSC dictated variations.See
399.88 400 400.12
ps
V
(1)
Unit interval
VTX-DIFFp-p
Differential peak-to-peak output
voltage
PETP,
PETN
VTX-DIFFp-p = 2*|VTXP – VTXN|.
0.8
–3
1.2
(2)
See
This value is the ratio of the VTX-DIFFp-p of the
second and following bits after a transition divided
by the VTX-DIFFp-p of the first bit after a transition.
VTX-DE-RATIO
De-emphasized differential output
voltage (ratio)
PETP,
PETN
–3.5
–4.0
dB
UI
(2)
See
The maximum transmitter jitter can be derived as
TTXMAX- JITTER = 1 – TTX-EYE = 0.25 UI.
TTX-EYE
Minimum TX eye width
PETP,
PETN
0.75
(2) (3)
See
Jitter is defined as the measurement variation of
the crossing points (VTX-DIFFp-p = 0 V) in relation to
recovered TX UI. A recovered TX UI is calculated
over 3500 consecutive UIs of sample data. Jitter is
measured using all edges of the 250 consecutive
UIs in the center of the 3500 UIs that are used for
TTX-EYE-MEDIAN-to-MAX-JITTER
Maximum time between the jitter
median and maximum deviation
from the median
PETP,
PETN
0.125
UI
(2) (3)
calculating the TX UI. See
TTX-RISE,
TTX-FALL
PETP,
PETN
(2) (4)
0.125
UI
See
Differential TX output rise/fall time
VTX-CM-ACp
RMS ac peak common mode output
voltage
VTX-CM-ACp = RMS(|VTXP + VTXN|/2 – VTX-CM-DC
VTX-CM-DC = DC(avg) of |VTXP + VTXN|/2
See
)
PETP,
PETN
20
mV
(2)
|VTX-CM-DC – VTX-CM-IDLE-DC| ≤ 100 mV
VTX-CM-DC-ACTIVE-IDLE-DELTA
Absolute delta of DC common mode
voltage during L0 and electrical idle.
VTX-CM-DC = DC(avg) of |VTXP + VTXN|/2 [during L0]
VTX-CM-IDLE-DC = DC(avg) of |VTXP + VTXN|/2 [during
electrical idle]
PETP,
PETN
0
100
mV
mV
(2)
See
|VTXP-CM-DC – VTXN-CM-DC| ≤ 25 mV when
VTXP-CM-DC = DC(avg) of |VTXP|
VTX-CM-DC-LINE-DELTA
Absolute delta of DC common mode
voltage between P and N
PETP,
PETN
0
0
25
VTXN-CM-DC = DC(avg) of |VTXN
See
|
(2)
VTX-IDLE-DIFFp
Electrical idle differential peak output
voltage
PETP,
PETN
VTX-IDLE-DIFFp = |VTXP-IDLE – VTXN-IDLE| ≤ 20 mV
20
mV
mV
(2)
See
VTX-RCV-DETECT
The amount of voltage change
allowed during receiver detection
The total amount of voltage change that a
transmitter can apply to sense whether a low
impedance receiver is present.
PETP,
PETN
600
VTX-DC-CM
The TX DC common mode voltage
PETP,
PETN
The allowed DC common mode voltage under any
condition
0
3.6
90
V
ITX-SHORT
TX short circuit current limit
PETP,
PETN
The total current that the transmitter can provide
when shorted to its ground.
mA
Minimum time that a transmitter must be in
electrical Idle. The receiver uses this value to start
looking for an electrical idle exit after successfully
receiving an electrical idle ordered set.
TTX-IDLE-MIN
Minimum time spent in electrical idle
PETP,
PETN
50
UI
UI
After sending an electrical idle ordered set, the
transmitter must meet all electrical idle
specifications within this time. This is considered a
de-bounce time for the transmitter to meet
electrical idle after transitioning from L0.
TTX-IDLE-SET-to-IDLE
Maximum time to transition to a valid
electrical idle after sending an
electrical idle ordered set
PETP,
PETN
20
(1) No test load is necessarily associated with this value.
(2) Specified at the measurement point into a timing and voltage compliance test load and measured over any 250 consecutive TX UIs.
(3) A TTX-EYE = 0.75 UI provides for a total sum of deterministic and random jitter budget of TTX-JITTER-MAX = 0.25 UI for the transmitter
collected over any 250 consecutive TX UIs. The TTX-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 TX 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.
(4) Measured between 20% and 80% at transmitter package terminals into a test load for both VTX-D+ and VTX-D–.
Copyright © 2007–2010, Texas Instruments Incorporated
Electrical Characteristics
135
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