Datasheet

Electrical Characteristics
178
March 5 2007 − June 2011SCPS154C
PCI Express Differential Transmitter Output Ranges (continued)
PARAMETER TERMINALS MIN NOM MAX UNITS COMMENTS
I
TX-SHORT
TX short circuit current
limit
TXP, TXN 90 mA
The total current the transmitter can provide when
shorted to its ground.
T
TX-IDLE-MIN
Minimum time spent in
electrical idle
TXP, TXN 50 UI
Minimum time a transmitter must be in electrical Idle.
Utilized by the receiver to start looking for an electrical
idle exit after successfully receiving an electrical idle
ordered set.
T
TX-IDLE-SET-to-IDLE
Maximum time to
transition to a valid
electrical idle after
sending an electrical
idle ordered set
TXP, TXN 20 UI
After sending an electrical idle ordered set, the
transmitter must meet all electrical idle specifications
within this time. This is considered a debounce time for
the transmitter to meet electrical idle after transitioning
from L0.
T
TX-IDLE-to-DIFF-DATA
Maximum time to
transition to valid TX
specifications after
leaving an electrical idle
condition
TXP, TXN 20 UI
Maximum time to meet all TX specifications when
transitioning from electrical idle to sending differential
data. This is considered a debounce time for the TX to
meet all TX specifications after leaving electrical idle.
RL
TX-DIFF
Differential return loss
TXP, TXN 10 dB Measured over 50 MHz to 1.25 GHz. See Note 7.
RL
TX-CM
Common mode return
loss
TXP, TXN 6 dB Measured over 50 MHz to 1.25 GHz. See Note 7.
Z
TX-DIFF-DC
DC differential TX
impedance
TXP, TXN 80 100 120 Ω TX dc differential mode low impedance
Z
TX-DC
Transmitter dc
impedance
TXP, TXN 40 Ω
Required TXP as well as TXN dc impedance during all
states
C
TX
AC coupling capacitor
TXP, TXN 75 200 nF
All transmitters are ac-coupled and are required on the
PWB.
NOTES: 4. No test load is necessarily associated with this value.
5. Specified at the measurement point into a timing and voltage compliance test load and measured over any 250 consecutive TX UIs.
6. A T
TX-EYE
= 0.75 UI provides for a total sum of deterministic and random jitter budget of T
TX-JITTER-MAX
= 0.25 UI for the transmitter
collected over any 250 consecutive TX UIs. The T
TX-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.
7. The transmitter input impedance results in a differential return loss greater than or equal to 12 dB and a common mode return loss
greater than or equal to 6 dB 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 is 50 Ω to ground for both the P and N lines. Note that the series
capacitors C
TX
is optional for the return loss measurement.
8. Measured between 20% and 80% at transmitter package terminals into a test load for both V
TXP
and V
TXN
.
Not Recommended for New Designs