XRT7295A/98ES-DS3 Exar, XRT7295A/98ES-DS3 Datasheet - Page 10

• Manufacturer Part Number: XRT7295A/98ES-DS3
• Description: Peripheral Drivers & Components - PCIs comeswith XRT7295A
• Manufacturer: Exar

Specifications of XRT7295A/98ES-DS3

• Product Category: Peripheral Drivers & Components - PCIs
• Rohs: yes

Digital Detection
In addition to the signal amplitude monitoring of the
analog LOS detector, the digital LOS detector monitors
the recovered data 1s density. The RLOS alarm goes
high if 160 +/-32 or more consecutive bits. The alarm
goes low when at least eight 1s occur in a a string of 32
consecutive bits. This hysteresis minimizes RLOS
chattering and guarantees a minimum RLOS pulse
width of 32 clock cycles.
NOTE:
RLOS chatter can still occur. When REQB=1, input signal
levels above the analog LOS threshold can still be low
enough to result in a high but error rate. The resultant data
stream (containing errors) can temporarily activate the
digital LOS detector, ad RLOS chatter can occur. There-
fore, RLOS should not be used as a bit error rate monitor.
RLOS chatter can also occur when RLOL is activated
(high).
Phase Hits
In response to a 180° phase hit in the input data, the
XRT7295AE returns to error-free operation in less than
2ms. During the reacquisition time, RLOS may be
temporarily indicated.
Recovered Clock and Data Timing
Table 6 and Figure 9 summarize the timing relation-
ships between the high-speed logic signals RCLK,
RPDATA, and RNDATA. All duty cycle and timing
relationships are referenced to V
RPDATA and RNDATA change on the rising edge of
RCLK and are valid during the falling edge of RCLK. A
positive pulse at RIN creates a high level on RPDATA
and a low level on RNDATA. A negative pulse creates
a high level on RNDATA and a low level on RPDATA,
and a received zero produces low levels on both
RPDATA and RNDATA.
XRT7295AE
Rev. 2.0.0
Figure 7. Test Set-up for Interference Immunity Requirements
DD
/2 threshold level.
10
Interference Immunity
The XRT7295AE complies with the interference test
detailed in Figure 7 and Table 5. The two data genera-
tors are non-synchronous.
In-Circuit Test Capability
When pulled low, the ICT pin forces all digital output
buffers (RCLK, RPDATA, RNDATA, RLOS, RLOL
pins) to be placed in a high output impedance state,
This feature allows in-circuit testing to be done on
neighboring devices without concern for XRT7295AE
buffer damage. When forced high, the ICT pin does not
affect device operation. An internal pull-up device
(nominally 50 k ) is provided on this pin; therefore,
users can leave this pin open for normal operation. This
is the only pin for which the internal pull-up/pull-down
is provided.
BOARD LAYOUT CONSIDERATIONS
Power Supply Bypassing
Figure 8 illustrates the recommended power supply
bypassing network. A 0.1 F capacitor bypasses the
digital supplies. The analog supply V
by using a 0.1 F capacitor and a shield bead that
removes significant amounts of high-frequency noise
generated by the system and by the device logic. Good
quality, high-frequency (low lead inductance) capaci-
tors should be used. Finally, it is most important that
all ground connections be made to a low-impedance
ground plane.
Parameter
Attenuator
Table 5. Interference Requirement
Min.
-20
Typ.
-16
Max.
DD
A is bypassed
Unit
dB