MAX4950
Quad PCI Express Equalizer/Redriver
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Detailed Description
The MAX4950 quad equalizer/redriver is designed to
support both Gen I (2.5GT/s) and Gen II (5.0GT/s) PCIe
data rates. The device contains four identical drivers
with idle/receive detect on each lane and equalization to
compensate for circuit-board loss. Signal integrity at the
receiver is improved by the use of programmable input
equalization circuitry. The MAX4950 output features a
redrive output swing selection input, O_AMP (Table 1),
and programmable output deemphasis, permitting opti-
mal placement of key PCIe components and longer runs
of stripline, microstrip, or cable.
Programmable Input Equalization
The MAX4950 features a programmable input equalizer
capable of providing 0dB, 3.5dB, or 6dB of high-fre-
quency boost by setting 2 control bits, INEQ1 and
INEQ0 (see Table 2).
Programmable Output Deemphasis
The MAX4950 features programmable output deempha-
sis by setting two control bits, OEQ1 and OEQ0, for de-
emphasis ratios of 0dB, 3.5dB, and 6dB (see Table 3).
Receiver Detection
The MAX4950 features receiver detection on each chan-
nel. Upon initial power-up, if EN is high, receiver detec-
tion initializes. Receiver detection can also be initiated
on a rising edge of the RX_DET input when EN is high.
During this time, the part remains in low-power standby
mode and the outputs are disabled, despite the logic-
high state of EN. Until a channel has detected a receiv-
er, receiver detection repeats indefinitely on each
channel. If a channel detects a receiver, the other chan-
nels are limited to three retries. Upon receiver detection,
channel output and electrical idle detection are enabled.
Note: With a slowly rising power supply, it is recom-
mended to toggle EN to avoid potential receiver detec-
tion timeout conditions.
Electrical Idle Detection
The MAX4950 features electrical idle detection to prevent
unwanted noise from being redriven at the output. If the
MAX4950 detects that the differential input has fallen
below V
TX-IDLE-THRESH
, the MAX4950 squelches the out-
put. For differential input signals that are above
V
TX-IDLE-THRESH
, the MAX4950 turns on the output and
redrives the signal. There is little variation in output
common-mode voltage between electrical idle and
redrive modes.
Power-Saving Features
The MAX4950 features a power-save mode to reduce
quiescent supply current. In power-save mode, electri-
cal idle and receiver detection circuitry for channels 1,
2, and 3 are turned off, and all channel operation is
slaved to channel 0. This feature is useful for reducing
power consumption in applications where all channels
operate simultaneously. During normal operation, all
channels have independent electrical idle and receiver
detection. Drive P_SAV high to activate power-save
mode; drive P_SAV low for normal operation. To further
reduce power consumption, the MAX4950 features a
standby input (EN) when the device is not needed. To
place the device in standby mode, drive EN low. To
enable the device, drive EN high. Table 5 shows typical
power consumption differences between normal mode,
power-save mode, and standby mode with different
output redrive strengths.
