Datasheet

MAX4950A
Dual PCI Express Equalizer/Redriver
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Detailed Description
The MAX4950A dual equalizer/redriver is designed to
support both Gen I (2.5GT/s) and Gen II (5.0GT/s) PCIe
data rates. The device contains two 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 MAX4950A features
individual channel output amplitude selection inputs,
O_AMPA and O_AMPB (Table 1), and programmable
output deemphasis, permitting optimal placement of
key PCIe components and longer runs of stripline,
microstrip, or cable.
Programmable Input Equalization
The MAX4950A features programmable input equaliz-
ers capable of providing 0dB, 3.5dB, or 6dB of high-
frequency boost on either channel (see Table 2).
Programmable Output Deemphasis
The MAX4950A features programmable output deem-
phasis on either channel by setting two control bits,
ODE_1 and ODE_0, for deemphasis ratios of 0dB,
3.5dB, and 6dB (see Table 3).
Receiver Detection
The MAX4950A features receiver detection on each
channel. Upon initial power-up, if EN is high, receiver
detection initializes. Receiver detection can also be ini-
tiated on a rising or falling 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
squelched, despite the logic-high state of EN. Once
started, receiver detection repeats indefinitely on each
channel. Once a receiver is detected on one of the
channels, up to three more attempts are made on the
other channel. Upon receiver detection, channel output
and electrical idle detection are enabled (see Table 4).
Electrical Idle Detection
The MAX4950A features electrical idle detection to pre-
vent unwanted noise from being redriven at the output.
If the MAX4950A detects that the differential input has
fallen below V
TX-IDLE-THRESH
, the MAX4950A squelch-
es the output. For differential input signals that are
above V
TX-IDLE-THRESH
, the MAX4950A turns on the
output and redrives the signal.
Power-Saving Features
The MAX4950A features an enable input (EN) to shut
down the device and reduce supply current. To place
the device in shutdown mode, drive EN low. To enable
the device, drive EN high. During normal operation,
supply current can also be reduced by reducing the
channel output amplitudes. Table 5 shows typical
power consumption differences between shutdown
mode and normal operation with different output redrive
strengths.
O_AMPA/
O_AMPB
DIFFERENTIAL OUTPUT VOLTAGE
(mV
P-P
)
0 1000 (typ)
1 750 (typ)
Table 1. Output Amplitude Selection
Table 2. Input Equalization
X = Don’t care.
X = Don’t care.
ODE_1 ODE_0
OUTPUT DEEMPHASIS RATIO
(dB)
0 0 0
0 1 3.5 (typ)
1 X 6 (typ)
Table 3. Output Deemphasis
RX_DET EN DESCRIPTION
X 0 Receiver detection inactive
01
Fol l ow i ng a r i si ng or fal l i ng ed g e,
i nd efi ni te r etr y unti l r ecei ver d etected
Ri si ng or
Fal li ng E dg e
1 Initiate receiver detection
11
Fol l ow i ng a r i si ng or fal l i ng ed g e,
i nd efi ni te r etr y unti l r ecei ver d etected
Table 4. Receiver-Detection Input
Function
X = Don’t care.
INEQ_1 INEQ_0
INPUT EQUALIZATION
(dB)
0 0 0
0 1 3.5 (typ)
1 X 6 (typ)