MAX14954 Datasheet, PDF (15/17 Pages) Maxim Integrated Products – Computer on Modules

MAX14954
Ruggedized Quad PCIe Redriver with
Equalization and Extended Temperature Operation
Detailed Description
The MAX14954 quad equalizer/redriver is designed to
support Gen III (8.0GT/s), Gen II (5.0GT/s), and Gen I
(2.5GT/s) PCIe data rates. The device contains four iden-
tical drivers with electrical idle/receive detect on each lane
and equalization/deemphasis/preshoot to compensate
for circuit-board loss. Programmable input equalization
circuitry reduces deterministic jitter, improving signal
integrity. The device output features a programmable
output deemphasis/preshoot, permitting optimal place-
ment of key PCIe components and longer runs of stripline,
microstrip, or cable.
Programmable Input Equalization
Programmable input equalization is controlled by two bits:
INEQ1 and INEQ0 (Table 1).
Table 1. Input Equalization
INEQ1
0
0
1
1
INEQ0
0
1
0
1
INPUT EQUALIZATION (dB)
5
8
12
16
Programmable Output Deemphasis/Preshoot
Programmable output deemphasis is controlled by three
bits: OEQ2, OEQ1, and OEQ0 for deemphasis/preshoot
ratios of 0dB, 3.5dB, 6dB, and 9dB (Table 2).
Table 2. Output Deemphasis/Preshoot
OEQ2 OEQ1 OEQ0
0
0
0
0
0
1
0
1
0
0
1
1
1
0
0
1
0
1
1
1
0
1
1
1
OUTPUT DEEMPHASIS/
PRESHOOT RATIO (dB)
0
3.5
6
6 (peak-to-peak swing is 1.2V)
3.5
6
9 (peak-to-peak swing is 0.9V)
9 (peak-to-peak swing is 1.0V)
Receiver Detection
The device features receiver detection on each channel.
Upon initial power-up, if EN is high, receiver detection
initializes. Receiver detection can also be initiated on a
rising or falling edge of the RXDET input when EN is high.
During this time, the device remains in low-power standby
mode and the outputs are disabled, despite the logic-high
state of EN. Until a channel has detected a receiver, the
receiver detection repeats indefinitely on each channel.
If a channel detects a receiver, the other channels are
limited to retries for 100ms (typ). For each channel upon
receiver detection, input common-mode termination and
electrical idle detection are enabled (Table 3).
Electrical Idle Detection
The device features electrical idle detection to prevent
unwanted noise from being redriven at the output. When
the device detects that the differential input has fallen
below the VTX-IDLE-THRESH low limit, it squelches the
output. For differential input signals that are above VTX-
IDLE-THRESH ^{high limit, the device turns on the output}
and redrives the signal. There is little variation in output
common-mode voltage between electrical idle and redrive
modes.
Table 3. Receiver Detection Input
Function
RXDET
X
EN
DESCRIPTION
0 Receiver detection is inactive.
Following a rising edge of the
EN signal, indefinite retries until
X
1
receiver detects at least one
channel. Retries stop after 100ms
(typ) if any channel receiver is
detected.
Rising/falling
edge
1 Initiates receiver detection.
X = Don’t care.
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