PM8621 PMC-Sierra, Inc., PM8621 Datasheet - Page 42

• Manufacturer Part Number: PM8621
• Description: NSE-8G Standard Product Data Sheet Preliminary
• Manufacturer: PMC-Sierra, Inc.

9.1.1
9.1.2
9.1.3
Proprietary and Confidential to PMC-Sierra, Inc., and for its Customers’ Internal Use
Document ID: PMC-2010850, Issue 1
At the system level, reliable operation will be obtained if proper signal integrity is maintained
through the signal path and the receiver requirements are respected. Namely, a worst case eye
opening of 0.7UI and 100 mV differential amplitude is needed. These conditions should be
achievable with a system architecture consisting of board traces, two sets of backplane
connectors, up to 1m of backplane interconnect. This assumes proper design of 100
lines and minimization of discontinuities in the signal path. Due to power constraints, the output
differential amplitude is approximately 350 mV
The LVDS system is comprised of the LVDS Receiver (RXLV), LVDS Transmitter (TXLV),
Transmitter reference (TXREF), data recovery unit (DRU), parallel to serial converter (PISO and
Clock Synthesis Unit (CSU).
LVDS Receiver (RXLV)
The RXLV block is a 777.6 Mbit/s Low Voltage Differential Signaling (LVDS) Receiver
according to the IEEE 1596.3-1996 LVDS Specification.
The RXLV block is the receiver in Figure 7, accepting 777.6 Mbit/s LVDS signals from the
transmitter, over RP[X]/RN[X] pins, amplifying them and converting them to digital signals, then
passing them to a data recovery unit (DRU). Holding to the IEEE 1596.3-1996 specification, the
RXLV has a differential input sensitivity better than 100 mV, and includes at least 25 mV of
hysteresis. There are 12 RXLV blocks in the NSE.
LVDS Transmitter (TXLV)
The TXLV block is a 777.6 Mbit/s Low Voltage Differential Signaling (LVDS) Transmitter
according to the IEEE 1596.3-1996 LVDS Specification.
The TXLV accepts 777.6 Mbit/s differential data from a “parallel-in, serial-out” (PISO) circuit
and then transmits the data off-chip as a LVDS on TP[X]/TN[X] pins.
The TXLV uses a reference current and voltage from the TXREF block to control the output
differential voltage amplitude and the output common-mode voltage.
There are 12 instances of the TXLV block in the NSE-8G.
LVDS Transmit Reference (TXREF)
The TXREF provides an on-chip bandgap voltage reference (1.20 V ±5%) and a precision current
to the TXLV (777.6 Mbit/s LVDS Transmitter) block’s. The reference Voltage is used to control
the common-mode level of the TXLV output, while the reference current is used to control the
output amplitude.
The precision currents are generated by forcing the reference Voltage across an external, off-chip
3.16 k (±1%) resistor. The resulting current is then mirrored through several individual reference
current outputs, so each TXLV receives its own reference current.
There is one instance of the TXREF in the NSE-8G.
NSE-8G™ Standard Product Data Sheet
differential
Preliminary
41