![](http://datasheet.mmic.net.cn/260000/PM7390-BI_datasheet_15944927/PM7390-BI_105.png)
Multi-Service Access Device For Channelized Interfaces
Telecom Standard Product Data Sheet
Production
Proprietary and Confidential to PMC-Sierra, Inc., and for its Customers’ Internal Use
Document ID: PMC-1990823, Issue 4
105
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 100mV differential amplitude is needed. These conditions should be
achievable with a system architecture consisting of board traces, two sets of backplane connectors
and up to 1m of backplane interconnects. This assumes proper design of 100 differential lines
and minimization of discontinuities in the signal path. Due to power constraints, the output
differential amplitude is approximately 350mV.
If an LVDS transmitter is not used, its outputs can be left floating. If an LVDS Receiver is not
used, its inputs can be left floating provided that the LVDS Receiver is disabled in software to
minimize power consumption. Alternatively, the LVDS Receiver’s inputs can be tied to ground if
the link will not be used. Since these are LVDS receivers and not CMOS, there is no electrical
problem in leaving them floating (as opposed to a CMOS input). Power dissipation is the same
regardless of whether the input is connected or not, and no damage to the device will occur. If a
hot-swap is desired, an LVDS Receiver can be left enabled and it will sync up when the far-end
Transmitter is connected.
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).
11.33.1 LVDS Receiver (RXLV)
The RXLV block is a 777.6 Mb/s Low Voltage Differential Signaling (LVDS) Receiver according
to the IEEE 1596.3-1996 LVDS Specification.
The RXLV block is the receiver in Figure 11, accepting up to 777.6 Mb/s LVDS signals from the
transmitter, 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 100mV, and includes at least 25mV of hysteresis.
11.33.2 LVDS Transmitter (TXLV)
The TXLV block is a 777.6 Mb/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 low voltage differential signal.
The TXLV uses a reference current and voltage from the TXLVREF block to control the output
differential voltage amplitude and the output common-mode voltage.
11.33.3 LVDS Transmit Reference (TXREF)
The TXLVREF provides an on-chip bandgap voltage reference (1.20V ±5%) and a precision
current to the TXLV (777.6 Mb/s LVDS Transmitter) blocks. 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.