i/oZONE Products for the week of April 19, 2004
Texas Instruments Says…
Over-Achiever: TI's Quad XAUI Backplane SerDes Supports
Error-free Transmission Over 80 Inches of Standard Backplane Trace
Providing high-speed, bi-directional, point-to-point data transmission
for backplane and front plane connections, Texas Instruments Incorporated
has introduced a new discrete serializer/deserializer (SERDES) capable of
error-free transmission over 80 inches of standard backplane trace. Manufactured
in TI's advanced 130nm CMOS technology, the TLK3118 is a flexible, redundant
XAUI serial transceiver compliant with the IEEE 802.3ae specification for
10 Gigabit Ethernet. Ideal for local, metropolitan and wide area network
applications, the device enables designers to reduce board space and design
time.
Within backplane designs, the TLK3118 enables higher port density systems by reducing board space, system costs and power consumption, ultimately packing more high-speed channels/ports in less space, in turn cutting costs for network service providers. The device performs the parallel-to-serial conversion, serial-to-parallel conversion and clock extraction functions for a physical layer interface. It provides a complete XGXS (10 Gigabit extended sublayer) function with a redundant serial (XAUI) port. Redundancy is critical to communication equipment makers that want to provide systems with high availability and superior Quality of Service (QoS). The serial transmitter is implemented using differential current mode logic with integrated termination resistors. The device employs state-of-the-art transmit and receive equalization technology for superior signal integrity over industry standard media such as FR4 backplanes. This equalization technology has enabled TI to achieve error-free data transmission over 80 inches of backplane with this device.
About TI's 130nm CMOS Technology
TI's advanced 130nm process technology enables TLK3118 to achieve extremely
low power dissipation of 1.6W (with HSTL termination turned off) at 3.125
Gbps. The device has been developed using the proprietary serial link core
technology within TI's 130nm standard cell library. The use of common serial
link core intellectual property across both ASIC and discrete SERDES solutions
provides customers the unique opportunity to choose between discrete and
ASIC-based solutions as they incorporate TI's advanced serial link technology.
The capability to deliver both discrete and ASIC-based serial link solutions
enables TI to service every phase of a customer's product life cycle with
consistent and proven technology.
analogZONE Says . . .
TI has joined the multi-Gbit transceiver fray with its TLK3118, a quad-port 3.125 Gbit/s (2.5 Gbit/s when you subtract out the 8B/10B coding overhead) part which features redundant architecture. Traffic from its XGMIII port can be directed to either of two quad bi-directional XAUI interfaces, a handy thing to have when you need fail-over-protection in carrier-class equipment. And speaking of redundancy, the TLK3118 shares an industry standard footprint & pinout shared with the Broadcom BCM8201 XAUI transceiver: a very rare (and useful) thing in this industry.
While not exceptionally exotic, TI has made significant improvements over the "vanilla" SerDes circuits you find in most XAUI products. They have taken a conscientious and solid approach to the challenges of shipping 3+ Gbit/s across the often-hostile environments found in backplanes, with a programmable analog equalizer on the receiver and a programmable pre-emphasis circuit on driver side. It's interesting to note that with all its DSP expertise, TI has chosen to use analog equalization techniques for the chip. The receiver's analog taps are controlled by digital logic to adjust for maximum eye opening.
Although TI calls its scheme "adaptive", I'd say that this is stretching the definition a bit since there is no in-band feedback channel built into the chip. If you want adaptive performance, you'll need to monitor BER and other parameters externally and set the EQ via an external control channel. But at "only" 3.125 Gbit/s, this is probably more than adequate. About the only thing this part does not come with is the echo cancellation found in their 6-Gbit/s SerDes chip reviewed here.
On the transmit side, the chip has some novel programmable pre-emphasis circuitry that can adjust a signal's voltage slew and amplitude. So far, TI has found the fastest slew rate almost always works best, but I'm willing to wager that somebody out there will be able to use a slower rise time to their advantage.
The device's nominal power consumption is 1.6 W (with HSTL termination turned off), around 100 mW/channel higher than the power claimed by Broadcom's part, and almost double some of the other quad XAUI solutions I've reviewed here. I think this is in good part due to the generous amounts of signal conditioning circuitry the designers crammed into this part. And while some of this may be unnecessary for "normal" (whatever that means) backplane traces, the extra equalization and pre-emphasis circuitry provides a good margin of performance for the more challenging conditions found in longer reaches and boards using older connectors.
This margin is demonstrated in TI's experiments with a Tyco HMZD FR-4-based backplane where they looped a signal through the 30-inch long signal path twice. When you consider the two FR-4 18-inch adapter blades used to get the signal on and off the board, you have well over the 80-inch length that TI claims. In truth, the device actually runs at up to 3.9 Gbit/s over shorter, up to 30 inch, paths. This extra speed is useful for two things. First, it gives you some extra receiver margin for less-than-perfect conditions, and, perhaps more important, is being able to move "supersized" packets, i.e. traffic which has additional appended tags for routing and control purposes. The ability to handle these oversized payloads, plus whatever in-band control messages a router might generate without impacting on the overall system throughput is a big plus that might well justify a little extra power in many applications.
The extra performance margin also allows the TLK3118 to support CX-4 operation over 15 m of standard InfiniBand cable, or 30 m of improved Gore "Eye Opener" cable without even kicking on the transmit pre-emphasis. While TI has not tested it in this mode yet, I'd expect that when they do, they'll have even better reach. This should help the TLK3118 do a brisk business powering interconnects in stacking products. Its exceptional reach may even help it find applications in short-haul inter-rack connections.
The TLK3118 is sampling in FCBGA-400 (21 mm x 21 mm) with production in the third quarter of 2004, priced at $60 in 1000-piece lots.
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