connectivityZONE Products for the week of September 17, 2007
National Semiconductor Says…
LVDS 4x4 Crosspoint Switch Features Industry’s Highest Performance
Delivers unparalleled 10 ps jitter performance for telecom, video routing, and ATE applications at data rates up to 3.125 Gbit/s
A new low-voltage differential signaling (LVDS) 4 x 4 crosspoint switch from National Semiconductor Corporation delivers the industry’s best jitter performance (10 ps typical) at data transmission rates up to 3.125 Gbits/s. The DS25CP104 is well-suited for clock and data switching/routing in telecom, professional video, storage and automated test equipment (ATE) applications. The low-power LVDS device’s superior jitter and signal conditioning performance enables OEMs to use less costly cable, connectors and components.
The DS25CP104 offers a feature set to enhance signal integrity in demanding applications such as XAUI (telecom) and SMPTE 424M (pro video). For example, the product consumes only 122 mW per channel while boosting and equalizing field-programmable gate array (FPGA) or applications-specific integrated circuit (ASIC) signals over cables and FR-4 backplanes. The device inputs have a wide common-mode voltage range that allows it to accept low-voltage positive-emitter-coupled logic (LVPECL), current-mode logic (CML) and LVDS signal levels without using coupling capacitors. The system designer has maximum flexibility configuring the DS25CP104 with external pin control or a serial System Management (SM) Bus. The crosspoint also features 8 kV electrostatic discharge (ESD) protection and 100 Ohm termination on the LVDS input and output pins to minimize insertion losses, component count and board space.
National also is introducing the DS10CP154, a lower-speed, lower-power 4 x 4 crosspoint switch targeted at applications up to 1.5 Gbits/s, that includes many of the same features as the DS25CP104.
Unglamorous, non-sexy, and straightforward nearly to the point of being boring, National’s new LVDS crosspoint switches are exceptionally handy for dealing with many of the ugly situations designers regularly encounter when handling high-speed SerDes signals. Their small size, low power and ability to clean up less-than-perfect signals make them good candidates for re-driver applications in cabling or backplane applications, as well as in the switching and failover interconnect tasks for which they were originally designed.
The switch receive equalization scheme is straightforward, delivering up to 12 dB worth of adjustable slope compensation in eight programmable steps. Its transmit pre-emphasis circuit provides four levels (0 dB to 9 dB) of gain and uses a 2-tap digital filter to adjust the signal level of the bit being transmitted based on the polarity of the previous bit. Both input and output circuits can be programmed on a per-channel basis via an integrated SM-bus interface, or hard-strapped via external pins.
National has been in the LVDS business for quite some time (heck, they pretty much invented it), but these new devices move up from the 1 - 2 Gbit/s that previous products support to somewhere north of 3 Gbit/s -- the sort of performance you’d see in a higher-power LDPECL or CML part. The SiGe/BiCMOS process they used to achieve the speed boost gives them a 50 GHz fT and the ability to match transistors more closely. Besides delivering exceptionally low jitter (10 ps) in these products, these capabilities hint at devices targeted for applications running in the neighborhood of 5 GHz (or higher) in the near future. The LLP packaging which keeps parasitics to a minimum in the current product line should be able to handle the higher speeds with little or no tweaking. And while we’re speculating about future products, it’s probably a good bet that larger switch matrices (8 x 8) are under development. When I asked about this, National said they could not comment on this but said that if such parts existed they’d find lots of applications in T&M and video switching.
The wide gain range and tight jitter spec makes them very useful as bi directional 2 x 2 redundancy cross-straps in backplanes but National says that its early customers are also having great success in using it in video routing and clock routing/distribution applications. As I mentioned earlier, the DS25CP104 (3.125 Gbit/s) and the DS10CP154 are also well suited for use as a re-driver in long PCB, backplane or cable runs, or to assist the margins on chip SerDes circuits found in some ASICs and merchant networking silicon. Their wide common-mode signal range (they can handle nearly anything between 0 V and Vcc. ) means that it can hook up to a wide range of devices, ranging from LVPECL drives to the SerDes transceivers on Broadcom Staratix Ethernet switches and Xilinx Virtex V4/V5 FPGAs.
The DS25CP104 (3.125 Gbit/s) and lower power DS10CP154 (1.5 Gbit/s) are available now in 40-pin LLP packages and are priced at $8.75 and $4.75, respectively, each in 1000-piece lots.
Data Sheet DS25CP104
Data Sheet DS10CP154