Electronic Design

Embedded Waveform Viewing Improves Signal Integrity Testing Without An Oscilloscope

Buses and backplanes keep getting faster. Ethernet now runs at 10 Gbits/s, and the XAUI interfaces are at 3.125 and 6.25 Gbits/s. Blade server serial buses like PCI Express are moving from 2.5 to 5 Gbits/s. The SAS and SATA interfaces are increasing from 1.5 to 3.0 to 6.0 Gbits/s. Fibre Channel is now at 8 Gbits/s. And, digital video is increasing from 1.5 to 3.0 Gbits/s as 1080p HDTV becomes more popular.

The result is more difficulty in testing and measuring these interfaces to ensure that the signal integrity will meet standards and specifications. The usual approach is to look at the signal lines at the receiver input with a real-time scope and use the internal equalization software to get a general idea of what the signals inside the interface ICs really look like. But oscilloscopes use equalization simulation techniques that only offer an extrapolated view of the signals inside the chip.

Vitesse Semiconductor’s VScope promises to improve upon that approach to signal integrity testing and analysis. The VScope embeds the scope function into the bus receiver chip (see the figure). It samples the output of the internal equalizer that follows the receiver and develops an output that goes to a USB port for connection to an external PC for display.

Also, the VScope uses dual adjustable sampling channels for simultaneously receiving and scanning. The dual samples are compared bit by bit, and the number of mismatches per unit time is captured to determine bit error rate (BER). The outcome is a more accurate view of the internal data stream as it avoids correlation errors between the measurement circuitry and live data path.

Post equalizer scanning with the VScope provides an unobstructed view of the internal IC signal. That way, you can more accurately measure the eye opening and the rise/fall time. It also more accurately determines BER on an external PC screen.

VScope can remotely monitor signals to implement network-based troubleshooting as well. Its digital data output can be sent via a network back to a central monitoring point so the overall health of the system can be determined, speeding up troubleshooting and eliminating truck rolls. With VScope, you can implement 24/7 visibility and predictability of failing links, reducing maintenance costs and potentially improving customer service.

The VScope technology is incorporated into Vitesse’s VSC3406, which is a 6.375-Gbit/s multirate backplane transceiver that operates from 125 Mbits/s to 6.375 Gbits/s. It incorporates a universal clock and data recovery (CDR) receiver for serial data and advanced equalization. Also, it can be used for signal conditioning, switching, and rate doubling applications.

The chip has six high-speed differential transmit and receive interfaces, complete with on-chip termination ideal for interfacing to a variety of media such as printed-circuit board traces, cables, or optoelectronic devices. The device’s 2-to-1 range multiplier mode allows data multiplication up to 6.375 Gbits/s, doubling bandwidth over existing backplanes. Coupled with the signal equalization function, the rate multiplier mode can be used to run double and quadruple the amount of bandwidth over existing copper traces.

The VSC3406 comes in an 81-pin 10- by 10-mm flip-chip ball-grid array (FCBGA) package. It costs $60 in volume quantities.

Vitesse Semiconductor Corp.


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