Addressing emerging test challenges for multilevel signaling devices

Multilevel analog signaling techniques are rapidly gaining favor for their ability to provide very high-speed symbol transfer rates at appreciably lower observed line rates. Early bipolar methods such as Alternate Mark Inversion have paved the way to signaling techniques using four or more levels. In light of rapidly growing interest in multimedia communications, a particularly important application of multilevel signaling methods is Gigabit Ethernet (1000Base-T), which combines Five-level Pulse Amplitude Modulation (PAM5) with the use of parallel differential. signal lines to increase symbol rates while retaining low line rates. For device manufacturers, however, multilevel signaling poses new challenges for achieving reliable, high-throughput testing needed to deliver required levels of quality and production volume. Documented in IEEE Std 802.3ab-1999, the IEEE offers recommendations for several tests for 1000Base-T PHY devices to ensure signal integrity, timing and functional performance. Among these recommendations, specific test scenarios address the need for measurements of a range of amplitude, voltage, distortion, timing, jitter and functional characteristics. In turn, the measurement of these characteristics in multilevel signaling devices carries specific implications for signal generation and measurement. Very high frequency arbitrary waveform generators (AWGs) win be needed to address higher bandwidth signals across multiple independent differential channels used in applications such as Gigabit Ethernet. Similarly, integrated timing digitizers will be needed to complete time measurements including single-shot propagation delay (Tpd), jitter and frequency. By anticipating these and other emerging test challenges associated with multilevel signaling, device manufacturers will be able to avoid potential delays in production test and speed delivery of devices for this evolving market segment.