Analog Angle Article

Active Thunderbolt cables get transceiver, power management IC support

Milpitas, Calif.—The days of a consumer cable being a passive interface component with connectors and wiring may be seeing a radical shift, as the Thunderbolt interface gets IC vendor support (see “Chipset family supports Thunderbolt 10.3 Gbps interface standard“). Designed to allow multiple PCI Express and Displayport devices to be connected to a PC via a single physical connector, Thunderbolt supports two differential 10.3125 Gpbs full-duplex channels via a thin, 3m copper cable or longer optical fiber cables.

But to make it happen, the cable connector ends themselves need active components. Intersil has joined the Thunderbolt effort with two critical ICs: the ISL37231 and the ISL80083:

•The ISL37231 is a 10.3125 Gbps retiming dual-channel transceiver, which includes up to 20 dB of cable-loss equalization, and retiming to meet jitter budget targets for STP, Twinax, or micro-coax copper cables. Incorporating an on-chip microcontroller, it handles 64b/66b encoding along with internal signal quality assessment and diagnostics, using an eye monitor, loop-back, and full self-test modes, all accessed via a UART interface.

To meet signal quality and BER requirements, it provides 9 dB of equalization at the PC board input, along with PC board output de-emphasis. Power consumption is under 500 mW for this IC, which is housed in a 5×5 aQFN package (since the cable connectors house active circuitry, small size is truly critical).

•Of course, ICs and multi-IC systems do not function on their own: they need power and power management. The ISL80083 power-system controller (actually, a mini-PMIC) includes a high-efficiency 800 mA, 2.5 MHz synchronous step-down controller;300 mA LDO; 33 MHz oscillator; 1.8 to 3.3 V level shifter; and input rail selector, along with an I2 C interface. The output voltage of the voltage regulators can be step-programmed via the interface. The input rail selector sees which voltage sources are available and chooses between them, and can switch between the two automatically and without interruption. Again, since space is at a premium in the cable-end connectors, the IC is available as a 24 lead, 2.17×2.15 mm CSP device.

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