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The MOST automotive protocol seems to add new hardware and software suppliers to its cadre daily. Parts suppliers are realizing the strong market opportunity in supporting a network that meets modern and future automotive infotainment system requirements with a high level of quality of service and at ever-improving cost levels.

A crucial element is the fiber-optic transceiver (FOT) circuit for the high-speed fiber version of the 150-Mbit/s protocol. In the early days of MOST, only one IC FOT was available. Since then, of course, there’s been a lot of progress.

HERE COME THE FOTs
New FOT offerings are now available from Avago Technologies, Hamamatsu, Melexis Integrated Systems, Nanotech Semiconductor, and Sharp Electronics. Moreover, the incorporation of a copper-wire physical-layer capability to the MOST standard has broadened the need for non-optical transceivers, which are simpler to manufacture than optical types.

Many of these components use red 650-nm wavelength light sources like lasers and LEDs and a silicon p-i-n photodiode for light detection. The choice of a red light source is mitigated by the automotive industry’s preference for making repair-shop jobs easier and by the relative transparency at 650 nm of plastic optical fiber carrying the light. Plastic optical fiber and, in particular, silicon plastic optical fiber with a core diameter of 1 mm are the most popular choices for the MOST protocol.

One of the newest FOTs on the market is the 150-Mbit, single-package MLX75605 from Melexis Integrated Systems. Housed in a 24-pin small-outline IC (SOIC), it contains an embedded ferrule clamp for connection to the core plastic optical fiber.

The MLX75605 features 3.3-V operation, a resonance- cavity LED light source that puts out at least 1.5 mW, a p-i-n photodiode with –23-dBm sensitivity, and transmitter minimum and maximum power of –6.5 and –1.5 dBm, respectively. Its integrated memory enables on-chip trimming of performance parameters. Furthermore, its integrated test mode supports emitted power adjustment.

Nanotech Semiconductor offers separate full-custom, digital CMOS, 150-Mbit/s transmitters (NT2103x) and receivers (NT21010). The transmitter can work with resonant-cavity LEDs, vertical-surface emitting lasers (VCSELs), and conventional LEDs, putting out 40 mA and consuming less than 48 mA operating at 3.3 and 5 V.

The receiver consists of an automatic-gain-control (AGC) transimpedance amplifier followed by a limiting amplifier with a transistor-transistor logic (TTL) output and a p-i-n photodiode. Sensitivity is –33 dBm (+2-dBm overload at 50 Mbits/s), operation is from 3.3 and 5 V, and power consumption is less than 23 mA.

Early on, Infineon Technologies developed an integrated FOT consisting of an LED transmitter and a p-i-n photodiode with a digital output (Fig. 1). The CMOS four-pin ODIN MOR4 02 FOT is attached to a leadframe “sidelooker” package that’s fixed in a cavity-as-interface (CAI) form via a transparent adhesive. The term “sidelooker” refers to the fact that the optoelectronic components are oriented toward the side of the package.

The device operates at 3.3 or 5 V with data rates up to 25 Mbits/s (50 Mbits/s biphase-coded) and can sense less than 10 µA of current. It features guaranteed sensitivity of –25 dBm at a wavelength of 650 nm and complies with the MOST Physical Layer Rev. 1.1 specification. Avago recently purchased Infineon’s optical product business, so this product is now part of its product line.

Additionally, Hamamatsu makes separate 50-Mbit/s sidelooker transmitters and receivers. Each is attached to a leadframe and encapsulated in a transparent plastic material.

The L10063-1 transmitter, which contains a red LED and driver IC incorporated in a clear plastic package, can be set to an operating mode that cuts the optical output level of –2 to –9 dBm in half. It consumes 40 mA maximum at an operating voltage of 2 V. The receiver uses a biphase p-i-n diode with a biphase input signal of –2.5 to –2 dBm and output voltage levels of 0.4 to 2.5 V. The receiver’s current consumption is 30 mA.

Sharp Electronics has also joined the MOST FOT supplier list with a pair of separate 25-Mbit/s MOST biphase optical fiber and transceiver ICs. These devices include the 5-V GP5M5T01AZ transmitter and the 5-V GP5M5R01AZ receiver. Both also come in 3.3-V versions.

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POWER-MANAGEMENT AND PROCESSOR ICs
Recently, STMicroelectronics launched the industry’s first integrated power-management IC for MOST. Designed in cooperation with SMSC, the L5961 includes a 3.3-V or 5-V, 650-mA power supply and MOST-compliant power-management control logic, together with enhanced diagnostic and system-monitoring circuitry, all in a PowerSS036 package (Fig. 2).

A chip set combining the L5961 and SMSC’s intelligent network-interface controller (INIC) can serve as a building block in any MOST-network node without being redesigned and re-evaluated each time it’s placed into an application.

SMSC’s INIC eLITE technology is a low-cost, entrylevel automotive networking solution for transporting multiple channels of digital audio and video content between various automotive components. It eliminates extra wiring and the added cost of transmitters, receivers, and analog-to-digital and digital-to-analog converters (ADCs and DACs) while maintaining high signal quality.

Freescale Semiconductor also supports MOST with its MPC5121e and i.MX31 mobileGT processors. The MPC5121e integrates a high-performance MPC603e series e300 core with a rich set of peripheral functions for communications and systems integration. The i.MX31 applications processor is designed for automotive infotainment systems.

Fujitsu recently announced the 32-bit MB91F467M microcontroller unit (MCU), which integrates SMSC’s MediaLB interface (Fig. 3). Designed for automotive audio applications, the chip acts as a gateway between the MOST bus, via its MediaLB INIC eLite interface, and up to 10 12S interfaces. In addition to data, it provides a clock path with extremely low jitter from the MOST backbone to or from these interfaces.