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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