ETC Chipset Overview |
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ETC system overview
The ETC system is allocated to the 5.8
GHz band and uses transmission (ETC
in-car unit →ETC gate) and reception
(ETC gate →ETC in-car unit) frequencies
that are separated by 40 MHz.
During transmission, after the local oscillator
signal generated by PLL, VCO, and
doubler circuits is modulated by an ASK
modulator, that signal is amplified by a
power amplifier to drive the antenna.
During reception, after the signal input
from the antenna is amplified by a low-noise
amplifier, it is downconverted to 40
MHz using a local oscillator signal. This
signal is ASK demodulated in the IF
block.
Since these devices handle the high frequency
of 5.8 GHz, most of the blocks
that operated in that frequency band were
fabricated in a GaAs process.
ETC chipset structure
One major feature of this newly-developed
ETC chipset is that unlike the four
chips required for the previous chipset,
this chipset only requires two.
Figure 2 shows the structures of both the
earlier four-chip chipset and the newly-developed
two-chip chipset. While in the
earlier chipset the IF (RSSI, limiter, and
peak hold) is implemented in the
CXA3304N, the PLL is implemented in
the CXA3314ER, and the VCO and doubler
are implemented in the CXG1133ER,
in the new chipset, the CXA3344ER
integrates the functions of all three of
these devices. At the same time, the
CXG1132AER was developed as a low-power
version of the CXG1132ER.
Thus the CXA3344ER and the
CXG1132AER implement a complete
ETC chipset with just two chips.
Reduced mounting area
Switching from a four-chip structure to
two-chip structure reduced the mounting
area by 27%. (See figure 3.)
Also, reducing the number of chips means
that the cost of the chipset as a whole can
be held to a minimum.
*: The mounting area is calculated as the sum
of the areas of the chip packages.
Lower power
To reduce power consumption in the
CXA3344ER and the CXG1132AER,
Sony used their unique technologies to
reduce the power in each semiconductor
device circuit. As a result, this chipset
reduces current consumption by 26%
during transmission and by 42% during
reception, thus achieving the industry’s
top class of low power performance. (See
figure 3.) |
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IF/PLL/VCO/Doubler(CXA3344ER) |
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Functions of three chips
integrated on one chip
The CXA3344ER is fabricated in the
latest SiGe BiCMOS process. The key to
implementing IF, PLL, VCO, and doubler
functions on a single chip was in discovering
how to implement the VCO and
doubler, which were previously implemented
using a GaAs process, in the SiGe
BiCMOS process.
In this IC, we made the 5.8 GHz block as
simple as possible, and designed the circuits
to take maximum advantage of the
capabilities of SiGe BiCMOS devices.
Reduced power consumption
The VCO and the doubler are the blocks
with the largest current consumption. A
new method was adopted for these blocks
and their circuits were optimized relative
to the other blocks, resulting in a total reduction
in power consumption for the IC
as a whole.
Figure 4 shows the structures of the VCO
and doubler. In the earlier method, after a
2.9 GHz signal was generated by the
VCO, that signal was amplified by a
buffer amplifier. In the doubler, the
secondary harmonic (5.8 GHz) of the 2.9
GHz signal was generated by amplifying
and distorting the 2.9 GHz signal. After
that, the 5.8 GHz signal was output by removing
the 2.9 GHz component with a
band elimination filter (BEF). This
method, however, involves a complex
sequence of circuits up to the point the
5.8 GHz is output and requires power proportional
to that complexity.
To resolve this problem, Sony developed
a new circuit that directly converts the 2.9
GHz differential signal generated by the
VCO to 5.8 GHz. This new system results
in a 43% reduction of the total current
consumption of the VCO and doubler
compared to the earlier method.
Automatic output level
adjustment circuit
Since the 5.8 GHz output signal level is
used by the CXG1132AER as the local
oscillator signal, it is desirable that there
be minimal changes in the output level
with manufacturing variations and
temperature fluctuations. To reduce
these sorts of output variations, the
CXA3344ER includes an automatic output
level adjustment circuit.
In this method, the output level is automatically
adjusted using the fact that the
doubler drive current and the output level
are correlated. Actually, a dummy circuit
(doubler dummy) is used and the VCO is
controlled so that drive current is the same
as the reference value to monitor the doubler
core drive current. This makes it possible
to hold the output level precision to
within ±2.5 dB regardless of manufacturing
variations or temperature changes.
Additionally, the circuit is designed so
that the output level setting can be adjusted
with an external resistor (Rext).
(See figure 5.) This makes it possible to
adjust the output level to a value optimal
for the customer’s application. |
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LNA/Mixer/Power Amplifier
(CXG1132AER) |
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Development of an RF
transceiver IC for ETC
Sony entered the market for cellular phone
RF front end MMICs in the early 1990s.
Since then Sony has continued to lead the
industry by developing large numbers of
MMIC* devices (including antenna
switches, low-noise amplifiers/mixers,
and power amplifiers) using GaAs process
technologies.
This ETC RF transceiver IC was designed
and tuned based on technologies developed
during the development of cellular
phone MMICs, and is the largest scale
MMIC Sony has yet attempted. By adopting
the junction-gate FET process, which
provides superlative sensitivity, distortion,
and manufacturing stability characteristics,
Sony achieved both high performance
and low cost.
*: MMIC: Microwave Monolithic Integrated Circuit
From the CXG1132ER to
the CXG1132AER
In developing the CXG1132AER of this
release, Sony focused on two issues:
reducing current consumption compared
to the earlier product (CXG1132ER) and
incorporating the externally applied bias
circuit on the same chip.
To reduce current consumption, Sony
reduced current consumption during
reception in the driver amplifier for the
local oscillator by optimizing the level
diagram. Additionally, Sony increased
the amplification efficiency of the local
oscillator driver amplifier during transmission be reevaluating the power supply. These reevaluations of the circuits
resulted in 43% and 17% reductions in
current consumption during reception and
transmission, respectively.
To incorporate the externally applied bias
on the chip itself, Sony modified the
circuits so that the power amplifier bias
was not need, thus improving the IC’s
ease of use. |
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Future Developments |
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Japan’s Ministry of Land, Infrastructure
and Transport is studying a wide range of
ITS* services that take advantage of ETC
communication technologies. These
include automatic toll payment and non-stop in and out at for-fee parking facilities and providing information to in-car
navigation systems at highway rest stops.
At the same time, Sony is proceeding with
the development of future generation ETC
chipsets that will take advantage of the
technologies nurtured in ETC chipset
development up to now to provide further
miniaturization, even lower power opera
tion, and lower costs.
Keep your eye on Sony for the latest in
high-frequency and process technologies.
*: ITS: Intelligent Transport Systems |
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See
all articles with figures and tables.  |
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Vol.40 |
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