Hitachi Cuts GaAs MMIC Costs For Car Radar
Hitachi has produced a prototype GaAs MMIC sensor module that offers precision vehicle velocity measurement at a price that s more competitive with silicon.
Toshiyuki Nagasaku unveiled the 77 GHz module targeting electronic automotive-control systems at the Compound Semiconductor IC Symposium in Monterey, California, on October 14.
Currently anti-lock braking systems (ABS) and automated cruise control (ACC) often use wheel-speed detection that cannot detect velocity during skids, when the tire is not rotating.
Radar systems can accurately measure relative velocity using the Doppler effect, and although GaAs currently dominates this application many expect cheaper silicon technology to displace it.
Now, Hitachi has made its GaAs sensor more economical by the building its circuit on a single 0.15 µm gate length PHEMT process MMIC, encapsulated in low-cost resin.
Normally specifically-designed and expensive modules are used to protect MMICs from resonances arising in their packaging. However, Nagasaku and colleagues have been able to avoid this by keeping the resin dimensions below a critical level.
Integrating the 2.7 mm x 1.3 mm single-chip sensor into the resin is a straightforward manufacturing process, without any flip-chip assembly or specialized wire bonding. Likewise, the final package has only two external connections, making it easy to handle and further reducing final module construction costs.
The MMIC includes a power amplifier, low noise amplifier, a transmit/receive antenna, FET mixer, plus an oscillator to generate a waveform for assessing speed via the Doppler effect. This level of integration is another crucial cost advantage for Hitachi.
A separate dielectric lens is needed on top of the resin to focus the microwave output, enabling 13.5 dBm transmit power and 8 dB receive gain.
With resin encapsulation and the lens on top, the final package measures 6.5 mm long, 4.5 mm wide and 6.0 mm high. Nagasaku's prototype module was simply made up of the sensor, a power supply and a signal processing unit and measured vehicle speed with just 1.5 percent standard deviation.
Hitachi already produces ACC systems using millimeter-wave radar that provide acceleration and braking assistance in maintaining distance from surrounding vehicles.
It expects the 77 GHz sensor to add near-range monitoring capability at the rear or side of a vehicle, to prevent collision with objects that the driver cannot see.
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