Fujitsu and the Fujitsu Research Institute have been working on developing low-noise signal generation circuits using millimeter-wave transceivers in silicon semiconductors. This breakthrough has enabled the practical implementation of millimeter-wave wireless communication terminals, such as on-board radars, leveraging the advantages of silicon-based technology.
Traditionally, high-frequency ICs for transmitting and receiving millimeter-wave signals relied on compound semiconductors. While there was strong interest in transitioning to silicon due to its potential for integration, higher functionality, and mass production, silicon's inherent noise had limited its real-world application. The challenge lay in achieving the necessary low noise and high stability required for reliable millimeter-wave communication.
The new millimeter-wave transceiver IC integrates a signal generation circuit that produces stable millimeter-wave signals. Previously, this circuit compared a low-frequency reference signal from an oscillator with a divided version of the millimeter-wave signal, ensuring synchronization and minimizing noise. However, the comparison was made only once per cycle of the reference signal, which limited the system's ability to suppress noise effectively.
This limitation became more pronounced when using silicon semiconductors, which inherently generate more noise than their compound counterparts. To address this, Fujitsu and Fujitsu Research Institute introduced a novel architecture that employs multiple phase-difference detection circuits and delay circuits in series. By increasing the frequency of the comparison signal and distributing the reference signal across multiple points, they significantly boosted the number of comparisons made per cycle.
With more comparisons, the difference signal generated during each cycle could be amplified relative to the noise from the phase-detection circuits. This approach dramatically reduced the impact of internal noise, resulting in a signal with approximately one-third the noise level of conventional circuits—about -5 dB improvement.
Thanks to this advanced circuit design, it is now feasible to develop millimeter-wave transceiver ICs using silicon semiconductors. This development is expected to play a key role in enhancing the performance and enabling mass production of millimeter-wave communication systems, including automotive radar applications.
Looking ahead, the two companies plan to integrate this technology into compact, high-performance millimeter-wave transceiver modules. Additionally, the technical details of this innovation were presented at the European Microwave Integrated Circuits Conference (EuMIC 2013), held in Germany starting October 6, 2013, marking a significant milestone in the field of microwave electronics.
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