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 paved the way for the practical implementation of millimeter-wave wireless communication terminals, such as on-board radars, using silicon-based technology.
Historically, high-frequency ICs used for transmitting and receiving millimeter-wave signals relied on compound semiconductors. While there was great interest in transitioning to silicon due to its potential for integration, advanced functionality, and mass production, silicon had a major drawback: it generated more noise, which delayed its real-world application.
The millimeter-wave transceiver IC includes a signal generation circuit that produces high-quality millimeter-wave signals. Traditionally, this circuit compared a low-frequency signal derived from the millimeter-wave oscillator with a low-noise, stable reference signal from an external oscillator. The comparison was made every cycle of the reference signal, ensuring stability and minimizing noise. However, this approach had limitations when it came to handling noise from phase-detection circuits, which could significantly affect signal quality.
Silicon semiconductors, being noisier than their compound counterparts, required advanced circuit technologies capable of generating clean, stable millimeter-wave signals. To address this challenge, Fujitsu and Fujitsu Research Institute introduced a new architecture that uses multiple phase-difference detection circuits and delay circuits in series. This design allows for multiple comparisons per cycle by increasing the frequency of the comparison signal and distributing the reference signal across several channels.
By increasing the number of comparisons, the system can amplify the difference signal relative to the noise generated by the phase-detection circuits. As a result, the overall noise level is reduced by approximately one-third (about -5 dB) compared to conventional designs. This advancement makes it feasible to develop millimeter-wave transceiver ICs using silicon semiconductors, which will greatly enhance the performance and cost-effectiveness of systems like on-board radar.
Looking ahead, the two companies plan to use this technology to develop fully integrated millimeter-wave transceiver modules. The details of this innovation were presented at the European Microwave Integrated Circuits Conference 2013 (EuMIC2013), held in Germany on October 6, 2013. This development marks a significant step forward in the field of millimeter-wave communication and highlights the growing potential of silicon-based solutions in high-frequency applications.
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