Fujitsu's new technology improves the quality of automotive radar

    In recent years, in order to improve the recognition of radar systems and the quality of wireless communications, researchers have made every effort to develop transceivers that can operate in the millimeter microwave band with a frequency greater than 30 GHz. High-frequency integrated circuits are used to receive and transmit millimeter microwave signals, and the physical properties of compound semiconductors are very suitable for high-frequency environments, so they are currently often used in high-frequency integrated circuits (Figure 1). However, in order to integrate signal processing circuits on a chip, improve product performance, and facilitate large-scale production, silicon semiconductors become more suitable (Figure 2), which is why silicon semiconductors were selected as components of millimeter microwave transceiver integrated circuits.

Figure 1 Compound semiconductor integrated circuit

Figure 2 Silicon semiconductor integrated circuit

    Millimeter microwave transceiver integrated circuits generate millimeter microwave signals by using a signal generation circuit. Traditional signal generation circuits compare a low-frequency comparator signal separated from the millimeter microwave oscillation signal with a low-noise, highly stable reference signal, where the comparator signal is separated from the millimeter microwave oscillation signal and the reference signal comes from a reference oscillator. These two signals are then integrated and synchronized together to ultimately generate a low-noise, highly stable signal (Figure 3).

Figure 3 Traditional signal generation circuit

    Since the reference signal and the comparator have the same frequency and the comparison process is performed only once in one cycle, the comparison result between the phase difference signal and the noise generated by the phase difference detection circuit will not be large enough, which will eventually lead to the problem of high noise level. It is also worth noting that the noise level generated by transistors processed by silicon semiconductors is higher than that of compound semiconductors. Reducing the noise level and generating high stability signals have become an important direction for the development of integrated circuit technology.

    This newly developed technology uses a completely new structure, where multiple phase difference detection circuits are linearly connected with delay circuits, making multiple comparisons possible. In the new integrated circuit, the frequency of the comparison signal is also increased, and the reference signal is separated into multiple signals, so that multiple comparisons can be performed in one cycle. Phase difference signals are generated after each comparison, and thanks to the larger number of differential signals, their relative size is much larger than the noise generated by the phase difference detection circuit, thus reducing the impact of noise.

Figure 4 New signal generation circuit

    The low-noise signal generation circuit also uses multiple comparators to achieve continuous comparison with the reference signal. The final noise level is reduced by 5 decibels, in other words, the noise is reduced by one-third on the basis of the original level. In addition, the lower noise level also reduces the consumption of electrical energy and even reduces the number of necessary components, reducing the burden on the environment.

    The low-noise signal generation circuit developed by Fujitsu has made all the preparations for the production of fully integrated millimeter microwave band transceiver circuits on silicon semiconductors. This new technology is expected to significantly improve the performance of automotive radar and other wireless transceivers. Of course, whether the product can be mass-produced is also an important factor affecting the future development of the technology. In order to apply this advanced technology, Fujitsu plans to build a single-chip millimeter microwave transceiver integrated circuit module. A large amount of data has been collected on this new technology in the "Advanced Technology Research of 79 GHz Radar System" carried out in Japan, and more details will be disclosed at the 2013 European Microwave Integrated Circuit Conference.