Fujitsu Laboratories Ltd. reported that it has produced a transceiver chip for millimeter-wave radar in a complementary metal-oxide-semiconductor (CMOS) implementation. The company notes that CMOS-based millimeter-wave radar are susceptible to noise. However, Fujitsu Laboratories produced a prototype CMOS transceiver chip using a 65nm CMOS process. According to the company, the CMOS transceiver chip suppresses oscillator noise on the receiver circuit using a frequency-conversion circuit that makes it compatible with the 76-81 GHz band of automotive millimeter-wave radar. The device’s resulting performance is said to be equivalent to or better than current SiGe chips.
The SSB noise index, which is an indicator of the receiver chip’s low-frequency noise, was 12 dB for the prototype, at the same level as existing SiGe products, representing an 18 dB improvement over the figure of 30 dB for CMOS units previously announced at academic meetings and other sources.
Compared to stereoscopic cameras and LiDAR, which use visible light, millimeter-wave radar is relatively unaffected by reflections, fog, or rain. Therefore, millimeter-wave radar can be used to detect obstacles if it can be made inexpensively. Low frequency noise has made it difficult for CMOS-based radar to detect obstacles with weak reflectance such as pedestrians.
Fujitsu Laboratories used a double-balanced resistive mixer in the frequency-conversion circuit of the receiver to reduce the Low frequency noise and reduce the DC current required to power the mixer transistor.