This brief gives an overview of recent advancements in CMOS automotive radar sensors, focusing on the most critical circuit design at mm-wave frequencies. Highly scaled CMOS technologies enable very low-power consumption, reduced costs, and higher data processing capacity and integration compared to state-of-the-art SiGe BiCMOS chip-set solutions commonly adopted in commercial products. The very bottleneck is still represented by the radio front-end due to the challenging requirements of long-range radars. Circuit topologies and design tradeoffs are here discussed with reference to critical building blocks of the mm-wave radar front-end, reporting circuit implementations for a 77-GHz long-range radar sensor in a 28-nm fully-depleted silicon-on-insulator CMOS technology.

This brief presents a fully CMOS voltage reference based on a self-biased topology, which provides low current consumption while saving silicon area. Temperature compensation is achieved by means of a subthreshold triode-based Widlar current reference and a proper arrangement of an active load. The proposed voltage reference was fabricated in a standard 0.13-μm CMOS technology and occupies a core area as low as 0.003 mm ² . The circuit properly operates with a power supply ranging from 2.4 V to 1.1 V while providing a reference voltage of around 800 mV with an average temperature coefficient of 100 ppm/°C and an overall current consumption below 25 nA. This performance makes the proposed voltage reference very suitable for RF-powered applications.

This paper presents a variable-gain amplifier (VGA) for automotive radar applications integrated in a 28-nm fully depleted (FD) silicon-on-insulator (SOI) CMOS technology. The amplifier operates at a power supply as low as 1 V and guarantees 30-dB linear-in-dB gain variation with a 3-dB step. The back-gate of the MOS transistors has been exploited to implement a back-gate control based offset cancellation loop, thus avoiding the use of inter-stage coupling capacitors that introduce frequency limitations due to parasitic capacitances. The VGA exhibits a bandwidth from 100 kHz to 20 MHz, which is compliant with typical frequency-modulated continuous wave (FMCW) radars. It also guarantees a 1-dB compression point (P1dB) better than -36 dBm and an input-referred noise (IRN) of 12.5 nV/Hz and 7 nV/Hz at 1 MHz and 10 MHz, respectively, with a power consumption as low as 1.7 mW.

This paper presents a switched capacitor low-pass filter in a 28-nm fully depleted silicon on insulator CMOS technology for 77-GHz automotive radar applications. It is operated at a power supply as low as 1 V and guarantees 5-dB in-band voltage gain while providing out-of-band attenuation higher than 36 dB and a programmable passband up to 30 MHz. A double sampling technique is adopted, which allows high operating frequency to be achieved while saving power. Moreover, low-voltage biasing and common-mode feedback circuits are exploited to guarantee an almost rail-to-rail output voltage swing. The proposed filter provides an output 1-dB compression point as high as 8.7 dBm with a power consumption of 9 mW. To the authors’ knowledge, this is the first SC-based implementation of a low pass filter for automotive radar applications.

This paper presents an extensive comparison of two 28-nm CMOS technologies, i.e., standard and mm-wave-optimized (i.e., thick metals and intermetal oxides) back-end-of-line (BEOL). The proposed comparison is carried out at both component and circuit level by means of a quantitative analysis of the actual performance improvements due to the adoption of a mm-wave-optimized BEOL. To this end, stand-alone transformer performance is first evaluated and then a complete mm-wave macroblock is investigated. A 77-GHz down-converter for frequency modulated continuous wave (FMCW) long-range/medium range (LR/MR) radar applications is exploited as a testbench. For the first time, it is demonstrated that thicker metals and intermetal oxides do not guarantee significant improvements at mm-wave frequencies and a standard (low-cost) BEOL is competitive in comparison with more complex (expensive) ones.