Research And Design Of ADC And Baseband Chip For 77 GHz Millimeter-Wave Automotive Radar

Automotive radar systems protect the safety of vehicles during driving.The 77GHz band millimeter-wave radar has become the core of current vehicle radar research because of its smaller chip size,higher detection accuracy,and higher resolution and bandwidth.Based on 55 nm CMOS process,this paper studies and designs a high-precision successive approximation analog-to-digital converter（SAR ADC）and high dynamic range analog baseband circuit（ABB）in the 77 GHz band millimeter-wave automotive radar system.The main research results include:（Ⅰ）According to the principles of millimeter-wave automotive radar ranging and speed detection,considering the space loss of millimeter-wave in the atmosphere and combining the link budget of the 77 GHz millimeter-wave automotive radar system,the performance indicators of SAR ADC and ABB circuits in this paper was obtained.（Ⅱ）An 8-bit 60 MS/s medium-precision SAR ADC was designed.A dual-loop structure including an asynchronous clock loop and a data loop was exploited in the proposed SAR ADC.A complementary CMOS sample-and-hold switch based on gate voltage bootstrap structure has an ENOB exceeds 13-bit and an SFDR exceeds 81 d B in all process corner at 27℃.A dynamic comparator with reset switches is proposed,which can make the voltage deviation of the symmetrical node close to 0 within the reset time of 35 ps,effectively improves the comparison accuracy of the comparator.Combined with reverse monotonic switching sequence can avoid erroneous comparison results in the low-bit quantization process.The chip is based on 55 nm CMOS process,and the measurement results show that the ADC achieves an FOMS of 145.5 d B,an SNDR of 44.56 d B and an SFDR of 53.21 d B under 30 MHz input signal,while consuming 2.4 m A current from 1.2 V power supply.The measured DNL and INL are-0.1/+0.28 LSB and-0.27/+0.52 LSB,respectively.（Ⅲ）According to the measurement results of 8-bit SAR ADC and the demand of high ADC conversion accuracy for 77 GHz millimeter-wave radar,a 12-bit 30 MS/s high-precision SAR ADC was designed.A comparator offset calibration technique was proposed to calibrate the comparator offset voltage by adjusting the comparator input to the tube voltage.After calibration,the comparator input offset voltage range is reduced from±27 m V to±1 m V.The V_CM-based switching sequence approach was adopted to ensure the constant input common-mode voltage of the comparator,so that the input offset voltage of the comparator only appears as an offset error.The split-recombination redundancy algorithm was used to correct the wrong voltage switching,avoiding the use of a large number of on-chip decoupling capacitors to stabilize the reference voltage source.The core layout area of the chip is 876μm×327μm.The post-simulation results show that the ADC achieves an FOM of 19.6 f J/c-s,an ENOB of11.58-bit,and an SFDR is 89.4 d B under the 27℃TT process corner and 10 MHz input frequency,while ADC core consumes 1.5 m A current from 1.2 V power supply.（Ⅳ）A high dynamic range analog baseband circuit（ABB）was designed.The main modules are:the pre-amplifier which as the first stage of the system provides a constant gain to optimize the noise performance of ABB system.The eighth-order Butterworth filter based on Tow＿Thomas structure achieves-35 d B out-of-band roll-off,with a constant bandwidth of 400 k Hz～10 MHz.The three-stage variable gain amplifier（VGA）and the three-stage constant gain amplifier（CGA）provide a gain range of 23.6d B to 85.6 d B for the millimeter wave automotive radar system,which is adjusted by a5-bit switch resistor array,and the gain step is 2 d B/step.Each stage is also equipped with a DC offset cancellation circuit to eliminate the DC offset voltage generated by the process error in the circuit under high gain.The core layout area of the chip is 1611μm×297μm,and the optimal noise figure is 28.4 d B.（Ⅴ）The total performance of the analog baseband circuit and high-precision ADC can meet the detection range of 77 GHz millimeter-wave automotive radar from 10 to150 m and the minimum receiver sensitivity of-111.65 d Bm at 40℃ TT process corner.