| The development of autonomous driving technology is inseparable from the advancement of environmental sensing technology.Millimeter-wave radar,as the most widely used automotive sensor system,has become a research focus recently.For short range detection in blind spot detection and APS,a large number of arrangements are required on the front and rear sides of the car,so the power and cost are the primary issues,so the 24 GHz radar which has a wide detection range is often used.For long range detection in front of a car in ACC,the detection range and resolution are the most critical factors,so the 77 GHz radar which has a wide bandwidth is often used.Therefore,a short range 24 GHz dual-mode radar transceiver chip for low power,and a long range 77 GHz eight-channel phased array radar transceiver chip for long detection range.The transmitting front-end in millimeter-wave radar is one of the most important modules in the system.This article focuses on the design of millimeter-wave power amplifiers in the 20-30 GHz and70-80 GHz frequency bands,and study the related key technologies of the transmitting front end deeply.Based on 55 nm CMOS process,a 24 GHz dual-mode short range millimeter-wave automotive radar transmitting front-end and a 77 GHz phased array long range millimeter-wave automotive radar transmitting front-end are designed respectively.The system structure of the 24 GHz dual-mode short range millimeter-wave radar transceiver chip is designed.The system can realize two modes:FMCW and Doppler.Speed and distance can be measured in FMCW mode,while the principle of Doppler mode speed measurement is simpler and it is able to achieve lower power consumption in Doppler mode.The system link budget and the performance requirements of the transmitting front-end are completed.A power amplifier is designed based on the 55 nm CMOS process and is applied to the 24 GHz dual-mode short-range millimeter-wave automotive radar transmitting front-end.The power amplifier adopts a cascode structure and the proposed common gate shorting techinique is used to improve the stability and gain.The dual-mode output network is realized by a controllable tertiary coil,which solves the matching problem of the Doppler mode and FMCW mode.In the TT corner,under the condition of 40℃,the FMCW mode can achieve output power greater than 7.5 d Bm,and the power consumption is 24 m W.And in the Doppler mode,0 d Bm output power is achieved,and the power consumption is only 9.5 m W.The overall design of the 24 GHz dual-mode short range millimeter-wave automotive radar transmitting front-end is completed,and realized based on 55 nm CMOS process in March,2021.The measurement preparations are now in progress.The post simulation results with the VCO show that the output power of about 0 d Bm can be achieved in the Doppler mode,and the DC power consumption is less than 11 m W in the Doppler mode under various scenarios.In FMCW mode,it can achieve output power greater than 6 d Bm,and DC power consumption is less than 32 m W.The system structure of the 77 GHz phased array long range millimeter-wave radar transceiver chip is designed.In order to meet the long detection range requirements and achieve a wider angle range detection,the system adopts an8-transmit and 8-receive phased array structure.Based on the 55 nm CMOS process,a pre-amplifier and a power amplifier are designed for the transmitting front-end of the77 GHz phased array long range millimeter-wave automotive radar respectively.A two-stage cascode structure with neutralization capacitances,common gate shorting and other technologies is used in the pre-amplifier.The post simulation indicates that the power gain of the pre-amplifier is greater than 14 d B in the 76-81 GHz range,the power gain reaches 18.5 d B at 78 GHz,the Psat is 15 d Bm,and the maximum PAE is12.5%.The power amplifier adopts a four-stage cascode structure with a multi-stage cascade resonance control technology.The power amplifiers achieve a power gain of34.5 d B at 78 GHz,a Psat of about 15 d Bm,and a PAE of 8.2%.The measurement results of two E-band power amplifiers（PA1 and PA2）have proved the proposed multi-stage cascade resonance control technology.The measurement results indicate that the high-gain PA1 uses resonance control technology to achieve a maximum power gain of 30 d B,a Psat of 13.2 d Bm,and the maximum PAE is 11%.The wide bandwidth PA2 with resonance control technology achieves a 19 GHz bandwidth,a Psat of 12.2 d Bm,with a maximum PAE of 9.7%.For other modules in 77 GHz transmitting front-end,a 4-bit digital phase shifter operating at 78 GHz is realized using three phase shift unit types:high-low-pass STPS,bridged low-pass T-type STPS,and bridged low-passπ-type STPS.In order to reduce the influence of the process corner on the phase error,a controllable length transmission line structure is utilized to realize phase shift units with corner phase error control.The post simulation results show that the insertion loss of the phase shifter is about-17 d B at the TT corner,the input and output reflection coefficients are less than-10 d B,and the root mean square phase errors are all no more than 5°.The Wilkinson power divider is designed,and a three-stage one-to-two Wilkinson power divider is cascaded to form a one-to-eight Wilkinson power divider.The reflection coefficient of each port is less than-10 d B,the isolation between the output ports is greater than 20 d B,and the insertion loss from the input port to the output port is less than-14 d B.The overall design of the 77 GHz phased array long range millimeter-wave automotive radar transmitting front-end based on 55 nm CMOS process is completed.The post simulation results show that the output power of the eight elements transmitting front-end is at 78 GHz and the output power is greater than 10 d Bm at all process corners.Within a scan angle of±40°,the side lobe level（SLL）is less than-10d B.And the ratio of the peak to null lobe is also less than-13 d B.The post simulation results with the VCO and the tripler show that,an output power greater than 10 d Bm can be achieved at the frequency range in various scenarios. |
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