《Compact single-chip W-band FMCW radar modules for commercial high-resolution sensor applications.pdf》由会员分享，可在线阅读，更多相关《Compact single-chip W-band FMCW radar modules for commercial high-resolution sensor applications.pdf（7页珍藏版）》请在三一文库上搜索。
1、IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, VOL. 50, NO. 12, DECEMBER 20022995 Compact Single-Chip ?-Band FMCW Radar Modules for Commercial High-Resolution Sensor Applications Axel Tessmann, Steffen Kudszus, Member, IEEE, Tobias Feltgen, Markus Riessle, Christoph Sklarczyk, and William H.
2、Haydl AbstractTwo compact single-chip 94-GHz frequency-modu- lated continuous-wave (FMCW) radar modules have been devel- oped for high-resolution sensing under adverse conditions and en- vironments. The first module contains a monolithic microwave in- tegrated circuit (MMIC) consisting of a mechanic
3、ally and elec- trically tunable voltage-controlled oscillator (VCO) with a buffer amplifier, 10-dB coupler, medium-power and a low-noise ampli- fier, balanced rat-race high electron-mobility transistor (HEMT) diode mixer , and a driver amplifier to increase the local-oscillator signal level. The ove
4、rall chip-size of the FMCW radar MMIC is 23.5 mm?. For use with a single transmitreceive antenna, a 94-GHz microstrip hexaferrite circulator was implemented in the module. The radar sensor achieved a tuning range of 1 GHz, an output signal power of 1.5 mW, and a conversion loss of 2 dB. The second F
5、MCW radar sensor uses an MMIC consisting of a var- actor-tuned VCO with injection port, very compact transmit and receive amplifiers, and a single-ended resistive mixer. To enable single-antenna operation,theexternalcirculator wasreplaced bya combinationofaWilkinsondividerandaLangecouplerintegrated
6、on the MMIC. The circuit features coplanar technology and cas- code HEMTs for compact size and low cost. These techniques re- sultinaparticularlysmalloverallchip-sizeofonly23mm?.The packaged 94-GHz FMCW radar module achieved a tuning range of 6 GHz, an output signal power of 1 mW, and a conversion l
7、oss of 5 dB. The RF performance of the radar module was successfully verified by real-time monitoring the time flow of a gas-assisted in- jection molding process. IndexTermsCoplanarwaveguides(CPWs),flip-chip, frequency-modulated continuous-wave (FMCW) radar, GaAs, monolithic microwave integrated cir
8、cuits (MMICs), packaging, -band. I. INTRODUCTION I NADDITIONtotheforward-lookingautomotiveradar,com- pact and efficient industrial sensors are the most promising commercial applications at-band frequencies. They are suit- abletocontrolindustrialmanufacturingprocessesbycontactless real-time monitorin
9、g the fabrication flow. Further applications are surface analysis, characterization of thin films on coated windows, quality control of welded joints, and level sensing. In Manuscript received April 5, 2002; revised August 23, 2002. A.Tessmann,T.Feltgen,M.Riessle,andW.H.HaydlarewiththeFraunhofer Ins
10、titute for Applied Solid State Physics, D-79108 Freiburg, Germany (e-mail: tessmanniaf.fhg.de). S. Kudszuswaswiththe Fraunhofer InstituteforApplied SolidStatePhysics, D-79108 Freiburg, Germany. He is now with Big Bear Networks, Milpitas, CA 95035 USA. C. Sklarczyk is with the Fraunhofer Institute fo
11、r Non-Destructive Testing, D-66123 Saarbruecken, Germany. Digital Object Identifier 10.1109/TMTT.2002.805162 contrast to ultrasonic, video, infrared, and laser sensors, radar sensorsarelesssensitivetoenvironmentalconditionssotheycan be used to penetrate vapor, heat, and dust. Signal frequencies at -
12、band are very attractive due to their high spatial resolution, the resulting compact chip size, and small antenna dimensions 14. For short-distance sensing, the signal output power is small, which is advantageous in many applications to reduce heatingofboththetestobjectandthesensoritself. In this pa
13、per, we present two low-cost single-chip 94-GHz frequency-modulated continuous-wave (FMCW) radar mod- ules. The monolithically integrated coplanar radar circuits include all components required for FMCW operation. The coplanar waveguide (CPW) technology is very attractive at millimeter-wave frequenc
14、ies due to the simplified fabrication process and its potential for flip-chip packaging 5. The cascode devices used in the amplifiers offer twice the gain of conventional high electron-mobility transistors (HEMTs) in a common-source configuration, while requiring the same chip area. For manufacturin
15、g the radar chips, we used a pseudomor- phic AlGaAs/InGaAs/GaAs HEMT technology with molecular beam epitaxy (MBE) growth on semi-insulating 4-in wafers. The T-shaped 0.15- m gates were written with e-beam, and the recess was dry etched. The transistors typically achieve a transit frequencyGHz and a
16、maximum oscillation frequency GHz. With 25% indium in the channel, a current densityof 1000 mA/mm is achieved. The extrinsic max- imum transconductance is 800 mS/mm. The-band FMCW radar monolithic microwave integrated circuits (MMICs) were packaged in WR-10 waveguide modules, using CPW-to-wave- guid
17、e transitions, realized on 127- m-thick quartz substrates. In addition to the conventional face-up mounting technique, we also investigated flip-chip packaging of the radar MMICs on doped silicon (n-Si) carriers 6. The monolithically integrated multifunctional radar chips, low fabrication cost, smal
18、l module size, and low weight combined with improved assembly techniques allow for the re- alization of high-performance-band sensors highly suitable for commercial applications and industrial markets. II. 94-GHz FMCW RADARMODULE#1 WITHHYBRID HEXAFERRITECIRCULATORASSEMBLY A. Circuit Design and Packa
19、ging A block diagram of the FMCW radar module #1 is shown in Fig. 1. The sensor incorporates a transceiver MMIC, a hexafer- 00189480/02$17.00 2002 IEEE 2996IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, VOL. 50, NO. 12, DECEMBER 2002 Fig. 1.Block diagram of the 94-GHz FMCW radar module #1 con
20、sisting of a GaAs MMIC, hexaferrite circulator, and waveguide antenna. Fig. 2.Inside view of the 94-GHz FMCW radar module #1 with hybrid hexaferrite circulator assembly. rite microstrip circulator, CPW-to-microstrip transitions, and a waveguide antenna. The key component is the integrated trans- cei
21、ver MMIC, incorporating all components for FMCW radar operation: A voltage-controlled oscillator (VCO) with buffer amplifier (AMP) as the signal source, a 10-dB line coupler, and a medium power amplifier (MPA) in the transmit path. The re- ceivepathisformedbyalow-noiseamplifier(LNA),abalanced rat-ra
22、ce HEMT diode mixer (MIXER), and a driver amplifier to increase the local oscillator (LO) signal level. The oscillator is electrically tunable with the gate voltage of the VCO HEMT. Additionally mechanical adjustment of the center frequency is possible by removing air bridges in the source lines 7.
23、A cas- code buffer amplifier raises the output power and improves the isolation of the oscillator. A fraction of the transmit signal is coupled out, amplified, and used as the LO signal for the mixer. A two-stage common source MPA feeds the circulator with the transmit power. In the receive path, a
24、single balanced rat-race hybrid mixer is utilized to generate the IF from the LO signal and the received signal, which is amplified by a two-stage cas- code LNA 8. The chip size of the FMCW radar MMIC is 23.5 mm . As shown in Fig. 2, all components were mounted in a gold-plated steel package, utiliz
25、ing conductive epoxy, except for the circulator, which had to be attached with nonconduc- tive epoxy to ensure a proper functionality. The hexaferrite microstrip circulator is a product of the Dorado International Corporation, Seattle, WA, and requires no external magnetic bi- asing 9. Coplanar-to-m
26、icrostrip transitions have been realized on 127- m-thick quartz substrates using a pair of ground-via Fig. 3.Photograph of the 94-GHz FMCW radar module #1 with microstrip hexaferrite circulator. Fig. 4.Radar module #1. Measured output power and signal frequency as a function of the tuning voltage. c
27、onnections. To be compatible with standard waveguide horn antennas, a microstrip-to-waveguide transition has been devel- oped using the Agilent HFSS simulator for optimization (see Section III). The transition is based on a conventional-plane probe and placed into a WR-10 waveguide with back short.
28、The width of the quartz substrate was chosen to eliminate possible waveguide modes in the microstrip cavity. The bond-wire interconnections were as short as possible using wedge-bonded 17- m gold wires. Chip capacitors of 120 pF, surface-mounted device (SMD) ceramic capacitors of 10 nF, and bias fil
29、ters have been implemented in the module to prevent low-frequency oscillations. We used SMA connectors for the IF and FM port, resulting in a package size of only 33209.5 mm . A photograph of the 94-GHz FMCW radar module is shown in Fig. 3. B. Performance and Experimental Results The measured output
30、 power and signal frequency of the in- tegrated VCO are shown in Fig. 4 as a function of the tuning voltage. We measured a frequency modulation sensitivity of 3GHz/Vandanoscillatorphasenoiseof67dBc/Hzat1-MHz offset from the carrier. The conversion loss of the single bal- anced rat-race hybrid mixer
31、was 13 dB at 94 GHz with an LO power of 6 dBm. The cascode LNAs had a gain of 8 dB per stage. The output power of the transmit driver amplifier was TESSMANN et al.: COMPACT SINGLE-CHIP-BAND FMCW RADAR MODULES2997 Fig. 5.Radar module #1. Measured output power and conversion gain of the receive path a
32、s a function of the frequency. Fig. 6.IF signal of small metal target (diameter? ?mm) at approximately 2-m distance. 10 dBm at 1-dB gain compression. The specified microstrip cir- culator isolation was 20 dB with an insertion loss of 1.3 dB. The waveguide-to-microstrip transition had shown an insert
33、ion loss of less than 0.5 dB, measured in a special test fixture. The bond-wire interconnections result in a reflection coefficient of approximately10dBduetotheirhighcharacteristicimpedance. Wemeasuredanoutputpowerof2dBmandaconversionlossof 2 dB at 50-MHz IF, as shown in Fig. 5. Due to the limited b
34、and- width ofthecirculator, asindicatedbythe conversiongain char- acteristicsoverfrequencyofthereceivepathshowninFig.5,the radar module only allows for a modulation depth of 1 GHz. As an example of a measured radar response, the IF signal obtained from the radar reflection from a small metal coin is
35、 showninFig.6.Thegatebiasoftheoscillatorwassweptatarate of10kHzover0.25Vusingasawtoothwaveform,resultingina frequency-modulation bandwidth of 1 GHz andan IF frequency of 67-kHz/m distance between the antenna and target. III. SINGLE-CHIP94-GHz FMCW RADARMODULE#2 WITH INTEGRATEDWILKINSONDIVIDER ANDLAN
36、GECOUPLER Due to the narrow bandwidth of the circulator, the modula- tion frequency of the FMCW radar module with a hexaferrite circulator is limited. Thus, we developed a second version of the FMCW MMIC 10. Fig. 7.Chip photograph of the 94-GHz single-chip FMCW radar MMIC #2. The chip size is 2?3 mm
37、 . Fig. 8.Block diagram of the 94-GHz FMCW radar MMIC #2. A. Circuit Design and On-Wafer Measurements In the second design (#2), the directivity and isolation for separating the transmit and receive paths, allowing for single antenna operation, were achieved by the combination of a Wilkinson power d
38、ivider and a Lange coupler. This configura- tion enables broad-band modulation and replaces the external circulator used in the first module, as described in Section II. The chip photograph in Fig. 7 illustrates the circuit topology of the second MMIC, using coplanar transmission lines with a metall
39、ization thickness of 3m and a ground-to-ground spacing of 50m. The block diagram in Fig. 8 shows the configuration of the 94-GHz FMCW radar chip. A newly de- veloped varactor-tuned VCO offers both large tuning range and the possibility to reduce the phase noise by injection locking, as described in
40、11. A very compact MPA, based on space-saving dual-gate devices, was used to amplify the oscillator signal 12. The receive path consists of a two-stage cascode LNA and a single-ended resistive mixer. The entire chip size of the second FMCW radar MMIC is only 23 mm . Fig. 9 shows the on-wafer measure
41、d output power and signal frequencyoftheradarMMICasafunctionofthetuningvoltage. A tuning bandwidth of 6 GHz and an output power of approx- imately 2 dBm were measured by varying the varactor voltage from3 to1 V. 2998IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, VOL. 50, NO. 12, DECEMBER 2002
42、 Fig. 9.94-GHz radar MMIC #2. On-wafer measured output power and signal frequency as a function of the tuning voltage. Fig. 10.Flip-chip substrate for the 94-GHz FMCW radar MMIC #2. The substrate size is 3?4 mm . B. Flip-Chip Packaging on Silicon Substrates In addition to the face-up mounting techni
43、que, we also in- vestigated flip-chip packaging of the 94-GHz MMIC on doped n-Si substrates to further improve reproducibility and ease fab- rication. Fig. 10 shows a photograph of a typical carrier sub- strate. The transmission lines on the substrate were realized as finite-ground coplanar waveguid
44、es (FGCPWs), to reduce the excitation of parallel-plate modes in the flip-chip substrate 13. For good heat dissipation, the 28- m-high galvanic gold bumps were placed close to the active devices. Additional bumps were used to form the RF and dc contacts and to improve the me- chanical stability, cou
45、nteracting the different thermal expansion coefficients of GaAs and Si. In Fig. 11, the RF performance of a flip-chip-mounted radar MMIC is shown. The measured tuning bandwidth and output power correspond to the on-wafer mea- surement results. This shows the superior performance of the flip-chip mou
46、nt due to the short low inductance interconnects. C. Face-Up Mounting and Module Performance To package the coplanar 94-GHz FMCW radar MMIC in a waveguide module, a CPW-to-waveguide transition using a 127- m-thick quartz substrate was developed. The substrate includes the transition from the CPW of
47、the chip to a microstrip line. At the end of the microstrip line, a small antenna patch allows a low-loss transition to the waveguide. To convert the coplanar modeintoamicrostripmode,twovia-holeswere used, connecting the coplanar ground on the substrate surface, with the backside metallization. A ph
48、otograph of a CPW-to-wave- guide transition and the schematic of a bond-wire-connected pair of back-to-back transitions are shown in Fig. 12(a) and Fig. 11.Flip-chip packaged 94-GHz FMCW radar MMIC #2. Measured output power and signal frequency as a function of the tuning voltage. Fig. 12.(a) Photog
49、raph of a CPW-to-waveguide transition. (b) Schematic of a bond-wire-connected pair of back-to-back transitions. The wedge-bonded gold wires have a diameter of 17?m. Fig. 13.Measured and simulated insertion and return losses of a pair of back-to-back transitions from 75 to 110 GHz. (b), respectively. For the simulation and optimization of the transitions, Agilent Technologys full-wave electromagnetic (EM) High-Frequency Structure Simulator (HFSS) software was used. The-plane probe structure was optimized to achieve a broad-band match covering the entire-band. The