A Fully Differential Low-Power High-Linearity77-GHz SiGe Receiver Frontend for Automotive

Radar SystemsDietmar Kissinger*, Benjamin Sewiolo*, Hans-Peter Forstner", Linus Maurer", and Robert Weigel*

*Institute for Electronics Engineering, University of Erlangen-Nuremberg, Cauerstr. 9, 91058 Erlangen, GermanyEmail: kissinger@ieee.org

tInfineon Technologies, Am Campeon 1-12, 85579 Neubiberg, Germany+Danube Integrated Circuit Engineering (DICE), Freistadter Str. 400, 4040 Linz, Austria

Abstract-This paper presents a single-chip receiver frontendconsisting of a low-noise amplifier and an active downconversionmixer, intended for application in automotive radar systems at77 GHz. The circuit has been implemented in a SiGe:C HBTtechnology with ft/fmax = 200/250 GHz and can operate eitherfully differential or in single-ended mode. The receiver frontendshows a conversion gain of 24 dB and a single sideband noise fig­ure of 14 dB when driven single-ended. Linearity measurementsshow a 1 dB input referred compression point of -10 dBm. Thecircuit draws 40 rnA from a 3.3 V supply and occupies a chiparea of 728 x 1028 fJm2 including bond pads.

I. INTRODUCTION

In the past years, automotive radar is finding an increasedinterest for comfort and safety applications. It enables theintegration of a wide variety of active and passive systems forimproved vehicular safety. Long-Range Radar (LRR) applica­tions use the frequency band from 76 to 77 GHz. Additionallythe band ranging from 77 to 81 GHz has been allocated forShort-Range Automotive Radar (SRR).

Silicon-based technologies featuring SiGe HeterojunctionBipolar Transistors offer the possibility to manufacture cost­efficient radar frontends with a high level of integration. Thesetechnologies show maximum oscillation frequencies and cutofffrequencies above 200 GHz [1]-[6] and their suitability formillimeter-wave applications has been shown by a number ofpublications.

Over the recent years several architectures for SiGe-baseddownconversion mixers have been published, resembling stan­dard double-balanced Gilbert cell approaches [7], [8] as wellas micromixer topologies [9], [10]. Published receiver fron­tends feature an additional low-noise amplifying stage priorto the mixer to reduce the overall noise figure of the receiverchain [11]-[16].

Hard specifications for the automotive environment define alarge dynamic range of the received signal. Besides a low noisefigure this necessitates a high linearity of the RF frontend. Thispaper presents the design and measurement results of a high­linearity receiver frontend for application in 77 GHz FMCWradar systems.

II. CIRCUIT DESIGN

The proposed receiver consists of a cascade of a low-noiseamplifier (LNA) followed by a mixer stage for direct downcon­version of the received signal. Both the LNA and the mixingstage are designed differentially. The inputs for the RF andLa signals feature a A/ 2 transmission line connected betweenthe differential pads. This line acts as a balun and enables thecircuit to be additionally driven in single-ended mode throughthe conversion of the 100 n differential impedance to 25 n forsingle-ended measurement equipment.

Fig. 1 shows the schematic of the low-noise amplifier. Itconsists of a cascode stage which is inductively degeneratedfor simultaneous noise and power matching. The input andoutput matching networks with integrated DC decoupling arerealized through transmission lines and capacitors. DC biasfor the common-emitter and cascode stage is fed through thevirtual ground nodes along the symmetry axis.

The schematic of the mixer is shown in Fig. 2. It consists ofa double balanced switching quad with L-matching networksfor the La and RF input ports. Instead of featuring theadditional transconductance stage of a Gilbert mixer the RF

RFout

RF;bt-1 ---4-----4-------1----'

Fig. 1. Schematic of the proposed cascode low-noise amplifier

978-1-4244-4565-3/09/$25.00 ©2009 IEEE

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26,---~--~--~---~--~--___,

2o- 6 - 4 -2LO power (dBm)

-812 L-- - -'----- - ---'---- - -----'-- - -'------ - -'----- - ---'- 10

Fig. 4. Receiver gain and noise figure versus LO power

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IF

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I

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Fig. 2. Schematic of the proposed high-linearity mixer

78.578 .0770 77 .5LO frequency (GHz)

76 .512 L-- - -----'-- - - ----'--- - - ---'---- - - ---'---- - -----.J76.0

26 ,-------~---~---~---~--_____,

Fig. 5. Receiver gain and noise figure versus LO frequency

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c

~ 18

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~ 16

Fig.4 shows the vanation of noise figure and conversiongain over the local oscillators power level for a fixed RF inputlevel of -16 dBm. The mixing stage works down to a level ofodBm without significant performance degradation. At 0 dBmLa power noise figure and conversion gain are 14dB and24 dB respectively. It can be expected that the noise figure isfurther improved by approximately 2 dB when the circuit isdriven differentially.

Referring to Fig.5 the frontend shows nearly constantbehavior for the gain and noise figure across the intendedfrequency range around 77 GHz at an La power of 0 dBm.

Fig. 6 shows the measured conversion gain versus the RFinput power for a La power of 0 dBm. The input referred 1dBcompression point is -10 dBm.

S-Parameter measurement have been carried out using anAgilent PNA8361A in combination with waveguide modules .Fig.7 shows the S-Parameter Measurements for the La andRF port. The input return loss is better than -10 dB for bothports at the operation frequency of 77 GHz.

Fig. 3. Die photograph of the fabricated receiver frontend

signal path is decoupled from the current source through AI4lines. The IF output of the mixer is connected to differentialemitter followers (not shown) which transform the outputimpedance to 100n (differential).

III. EXPERIMENTAL RESULTS

Fig. 3 shows a die photograph of the receiver frontend withdifferent indicated stages of the circuit. The overall pad limitedchip area is 728 x 1028 urn2 .

The characterization of the receiver frontend has been doneby single-ended on-wafer measurements with a measurementsetup described in [17]. Noise parameters have been measuredat an intermediate frequency of 4.8 MHz.

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TABLE ICOMPARISO N OF SIGE-BAS ED STANDALO NE MIX ERS AND RECEIV ERS IN TH E 76 -81 GH z BAN D

Ref. Architecture" Gain (dB) NF (dB) b P-1dB(in) (dBm) Vee (V) Pile (mW) C PI.O (dBm) FOMI FOM2

[7] Mixer 24 14 -30 5.0 300 2 154 127

[8] Mixer 11 16.5 -0.3 5.5 412 -3 168 145

[9] Mixer 13.4 18.4 -12 4.5 176 4 157 131

[10] Mixer 15.5 16 -3 5.5 187 -2 171 150

[11] LNA + Mixer 28 II -16 5.5 1072 I 175 144

[12] LNA + Mixer + YCO 37 8 -28.5 2.5,3 .5 161 175

[13] LNA + Mixer 30 11.5 -26 5.5 440 0 167 140

[14] LNA + Mixer + YCO 21.7 10.2 (sim.) -35 5.5 (595) 151

[15] LNA + Mixer + YCO 40 6.9 -35 2.5 115 172

[16] LNA + Mixer (+ YCO) 40 7-9 -38 122 (195) -2 168 149

This work LNA + Mixer 24 14 -10 3.3 132 0 174 153

abraekets denote different published realizations with external and on-ch ip YCO respectivelybsingle-sideband (SSB) noise figure, reported double-sideband (DSB) noise figures have been increased by 3 dBCtotal power consumpt ion without YCO, power consumpt ion including YCO in brackets

(I)

(2)

174 + Gain - NF + P.'dB(in)

FOM, - Pile (dBm) - Pw

FOM,

FOM2

ACKNOWLEDGMENTS

IV. CONCLUSION

A high-linearity integrated receiver frontend in a high­performance SiGe:C technology for application in 77 GHzautomotive radar is presented. The fabricated chip can beoperated in differential or single-ended mode and on-wafermeasurements show a gain of 24 dB and a noise figure of 14dBwhen driven single-ended with an LO power of 0 dBm. Aninput related I dB compression point of -10 dBm is achievedwith a total power consumption of 132mW from a 3.3 Vsupply. The overall occupied chip area is 728 x 1028 f-lm 2

including bond pads.Table I shows a summary of published downconversion

mixers and receiver frontends in the frequency range of 76 to81 GHz in SiGe technology. In (I) the calculation of the figureof merit for the performance of FOM, is shown. An additionalfigure of merit FOM2 which also takes the power consumptionand the necessary LO drive into account is presented in (2).

In comparison to other published receiver frontends the perfor­mance related figure of merit FOM, of this work is among thehighest published so far. In addition it simultaneously achievesthe best performance to power consumption ratio which isexpressed through FOM2 •

The authors would like to thank the team from InfineonTechnologies for the fabrication of the presented chip, aswell as the radar design group from DICE for their supportand helpful discussions . This work has been supported bythe German Bundesministerium fiir Bildung und Forschung(BMBF) through the research project RoCC - Radar on Chipfor Cars under contract number 13N9821.

o- 2

Receiver gain versus RF input power

-1 2 -1 0 -8 -6 - 4RF power (dBm)

- 14

Fig. 6.

12L-- ---'--- ----' - - --'---- ---'- - -'----- ---"-- - -'----- ---.J- 16

26 r-- --,-- ---,- - --.--- ---,- - -.-- ---,-- - -,--- --,

14

- 3(J-- -'----- -'----- -'----- -'----- -'----- -'----- -'----- -'----- '---- -----.J10 20 30 40 50 60 70 80 90 100 110

Frequency (GHz)

Fig. 7. S-Parameter Measurement of La and RF input return loss

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