A SiGe BiCMOS double-balanced mixer with active balun for X-band Doppler radar

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1 Downloaded from orbit.dtu.dk on: Jul 27, 2018 A SiGe BiCMOS double-balanced mixer with active balun for X-band Doppler radar Michaelen, Ramu Schandorph; Johanen, Tom Keinicke; Tamborg, Kjeld M. ; Zhurbenko, Vitaliy Publihed in: Proceeding SBMO/IEEE MTT-S International Microwave and Optoelectronic Conference (IMOC) Link to article, DOI: /IMOC Publication date: 2015 Document Verion Peer reviewed verion Link back to DTU Orbit Citation (APA): Michaelen, R. S., Johanen, T. K., Tamborg, K. M., & Zhurbenko, V. (2015). A SiGe BiCMOS double-balanced mixer with active balun for X-band Doppler radar. In Proceeding SBMO/IEEE MTT-S International Microwave and Optoelectronic Conference (IMOC) IEEE. DOI: /IMOC General right Copyright and moral right for the publication made acceible in the public portal are retained by the author and/or other copyright owner and it i a condition of acceing publication that uer recognie and abide by the legal requirement aociated with thee right. Uer may download and print one copy of any publication from the public portal for the purpoe of private tudy or reearch. You may not further ditribute the material or ue it for any profit-making activity or commercial gain You may freely ditribute the URL identifying the publication in the public portal If you believe that thi document breache copyright pleae contact u providing detail, and we will remove acce to the work immediately and invetigate your claim.

2 A SiGe BiCMOS Double-Balanced Mixer with Active Balun for X-Band Doppler Radar Ramu S. Michaelen (1,2), Tom K. Johanen (1), Kjeld M. Tamborg (2), and Vitaliy Zhurbenko (1) (1) Technical Univerity of Denmark, Department of Electrical Engineering 2800 Kg. Lyngby, Denmark (2) Weibel Scientific A/S, 3450 Allerød, Denmark Abtract In thi paper, we preent an X-band doublebalanced mixer in SiGe BiCMOS technology. The mixer core conit of a LO Matched quad diode ring uing diode-connected Heterojunction Bipolar Tranitor (HBT). The mixer i integrated with a low-noie, high-linearity active balun on the RF port and a miniaturized Marchand balun on the LO port. Experimental reult how a converion gain of +4 db at 10.5 GHz with an LO drive level of 15 dbm. The LO-IF and RF-IF iolation i better than 36 db and 26 db, repectively, in the entire band of operation. The input referred 1 db compreion point i better than -11 dbm. The IIP2 i +13 dbm at a upply voltage of 3 V and dbm at a upply voltage of 6 V. The meaured noie figure i found to be ~6.5 db at 10.5 GHz. Keyword Active balun, Marchand balun; mixer; MMIC; diode connected HBT; I. INTRODUCTION High preciion Doppler radar can be ued for a high number of application ranging from vital ign detection, tracking of aircraft, UAV, atellite, and pace-huttle to velocity tracking radar for artillery. The requirement to the dynamic range in the Doppler radar receiver continue to evolve a new application emerge. The trend toward multiple receiver for phaed array Doppler radar mean that a monolithically integrated receiver with high dynamic range mut be developed. One of the mot critical component in the Doppler radar receiver i the mixer. A the Doppler hift fall in the range from a few Hz to approximately 1 KHz, direct converion mixer mut be employed. It i well-known that direct converion mixer uffer from DC offet problem and high 1/f-noie [1]. Thi ha led to reearch into paive doublebalanced mixer uing either CMOS reitive mixer [2] or diode-ring mixer [3]. In a SiGe BiCMOS technology, the 1/fnoie propertie are believed to be bet for the bipolar tranitor compared to the MOSFET. Thi i becaue the MOSFET uffer from trap in the oxide, which lead to an increae in 1/f-noie. The bipolar tranitor on the other hand are bulk conduction device and have an order of magnitude lower 1/f-noie compared to the urface channel conduction of CMOS device [4]. Recently, the author compared the 1/fnoie performance of paive double-balanced mixer uing diode-connected HBT and Schottky diode implemented in a SiGe BiCMOS technology. It wa found that the diodeconnected HBT lead to much lower 1/f-noie corner frequency than the Schottky diode. Therefore, the diode-connected HBT in a ring tructure i believed to be the mot uitable mixer configuration for Doppler radar receiver. The ue of paive balun on the port of the mixer, however, introduce ignificant loe which alo increae the noie figure. Modifying the double-balanced mixer to include an active balun on the RF port hould lead to radar receiver with lower noie figure. It i well known, however, that active balun may lead to poor linearity. Therefore, technique to improve the linearity of the active balun hould be employed in their deign. In thi paper, the deign of an X-band double balanced mixer with active balun on it RF port and paive balun on the LO port i reported. The mixer i fabricated in a 0.25 µm SiGe:C BiCMOS proce from Innovation for High Performance Microelectronic (IHP) in Germany. The technology feature high-performance npn-tranitor with a f T of 110 GHz and f max of 180 GHz. The technology ha metalinulator-metal (MIM) capacitor and five metal layer for paive and low-lo interconnect [5]. II. CIRCUIT DESIGN The block-diagram of the double-balanced mixer i hown in Fig. 1. The mixer ha the active balun placed at the RF port. A paive miniaturized Marchand balun i preferred at the LO port due to conideration about potential 1/f-noie upconverion and bandwidth at the LO port. The IF extraction network of the mixer, hown in Fig. 1, provide the neceary return current path from the diode ring mixer core and hield the RF from the IF port. Fig. 1. Block diagram of double-balanced mixer. A. Active Balun Fig. 2 how the chematic of the active balun. The deign ue a differential cacode amplifier for high gain and good iolation. The input of one port of the differential cacode amplifier i matched uing a hunt capacitor, C in, and erie inductor, L in. The erie capacitor, C De, i included at the input port mainly for coupling of the AC ignal. The ame type of /15/$ IEEE

3 δ = R Z Z R 2 frf 2 fc where R i the erie reitance, Z i the real diode junction input reitance (depend on pump power), and f c =1/(2πR C j ) i the cut-off frequency of the diode. From the high doping in the emitter, the diode capacitance, C j, i expected to be high but imulation how that the ratio of the deign frequency to cutoff frequency f rf /f c remain low even at X-band frequencie. Thi obervation applie at leat for the mall-area SiGe HBT conidered here and indicate that the mixer core operate mainly in a reitive mode. Inductor, L match, are added to the diode ring tructure to provide matching to the miniaturized Marchand balun at the LO port. Fig. 2. Schematic of active balun. capacitor hort the AC ignal at the unued input port to ground. Thi cheme allow eay biaing of the tranitor through high valued reitor, R Bia. The inherent high common-mode rejection ratio of the differential cacode amplifier convert the ingle-ended ignal at the input into a differential ignal at the output. The output i matched uing an RF inductor, L VCC, and erie coupling capacitor, C De. The RF inductor alo erve for biaing while the erie capacitor i needed for decoupling the output of the active balun from the return current flowing from the mixer core. For increaed tability, a erie network coniting of R and C i placed at the output. The noie and linearity of the active balun i optimized by adjuting the ize of the HBT and increaing the bia current and voltage upply. The bia current of the differential cacode amplifier i et through the reitor R DC. Thi choice i better than an active current ource for highfrequency integrated circuit becaue of the lower paraitic capacitance [6]. The value of thi reitor i choen a a tradeoff between noie, common-mode rejection ratio, and required bia upply of the active balun. The nominal upply voltage, V cc, i et to 6 V. The layout i EM imulated and coupled together with S-parameter and Harmonic-balance imulation to give a realitic impreion of the circuit before manufacturing. According to thee imulation the active balun ha a gain of 16.3 db and noie figure of 4.8 db at the center frequency of 10.5 GHz. The imulated amplitude and phae mimatch i below 1.5 db and 3 degree, repectively, over the band from 10 to 11 GHz. The input referred 1 db compreion point i -6 dbm. B. Mixer Core The mixer core conit of a quad ring of diode-connected HBT a hown in Fig. 3. The bae-emitter junction i the preferred diode junction for mixer application due to the heavier doping of the n-region of the emitter compared to the collector. The ue of diode-connected HBT with bae and collector tied together alo prevent ubtrate injection [7, pp. 477]. The heavy doping i neceary to reduce the o-called converion-lo degradation factor [8]: Fig. 3. Quad ring mixer uing diode connected HBT. C. Marchand Balun A mentioned above, a miniaturized Marchand balun i ued at the LO port of the double-balanced mixer. The lumped-element repreentation of the Marchand balun i hown in Fig. 4. In thi repreentation the input port i called P 1 and the two complementary output port are called P 2 and P 3. The lumped element repreentation ue offet broadide coupled piral inductor, L, together with external capacitor, C and C m, to realize the quarter-wave coupled line needed in the ditributed Marchand balun. The inductive and capacitive coupling between the piral i repreented by k and C c, repectively. Fig. 4. Schematic of lumped element Marchand balun. For equivalence with the ditributed Marchand balun at the deign frequency, ω LO, the following deign formula are applied [9]:

4 L Z + Z oe oo = (1a) 2ωLO calibrated out. The microphotograph of the fabricated mixer i hown in Fig. 6. The ize i µm 2. k Z Z 2ω L oe oo = (1b) LO LO 1 C = (1c) ω Z oe 1 Cc = 0.5C (1d) 2 ω Z C m LO oo Cc kcc = 2 (1e) k where Z oe and Z oo are the even and odd mode characteritic impedance of the coupled line in the ditributed Marchand balun. In practice it proof difficult to imultaneouly fulfil equation (1a) to (1e). For a given inductive and capacitive coupling of k and C c, repectively, detailed analyi how that equation (1e) give the ufficient condition for ideal balance in the Marchand balun. The mot critical part for proper balun performance i thu to elect C m to fulfil equation (1e). The minituarized Marchand balun i optimized uing EM imulation. The imulated inertion lo at 10.5 GHz i around 5.1 db while the amplitude and phae mimatch i 0.18 db and 0.7 degree, repectively. Simulation of the inductance, L, and the quality-factor, Q, of the piral inductor i hown in Fig. 5. The rather high lo i caued by the low quality-factor of the broadide coupled piral inductor. I. CONCLUSIONS After the text edit ha been completed, the paper i ready Fig. 6. Microphotograph of the double-balanced mixer, ize i µm 2. The converion gain a a function of LO drive level for upply voltage of 3V and 6V are hown in Fig. 7(a) and Fig. 7(b), repectively. The meaurement are performed on everal ample with good uniformity. The LO frequency i et to 10.4 GHz and the RF frequency i et to 10.5 GHz. The current conumption for the two upply voltage are 17 ma and 38 ma, repectively. a) Fig. 5. Simulated inductance and quality-factor of piral inductor. III. EXPERIMENTAL RESULTS In thi ection, the experimental reult of the doublebalanced mixer are dicued. The meaurement are made onwafer uing a probe tation. Loe in cable and probe are b) Fig. 7. Converion gain verion LO power at (a) V cc=6.0 V The converion gain at a upply voltage of V cc =6.0 V, hown in Fig. 7(a), aturate at a level around ~-1 db for an LO drive level above ~10 dbm. Thi i ignificant lower than

5 predicted by the imulation. Reducing the bia voltage to V cc =3.0 V, increae the converion gain, a hown in Fig. 7(b). The aturated level i around ~4.6 db, well in line with the imulation. The exact reaon for the oberved behavior i a yet unknown. A poible caue may be that the collectoremitter voltage acro the HBT in the active balun with a upply voltage of V cc =6.0 V are o high (cloe to breakdown) that the tranitor model become inaccurate. Fortunately, the performance of the double balanced mixer i acceptable at a upply voltage of V cc =3.0 V. Therefore, all the following meaurement have been performed at thi upply voltage. Fig. 8 how the converion gain a a function of frequency at a fixed IF of 100 MHz. The LO drive level i fixed at +15 dbm. The converion gain peak of ~4.6 db i around the deign frequency of 10.5 GHz and the -3 db bandwidth i ~2.5 GHz. The bandwidth i mainly limited by the active balun. In general, the frequency repone of the converion gain i well predicted by the imulation. input referred econd-order intercept point (IIP 2 ) i meaured with two RF tone at frequencie of 10.5 and GHz given a econd-order product at 13 MHz. Iolator are placed after the ignal generator to avoid leakage and intermodulation of the ignal before they are applied to the mixer. Fig. 10 provide a comparion between the IIP 2 both at a upply voltage of 3V and 6V. The IIP 2 meaured at a upply voltage of 3 V i +13 dbm while it i dbm at a upply voltage of 6 V. Fig. 10. Comparion of IIP2. The ingle ideband noie figure veru RF frequency, hown in Fig. 11, i meaured under the ame condition a the converion gain in Fig. 8. It reache a minimum of ~6.5 db around the deign frequency of 10.5 GHz. Compared to the purely paive X-band double balanced ring mixer in [3] thi repreent an improvement of ~3.3 db due to the good noie performance of the active balun. Fig. 8. Converion gain veru RF frequency. Fig. 11. Single-ideband noie figure veru RF frequency. Fig. 9. LO-IF and RF-IF iolation veru RF frequency. The LO-IF and RF-IF iolation verion RF frequency i hown in Fig. 9. In the entire band of operation the LO-IF and RF-IF iolation i better than 36 db and 26 db, repectively. Thee value indicate a good balance of both the active balun and miniaturized Marchand balun. The meaured 1 db input referred compreion point of the double balanced mixer i ~-11 dbm. Thi i omewhat lower than the -6 dbm imulated for the active balun alone but till acceptable for a mixer with active balun on it RF port. The IV. CONCLUSIONS The deign of a double balanced mixer in a 0.25 µm SiGe BiCMOS technology ha been preented. The mixer i a direct converion mixer for ue in X-band Doppler radar. The double balanced mixer integrate an active balun optimized for low noie and high linearity on the RF port and a miniaturized Marchand balun on the LO port. The mixing element conit of diode connected HBT.

6 At the deign frequency of 10.5 GHz the mixer ha a converion gain of ~4.6 db and a ingle-ideband noie figure of ~6.5 db. It require a relatively high LO level of ~15 dbm for bet performance. REFERENCES [1] B. Razavi, Deign Conideration for Direct-Converion Receiver, IEEE Tran. Circuit Syt. II, vol. 44, no. 6, pp , June [2] C. Song, O. B.-Lubecke, and I. Lo, 0.18-µm CMOS Wideband Paive Mixer, Microw. Optical Tech. Letter., vol. 55, no. 1, pp , Jan [3] R. S. Michaelen, T. K. Johanen, K. M. Tamborg, and Vitaliy Zhurbenko, Deign of a broadband paive X-band double-balanced mixer in SiGe HBT technology, Int. Jour. Microw. Wirele Techn., pp , [4] J. Babcock, B. Loftin, P. Madhani, X. Chen, A. Pinto, and D. Schroder, Comparative low frequency noie analyi of bipolar and MOS tranitor uing an advanced complementary BiCMOS technology, in IEEE Conf. Cutom Integrated Circuit, pp , [5] IHP webite: [6] S. Voinigecu, High-Frequency Integrated Circuit, Cambridge Univerity Pre, [7] M. Reich, High-Frequency Bipolar Tranitor, Springer, Berlin, Germany, [8] S. A. Ma, Microwave Mixer, 2 nd edition, Artech Houe, Norwood, MA, USA, [9] T. Johanen and V. Krozer, Analyi and Deign of Lumped Element Marchand Balun, in IEEE MIKON conference proceeding, pp , 2008.