Avitabile, G.

Cidronali, Alessandro

English

Florence Research

show the best performance with a DC-current gain of 5.3 and anJ; of -18GHz at 18K. The analysis of the DC and high-frequency data of the THETA structure at cryogenic temperatures indicate a lower output conductance, lower leakage current, higher current gain, and lower base-emitter capacitance. 0 IEE 1997 Electronics Letters Online No: 19970472 M.R. Murti and J. Laskar (Microelectronics Research Center and School of Electrical and Computer Engineering, Georgia Instiute of Technology, Atlanta, GA 30332, USA) T.S. Moise and Y.C. Kao (Corporate Research andmDevelopmen1, Texas Instruments, Dallas, T X  75265, USA) 17 March 1997 References 1 HEIBLUM, M., and FISCHETTI, M.V.: ‘Ballistic hot-electron transistors’, IBM J. Res Develop., 1990, 34, pp. 530-549 2 HAYES, J.R., LEVI. A.F.J., and WIEGMANN, w.: ‘Hot-electron spectroscopy of GaAs’, Phys. Rev. Lett., 1985, 54, pp. 1570-1572 3 HEIBLUM, M., ANDERSON, I.M., and KNOEDLER, c.M.: ‘DC performance of tunnelling hot-electron transfer amplifiers’, Appl. Phys. Lett., 1986, 49, pp. 207-209 4 LEVI, A.F J., and CHIU, T.H : ‘Room-temperature operation of hot- electron transistors’, Appl. Phys. Lett., 1987, 51, pp. 984986 5 MOSIE, T.s., KAO, Y.c., and SEABAUGH, A.c.: ‘Room-temperature operation of a tunnelling hot-electron transfer amplifier’, Appl. Phys. Lett., 1994, 64, pp. 1138-1140 6 MORI, T., ADACHIHARA, T., TAKATSU, M., OHNISHI, H., IMAMURA, K., MUTO, s., and YOKOYAMA, N.: ‘121 GHz resonant-tunnelling hot electron transistors having new collector barrier structure’, Electron Lett., 1991, 27, pp. 1523-1524 EAST, J R., and MAINS, R.K.: ‘InGaAdInP hot electron transistors grown by chemical beam epitaxy’, Appl. Phys. Lett., 1992, 61, pp. 8 SEO, K., HEIBLUM, M., KNOEDLER, C .M,  OH, J. ,  PAMULAPATI, J., and RHATTACHARYA, P.: ‘High-gain pseudomorphic InGaAs base ballistic hot electron device’, IEEE Electron Device Lett., 1989, 10, 9 KLIMECK, G., LAKE, R., BOWEN, R.c., FRENSLEY, w.R., and MOISE, T.s.: ‘Quantum device simulation with a generalised tunnelling formula’, Appl. Phys. Lett., 1995, 67, (17), pp. 2539-2541 10 HEIBLUM, M., NATHAN, M.I., THOMAS, D.c., and KNOEDLER, c.M.: ‘Direct observation of ballistic transport in GaAs’, Phys. Rev. Lett., 1985, 55, pp. 2200-2203 11 HEIBLUM, M ,  NATHAN, M.I., THOMAS, D.c., and KNOEDLER, c.M.: ‘High-gain pseudomorphic InGaAs base ballistic hot-electron device’, IEEE Electron Device Lett., 1989, 10, pp. 73-75 12 HAMAI, M.: ‘On effective parameter extraction of techniques for microwave heterostructure field effect devices from room to cryogenic temperatures’. M.S. Thesis, University of Hawaii, Honolulu, 1994 7 CHEN, W.L., SUN, J.P., HADDAD, GI . ,  SHERWIN, M E., MUNNS, G.O., 189-1 9 1 pp. 73-75 GaAs MMIC switch for high speed applications G.F. Avitabile and A. Cidronali Indexing terms: MMIC, Gallium arsenide, Switches An MMIC switch for fast sampling applications is described. The proposed structure, along with the design procedure are discussed. MESFET based prototype measurements are reported. Introduction: Fast sampling circuits are widely used in sampling oscilloscopes, digtal receivers [l], and so on. Common require- ments for these applications are low insertion loss, fast recovery time and high isolation. These requirements are normally met with a design based on a diode bridge sampling gate, which is always arranged in a balanced configuration. In fact, a fully differential command of the sampling gate minimises the feedthrough, reduc- ing the jitter aperture, the commutation pedestal and the settling time all at the same time. A number of different passive and active configurations which provide an adequate driving signal may be found [2, 31. The use of passive baluns suffers several limitations, mostly due to their intrinsic passband response (i.e. the output has non-DC content) and due to the troublesome integration of such structures. Con- versely, active structures usually rely on digital circuits for bal- anced pulse generation. As a consequence, problems can be expected where a sample-to-hold ratio different from unity is required. In this Letter, a fast sampling MMIC switch is described which is based on an original active transformer that accepts as sampling trigger an unbalanced pulse with arbitrary duty cycle. Fig. 1 Schematic diagram of’ MMIC switch Basic operations: A schematic diagram of the switch is shown in Fig. 1. The upper block is a standard MES-diode sampling gate, D,,z,j,4, that ensures, as stated before, good isolation and fast switching characteristics if driven by an accurately balanced pulse. Because the switch is mainly conceived for digital receiver appli- cations, an ON-to-OFF ratio of much less than unity must be assumed, thus requiring the use of pulse sources which have a typ- ically unbalanced output. As a consequence, proper switch opera- tions require a pulse transformer to drive the bridge. This transformer must cover a multiple octave bandwidth with a low- pass transfer function, in order to preserve the DC content of the pulse signal, which, in turn, ensures correct balance of the diode bridge. +a---- RF signal c e e CI (44112/ b *A L I A L Fig. 2 Equivalent circuit of switch a During ON state b During OFF state A schematic diagram of the balanced pulse transformer is sketched in the lower block of Fig. 1. The four MESFETs are arranged in a classical Wien bridge configuration. The bridge is anti-symmetrical with respect to the vertical diagonal; the two ele- ments driven by the driving pulse unbalance the bridge and gener- ate i i  differential voltage which appears across the opposite diagonal of the bridge. The active pulse transformer requires two active loads each implemented by a single MESFET with the gate shorted to the source or by two MESFETs in single-cascode self bootstrapped configuration [4]. Typical diode bridges are efficiently driven with a few milliam- pere current, ID, and without offset pedestal. In the sample mode (Fig. 2a), the diode bridge can be modelled using four resistors, RON, whose value is determined by the I,/2 current supplied by the generator. Let us consider. in the ON mode, that the pulse transformer active loads are represented by ideal current generators, IAL. The two driver MESFETs are biased in their pinch-off regions. In such conditions, I, equals IAL. As a consequence, the equivalent imped- ance seen by the bridge diodes is several orders of magnitude ELECTRONICS LETTERS 10th April 1997 Vol. 33 No. 8 713 Authorized licensed use limited to: Universita degli Studi di Firenze. Downloaded on May 21,2010 at 09:13:16 UTC from IEEE Xplore.  Restrictions apply. higher than their dynamic impedance. No feedthrough from the radio frequency source to the transformer is theoretically expected, thus minimising the insertion loss. IAL defines the active load MESFET size. Assuming that ID is the value needed to drive in the sample mode, the diode bridge and IDS, is the drain to source saturation current, then NALWALIDSS = ID (1) where N,, = number of fingers and W,, = gatewidth. During the OFF mode (Fig. 2b), the active loads work in their saturation region and the current flows through the two driver MESFETs, now biased in their linear region. The potential of B is forced to zero with respect to A. The diodes are off and replaced by their junction equivalent capacitances, CoFP The driver MES- FETs are designed to work in their linear region and could be rep- resented by an equivalent impedance, Z, which is negligible with respect to the impedance of the diode bridge, due to CoFp Following the above technique, the residual feedthrough is shunted to ground via the small drive impedance increasing the RF port to IF port isolation. The size of the driver MESFETs must satisfy the following relation: NDRIVEWDRIVEIDSS > ID  (’4 Design and experiments: Some prototypes of the switch have been designed and tested using the GEC-Marconi F20 process. Active loads have been implemented by using a single MESFET with the source shorted to the gate. Transistor sizes were determined using eqns. 1 and 2. Assuming a l0mA total bridge current and I,,, = 1 5 0 d m m ,  the active load size is defined by: N A L  = 2 and W A L  = 3 3 p ,  while for the two driver MESFETs the parameters are: NDRIVE = 2 and W,,,, = 5 0 p .  The diode bridge has been imple- mented by fow MES-diodes with a 2 x 20pn size (the equivalent circuit values are: RON = 10C2 and CO, = 4OfF). The performance of the proposed circuit has been tested using a chip-and-wire tech- nology to connect the MMIC prototype to a 254pn RTDuroid m U m 3 m 0 C -2 c c La, -601 1-10 0 045 20 frequency, GHz Fig. 3 Comparison between measures and data in [5] (I) insertion loss in ON state (ii) isolation in OFF state measured data in [5] - - _ _  110.74 114.24 11 7.74 ns 14411( Fig. 4 MMIC pulse transformer output waveforms 200mV/div vertical scale, 700psidiv. horizontal scale Ch.2: 200mV/div., Ch. 3: 200mV/div. Timebase: 700ps/div., delta V = 565mV, Vmarker 1 = 40mV Offset = OV, delay = 110.74ns, Vmarker 2 = 605mV Trigger on external pos. edge at 714mV 6502 plastic substrate test fiiture. In Fig. 3a, the insertion loss in the ON mode is compared with the theoretical results reported in [5] for a conventional FET switch. Fig. 3b reports the same com- parison for isolation during the OFF state. The experiments show an isolation better than -25dB, up to 20GHz. This result repre- sents a significant improvement in the isolation characteristics in comparison to single stage (i.e. nonmultiple cascaded switch cells) conventional designs. To test the active pulse transformer, an input unbalanced pulse was used, with 4ns period, 7% duty cycle and a loops rise-time (-50 to -950mv) and 9 x 103mV/ns slew rate. The characterisation was obtained using the HP54121T ( 1 7 . 5 ~  rise time) sampling oscilloscope, and a couple of active high-impedance probes sensing the two diode bridge control points, A and B in Fig. 2b. Fig. 4 shows the balanced waveform; the rise time is 50ps and the voltage swing is consistent with the diode threshold. The output waveform has a very low offset bias (<50mV) determined by the presence of two further diodes, con- nected to the negative bias supply. These diodes prevent the circuit to be damaged by the typical overshot generated by the SRD pulse sources. Conclusion: The MMIC proposed exhibits an enhanced isolation up to 20GHz during the OFF state, preserving those characteris- tics which are consistent with conventional FET designs during ON state. This improved performance is obtained while maintain- ing a reduced chip area (0.778 x 0.778” for the prototype reported). 0 IEE 1997 Electronics Letters Online No: I9970474 G.F. Avitabile and A. Cidronali (Electronic Engineering Department, University of Florence, V.S. Marta, 3 50139 Florence, Italy) 26 February 1997 References 1 AVITABILE, G , CIDRONALI, A., and MANES, G.: ‘A S-band digital down converter for radar applications’, to be published in ZEE Proc. G, 1991 POLMAN, M.D., GEISSBERG, A.E , and SADLER, RA.: ‘GaAs IC’s fabricated with the high performance high-yield multifunction self- aligned gate process for radar and EW applications’, IEEE Trans., 3 WHITELEY, w.c., KUNZ, w.E., and ANKLAM, w.J.: ‘A 5OGHz sampler hybrid utilizing a small shockline and an internal SRD’. IEEE 4 TOUMAZOU, c., and HAIGH, D.G.: ‘Design of GaAs operational amplifiers for analogue sampled data applications’, IEEE Trans., 5 IMAI, N., MINAKAWA, A., and OKAZAKI, H.: ‘Novel high-isolation 2 BAHL, J.L., WILLEMS, D.A., NABER, J.F,  SINGH, H.P., GRIFFIN, E.L., 1993, MTT-38, pp. 1232-1239 MTT-Swp., 1991, pp. 895-898 1990, CAS-37, pp. 992-935 FET switches’, IEEE Trans., 1996, MTT-38, pp. 1232-1239 High frequency GalnP/GaAs heterostructure-emitter bipolar transistor with low offset voltage Hai-Jiang Ou ,  Chung-Chi  Hsu ,  Yue-Fei Y a n g  a n d  E.S. Y a n g  Indexing terms: Bipolar transistors, Heterojunction bipolar transistors A carbon doped GaInPiGaAs heterostmcture-emitter bipolar transistor (HEBT) grown by MOCVD is reported with high RF performance. A cutoff frequency of 50GHz and maximum oscillation frequency of 90GHz were obtained for the device. An offset voltage as low as 90mV was achieved. It is shown that the GaInP/GaAs HEBT wth a high frequency and a low offset voltage is a good candidate for low battery power device applications. Introduction: Heterojunction bipolar transistors (HBTs) are attrac- tive for microwave and power applications because of their high 714 ELECTRONICS LETTERS 10th April 1997 Vol. 33 No. 8 Authorized licensed use limited to: Universita degli Studi di Firenze. Downloaded on May 21,2010 at 09:13:16 UTC from IEEE Xplore.  Restrictions apply. 

GaAs MMIC switch for high speed applications

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GaAs MMIC switch for high speed applications

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