746 IEEE MICROWAVE AND WIRELESS COMPONENTS LETTERS, VOL. 19, NO. 11, NOVEMBER 2009 50-W LTCC Transmitter Utilizing 28-V GaAs With Integrated High-Speed Pulse Modulation Christopher T. Rodenbeck, Senior Member, IEEE, Richard T. Knudson, Member, IEEE, Charles E. Sandoval, Member, IEEE, Kenneth A. Peterson, Jeffrey M. Pankonin, Member, IEEE, Robert Eye, Senior Member, IEEE, Donald Allen, Member, IEEE, Gailon Brehm, Fellow, IEEE, Richard Binney, Frank Smith, and Jeffrey W. Dimsdle, Member, IEEE Abstract—This letter presents an S-band 50-W low-temperature cofired ceramic (LTCC) transmitter module. The module is based on a gallium arsenide (GaAs) chipset that operates over the 2–3 GHz range and includes a 28-V single-chip power amplifier with integrated high-speed drain modulator. The transmitter has rise/ fall times 7 nsec, linear frequency tuning, and excellent thermal performance. Index Terms—Monolithic microwave integrated circuits (MMIC) transmitters, multichip modules, pulse modulation. I. INTRODUCTION N EXT-GENERATION microwave transmitters will in- tegrate increasingly greater amounts of output power onto a single-chip. Technologies that enable this trend include high-voltage silicon LDMOS [1] and GaAs HEMT [2], [3] as well as GaN [4] and SiC [5]. Recognized advantages of single-chip integration are reduced size and reduced power combining losses. An additional advantage is the opportunity to integrate additional circuit functions for improvements in performance and cost. Associated challenges, however, exist at the next level of assembly; these include the need to deal with higher interconnect density and the need to mitigate ele- vated semiconductor junction temperatures [6]–[9]. This letter presents a 50-W pulsed transmitter design that addresses the benefits and challenges of high-power MMIC integration and assembly. The transmitter is based on a GaAs RFIC chipset that operates over the 2–3 GHz range and includes a 28-V single chip power amplifier fabricated in a high-voltage pHEMT MMIC process. This power amplifier (PA) incorporates a drain modulator onto the MMIC itself in order to achieve switching times less than 10 nsec. To the authors’ knowledge, this is the first report in public literature of a drain modulator and power Manuscript received May 09, 2009; revised August 15, 2009. First published October 20, 2009; current version published November 06, 2009. This work was supported by the Sandia (a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy’s National Nuclear Security Administration) under Contract DE-AC04- 94AL85000. C. T. Rodenbeck, R. T. Knudson, C. E. Sandoval, K. A. Peterson, and J. M. Pankonin are with Sandia National Laboratories, Albuquerque, NM 87123 USA (e-mail: chris.rodenbeck@ieee.org). R. Eye, D. Allen, and G. Brehm are with TriQuint Semiconductor, Dallas, TX 75080 USA. R. Binney, F. Smith, and J. W. Dimsdle are with Honeywell Federal Manu- facturing and Technologies, Kansas City, MO 64131 USA. Color versions of one or more of the figures in this letter are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/LMWC.2009.2032025 Fig. 1. Simplified block diagram of the S-band pulsed transmitter. amplifier integrated onto a single GaAs MMIC. The GaAs RFICs and power amplifier are assembled within a multilayer LTCC module with excellent thermal performance. This result and implementation are expected to advance the state-of-the-art in microwave transmitter module design. II. DESIGN A simplified block diagram of the transmitter is shown in Fig. 1. The transmitter contains two signal sources, a stable ref- erence oscillator operating at a reference frequency and a voltage-controlled oscillator (VCO) operating at a frequency tunable over S-band. The upconverted tone at is coded by a BPSK modulator and pulse mod- ulated at a rate . A 100-mW pulsed amplifier drives the final 50-W power amplifier. The PA is fabricated in a 28-V pHEMT process with an activation energy of 1.9 eV and estimated MTTF of 5 million hours at a junction temperature of 200 [2]. The electronic functions preceding the PA are im- plemented using custom RFICs designed in a high-volume en- hancement/depletion-mode pHEMT process [10]. The photograph and diagram in Fig. 2 illustrate the PA assembly and LTCC module concept. The GaAs PA die is and attaches to a 2-mm-thick 15%–85% CuW heat spreader using a 0.05-mm-thick 80%–20% AuSn solder preform. Acoustic imaging indicates solder voiding as low as 1 to 3% for this attachment. The heat spreader/PA assembly mounts to an AlSiC backplate using Diemat 6030HK-SD conductive epoxy. The AlSiC backplate is an injection-molded metal composite matrix [11] composed of 37% aluminum and 63% SiC. Both the spreader and backplate have thermal conductivity of 180–190 W/m-K and are plated with electroless NiAu. The thermal expansion coefficients of the die, spreader, and backplate are 5.7, 6.7, and 8.0 ppm/K, respectively, which matches the AlSiC backplate and LTCC while placing the PA MMIC safely in a state of slight compression. The heat spreader and PA are embedded within a larger mul- tichip module. The module is built using 13 layers of DuPont 1531-1309/$26.00 © 2009 IEEE