A Novel Tunable Broadband Power Amplifier Module Operating from 0.8 GHz to 2.0 GHz Haitao Zhang, Huai Gao, Guann-Pyng Li Electrical Engineering & Computer Science, Integrated Nanosystems Research Facility, University of California Irvine, Irvine, CA, 92697, US Abstract — In this paper, an InGaP/GaAs HBT broadband power amplifier with a novel tunable output matching circuit is first proposed and implemented. The 3-stage broadband power amplifier is realized by using the compensating matching technique and optimizing the distribution of power gain among stages. The output matching circuit is implemented with parallel L_C tank circuits using PIN diodes to control the inductor value. This broadband amplifier module offers the advantage of fewer components, less power insertion loss, small size and high linearity. The broadband power amplifier module demonstrates 28 dB power gain, 30 dBm output power and higher than 30% power added efficiency (PAE) at frequencies covering dual bands from 0.85GHz to 0.95 GHz and from 1.71GHz to 1.95GHz, which can be used in the GSM, DCS, PCS and CDMA systems. Index Terms — Heterojunction bipolar transistors, MMIC power amplifiers, power bipolar transistor amplifiers, reconfigurable architectures, semiconductor diode switches, tunable circuits and devices. I. INTRODUCTION In the past decade, InGaP HBTs have been the key technology in delivering solutions for both high efficiency and high linearity PAs in various wireless communication systems [1-2], such as GSM, DCS, PCS, CDMA and WLAN. Traditionally, these PAs are designed for narrow band operation and can not be used as a broadband solution covering multiple bands in wireless communication systems. Recently, broadband PA modules with multiple narrow band power amplifier chips and corresponding matching circuits integrated into a platform and controlled by switches for frequency bands tuning are demonstrated [3-4]. In order to reduce the number of components in PAs and matching circuits, alternative single chip solutions have been proposed. For example, while a balanced amplifier is a good candidate, its requirement of using quarter wavelength size of the couplers is usually not practical in MMIC’s. Another consideration is a distributed amplifier, which suffers from low gain, low efficiency and requires a relatively large chip size. The feedback amplifiers are also considered for broadband amplifiers. This approach yields a relatively small chip size, however the gain is low at microwave frequencies and the efficiency is compromised when resistive feedback is used. As shown in [5-6], lossy matching networks were used to achieve better gain flatness, trading off the power gain. In this paper, a three-stage InGaP/GaAs HBTs broadband power amplifier is designed by incorporating the compensating matching technique and optimum power gain distribution among stages. It will not suffer the gain, power, and efficiency losses and will not compromise the chip area. Furthermore, a novel reconfigurable output matching circuit using PIN diodes to adjust inductor values in the LC tank without compromising power insertion loss and linearity is proposed for the first time. The broadband PA module demonstrates more than 30% PAE, 28 dB power gain and 30 dBm output power at frequency band from 0.85 GHz to 0.95 GHz and from 1.71GHz to 1.95 GHz. II. A NOVEL RECONFIGURABLE OUTPUT MATCHING CIRCUIT DESIGN The proposed broadband PA module is composed of a MMIC broadband power amplifier and an output matching circuit with two voltage control ports, as shown in Figure 1. Since the input impedance of the power amplifiers is designed around 50 Ohm, the input matching circuit is easily designed for broadband with fixed values of its components. Fig. 1. Proposed broadband power amplifier module It is noted that the output matching circuit is typically realized either by a low pass or a high pass filter, and that output impedance of the main amplifier is generally much lower than 50 Ohm. To optimize the power matching condition, one needs to adjust components’ values in the output matching circuit of broadband PA module for satisfying the impedance transformation ratio requirement at various frequencies. The truth table of Figure 1 gives the operating frequency bands with different control biases (CT1 and CT2). 0-7803-8846-1/05/$20.00 (C) 2005 IEEE 661