694 IEEE JOURNAL OF SOLID-STATE CIRCUITS, VOL. 37,NO. 6, JUNE 2002 Analysis, Design, and Optimization of InGaP–GaAs HBT Matched-Impedance Wide-Band Amplifiers With Multiple Feedback Loops Ming-Chou Chiang, Shey-Shi Lu, Senior Member, IEEE, Chin-Chun Meng, Shih-An Yu, Shih-Cheng Yang, and Yi-Jen Chan Abstract—The realization of matched impedance wide-band amplifiers fabricated by InGaP–GaAs heterojunction bipolar transistor (HBT) process is reported. The technique of multiple feedback loops was used to achieve terminal impedance matching and wide bandwidth simultaneously. The experimental results showed that a small signal gain of 16 dB and a 3-dB bandwidth of 11.6 GHz with in-band input/output return loss less than 10 dB were obtained. These values agreed well with those predicted from the analytic expressions that we derived for voltage gain, tran- simpedance gain, bandwidth, and input and output impedances. A general method for the determination of frequency responses of input/output return losses (or , ) from the poles of voltage gain was proposed. The intrinsic overdamped characteristic of this amplifier was proved and emitter capacitive peaking was used to remedy this problem. The tradeoff between the input impedance matching and bandwidth was also found. Index Terms—InGaP–GaAs, multiple feedback, trans- impedance amplifier, wideband. I. INTRODUCTION W IDE-BAND amplifiers are used in variety of modern electronic systems such as microwave/lightwave com- munication and instrumentation [1]. Among the many versions of wide-band amplifiers, the so-called Kukielka configuration [2] is one of the popular circuits. It has been fabricated by silicon bipolar, AlGaAs–GaAs heterojunction bipolar transistor (HBT), and InAlAs–InGaAs HBT processes with excellent performance [3]–[5]. Recently, InGaP–GaAs HBT technology has attracted much attention because of its uniformity [6]–[9] and reliability [10]. However, no detailed account of the performance of the InGaP HBT wide-band amplifiers with Kukielka configuration has been reported in the literature. The design equations based directly on the Kukielka configuration also have not been given before. Manuscript received July 9, 2001; revised March 3, 2002. This work was supported by the National Science Council and Ministry of Education, Taiwan, R.O.C., under Grant NSC90-2219-E002-009, Grant NSC90-2219-E005-001, and Grant 89-E-FA-06-2-4. M.-C. Chiang, S.-S. Lu and S.-A. Yu are with the Department of Electrical Engineering and Graduate Institute of Electronics, National Taiwan University, Taipei, Taiwan, R.O.C. (e-mail: sslu@cc.ee.ntu.edu.tw). C.-C. Meng is with the Department of Electrical Engineering, National Chung-Hsing University, Taichung, Taiwan, R.O.C (e-mail: ccmeng@ nchu.edu.tw). S.-C. Yang and Y.-J. Chan are with the Department of Electrical Engi- neering, National Central University, Chung-Li, Taiwan, R.O.C. (e-mail: yjchan@ee.ncu.edu.tw). Publisher Item Identifier S 0018-9200(02)04935-1. Therefore, in this paper, we present the first demonstration of Kukielka wide-band amplifiers using InGaP–GaAs HBT process. Multiple feedback loops were used to achieve terminal impedance matching and wide bandwidth simultaneously. The capacitive peaking technique [11] was used to overcome the intrinsic overdamped frequency response of the Kukielka amplifiers and thus enhance the bandwidth. The experimental results showed that a small signal gain of 16 dB and a 3-dB bandwidth of 11.6 GHz with in-band input/output return loss less than 10 dB were achieved. These values were in good agreement with the values predicted by the analytic expressions that we derived for voltage gain, bandwidth, and input and output impedances. A method to calculate the frequency responses of input/output return losses based on the poles of voltage gain is also presented. II. PRINCIPLES OF CIRCUIT DESIGN The circuit topology of the Kukielka wide-band amplifier is shown in Fig. 1(a). The input stage consists of a single transistor driving the output stage consisting of a transistor with local shunt ( ) and series ( ) feedback. There is also an overall shunt-series feedback loop composed of resistors and . Local shunt feedback around gives a low impedance at the collector node of for the output terminal impedance matching. Then, global shunt feedback is applied around this voltage amplifier via to achieve the input matching condition. Clearly, this amplifier can be approximated by a two-pole system with the closed-loop poles determined by the following characteristic equation: (1) where is open-loop gain at low frequencies, is the feed- back factor, and and are the two poles of the A circuit. Thus, the closed-loop poles and are given by (2) From this equation, we see that as the loop gain is increased from zero, the poles are brought closer together. Then a value of loop gain is reached at which the poles become co- incident. If the loop gain is further increased, the poles become 0018-9200/02$17.00 © 2002 IEEE