Intrinsic noise variation in an amplifier based on a heterojunction bipolar transistor amplifier in nonlinear mode
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CROELECTRONIC DEVICES AND SYSTEMS
Intrinsic Noise Variation in an Amplifier Based on a Heterojunction Bipolar Transistor Amplifier in Nonlinear Mode A. M. Bobreshov^, L. I. Averina, A. V. Khripushin, and D. A. Makarenko Voronezh State University, Universitetskaya pl. 1, Voronezh, 394693 Russia ^e-mail: [email protected] Submitted February 9, 2007
Abstract—Intrinsic noise variation in a heterojunction bipolar transistor amplifier with intense interference at its input was analyzed using the Volterra series method. During the analysis, the nonlinearity of correlated sources of collector and base noise currents was considered. It was shown that the change in noise at the amplifier output caused by interference depends on both nonlinear properties of the transistor and its dc operation mode, as well as the ratio of the levels of all its intrinsic noise sources. PACS numbers: 85.30.De, 85.30.Pq DOI: 10.1134/S1063782608130198
1. INTRODUCTION Parameters of modern heterojunction bipolar transistors (HBTs) approach those of high electron mobility transistors (HEMTs) [1], which allows them to be used in low-noise amplifiers (LNAs) of microwave radio receivers. Since interferences with a level exceeding the upper limit of the dynamic range can appear at the amplifier input in a complex electromagnetic environment, it is of interest to study nonlinear effects that occur in HBT amplifiers. The interaction of intense interference whose power exceeds the linearity limit with the desired signal, intrinsic, and external noises of the amplifier causes a change in the signal and noise levels at the amplifier output and, hence, a change in the noise factor [2]. External noise amplified together with the signal and intrinsic noise formed within the transistor interacts differently with an intense interference. Analysis of such an interaction and calculation of changes in signal and noise powers in the nonlinear mode are important stages in the determination of the receiving system sensitivity loss. Such studies were already performed for the Schottky-gate field-effect transistor [3] HEMT [4] amplifiers. In this paper, we report the results of studying HBT amplifier noise characteristics in the nonlinear mode.
tion in the nonlinear mode is shown in Fig. 1. Nonlinear elements of the equivalent circuit are base–emitter CBE and base–collector CBC capacitances and base and collector current sources characterized by transconductances gB and gC, respectively. As a nonlinear analysis technique, we chose the Volterra series method; the nature of the nonlinearity is determined by expanding all nonlinear elements in voltage powers in the vicinity of the operating working point. Main sources of intrinsic noise in an HBT in the microwave range are base and collector shot noise and thermal noise of parasitic resistances of the base and emitter. Therefore, parasitic resistance noise levels are not correlated to one another or the base and collector noise levels, while base and collector noise levels do correlate to one another. The root-mean-sq
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