The First Active Tunable Wideband Impedance Matching Circuit

The first transistor-based impedance matching circuit for radio-frequency (RF) applications is introduced in this paper. It adapts arbitrary output impedances of RF blocks to desired values between 50 and 250 , from 0 to 5GHz, while occupying only 0.005mm2 of circuit area in a 0.35μm SiGe BiCMOS process. Its superiority over traditional passive-element networks can be resumed by the following facts: flexible performance without the need for redesigning the components; adaptation of arbitrary impedances to desired values by the simple means of biasing current; extremely small form factors (the smallest observed); and matching over several gigahertz. Application to a low-noise amplifier validates the new topology. Index Terms — Active impedance matching, current conveyors, SiGe BiCMOS, wideband matching. INTRODUCTION The importance of impedance adaptation in wireless receivers cannot be overstated. Individual transceiver components are often fabricated in different technologies, giving rise to multi-chip architectures. For these components (or sub-systems) to be compatible, they must present terminating impedances that are compatible. This article is dedicated to impedance matching circuits. Section II will be a brief reminder of the basic principle of impedance. Section III will serve as a review of impedance adaptation circuits encountered in wireless systems. It will be observed that matching relies entirely on passive components like inductors, transformers and quarterwavelength lines. Section III will also serve as a backdrop against which a novel transistor-based (“active”) output impedance matching circuit will be proposed and presented (section IV). This new method makes use of the second generation controlled current conveyor (CCCII) as its building block. In-depth analyses of the new method and its simulated performance will be presented in section V. An application example for the new matching circuit will be presented in section VI. It will be shown that the new circuit effectively matches the output of the amplifier, without deteriorating its other parameters. Measurement results on the fabricated circuit will be presented in section VII. The conclusions will highlight the novelty of the new approach by comparing it with traditional matching circuits. BASICS OF IMPEDANCE MATCHING A. Scattering Parameters For a two-port circuit, with an input (port 1) and an output (port 2), represented in fig. 1, the impedances at the input and the output, ZIN and ZOUT, respectively determine the degree of matching to the source and load. The degree of (mis)match between these impedances is represented in terms of the scattering parameters of the two-port. The relevant reflection parameters are S11 at the input and S22 at the output, defined as: