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By reducing the components count to just a couple of circuit elements, it is possible to generate impedance matching networks for a wide range of low-noiseamplifier matching conditions.
(ProQuest-CSA LLC: ... denotes formulae omitted.)
Low-noise amplifiers (LNA) set the general noise figure and sensitivity of receivers and other high-frequency systems. Although a variety of excellent low-noise transistors is currently available based on numerous process technologies, achieving good amplifier low-noise performance depends strongly on the required LNA device input impedances and the choice of impedancematching topologies. By analyzing these choices, it should be possible to find an optimum topology for a given device impedance.
For the example amplifier in Fig. 1, R^sub 0^ is the signal source impedance (typically 50 Ω), Z^sub in^ is the amplifier input impedance, and M is a matching network. For simplicity, assume that the matching network is designed for an ideal conjugate (maximum power) match; i.e., it transforms the impedance Z^sub in^ to the impedance R^sub 0^. In most cases, the input of an LNA will be matched for minimum noise figure, which may result in a mismatch in terms of power performance. In the case of a lossless matching network, the perfect conjugate match condition implies the following property: if a plane is drawn anywhere within the matching network or at its terminals connected to R^sub 0^ and Z^sub in^, impedances looking in opposite sides of the plane must be conjugate to each other.
For example, impedance looking into the left-hand side of the plane drawn in Fig. 1 must be Z^sub in^*. Even if a matching network has loss, it is possible to rearrange its boundaries such that it is purely reactive and all losses are added to either R^sub 0^ or Z^sub in^. So, the property of the conjugate impedances can still be used.
The losses in a matching network are due to the finite quality factors (Qs) of the components used in the matching network. The Qs of surface-mount or even on-chip metal-insulator-metal (MIM) capacitors are usually very high and their contributions to the losses can be neglected. For example, the Q of a typical 2-pF 0402-sized capacitor is about 600 at 1 GHz while the Q of a 10-nH 0402-sized ceramic inductor is only...