Abstract
In this paper, we present a study on a transformer-based impedance matching network. We use a simplified transformer model comprising two magnetically coupled coils, which are driven by a source and terminated by a load. The formulae of the load and the source impedance for conjugate matching of both sides of the transformer are presented, and a figure of merit is proposed for the evaluation of the power transfer efficiency of the transformer under conjugate matching conditions. Analytical expressions are provided for constructing the widely used transformer network consisting of a resistive load and a parallel tuning capacitor. To verify the proposed work, we examined various on-chip transformers implemented in 0.18 μm CMOS technology. Simulation and measurement results for a matching network synthesized using the aforementioned analytical expressions corresponded well with the result of analysis for operating frequencies up to 72% of the self-resonant frequency of the transformer. The presented results confirm that the proposed analytical formulae based on the simplified transformer model are useful for the design and optimization of transformer-based impedance matching networks in the microwave and millimeter-wave regimes.
Highlights
At present, numerous radio frequency integrated circuit (RFIC) designs are being implemented with transformers for various purposes such as impedance matching, impedance transformation, and signal conversion between single-ended and differential signals in various frequency bands ranging from the radio frequency (RF) to terahertz regimes
To develop design guidelines for the optimization of a transformer network, we investigated the role of the resistive and the reactive parts of the source and load in achieving the maximum power transfer
We present the design formulae, obtained from the aforementioned analysis, for the optimum source and load impedance of a given transformer for the case where a parallel tuning capacitor is used to achieve optimal power transfer in the transformer network
Summary
Numerous radio frequency integrated circuit (RFIC) designs are being implemented with transformers for various purposes such as impedance matching, impedance transformation, and signal conversion between single-ended and differential signals in various frequency bands ranging from the radio frequency (RF) to terahertz regimes. Based on the work in [17], a comprehensive solution of the load and the source for inductively coupled coils for the wireless power transfer application was presented in [26] It did not cover the transformer-based impedance matching network with a shunt tuning capacitor which has been widely used in RFIC design. We extracted the effective transformer parameters for the two magnetically coupled coils from Z-parameters, and the extracted parameters were used in the derived analytical formulae to design a simultaneous conjugate matching network, which demonstrated a promising accuracy of the maximum power transfer by the frequency response up to 72 % of the selfresonant frequency (SRF) of the transformer within a percentage error of 10 %.
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