Create Transmission-Line Matching Circuits For Power Amplifiers

摘要

MATCHING circuits allow power amplifiers (PAs) to attain high gain, high linearity, high efficiency, and high stability over a narrow or wide frequency band. The techniques for designing PA-matching circuits are especially important for circuits that use transmission lines, where determining circuit parameters is more complicated than for lumped-element matching circuits. An effective approach is to use a theoretical analysis to define the appropriate matching circuit, then calculate the matching-circuit parameters to minimize final tuning and attain a stable operation mode. This article presents a transmission-line matching-circuit design based on analytical equations to calculate the circuits elements for L, π, and T transformers. The introduction of a principle of equal quality factors for multisection L transformers simplifies the calculation procedure and requires only one Q circle on the Smith chart. The article demonstrates these matching principles—analytically and by Smith chart—using two examples: a narrowband, microwave, bipolar PA, and a broadband, ultra-high-frequency (UHF), laterally-diffused-metal-oxide-semiconductor-field-effect-transistor (LDMOSFET), high-power amplifier.