Design and Analysis of Frequency-Tunable Amplifiers using Varactor Diode Topologies

The design of frequency-tunable amplifiers is investigated and the tradeoff between linearity, efficiency and tunability is revealed. Several tunable amplifiers using various varactor diode topologies as tunable devices are designed by using loadpull techniques and their performances are compared. The amplifier using anti-series distortion-free varactor stack topology achieves 38% power added efficiency and it may be tuned from 1.74 to 2.36 GHz (about 35% tunable range). The amplifier using anti-series/anti-parallel topology is tunable from 1.74 to 2.14 GHz (about 23% tunable range) and provides 42% power added efficiency. It is demonstrated that tunable amplifiers using distortion-free varactor stack topologies provide better power added efficiency than the tunable amplifiers using reverse biased varactor diodes and their linearity is similar to that of a conventional amplifier. These amplifiers may facilitate the realization of frequency agile radio frequency transceiver front-ends and may replace several parallel connected amplifiers used in conventional multimode radios.