Automatic resonant frequency matching of power amplifier by transformer loop sampling

Abstract

An eight-wavelength hybrid Si/AlGaInAs/InP microring laser array coupled with an underlying silicon waveguide has been fabricated based on the bonding technique, with the radii varying from 15 to 15.14 m at a step of 20 nm and with a microring width of 2 m. Continuous-wave (CW) electrically injected operation is obtained at 280 K, with threshold currents of about 6 mA, channel spacing of about 2 nm and sidemode-suppression ratios above 20 dB. A new automatic resonant frequency matching technique based on voltage detection by sampling the output transformer loop of the radio-frequency power amplifier (PA) in ultrasonic medical applications is proposed. The proposed automatic resonant frequency matching circuitry is composed of a single-loop coil added to a PA output transformer, voltage divider, diode detector and micro-controller unit for frequency adjustment. Using the proposed circuitry, the resonant frequency shift due to output load variations can be effectively tracked and compensated to provide optimised power transfer to a nonlinear load. For verification, a prototype ultrasonic medical application using a piezoelectric transducer is implemented and examined with silicone oil to check the resonance. © The Institution of Engineering and Technology 2015.