An RF amplifier linearised by RF feedback, and having a loop filter resonator of enhanced Q

摘要

An RF amplifier 2 is linearised by RF feedback 4,6. The centre frequency Q of a resonator in the loop filter is adjusted by a control loop 10, 11,26 so that the resonator centre frequency follows the frequency of the input RF signal 1. The Q of the resonator, which is enhanced by local positive feedback, is similarly optimised by a control loop 10, 11,27. The low Q factor of integrated circuit resonators can be enhanced. The arrangement is much simpler than a Cartesian feedback circuit. High linearity and stability is achieved at low cost.