A transmitter amplifier with linearising RF feedback and automatic control of resonator Q, resonator frequency, loop phase, and loop gain

摘要

An RF amplifier 2 is linearised by negative RF feedback 4,6. The Q and centre frequency of a loop filter resonator are automatically adjusted by control loops 10,11,26,27, and the block 35 allows control of loop phase and loop gain. The loop phase may be set initially by the resonator frequency tuning signal 26 and then fine tuned by a control arrangement 32-37 acting to equalise the noise floor at frequencies above and below the resonator frequency. The noise floor may also be used to adjust the loop gain. The input signal 1 may be attenuated 31 when the loop error signal increases due to saturation of amplifier 2. The low Q factor of integrated circuit resonators may be overcome. The arrangement is simpler than a Cartesian feedback circuit, and high linearity and stability are achieved at low cost.