Wideband Q-VCO using tail-current shaping based automatic amplitude control

A wideband Q-VCO circuit with two tail-current branches ranging from 1.54 GHz to 2.8 GHz is proposed by tail-current shaping based automatic amplitude control (AAC). In Q-VCO's outputs, the AC component combing with the negative peak are injected back to the tail-current transistors as biasing voltage so as to reduce the tail-current noise contribution and realize the AAC. Moreover, an extra current path is enabled at higher frequency in order to suppress the tail-current increment for further LC-tank amplitude reduction, which is connected between the two tail-current branches. The proposed circuit was analyzed by SpectreRF simulator using TSMC 0.18 μm CMOS technology with a power supply of 1.8 V. The phase noise at 1 MHz frequency offset is from −132.6 dBc/Hz at 1.54 GHz to −125.3 dBc/Hz at 2.8 GHz while the FOM is about −182 dBc/Hz. Besides, within the tuning frequency, the maximum LC-tank amplitude variation is only 326 mV, which is 2.25 times less than that of the Q-VCO without the AAC.