Design of a wide-tuning-range lithium tantalate low-phase-noise voltage-controlled oscillator

In this brief, a lithium tantalate crystal with a low capacitance ratio and a wide tuning range is used to design a Butler common-base wide-tuning-range low-phase-noise oscillator considering a reasonable compromise between seeking high loaded quality factor and maintaining oscillator output power. The formulation of is derived from analysis of the Butler oscillator circuit and calculated with MATLAB. The unloaded quality factor of the crystal utilized in the design is about 1.24 K, and the frequency of the crystal is about 10.727 MHz. In the phase noise measurement experiments, of the Butler common-base oscillator is about 33% of , and the output power is about 11 dBm. The measured phase noise level without voltage control is 145 dBc/Hz at 1 kHz, and noise floor is better than 180 dBc/Hz. The tuning ability of the prototype oscillator is tested, and voltage control ability is also tested by increasing a low-voltage varactor BB155. After increasing a varactor capacitance, the measured phase noise at 1-kHz offset and noise floor are better than 142 and 180 dBc/Hz, respectively, when voltage-controlled slope are 86.6 and 19.2 ppm/V for a control voltage range of 2-10 V. Experimental results show that the Butler common-base oscillator with a wide tuning range can realize the characteristics of low phase noise based on the reasonable compromise between seeking high and maintaining output power.