Design of a Wide-Tuning-Range Lithium Tantalate Low-Phase-Noise Voltage-Controlled Oscillator

摘要

In this brief, a lithium tantalate $(hbox{LiTaO}_{3})$ 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 $Q_{L}$ and maintaining oscillator output power. The formulation of $Q_{L}$ is derived from analysis of the Butler oscillator circuit and calculated with MATLAB. The unloaded quality factor $Q_{0}$ of the $hbox{LiTaO}_{3}$ crystal utilized in the design is about 1.24 K, and the frequency of the $ hbox{LiTaO}_{3}$ crystal is about 10.727 MHz. In the phase noise measurement experiments, $Q_{L}$ of the Butler common–base oscillator is about 33% of $Q_{0}$, 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 $hbox{LiTaO}_{3}$ oscillator with a wide tuning range can realize the characteristics of low phase noise based on the reasonable compromise between seeking high $Q_{L}$ and maintaining output power.