Optimization and Realization of a 315-MHz Low-Phase-Noise Voltage-Controlled SAW Oscillator

In this paper, the formulation of Q_L is derived from the analysis of the Butler common-base surface acoustic wave (SAW) oscillator circuit. The prototype 315-MHz Butler SAW oscillator is designed, and phase-noise results before and after adding voltage-control components are measured. The SAW resonator utilized is R315 with an unloaded quality factor Q₀ of about 1.06×10⁴. The measured results of phase noise without voltage control are -159 dBc/Hz at 10 kHz and better than -165 dBc/Hz at 100 kHz. After adding the low-voltage varactor BB155, the measured phase-noise results with different control voltages are presented. When only one varactor is added in the actual circuit, the voltage-controlled slope is 4.8 kHz/V, and the measured phase-noise results are better than -155 dBc/Hz at 10 kHz and -165 dBc/Hz at 100 kHz with different control voltages of 4, 6, and 8 V. When two varactors in series are used, the voltage-controlled slope is 9.5 kHz/V, and the measured phase-noise results are better than -155 dBc/Hz at 10 kHz and -165 dBc/Hz at 100 kHz with different control voltages of 4, 6, and 8 V. Experimental results show that the phase-noise level of the 315-MHz voltage-controlled SAW oscillator with a wide voltage-controlled range can be ameliorated based on improving Q_L.