Very wide tuning range, low-noise voltage controlled oscillators using ladder type leaky surface acoustic wave filters

This paper presents results from a study on a new type voltage controlled oscillator (VCO) that can operate at GHz frequencies and provide smooth tuning over a 2 to 5% tuning bandwidth. The VCO uses the feedback surface acoustic wave (SAW) oscillator principle and exhibits a phase noise performance substantially better than LC-type oscillators in the same frequency range. The key to achieving the high tuning range is the leaky SAW ladder type filter in the loop, stabilizing the VCO frequency. VCOs providing 45 and 92 MHz of tuning bandwidth at 940 and 2480 MHz center frequency respectively, are described. The 940 MHz VCO generates an output power of up to 16 dBm and exhibits a phase noise suppression of about -80 dBc/Hz at 1 kHz offset from carrier. The noise floor was calculated as -180 dBc/Hz. Another 940 MHz VCO prototype, designed to meet the requirements of portable communications, runs from a 2.8 V d. C. source, draws a current of 3.6 mA, generates -3 to -5 dBm of output power and provides 32 MHz of tuning bandwidth with a tuning voltage varying from 0 to 2.8 V. Excellent tuning linearity, low power variation with tuning and a clean spectrum are achieved with the 2.48 GHz VCO providing a tuning range of 52 MHz and an output power of 2 to 3 dBm.