Design and performance of voltage-controlled oscillators using TFR stacked-crystal filters

Two applications of thin-film resonator (TFR) technology are presented. These designs are: a 1-GHz voltage-controlled oscillator (VCO) with a 0.5% tuning range, and a frequency-agile 1-GHz oscillator which provides discrete frequency shifts of 4 MHz. The basic TFR frequency-control structure is a stacked-crystal filter (SCF) synthesized using multiple layers of AlN for piezoelectric transduction sandwiched between Al electrodes. Filters can be synthesized with single-mode bandpass or multiple (over-moded) bandpass characteristics. Typical performance for a single-mode double-stacked filter, when used in a 1-GHz VCO, provides an insertion loss as low as 1.5 dB, a linear phase extending over a 20-MHz passband, and an open-loop Q = 80. The VCO was designed using a large-signal perturbational S-parameter technique.