A high performance waveguide-coupled resonator SAW VCO

A quadrature balanced amplifier is used with a four-pole waveguide-coupled resonator filter to form a feedback oscillator. The effects of emitter degeneration under large signal conditions are examined. These effects govern the up-mixing of transistor low-frequency noise and can be used to reduce close-in amplifier residual phase noise. It has been found that a well designed loop amplifier can have lower close-in residual phase noise than the surface acoustic wave (SAW) filter itself. It is shown that degeneration need not degrade the noise floor. The quadrature amplifier configuration permits matching and gain compression without disturbing the loop interface impedance. A low-noise active bias scheme is described. The oscillator is power-efficient, achieving 80 dBc/Hz at 10 Hz offset, with a SAW drive level of + 11 dBm. The amplifier is biased at 10 mA per transistor