Low Noise Tuning Diodes for Voltage-Controlled Oscillators

An oscillator noise model distinguishes between various noise sources and predicts their influence on voltage-controlled oscillator (VCO) single sideband noise. Tuning diodes are the most critical elements. A test oscillator validates the predicted performance. An equivalent noisy resistor is introduced as a figure of merit for low noise diodes. Finally, the important fabrication considerations for low noise diodes are presented and validated in the test oscillator. At 10 kHz offset, the noise contribution of optimized tuning diodes in the oscillator adds only 10 dB of noise compared to a fixed capacitor design.