Suppress noise output of YIG-tuned sources

The design of drive circuits aimed to reduce the noise output of YIG-tuned oscillators is presented. The noise reduction technique is illustrated by analysis of a low-noise electronically tunable oscillator in a spectrum analyzer. A variety of noise types (thermal, broadband operational amplifier, and popcorn noise) are evaluated, and measures to avoid the harmful constituents at each stage of the driver are indicated. It is mentioned that in a well-designed driver, operational amplifier noise is the limiting factor. Low-frequency drift as a source of signal variations is considered. Special attention is given to the driver's final stage design, noting the need to consider ground-potential drops resulting in the upset of the voltage/frequency relationships of earlier stages.