A Flexible Oscillator for Measurement of Varactor-Tuned Resonators

A new version of RF oscillator with high linearity (THD<1%) and wide zone of adjusting its amplitude (min. 40 dB) is presented in this contribution. Oscillator is designed for single and quickly measurement of non-linearity effects in varactor-tuned LC resonators, and it is usable in frequency band from LF up to 50 MHz. Active part of the oscillator consist of high-speed OA of type VFB (voltage feedback), or CVB (current feedback) and resistive feedback circuit. Herein are presented analytical relationships derived for parameters input characteristics for both VFB OA and CVB OA respectively. OA with positive feedback has in the centre its input characteristics negative resistance, which give the possibility to compensate losses in parallel LC resonator. For simple and effective control of the oscillation amplitude is used backward biased diode detector with control voltage. In contributions are also presented measured parameters of the oscillator and there are given some examples of measured tuning characteristics with varactors.