Configuration for Realizing a Push-Push Parallel-Feedback Oscillator Through a Differential Bandpass Filter

Abstract

A push–push parallel-feedback oscillator constructed through a differential bandpass filter (BPF) is investigated in this paper. For the first time, the differential filter has been utilized as the parallel-feedback element to provide differential outputs in designing the push–push oscillator. Low phase noise performance and easy design process can be obtained due to the parallel feedback circuits compared with series feedback ones. The complex quality factor ( $Q_{\textrm {sc}}$ )-peak frequency of the BPF is chosen as the half final output frequency to further improve the phase noise performance. Also, the improvement of the odd harmonic suppression and even harmonic enhancement can be easily obtained. Moreover, due to the existence of the common mode suppression, only 180° out-of-phase mode will be achieved which makes the oscillator run in a stable condition. To validate the design concept, a push–push oscillator based on a microstrip differential BPF has been achieved which is operating at 8.37 GHz. The measured results show that the output power is −5.4 dBm with a phase noise of −134.6 dBc/Hz at 1-MHz offset.