A Low Phase-Noise Dual-Frequency Oscillator Based on Filter Switching Technique

This letter presents a parallel-feedback dual-frequency oscillator (DFO) with low phase noise. It is achieved based on the filter switching technique. By using four switches to control two oscillator loops with a common active device, the oscillation frequency of the proposed DFO can be switched from one to another. Due to the high isolation level of the employed switches, the two oscillator loops almost operate independently. Thus, there is no intermodulation (IM) spurs generated in the output spectrum of the proposed DFO. In the meantime, to improve the phase noise performance of the DFO, each oscillator loop utilizes a high frequency-selectivity bandpass filter with high group delay (GD) as a frequency selective element. In this way, the low phase-noise DFO is developed. For demonstration, the DFO is designed, fabricated, and tested. As seen from the measurement results, the oscillator can oscillate at 2.04 or 3.092 GHz by controlling the four switches. At 100 kHz and 1 MHz frequency offset from the carrier frequency, the phase noises are −108.5 and −129.7 dBc/Hz for 2.04 GHz, while −112.7 and −135.7 dBc/Hz for 3.092 GHz.