A 4–1 Multiplexer-Based Frequency Discriminator Used for Oscillator Phase Noise Suppression

In this article, we present a new phase noise reduction structure for oscillators based on a six-port frequency discriminator (FD) using a multiplexer. In general, the FD for oscillators requires the inputs to be orthogonal, while the proposed FD circuit can operate at any phase condition. In this way, the circuit can be greatly simplified since no phase controls are needed. Unlike previously reported solutions where analog multipliers were used, the proposed FD uses a multiplexer to achieve an infinite phase extraction range. The replacement of multiplier by the multiplexer in FD benefits from a wider power detection range and lower power consumption, which makes it more suitable for integration. An experimental FD prototype for phase noise suppression of a 10.7 GHz dielectric resonator oscillator (DRO) has been carried out and the results show that 30 dB phase noise suppression at close-in offset frequencies (30 Hz–3 kHz) has been achieved.