Low-noise biasing of voltage-controlled oscillators by means of resonant inductive degeneration

Many of the existing theories on phase-noise generation in oscillators are concerned with the noise originating from the active part and the resonator, while the contribution of the biasing noise is usually neglected. However, some recent theories have enlightened that the contribution of the biasing noise to the overall phase noise of the oscillator, actually, overwhelms all the other contributors together. Therefore, the concept of biasing to minimize the noise contribution of the oscillator´s tail-current source is described in this paper. The procedure followed in the noise optimization of the inductively-degenerated low-noise amplifier scheme is here applied to the tail-current source. Noise at close to double the oscillating frequency is identified as the main contributor of biasing-noise to the over-all oscillator phase noise, and a design procedure is developed accordingly. The presented analysis gives full insight into the performances of the low-noise biasing scheme, i.e., the resonant inductive degeneration of the current source, proving that this topology is an excellent trade-off between design effort and phase-noise performance.