Gm-Boosted Oscillator Biasing for Low Phase Noise
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Solution Overview
Problem
Existing oscillators, particularly cross coupled negative resistance oscillators, suffer from high power consumption and poor phase noise performance due to their design, which affects their overall efficiency and signal quality.
Innovation Solution
The oscillator incorporates a resonance unit, a cross coupled current source unit, and a positive feedback unit to form a Gm-boosted structure, allowing for adjustable bias current provision and reduced power consumption while maintaining low phase noise. This is achieved through a design that includes specific MOS transistors, capacitors, and inductors, along with a switched capacitor array to control frequency and reduce the time MOS transistors are turned on.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a cross coupled negative resistance oscillator is used, then the oscillator can generate stable oscillation signals, but the phase noise is high and power consumption is high
Solution Approach 1:
The oscillator is divided into separate functional blocks: a resonance unit (with inductors and capacitors) and a cross-coupled active unit (with MOS transistors). This segmentation allows independent optimization of each unit, enabling the resonance unit to generate oscillations while the active unit provides controlled negative resistance, thereby reducing overall power consumption while maintaining stability.
Solution Approach 2:
The patent optimizes key parameters including the negative resistance value (|Rneg|), quality factor (Q), and bias current (IB). By carefully controlling these parameters, the oscillator achieves low power consumption while maintaining sufficient negative resistance to overcome losses and generate stable oscillations. The phase noise is reduced by optimizing the ratio of negative resistance to resonator impedance.
2Reliability
If a cross coupled negative resistance oscillator is used, then the oscillator can generate stable oscillation signals, but the phase noise performance is poor
Solution Approach 1:
The patent optimizes the negative resistance parameter |Rneg| to achieve an optimal balance between oscillation stability and phase noise. By controlling the bias current IB and transistor dimensions, the negative resistance is tuned to compensate for resonator losses while minimizing phase noise. The quality factor Q is also optimized to reduce phase noise without compromising oscillation startup and stability.
Solution Approach 2:
The oscillator operates in a dynamic regime where the cross-coupled transistors are switched on only during specific portions of the oscillation cycle. This dynamic operation allows the negative resistance to be applied only when needed for oscillation maintenance, reducing continuous power consumption and minimizing phase noise injection into the oscillation signal.
3Reliability
If bias current is increased to maintain oscillation stability, then oscillation signals remain stable, but power consumption increases
Solution Approach 1:
The patent identifies and optimizes the bias current IB as a critical parameter. By carefully selecting IB, the oscillator achieves the minimum current required to maintain stable oscillations while minimizing power consumption. The negative resistance provided by the cross-coupled transistors is tuned to match the resonator losses, allowing oscillation stability with reduced bias current compared to conventional designs.
Data Source
Figure 1a~1b
Figure 2~3
Figure 4a
AI summary
Embodiments of the present invention provide an oscillator, so as to provide an oscillator having low phase noise. The oscillator includes: a resonance unit, a cross coupled current source unit, and a positive feedback unit coupled between the current source unit and the resonance unit, where the resonance unit is configured to generate a differential oscillation signal having a first oscillation frequency; the positive feedback unit is configured to receive the differential oscillation signal, and amplify a gain of the differential oscillation signal, to obtain a differential output oscillation signal; and the current source unit is configured to provide an adjustable bias current for the resonance unit and the positive feedback unit. Because the current source unit provides the adjustable bias current for the positive feedback unit and the resonance unit, and forms a Gm-boosted structure with the positive feedback unit, the positive feedback unit can amplify the gain of the received differential oscillation signal, to obtain the differential output oscillation signal. Therefore, under a condition that the oscillator is ensured to be started up normally, power consumption of the oscillator provided in the embodiments of the present invention can be lowered by reducing the bias current.