Pierce Oscillator Circuit for Low Far-Out and Closed-In Phase Noise
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Solution Overview
Problem
Conventional Pierces oscillators are unable to simultaneously reduce far-out phase noise (frequency offsets above 10 KHz) and closed-in phase noise (frequency offsets below 100 Hz) due to limitations in voltage signal amplitude, which affects device driving capability and nonlinearity effects.
Innovation Solution
An oscillator apparatus with an oscillator core circuit featuring an inverting transconductance amplifier, capacitors with different capacitances, and a resonator, where the capacitance of the first capacitor is smaller than the second capacitor, and a DC coupling circuit to enhance signal amplitude and avoid non-linear effects, allowing for independent common mode definition and reduced phase noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional Pierce oscillator generates and outputs a smaller voltage signal to reduce closed-in phase noise, then closed-in phase noise is reduced, but device driving capability becomes limited
Solution Approach 1:
The oscillator circuit is divided into separate functional blocks: a first oscillator core circuit generating a first signal, and a second oscillator core circuit generating a second signal. These separate circuits allow independent optimization of each stage, enabling the first circuit to operate at lower amplitude for reduced phase noise while the second circuit provides sufficient driving capability.
Solution Approach 2:
A buffer circuit is introduced as an intermediary between the first oscillator core circuit and the output stage. This buffer circuit isolates the first oscillator from loading effects while providing impedance transformation, allowing the oscillator to maintain low amplitude operation without compromising driving capability at the output.
2Measurement precision
If a conventional Pierce oscillator generates and outputs a larger voltage signal to reduce far-out phase noise, then far-out phase noise is reduced, but active devices are affected by nonlinearity effects
Solution Approach 1:
The oscillator is segmented into multiple stages with different amplitude levels. The first oscillator core circuit operates at lower amplitude to avoid nonlinearity, while a subsequent stage (second oscillator core circuit or buffer) provides the higher amplitude output needed for reduced far-out phase noise. This segmentation allows each stage to operate in its optimal region.
Solution Approach 2:
Different parts of the oscillator circuit are designed with different signal amplitude characteristics. The input stage maintains low amplitude to preserve linearity and avoid nonlinearity effects, while the output stage provides high amplitude to reduce far-out phase noise. This local differentiation of signal quality resolves the contradiction between linearity and phase noise performance.
3Measurement precision
If both far-out phase noise and closed-in phase noise are to be reduced simultaneously, then signal quality improves, but conventional oscillator architectures cannot achieve both goals
Solution Approach 1:
The oscillator is divided into multiple functional blocks that can be implemented using standard circuit design techniques. The first oscillator core circuit, second oscillator core circuit, and buffer circuit are separate modules that can be designed and optimized independently, then integrated together. This modular segmentation achieves superior phase noise performance without excessive overall complexity.
Solution Approach 2:
The buffer circuit serves multiple functions: it provides impedance transformation, isolates the oscillator core from loading effects, and can provide additional gain if needed. This multi-functionality reduces the need for separate dedicated circuits, thereby achieving the dual phase noise reduction goal without proportionally increasing complexity.
Data Source
AI summary
An oscillator apparatus includes an oscillator core circuit. The oscillator core circuit includes an inverting transconductance amplifier, at least one first capacitor, at least one second capacitor, and a resonator. The at least one first capacitor is connected between an input of the inverting transconductance amplifier and a ground level. The at least one second capacitor is connected between an output of the inverting transconductance amplifier and the ground level. The resonator has a first port connected to the input of the inverting transconductance amplifier and a second port connected to the output of the inverting transconductance amplifier. The first port is decoupled from the second port.