Quadrature VCO Phase-Shift Circuit for Stable Low-Noise Tuning
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Solution Overview
Problem
Traditional quadrature voltage-controlled oscillators face unpredictability in operating frequency due to symmetric operating modes and uncertain signal injection direction, leading to instability and limited tuning range without increasing phase noise.
Innovation Solution
A quadrature voltage-controlled oscillator circuit with phase shift is designed, utilizing a cascode structure in both the cross-coupled oscillating and injection locking circuits to provide stable operation in one mode and enhance tuning range, while maintaining low phase noise, by connecting transistors in a specific configuration to achieve phase shift without additional complex circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a traditional injection locking quadrature oscillator is used, then the circuit structure is simple, but the operating frequency is unpredictable due to symmetric operating modes and uncertain signal injection direction
Solution Approach 1:
The patent introduces a phase shift of 36 degrees into the oscillation loop by configuring the injection locking circuit to inject signals at a specific phase angle relative to the oscillation signal. This asymmetric phase relationship breaks the symmetry between the two operating modes, making one mode significantly more stable than the other, thereby ensuring predictable and stable operation at a specific frequency.
2Adaptability or versatility
If the tuning range is expanded, then the frequency adjustment capability is improved, but the phase noise increases
Solution Approach 1:
The patent employs voltage-controlled current sources that dynamically adjust the oscillation frequency by controlling the current magnitude. The injection locking circuit dynamically locks onto the desired frequency by adjusting the phase and amplitude of the injected signal. This dynamic control mechanism allows for a wide tuning range while maintaining low phase noise through active frequency stabilization.
3Manufacturing precision
If a phase shift circuit is added to provide phase shift, then the phase shift performance is improved, but the circuit complexity and occupied area increase
Solution Approach 1:
The patent merges the phase shift function with the existing injection locking circuit by configuring the injection timing and phase to inherently provide the required 36 degrees phase shift. Rather than adding a separate phase shift circuit, the phase shift is achieved through the phase relationship between the injection signal and the oscillation signal, thereby avoiding additional circuit complexity and occupied area.
Data Source
AI summary
A quadrature voltage-controlled oscillator circuit with phase shift includes two voltage-controlled oscillators with the same structure, wherein the two voltage-controlled oscillators are connected to each other through input and output ports, and the two voltage-controlled oscillators respectively include a cross-coupled oscillating circuit, an injection locking circuit, a resonant circuit and a voltage-controlled current source circuit which are electrically connected to each other; and signals are injected through the injection locking circuit and coupled with the oscillating circuit, so as to output a quadrature signal. An oscillator is enabled to operate stably in one mode by means of a simple circuit structure, and a good phase shift can be provided for the resonant circuit in a lower frequency band; and meanwhile, a tuning range of the oscillator is improved without increasing phase noise.