PLL Phase Shifting Circuit for Constant High-Frequency Phase Control
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Solution Overview
Problem
Conventional phase shifting circuits face challenges with large variations and difficulty in electronically adjusting phase over a small range due to open-loop implementation and precision limitations of RC filter elements, especially at high frequencies and under power supply voltage fluctuations.
Innovation Solution
A phase shifting circuit with a PLL loop that controls phase shift using a reference frequency branched into two signals, processed through phase comparators and differential amplifiers, with low-pass filters and varactor capacitance for precise phase adjustment, allowing for constant phase shift and resilience to element variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional RC filter-based phase shifting circuits are used, then the circuit structure is simple, but the phase shift varies significantly due to element variations and power supply fluctuations
Solution Approach 1:
The patent implements a PLL (Phase-Locked Loop) feedback mechanism where the phase detector compares the input signal with the phase-shifted signal, and the low-pass filter feeds back a control voltage to the varactor capacitor to maintain constant phase shift. This closed-loop feedback system compensates for element variations and power supply fluctuations, resolving the contradiction between reliability and complexity.
Solution Approach 2:
The patent changes the capacitance parameter dynamically using a varactor capacitor whose capacitance is controlled by a DC voltage from the low-pass filter. This allows the phase shift to be adjusted and stabilized electronically, improving reliability while managing complexity through parameter control rather than fixed physical components.
2Measurement precision
If RC filter elements are used for phase shifting, then the implementation is straightforward, but precision is limited due to manufacturing variations
Solution Approach 1:
The PLL feedback mechanism continuously monitors the phase difference and adjusts the varactor capacitor to compensate for manufacturing variations in RC elements. This feedback control achieves high phase shift accuracy independent of component tolerances, resolving the contradiction between measurement precision and manufacturing precision.
Solution Approach 2:
The circuit uses its own output signal as a reference for self-correction. The phase detector compares the input signal with the phase-shifted signal and automatically adjusts the phase shift through the low-pass filter and varactor capacitor, enabling self-calibration that overcomes manufacturing imprecision.
3Adaptability or versatility
If open-loop phase shifting is implemented, then the circuit is simple, but electronic adjustment capability is limited
Solution Approach 1:
The patent transforms the static RC filter into a dynamic system by introducing a varactor capacitor whose capacitance can be continuously adjusted via DC voltage control from the low-pass filter. This enables electronic phase adjustment over a wide range while maintaining circuit simplicity through voltage-controlled tuning rather than mechanical or switched component changes.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution ensures constant phase shift, improves accuracy, and mitigates the effects of element variations and power supply fluctuations, enabling precise phase control and stability in high-frequency applications.
Implementation Method 1
the output signal of the phase comparator is supplied to one input terminal of a differential amplifier via a low-pass filter
Implementation Method 2
with low-pass filters and varactor capacitance for precise phase adjustment
Data Source
AI summary
Disclosed is a phase shifting circuit that includes a PLL loop in which a reference frequency received is branched into first and second signals. The first signal becomes one input to a phase comparator and the second signal becomes another input to the phase comparator after being shifted in phase via a phase shifter. The output of the phase comparator is supplied to one input terminal of a differential amplifier via a low-pass filter. The amount of phase shift of the phase shifter is controlled by the output signal of the differential amplifier. The amount of phase shift of the phase shifter is decided by a reference voltage applied to another input terminal of the differential amplifier.