Dual-Path PLL Feedback for Beamforming Phase Control
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Solution Overview
Problem
5G cellular systems operating in millimeter wave frequencies require stringent phase noise control and programmable phase shifts for accurate beamforming, which existing phase locked loops struggle to achieve without excessive power consumption and increased chip area.
Innovation Solution
A phase locked loop design that uses a loop filter to generate a control signal for a controllable oscillator, with a frequency divider providing delayed feedback signals to comparator paths, allowing for precise phase control and reduced current matching requirements, enabling linear phase adjustment and reduced chip area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional phase locked loop is used to provide mixing frequency signals for 5G millimeter wave systems, then the basic frequency conversion function is achieved, but the phase noise requirements for closer sub-carrier spacing and the programmable phase shift requirements for beamforming cannot be met simultaneously without excessive power consumption and chip area
Solution Approach 1:
The feedback signal path is segmented into multiple paths, each with different delay elements. The first feedback signal path includes a first delay element while the second feedback signal path includes a second delay element with different delay characteristics. This segmentation allows independent optimization of each path for specific phase control requirements, enabling precise phase noise control while maintaining low power consumption by avoiding the need for a single complex high-power feedback path.
Solution Approach 2:
The phase locked loop incorporates dynamically adjustable delay elements that can be programmed to provide different phase shifts for beamforming operations. The delay elements are controlled by control signals that can be adjusted in real-time to match different beamforming requirements and sub-carrier spacing configurations, enabling the system to adapt to varying phase noise requirements without increasing power consumption.
2Measurement precision
If a conventional phase locked loop is used to provide mixing frequency signals for 5G millimeter wave systems, then the basic frequency conversion function is achieved, but the phase noise requirements for closer sub-carrier spacing and the programmable phase shift requirements for beamforming cannot be met simultaneously without excessive chip area
Solution Approach 1:
The feedback signal path is segmented into multiple paths, each with different delay elements. The first feedback signal path includes a first delay element while the second feedback signal path includes a second delay element with different delay characteristics. This segmentation allows independent optimization of each path for specific phase control requirements, enabling precise phase noise control while maintaining low power consumption by avoiding the need for a single complex high-power feedback path.
Solution Approach 2:
Multiple feedback signal paths with different delay characteristics are merged at the phase detector input. The first feedback signal from the first delay element and the second feedback signal from the second delay element are combined to provide comprehensive phase control capability. This merging approach consolidates multiple phase control functions into a single integrated structure, reducing the overall chip area compared to implementing separate phase control circuits for each function.
3Adaptability or versatility
If beamforming is implemented with a large number of antenna elements requiring individual phase shifts on the oscillator signal, then beam direction control is achieved, but the requirement for accurate programmable phase shifts increases the complexity and power consumption of the phase locked loop
Solution Approach 1:
The phase locked loop incorporates dynamically adjustable delay elements that can be programmed to provide different phase shifts for beamforming operations. The delay elements are controlled by control signals that can be adjusted in real-time to match different beamforming requirements and sub-carrier spacing configurations, enabling the system to adapt to varying phase noise requirements without increasing power consumption.
Solution Approach 2:
The multi-path feedback structure with adjustable delay elements serves multiple functions simultaneously: it provides phase noise control for closer sub-carrier spacing, enables programmable phase shifts for beamforming, and maintains compatibility with different frequency channels and bands. This universal design consolidates what would otherwise require separate dedicated circuits for each function, thereby reducing overall device complexity while maintaining high adaptability.
Data Source
Figure 1
Figure 2~4
Figure 3A~3B
AI summary
A phase locked loop, for a particularly in a beamforming system comprises a loop filter (1) to provide a control signal (FC) to a controllable oscillator (2); a frequency divider (3) configured to provide a first feedback signal (FB) and a second feedback signal (FBD) in response to an oscillator signal (FO), the second feedback signal (FBD) delayed with respect to the first feedback signal (FB); a first comparator path (4) configured to receive the first feedback signal (FB) and a second comparator path (5) configured to receive the second feedback signal (FBD), each of the first and second comparator path (4, 5) configured to provide a respective current signal (CS1, CS2) to the loop filter (1) in response to a respective adjustment signal (FA1, FA2) and a phase deviation between a common reference signal (FR) and the respective feedback signal (FB, FBD).