Interpolated Feedback PLL for Low-Noise Programmable Phase Shifts
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Solution Overview
Problem
5G cellular systems require stringent phase noise and programmable phase shifts for millimeter wave frequencies, which existing phase locked loops struggle to meet due to high frequency demands and large antenna arrays, leading to challenges in beamforming and signal accuracy.
Innovation Solution
A phase locked loop design that uses an interpolator to generate an interpolated feedback signal by comparing a reference signal with a delayed feedback signal, allowing for digitally programmable phase adjustments and reduced phase noise, enabling accurate beamforming and frequency control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional phase locked loops are used for millimeter wave frequencies, then frequency generation is achieved, but phase noise requirements become stringent and programmable phase shift capability is limited
Solution Approach 1:
The feedback signal is divided into multiple paths: a main feedback path and a delayed feedback path. The delayed path is further segmented into multiple taps that can be individually selected and weighted. This segmentation enables independent control of different phase components while maintaining overall phase noise performance.
Solution Approach 2:
The patent changes the temporal parameter by introducing a controlled delay in the feedback path. By adjusting the delay time and selecting different taps in the delayed path, the system achieves programmable phase shifts. The phase control word dynamically changes which delayed tap is active, enabling versatile phase adjustment without degrading phase noise characteristics.
2Productivity
If beamforming with large antenna arrays is implemented, then system range and capacity increase, but individual phase shift accuracy requirements become more stringent
Solution Approach 1:
The patent implements a feedback mechanism where a portion of the oscillator output is fed back through a delayed path and combined with the main feedback signal. This feedback structure enables continuous phase error correction while maintaining the ability to apply programmable phase shifts. The phase detector compares the combined feedback signal with the reference signal, providing accurate phase information for beamforming control.
Solution Approach 2:
The delayed feedback path pre-processes the oscillator signal by introducing controlled delays and selecting specific taps before combining it with the main feedback. This preliminary action prepares the phase-shifted component in advance, enabling accurate and rapid phase adjustment for beamforming without real-time computation overhead.
3Adaptability or versatility
If multiple feedback paths are used for phase control, then programmable phase shift is achieved, but circuit complexity increases
Solution Approach 1:
The patent merges the main feedback path and the delayed feedback path into a single combined feedback signal that is fed to the phase detector. Multiple delayed taps are combined through selective switching rather than requiring separate processing circuits for each path. This merging approach maintains phase control flexibility while significantly reducing circuit complexity compared to fully parallel implementations.
Solution Approach 2:
The delayed feedback path acts as an intermediary between the oscillator output and the phase detector. Instead of directly controlling multiple independent phase shifters, the system uses the delayed path as a mediator to provide pre-shifted feedback signals. This intermediary structure simplifies the overall control architecture while achieving the desired phase control versatility.
4Measurement precision
If high linearity phase adjustment is implemented, then beamforming accuracy improves, but current source matching complexity increases
Solution Approach 1:
The patent replaces complex current source matching mechanisms with a temporal delay-based approach. Instead of relying on precise current amplitude matching across multiple sources, the system uses controlled time delays and digital tap selection to achieve linear phase adjustment. This substitution of mechanical/electrical matching with temporal control significantly reduces the complexity of current source design while maintaining high linearity.
Data Source
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), wherein the second feedback signal (FBD) is delayed with respect to the first feedback signal (FB). An interpolator is configured to receive the first and the second feedback signal (FB) and to provide an interpolated signal thereof between the first and second feedback signal and in response to a phase control word. A comparator path is configured to receive the interpolated signal and to provide a respective signal to the loop filter (1) in response to a phase deviation between a common reference signal (FR) and the interpolated signal.