VCO Multi-Point Modulation with Fast-Path Linearization
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Solution Overview
Problem
Existing linearization techniques for voltage controlled oscillators (VCOs) are not readily applicable to advanced loop architectures, particularly in high-data-rate communications, where precise modulation and rapid phase changes are required, and are hindered by spurious output signal transitions and limited time resolution.
Innovation Solution
A multi-point modulation linearization technique is introduced, utilizing a correction table to form a corrected control variable affecting the fast modulation path, with the slow modulation path controlled by an error-forming circuit and loop filter, enabling more rapid phase changes and improved modulation properties in advanced loops like mostly-digital frequency locked loops and phase locked loops.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional linearization techniques are used for VCOs, then the linear operating region can be extended, but these techniques are not applicable to advanced loop architectures requiring rapid phase changes
Solution Approach 1:
The patent segments the control signal into multiple components: a coarse control signal for slow modulation and a fine control signal for fast modulation. This segmentation allows the system to handle both rapid phase changes and maintain compatibility with advanced loop architectures by treating different time scales separately.
Solution Approach 2:
The patent pre-calculates and stores correction values in a lookup table based on the coarse control signal. This preliminary action enables the fine control signal to be generated rapidly without real-time computation, thus supporting fast phase changes while maintaining accuracy in advanced loop architectures.
2Speed
If multi-point modulation is used to enable rapid phase changes, then speed is improved, but device complexity increases due to multiple modulation paths
Solution Approach 1:
The patent merges the coarse and fine control signals at a summing node to produce the final VCO control signal. This combining approach achieves rapid phase changes through the fine signal while keeping the overall structure relatively simple by reusing the existing coarse control path rather than creating entirely separate modulation systems.
Solution Approach 2:
The patent introduces a lookup table as an intermediary component that converts the coarse control signal into pre-computed correction values. This intermediary simplifies the complexity by handling the computationally intensive part offline, allowing the real-time system to operate with simpler logic and fewer active components during rapid phase changes.
3Measurement precision
If loop bandwidth is reduced for smoother lock, then modulation precision is improved, but the ability to track rapid phase changes deteriorates
Solution Approach 1:
The patent creates a dynamic control system where the effective loop bandwidth can adapt to different operating conditions. The fine control path with lookup table provides high-speed response for rapid phase changes, while the coarse control path maintains precision for smooth locking, effectively allowing the system to exhibit different bandwidth characteristics as needed without physical hardware changes.
Data Source
AI summary
The present invention, generally speaking, provides a VCO linearization technique applicable to advanced loop architectures. In particular, the linearization technique is applicable to a mostly-digital frequency locked loop (FLL), phase locked loop (PLL) or the like using multi-point modulation. In an exemplary embodiment, a correction table is used to form a corrected control variable that affects one modulation point only (e.g., a fast modulation path) of the multi-point modulation circuit. The other modulation point (e.g., a slow modulation path) of the multi-point modulation circuit is controlled in accordance with an error-forming circuit including a loop filter. The use of correction within the fast path enables the VCO to achieve more rapid phase changes than would otherwise be possible, an advantage in high-data-rate communications applications, for example.