PLL Loop Filter Slope Alternator for Fast Frequency Modulation
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Solution Overview
Problem
Existing frequency modulation methods using phase-locked loops face limitations in bandwidth, leading to signal distortion during fast modulation, and are not suitable for compound-based processes or high-frequency operations due to complexity and area inefficiency.
Innovation Solution
A frequency modulation method based on a phase-locked loop that generates an offset current using a slope alternator circuit in the integral path of the loop filter, allowing for fast modulation independent of bandwidth, suitable for compound-based processes and high-frequency operations, by determining the moment of change from modulation rise to fall and summing the offset and charge pump currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional phase-locked loop frequency modulation method is used, then the system structure is simple, but the modulation signal is distorted during fast modulation due to bandwidth limitations
Solution Approach 1:
The loop filter is divided into two independent paths: a proportional path and an integral path. The proportional path handles fast modulation responses while the integral path maintains steady-state accuracy, allowing the system to achieve fast modulation independent of bandwidth without requiring a completely new architecture
Solution Approach 2:
The slope alternator dynamically switches the proportional path between enabled and disabled states based on modulation direction changes. During fast modulation transitions, the proportional path is enabled to provide rapid response, while during steady-state operation, it is disabled to prevent distortion, making the system adaptive to different operational conditions
2Speed
If the modulation bandwidth is increased to enable fast modulation, then fast modulation ability is improved, but the system complexity and area increase
Solution Approach 1:
The slope alternator detects modulation direction changes in advance and proactively switches the proportional path before the actual modulation transition occurs. This preliminary action ensures the system is already in the correct configuration to handle fast modulation, eliminating the need for increased bandwidth while maintaining modulation speed
Solution Approach 2:
The proportional path acts as an intermediary between the charge pump and the integral path. It provides a direct current path during fast modulation transitions, bypassing the bandwidth-limited integral path, thereby enabling fast modulation without increasing the overall system bandwidth requirements
3Speed
If the proportional path is always enabled for fast modulation, then modulation response is improved, but signal distortion occurs during steady-state operation
Solution Approach 1:
The proportional path is dynamically controlled rather than always enabled. The slope alternator monitors modulation direction and switches the proportional path on during transitions and off during steady-state operation, allowing the system to adapt its characteristics to match the operational requirements at each moment
Solution Approach 2:
The proportional path is activated periodically only when modulation direction changes are detected, rather than operating continuously. This periodic activation provides fast response when needed while avoiding the signal distortion that would result from continuous operation during steady-state conditions
Data Source
AI summary
The present invention relates to a frequency modulation method based on a phase-locked loop capable of performing fast modulation independent of bandwidth.A frequency modulation system based on a phase-locked loop capable of performing fast modulation independent of bandwidth according to the present invention includes a loop filter including a proportional path and an integral path to determine a bandwidth of a phase-locked loop, a voltage-controlled oscillator configured to adjust a frequency according to an output of the loop filter, and a slope alternator configured to alternate an input current of the loop filter, wherein the slope alternator is located in the integral path of the loop filter to generate an offset current at a moment of change from a modulation rise to a modulation fall.