Fractional-N PLL Timing Offset Compensation With Integer PLL Control
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Solution Overview
Problem
Frequency synthesizers, particularly fractional-N synthesizers, suffer from unpredictable phase startup, large static phase offset, and poorly controlled timing offset behavior, which can lead to instability and inaccurate timing relationships in electronic systems, especially in applications like phased array communication systems.
Innovation Solution
Incorporating an integer phase-locked loop (PLL) that generates a phase adjustment signal to compensate for timing offsets in frequency synthesizers, allowing for deterministic control of the output clock signal's phase and reducing phase offset variations, even across temperature changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a fractional-N frequency synthesizer is used to provide finer output frequency steps, then frequency adjustment precision is improved, but timing offset control deteriorates (large and unpredictable phase offset)
Solution Approach 1:
The system is divided into two independent frequency synthesizers: a fractional-N synthesizer for fine frequency adjustment and an integer-N synthesizer for timing offset compensation. Each synthesizer handles a specific function, allowing the fractional-N to provide precise frequency steps while the integer-N maintains stable timing reference
Solution Approach 2:
A phase adjustment signal acts as an intermediary between the two synthesizers. The integer-N synthesizer generates this signal to compensate for the timing offset of the fractional-N synthesizer, mediating the timing relationship between them
2Stability of the object's composition
If an integer-N frequency synthesizer is used to maintain stable timing reference, then timing stability is improved, but frequency adjustment flexibility deteriorates (cannot provide fractional frequency steps)
Solution Approach 1:
The frequency synthesis function is segmented between two synthesizers: the integer-N synthesizer maintains stable timing reference while the fractional-N synthesizer provides fine frequency adjustment capability, combining both advantages in a unified system
Solution Approach 2:
The system achieves multi-functionality by combining both integer-N and fractional-N synthesizers, allowing it to simultaneously provide timing stability (from integer-N) and frequency adjustment flexibility (from fractional-N)
3Measurement precision
If phase adjustment is applied to compensate timing offset, then timing accuracy is improved, but system complexity increases (requires additional PLL circuitry)
Solution Approach 1:
The integer-N synthesizer automatically generates the phase adjustment signal to compensate for its own timing offset, making the system self-correcting without requiring external intervention or complex control mechanisms
Data Source
AI summary
Apparatus and methods for timing offset compensation of frequency synthesizers are provided herein. In certain embodiments, an electronic system includes a frequency synthesizer, such as a fractional-N phase-locked loop (PLL), which generates an output clock signal based on timing of a reference clock signal. Additionally, the electronic system includes an integer PLL configured to compensate for a timing offset, such as a phase offset and/or frequency offset, of the frequency synthesizer based on timing of the output clock signal.