Fractional-N Synthesizer with Cascaded Dividers for Wide Frequency Tuning
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Solution Overview
Problem
Conventional tunable synthesizers have limited frequency-tuning ratios, making them inadequate for covering the entire wireless communication spectrum from 300 MHz to 3 GHz, which is required for multi-standard and multi-band transceivers.
Innovation Solution
A tunable synthesizer design utilizing cascaded frequency dividers and CMOS-based tunable oscillators, integrated onto a single ASIC chip, with a multiplexer to select frequency-dividing outputs, achieving a frequency-tuning ratio of 16 and a wide tuning range by using multiple frequency-dividing circuit branches with different division factors, including powers of 2.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional tunable synthesizers are used, then the device complexity is low, but the frequency-tuning ratio is limited and cannot cover the entire wireless communication spectrum
Solution Approach 1:
The synthesizer is divided into multiple frequency-dividing circuit branches, each with a different division factor (e.g., 1, 2, 4, 8). Each branch processes the VCO output independently, and a multiplexer selects the appropriate branch output. This segmentation allows the system to achieve a wide frequency-tuning ratio (up to 16:1) by combining multiple simpler stages, resolving the contradiction between versatility and complexity.
Solution Approach 2:
The synthesizer employs a tunable VCO whose output frequency can be dynamically adjusted, combined with a multiplexer that dynamically selects among different frequency-dividing branches. This dynamic configuration enables the system to adapt to different frequency requirements (from 187.5 MHz to 3 GHz) while maintaining a manageable device complexity through controlled reconfiguration rather than fixed architecture.
2Adaptability or versatility
If multiple frequency-dividing circuit branches with different division factors are used, then the frequency coverage is expanded, but the device complexity increases
Solution Approach 1:
Multiple frequency-dividing circuit branches share common components including the VCO input stage, power supply, and control logic. The multiplexer acts as a universal selector that can route to any branch. This multi-functionality approach allows different division factors to be implemented using similar circuit topologies, expanding frequency coverage while minimizing the increase in overall device complexity through component sharing.
Solution Approach 2:
The frequency-dividing branches are structured in a nested hierarchy where each branch builds upon the common VCO input and control infrastructure. The multiplexer integrates all branch outputs into a single unified output interface. This nesting allows the system to incorporate multiple division factors (1, 2, 4, 8) without proportionally increasing complexity, as each additional branch leverages the existing architectural framework.
3Adaptability or versatility
If the synthesizer covers the entire wireless communication spectrum (300 MHz to 3 GHz), then the adaptability for multi-standard transceivers is improved, but the manufacturing precision requirements increase
Solution Approach 1:
By segmenting the frequency synthesis into multiple branches with discrete division factors, each branch can be optimized for specific frequency ranges. The VCO operates in a higher frequency range (e.g., 1.875 GHz to 3 GHz), and the frequency dividers systematically reduce these to cover lower bands. This segmentation reduces the manufacturing precision burden on individual components compared to designing a single wide-band synthesizer, as each segment operates within tighter, more controllable parameters.
Solution Approach 2:
The system achieves multi-standard support by changing the effective output frequency parameter through selective activation of different frequency-dividing branches rather than requiring each component to precisely cover the entire 300 MHz to 3 GHz range. The VCO frequency and divider selection are adjusted as parameters to adapt to different standards (GSM, W-CDMA, etc.), reducing manufacturing precision requirements while maintaining broad adaptability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables a synthesizer with a frequency-tuning range of 187.5 MHz to 3 GHz, effectively supporting the entire wireless communication spectrum, addressing the limitations of conventional synthesizers with enhanced frequency coverage.
Implementation Method 1
The tunable synthesizer includes one or two tunable synthesizer sources and multiple frequency-dividing circuit branches
Implementation Method 2
multiple frequency-dividing circuit branches, each providing a tunable output at a different frequency band
Implementation Method 3
a multiplexer to select frequency-dividing outputs
Data Source
AI summary
One embodiment of the present invention provides a synthesizer. The synthesizer includes one or more tunable oscillators, a frequency-dividing circuit coupled to the tunable oscillators, and a multiplexer coupled to the frequency-dividing circuit. The frequency-dividing circuit includes a number of frequency dividers, and is configured to generate a number of frequency-dividing outputs. At least one frequency-dividing output has a different frequency division factor. The multiplexer is configured to select a frequency-dividing output.