Frequency Divider Range Extension Across Octave Boundaries
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Solution Overview
Problem
Existing frequency dividers with extended division range architectures suffer from phase discontinuities when the divisor value crosses an octave boundary, leading to incorrect division and holes in the frequency plan, particularly in fractional-N synthesizers.
Innovation Solution
A frequency divider circuit comprising a series of divide-by-2/3 cells and divide-by-1/2/3 cells, designed to maintain continuity across octave boundaries by using latches, inverter gates, and OR gates, allowing for seamless transitions in divisor values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a cascade of divide-by-2/3 cells is used to extend division range beyond one octave, then the division range is extended, but phase discontinuities occur when crossing octave boundaries
Solution Approach 1:
A synchronous enable circuit acts as an intermediary between the divide-by-2/3 cells and the clock signal. This enable circuit generates synchronized enable signals that coordinate the operation of all divide cells across octave boundaries, preventing phase discontinuities while maintaining the extended division range capability.
Solution Approach 2:
The enable circuit anticipates octave boundary crossings by monitoring the division state and proactively generates enable signals before the transition occurs. This preliminary action ensures that all divide cells are properly synchronized and prepared for the octave boundary crossing, eliminating phase discontinuities.
2Reliability
If divide-by-1/2/3 cells are used with latches and OR gates to maintain continuity, then phase continuity is maintained across octave boundaries, but circuit complexity increases
Solution Approach 1:
The divide-by-1/2/3 cells are designed to perform multiple functions: they can divide by 1, 2, or 3 depending on control signals, and they can operate in synchronized or asynchronous modes. This multi-functionality allows a single circuit design to handle both intra-octave and inter-octave transitions without requiring separate circuits for each mode.
Solution Approach 2:
The enable circuit combines the output signals from multiple divide-by-1/2/3 cells through OR gates to generate a unified enable signal. This merging approach consolidates the control logic and reduces the overall circuit complexity compared to having separate control circuits for each divide cell.
Data Source
Figure 1
Figure 2A~2B
Figure 3A~3C
AI summary
A frequency divider based on a series of divide-by-2/3 cells and divide-by-1/2/3 cells using extended division range is disclosed. The frequency divider uses modified divide-by-1/2/3 cells and additional circuit elements to correctly divide an input frequency by a divisor on successive output cycles while the divisor transitions across an octave boundary. The frequency divider creates a divide-by-1 mode for unused divide-by-1/2/3 cells in the series of cells. The divide-by-1 mode passes the input clock in the unused latches of each unused divide-by-1/2/3 cell as opposed to having each unused divide-by-1/2/3 cell implement divide-by-3 mode.