Quadrature Divide-by-Three Frequency Divider With Feedback Delay
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Solution Overview
Problem
Existing frequency dividers in local oscillators for radio receivers and transmitters face challenges in achieving a wide VCO tuning range, particularly when generating quadrature signals, as traditional divide-by-three frequency dividers do not produce signals 90 degrees out of phase, making them unsuitable for applications requiring phase shift keying modulation and image canceling.
Innovation Solution
A programmable frequency divider is introduced, incorporating a divide-by-three circuit, a delay circuit, and a feedback circuit to generate 50% duty cycle quadrature signals that differ by 90 degrees, allowing the frequency divider to be set to divide by three while maintaining phase accuracy across temperature and voltage variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a traditional divide-by-three frequency divider is used, then the frequency division ratio is reduced, but the output signals are not 90 degrees out of phase making them unsuitable for quadrature applications
Solution Approach 1:
The frequency divider is segmented into three separate divide-by-three circuits (first, second, and third circuits) that generate three phase-shifted signals. Each circuit handles a specific phase component, allowing the system to achieve both frequency division and proper quadrature phase relationships through the combination of these segmented circuits.
Solution Approach 2:
A delay circuit is introduced as an intermediary component between the divide-by-three circuits and the final output. This delay circuit adjusts the timing of signals to ensure that the output signals are precisely 90 degrees out of phase, mediating the phase relationship between the frequency-divided signals.
2Adaptability or versatility
If the VCO tuning range is widened to cover multiple frequency bands, then adaptability is improved, but the VCO design becomes more difficult and complex
Solution Approach 1:
The system uses programmable frequency dividers with adjustable division ratios (N and M) that can be dynamically configured through control signals. This dynamic reconfigurability allows the same VCO to serve multiple frequency bands by changing the division ratios rather than requiring a wide tuning range, simplifying the VCO design while maintaining adaptability.
Solution Approach 2:
The invention changes the operational parameters (division ratios) of the frequency divider circuits to adapt to different frequency bands. By programmatically adjusting the division ratios N and M, the system can cover multiple frequency bands without requiring the VCO to be designed for an excessively wide tuning range, thereby reducing VCO design complexity.
3Productivity
If frequency division by three is implemented without quadrature output, then the division ratio is reduced, but the local oscillator cannot support phase shift keying modulation and image canceling
Solution Approach 1:
The frequency divider system is designed to be universal by simultaneously achieving frequency division by three and generating quadrature outputs. The multiple divide-by-three circuits combined with the delay circuit create a multi-functional system that supports both frequency division and quadrature signal generation, enabling the local oscillator to support phase shift keying modulation and image canceling while maintaining the reduced frequency division ratio.
Data Source
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AI summary
A local oscillator includes a programmable frequency divider coupled to the output of a VCO. The frequency divider can be set to frequency divide by three. Regardless of the divisor, the frequency divider outputs quadrature signals (I, Q) that differ from each other in phase by ninety degrees. To divide by three, the frequency divider includes a divide-by-three frequency divider. The divide-by-three frequency divider includes a divide-by-three circuit, a delay circuit, and a feedback circuit. The divide-by-three circuit frequency divides a signal from the VCO and generates therefrom three signals C, A' and B that differ from each other in phase by one hundred twenty degrees. The delay circuit delays signal A' to generate a delayed version A of the signal A'. The feedback circuit controls the delay circuit such that the delayed version A (I) is ninety degrees out of phase with respect to the signal C (Q).