Offset Frequency Synthesis for Multi-Stream Receiver VCO Pulling
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Solution Overview
Problem
In multi-stream TV receivers, the issue of VCO pulling occurs due to the simultaneous operation of oscillators, leading to unacceptable reception quality, especially in broadband applications where bonded channels are used, causing interference and degradation in signal reception.
Innovation Solution
The implementation of an offset frequency synthesizer architecture that maximizes the frequency distance between LC-VCOs by generating an on-demand offset frequency, using fractional-N and integer-N phase-locked loops, and a single sideband mixer to adjust the frequency planning dynamically, thereby minimizing VCO pulling and maintaining high reception quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multiple LC-VCOs operate simultaneously in multi-stream receivers, then multi-stream reception capability is improved, but VCO pulling occurs causing frequency degradation and reception quality deterioration
Solution Approach 1:
The patent divides the frequency synthesis function into separate segments for each receiver stream, with each stream having its own LC-VCO and frequency synthesizer. This segmentation allows independent frequency control for each stream, preventing mutual interference and VCO pulling while maintaining multi-stream reception capability
Solution Approach 2:
The patent applies local quality by optimizing the frequency planning and offset frequency generation specifically for each receiver stream's local oscillator. Each stream receives a tailored frequency plan that maximizes frequency distance from other streams, thereby maintaining high reception quality for each individual stream while enabling multi-stream operation
2Reliability
If frequency distance between LC-VCOs is maximized to avoid VCO pulling, then reception quality is improved, but frequency planning complexity increases
Solution Approach 1:
The patent implements dynamic frequency planning where offset frequencies are generated on-demand based on the specific channel selections and receiver configurations. The system dynamically adjusts frequency offsets to maintain optimal frequency distance between concurrent streams, rather than using fixed frequency plans, thereby managing complexity through adaptive control
Solution Approach 2:
The patent introduces an offset frequency generator as an intermediary component that mediates between the channel selection logic and the LC-VCOs. This intermediary calculates and applies appropriate frequency offsets to maximize frequency distance between streams, simplifying the overall frequency planning by centralizing the offset calculation function
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
This solution effectively reduces VCO pulling, allowing for simultaneous multi-stream reception without signal degradation, enabling efficient operation in broadband applications by maintaining a significant frequency distance between oscillators, thus preventing coupling and ensuring high-quality signal reception.
Implementation Method 1
using fractional-N and integer-N phase-locked loops
Implementation Method 2
a single sideband mixer to adjust the frequency planning dynamically
Data Source
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AI summary
A method of operating a multi-stream reception scheme, such as DOCSIS (Data Over Cable Service Interface Specifications), comprising at least two receivers (10, 12, 14) having respective voltage controlled oscillators (16), the method including monitoring a change in local oscillator frequency in a selected one of the at least two streams and, if the frequency distance between the local oscillator frequencies is below a value likely to cause pulling or coupling between the voltage controlled oscillators of the at least two receivers, resetting the frequency planning of the selected one of the at least two streams to maximise the frequency distance of the voltage controlled oscillator of the selected stream with the voltage controlled oscillators of the or the other streams.