Single-Conversion Tuner With Image-Reject Mixing and Flat Passband
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing television tuners face challenges in achieving high image rejection and pass band flatness for both off-air and cable reception, leading to suboptimal reception quality due to the different modulation schemes used in these scenarios, and current solutions either require complex dual-conversion architectures or separate tuners optimized for each type of reception.
Innovation Solution
A single conversion tuner incorporating a pre-select filter, amplifier, and image reject mixer that down-converts RF signals directly to an IF frequency, utilizing a tuneable bandpass filter for channel selection and providing high linearity and pass band flatness, allowing for efficient channel selection and improved image rejection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single conversion tuner is used for both off-air and cable reception, then device complexity is reduced, but it cannot simultaneously achieve high image rejection for off-air reception and high pass band flatness for cable reception
Solution Approach 1:
The patent employs a dynamically reconfigurable filter structure that can switch between different operational modes. The filter's characteristics (bandwidth, center frequency, order) are dynamically adjusted based on the detected signal type (8VSB or QAM), allowing the same hardware to optimize performance for both off-air and cable reception without requiring separate dedicated tuners
Solution Approach 2:
The invention changes the filter parameters (bandwidth, order, center frequency) based on the modulation scheme being received. For 8VSB off-air signals, the filter operates with higher order and narrower bandwidth to maximize image rejection, while for QAM cable signals, it transitions to lower order and wider bandwidth to ensure pass band flatness and linearity
2Measurement precision
If dual-conversion architecture is used to achieve high image rejection, then image rejection performance is improved, but device complexity and noise increase
Solution Approach 1:
The patent extracts the image rejection function from the frequency conversion process and implements it separately through a dedicated reconfigurable filter stage. Instead of relying on multiple conversion stages to achieve image rejection, the invention isolates and optimizes the filtering function to provide high image rejection in a single conversion architecture, thereby reducing overall system complexity
Solution Approach 2:
The reconfigurable filter acts as an intermediary element between the RF input and the mixer stage. By positioning this high-selectivity filter before the mixer, the system achieves image rejection without requiring dual conversion, as the filter pre-selects and conditions the signal before frequency conversion occurs
3Measurement precision
If narrow bandwidth filter is used to reject image signals, then image rejection is improved, but pass band flatness deteriorates
Solution Approach 1:
The filter dynamically adapts its bandwidth and order based on the reception mode. When operating in 8VSB mode, the filter transitions to a higher order with narrower bandwidth to maximize image rejection. When switching to QAM mode, it reconfigures to a lower order with wider bandwidth to ensure adequate pass band flatness for cable reception
Solution Approach 2:
The filtering function is segmented into multiple reconfigurable stages with different characteristics. The system can activate different filter sections or adjust the parameters of existing stages to provide appropriate bandwidth and selectivity for different modulation schemes, allowing optimization of both image rejection and pass band flatness as needed
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
The proposed tuner achieves enhanced image rejection and pass band flatness, reducing noise and improving sensitivity, making it suitable for both off-air and cable reception without the need for dual conversion or separate tuners, thus enhancing overall reception quality.
Implementation Method 1
an image reject mixer, wherein the pre-select filter receives an RF signal having multiple TV channels, the tuneable bandpass filter provides a first selection of a desired channel, the image reject mixer down-converts a selected channel to an IF frequency
Data Source
AI summary
A single conversion tuner suitable for receiving RF signals having different requirements as to selectivity, linearity and image rejection is presented. Tuners of this kind are particularly useful for digital terrestrial as well as cable reception, where different modulation schemes require very high image rejection ratios on one hand and high linearity or pass band flatness on the other hand. The inventive tuner features a double-tuned tuneable filter in combination with an image reject mixer. The double-tuned filter provides excellent pass band flatness, while the image reject mixer provides a high intrinsic image rejection. The image rejection ratio of the combination of image reject mixer and tuneable filter is very high and fulfils the requirements of commonly used modulation schemes such as 8VSB, while the pass band flatness is compliant with the requirements for modulation schemes such as QAM.