Receiver Feedback Filter Circuit for Interference Rejection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing television receivers face challenges in maintaining sensitivity and linearity in the presence of strong interference signals, particularly due to the need for high-quality filters that are costly and inefficient, especially in silicon tuners where the selective filter is placed after the LNA, leading to increased noise figures and degraded performance.
Innovation Solution
A receiver design incorporating a feedback path with a tuneable filter and buffer amplifier, where the filter is input-referred due to the Miller effect, allowing it to filter out unwanted signals before they reach the amplifier, thereby reducing the amplifier's processing burden and enabling better sensitivity for weak signals without requiring high-quality components across the full frequency spectrum.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a selective filter is placed in series at the input of the amplifier, then interference signals are attenuated and receiver sensitivity is improved, but high-quality filters are required which increases cost and complexity
Solution Approach 1:
The patent introduces a buffer amplifier as an intermediary component between the amplifier and the filter. This buffer amplifier isolates the filter from the amplifier's input, allowing the filter to be placed in a feedback path rather than directly at the amplifier input. This intermediary arrangement enables the use of lower-quality, less expensive filters while maintaining the same interference attenuation performance, as the buffer amplifier handles the impedance matching and signal buffering functions that would otherwise require a high-quality filter to perform.
2Ease of manufacture
If the filter is placed after the LNA in silicon tuners, then the circuit integration is simplified, but the noise figure increases and performance degrades
Solution Approach 1:
The patent employs feedback by placing the filter in a feedback path that connects the amplifier output back to its input through the buffer amplifier. This feedback configuration allows the filter to affect the amplifier's input signal while maintaining circuit integration. The feedback mechanism enables the filter to perform its selective attenuation function effectively even though it is not directly in the forward signal path, thus improving noise figure while maintaining ease of manufacture through integrated circuit implementation.
3Reliability
If the amplifier processes strong unwanted signals across the full frequency spectrum, then linearity must be high to avoid SNR degradation, but this increases the amplifier's design complexity and reduces sensitivity for weak signals
Solution Approach 1:
The patent applies preliminary action by having the filter perform selective attenuation of interference signals before these strong unwanted signals reach the amplifier. The filter is positioned in the feedback path where it can preemptively remove harmful frequency components from the signal that will be processed by the amplifier. This preliminary filtering action reduces the linearity burden on the amplifier, allowing it to focus on amplifying weak desired signals without being overwhelmed by strong interferers, thus improving SNR performance while reducing amplifier design complexity.
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 configuration enhances the receiver's sensitivity and noise figure performance by filtering out interference signals before they are processed, allowing for higher gain without signal distortion, and reduces the need for expensive, high-quality filters, improving overall receiver performance and cost-effectiveness.
Implementation Method 1
Use of the buffer amplifier can enable the gain of the amplifier to be independent from the impedance of the filter, as the buffer amplifier can adapt the impedance between the output of the amplifier and the filter
Implementation Method 2
the filter is configured to pass signals having a desired frequency... the filter performs as if it were connected directly to the input of the amplifier, thereby filtering out unwanted signals before they are processed by the amplifier
Implementation Method 3
The filter is input-referred and due to the Miller effect it performs as if it were connected directly to the input of the amplifier
Data Source
AI summary
A receiver (400; 500) comprising an amplifier (406; 506) having an input (408) and an output (410). The input (408) of the amplifier is configured to receive a signal. The receiver also comprises a feedback path (412; 512) between the output (410) and the input (408) of the amplifier (406; 506), wherein the feedback path (412; 512) includes a filter (402; 502) and a buffer amplifier (414; 514) in series. The input of the buffer amplifier (414; 514) is connected to the output (410; 510) of the amplifier (406; 506). The output of the buffer amplifier (414; 514) is connected to the input of the filter (402; 502). The output of the filter (402; 502) is connected to the input (408; 508) of the amplifier (406; 506). The filter (402; 502) is configured to pass signals having a desired frequency.