Feedforward Notch Filter Circuit for Tunable Spurious Rejection
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Solution Overview
Problem
Existing RC low-pass filters are insufficient in certain applications, and designing notch filters to further attenuate spurious emissions is challenging.
Innovation Solution
A transconductance circuit with a feedforward notch filter configuration, utilizing series resistors and capacitors to achieve a tunable notch frequency with minimal in-band noise, incorporating adjustable capacitors to tune the notch frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If an RC low-pass filter is used, then signals below cutoff frequency are passed, but spurious emissions at higher frequencies are not sufficiently attenuated
Solution Approach 1:
The patent combines a low-pass filter and a notch filter into a single integrated circuit structure. The low-pass filter section (R1, C1) and notch filter section (R2, C2, R3, C3) share common nodes and are implemented in a unified manner, allowing both functions to work together to attenuate spurious emissions while maintaining ease of manufacture.
Solution Approach 2:
The filter circuit performs multiple functions simultaneously: it acts as a low-pass filter for general frequency attenuation and as a notch filter for targeted spurious emission rejection. This multi-functionality is achieved through the specific configuration where the output of the low-pass filter feeds into the notch filter section, creating a composite filter with enhanced capabilities.
2Object-affected harmful factors
If a notch filter is added to attenuate spurious emissions, then frequency selectivity is improved, but circuit design complexity increases
Solution Approach 1:
The patent merges the notch filter design with a low-pass filter structure, sharing common components and nodes. The resistor R1 and capacitor C1 form the low-pass section that also serves as part of the overall filter topology, reducing the number of discrete components needed compared to a standalone notch filter.
Solution Approach 2:
The notch frequency is controlled by adjusting the values of R2 and C2, while the cutoff frequency is controlled by R1 and C1. This parameter-based design allows flexible tuning of the filter characteristics without changing the fundamental circuit topology, simplifying the design process for different frequency requirements.
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
Provides a tunable notch frequency with minimal in-band noise impact, suitable for wireless communications circuitry, enhancing signal rejection at specific frequencies.
Implementation Method 1
a first capacitor having a first terminal coupled to a node disposed between the first and second series resistors and having a second terminal coupled to a ground power supply line
Implementation Method 2
a first series resistor having a first terminal coupled to the input of the transconductance circuit and having a second terminal and a second series resistor having a first terminal coupled to the second terminal of the first series resistor
Data Source
AI summary
Circuitry is provided that includes a transconductance circuit and a notch filter coupled along a feedforward path between an input of the transconductance circuit and an output of the transconductance circuit. The notch filter can include a first series resistor having a first terminal coupled to the input of the transconductance circuit and having a second terminal and can further include a second series resistor having a first terminal coupled to the second terminal of the first series resistor and having a second terminal coupled to the output of transconductance circuit. The notch filter can have a notch frequency that is a function of a resistance of the first and second series resistors. The notch frequency can be adjusted.