Active Frequency-Selective Circuit for High-Q Low-Noise Filtering
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Solution Overview
Problem
Existing frequency selective circuits, such as low-pass filters, face challenges in achieving high Q filtering while minimizing output noise, often requiring additional stages that increase area and noise levels, corrupting the desired signal.
Innovation Solution
A frequency selective circuit design incorporating transistors, capacitors, and resistors, with an optional inductive element, configured to enhance the Q-factor and reduce noise by optimizing the transfer function and incorporating cascode stages or multiple sub-circuits for high-order filtering, allowing for high Q filtering without increasing noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If more stages of RC filters are cascaded to achieve better signal rejection, then the rejection performance is improved, but the output noise increases and the circuit area occupies more space
Solution Approach 1:
The patent replaces traditional passive RC filter stages with an active filter circuit using transconductance amplifiers (gm-C filters). This substitution allows the circuit to achieve high Q-factor and good signal rejection without requiring multiple cascaded RC stages, thereby reducing output noise while maintaining rejection performance.
Solution Approach 2:
The patent changes the filtering mechanism from passive RC time constants to active transconductance-based frequency selection. By adjusting the transconductance parameters of the amplifiers and the values of capacitors, the circuit achieves high Q-factor filtering with controlled noise performance, avoiding the noise accumulation inherent in multiple passive RC stages.
2Reliability
If more stages of RC filters are cascaded to achieve better signal rejection, then the rejection performance is improved, but the circuit area occupies more space
Solution Approach 1:
The patent replaces multiple passive RC filter stages with a compact active filter implementation using transconductance amplifiers. This substitution achieves the same or better rejection performance in a smaller area because active filters can provide higher Q-factors with fewer stages, reducing the overall circuit footprint.
Solution Approach 2:
The transconductance amplifier-based filter circuit serves multiple functions: frequency selection, signal amplification, and impedance matching, all within a compact structure. This multi-functionality eliminates the need for separate RC stages, reducing the total circuit area while maintaining rejection performance.
3Device complexity
If simple LPF with passive RC filters is used, then the circuit complexity is low, but the Q-factor is low and rejection is insufficient
Solution Approach 1:
The patent substitutes passive RC filters with active transconductance amplifier-based filters. This substitution increases the Q-factor significantly because active filters can provide higher quality factors through feedback mechanisms and transconductance control, while the circuit complexity remains manageable due to the modular nature of the gm-C filter design.
Data Source
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AI summary
A frequency selective circuit includes a first transistor, an impedance element, a first capacitive element, a second capacitive element, a second capacitive and a second transistor. The first transistor includes a first terminal, a second terminal and a control terminal. The impedance element is coupled between the first terminal and the control terminal of the first transistor. The first capacitive element is coupled to the first terminal of the first transistor. The second capacitive element is coupled to the control terminal of the first transistor. The second transistor includes a first terminal, a second terminal and a control terminal, wherein the control terminal of the second transistor is coupled to the control terminal of the first transistor.