Dual-band Active Filter with Cascade Gain Stages
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Solution Overview
Problem
Conventional dual-band filters for microwave and millimeter-wave communication systems face challenges in achieving positive gain and high stop-band rejection due to their passive nature, which results in signal loss and the need for additional passive filters to suppress out-of-band interference.
Innovation Solution
A dual-band active filter design comprising multiple gain stages and match units constructed from L-type networks with inductors and capacitors, providing bandpass, high-pass, and low-pass filtering responses, while maintaining positive gain and allowing for precise prediction of filter performances and transmission zeros.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional passive dual-band filter structures are used, then the filter provides stop-band suppression, but the filter suffers from signal loss and provides no positive gain
Solution Approach 1:
The patent merges the filtering function and amplification function into a single dual-band active filter structure. The filter includes gain stages with transistors that provide both frequency selection and signal amplification, eliminating the need for separate passive filters and amplifiers. This integration resolves the contradiction by providing both stop-band suppression and positive gain simultaneously.
Solution Approach 2:
The dual-band active filter performs multiple functions within a single device: it provides dual-band frequency filtering, stop-band suppression, and signal amplification. The gain stages are designed to operate across both frequency bands while maintaining filtering characteristics, making the filter universally functional for both signal selection and amplification needs.
2Adaptability or versatility
If conventional passive dual-band filter structures are used, then the filter achieves dual-band operation, but the filter provides poor stop-band suppression and requires extra passive filters
Solution Approach 1:
The patent combines multiple filtering functions into a unified active filter structure. The filter includes series and shunt resonators configured to provide both dual-band passband operation and enhanced stop-band suppression. By merging these functions into a single active structure rather than cascading separate passive filters, the patent achieves both dual-band operation and strong stop-band rejection.
Solution Approach 2:
The patent uses parameter optimization in the active filter design, including adjusting resonator dimensions, transistor biasing conditions, and coupling coefficients to achieve both dual-band operation and improved stop-band suppression. The gain stages are designed with specific impedance values and frequency responses that enhance rejection in stopbands while maintaining passband performance.
3Reliability
If off-chip passive filters are used, then the filter achieves good filtering performance, but the filter becomes bulky and difficult to implement as true single-chip
Solution Approach 1:
The patent integrates the active filter circuitry directly onto a single chip, combining amplification and filtering functions in one monolithic device. The gain stages, resonators, and matching networks are all fabricated on the same semiconductor substrate, eliminating the need for bulky off-chip passive components and enabling true single-chip implementation with compact form factor.
Solution Approach 2:
The patent replaces traditional mechanical/passive filter structures with an active electronic filter implementation using transistors and integrated circuit components. This substitution enables miniaturization and single-chip fabrication while maintaining or improving filtering performance through active device characteristics and integrated design.
Data Source
AI summary
The present invention discloses a dual-band active filter having filtering response and positive pass-band gain. The dual-band active filter includes an input match unit for gain match of the dual-band active filter and for having a band-pass filtering response; a first gain stage electrically connected to the first input match unit for providing the flat gain of the dual-band active filter; an inter-stage unit electrically connected to the first gain stage for matching gain and for having a band-stop filter response; a second gain stage electrically connected to the inter stage unit for providing the flat gain of the dual-band active filter; and an output unit electrically connected to the second gain stage for matching the dual-band active filter and for having a low-pass filtering response. The dual-band active filter according to the present invention uses the cascade connection of multiple filter stages to have band-pass filtering response at two different frequency bands and obtain high stop-band attenuation by providing plural transmission zeros in the stop-band.