Active Tunable RF Bandpass Filter With Selective Degeneration
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Solution Overview
Problem
Wireless communications products face challenges with the need for multiple surface acoustic wave (SAW) or bulk acoustic wave (BAW) bandpass filters across various frequency bands, which are expensive and occupy significant layout space, and require numerous receive connections between RF front end modules and system on a chip (SoC), complicating RF signal isolation from digital signals.
Innovation Solution
A first active tunable low-noise RF bandpass filter combines low noise amplifier (LNA) and tunable bandpass filter functionalities into a single active RF bandpass filter using a tunable frequency selective degeneration circuit, reducing gain outside the passband to improve linearity and eliminate the need for passive filters like SAW and BAW filters, while allowing center frequency tuning to reduce the number of receive paths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple passive bandpass filters (SAW/BAW) are used for different frequency bands, then frequency selectivity is improved, but device size and cost increase
Solution Approach 1:
The patent combines multiple bandpass filters for different frequency bands into a single active filter structure using frequency-selective degeneration. The shared filter structure uses switching mechanisms to selectively activate different frequency responses, replacing what would traditionally require multiple separate passive filters. This merging approach maintains frequency selectivity while significantly reducing the total device area and component count.
Solution Approach 2:
The active filter structure is designed to perform multiple frequency filtering functions simultaneously. By using frequency-selective degeneration with switching control, a single filter circuit can be tuned to provide appropriate frequency response for different frequency bands, making the filter universal across multiple bands rather than requiring dedicated filters for each band.
2Adaptability or versatility
If multiple receive connections are provided for different frequency bands, then frequency band support is improved, but layout complexity and RF-digital isolation difficulty increase
Solution Approach 1:
The patent merges multiple receive paths into a single shared path by implementing frequency-selective filtering within a common filter structure. Instead of providing separate receive connections for each frequency band, the system uses a single receive path with an active filter that can be tuned to different frequency bands through switching control, thereby reducing layout complexity and the number of RF-digital isolation requirements.
Solution Approach 2:
The filter structure incorporates dynamic switching mechanisms that allow the same physical circuit to be reconfigured for different frequency bands. This dynamic reconfiguration capability enables a single receive connection to serve multiple frequency bands, reducing the static layout complexity that would otherwise require multiple dedicated connections.
3Area of stationary object
If passive bandpass filters are eliminated, then device size and cost are reduced, but linearity in the presence of strong interfering RF signals deteriorates
Solution Approach 1:
The patent employs frequency-selective degeneration, which is a form of feedback mechanism. By introducing a feedback path through the degeneration circuit that is selective to specific frequency bands, the system can control the gain and linearity characteristics dynamically. This feedback approach allows the active filter to maintain linearity when processing strong interfering signals while still providing the size and cost benefits of eliminating traditional passive filters.
4Ease of manufacture
If a single active RF bandpass filter is used instead of multiple passive filters, then device integration is improved, but gain control complexity increases
Solution Approach 1:
The patent uses dynamic switching mechanisms controlled by band selection signals to adjust the degeneration impedance and gain characteristics. The switching control logic is simplified by using the existing band selection signals from the RF front end, so the gain control complexity is managed through coordinated switching rather than requiring independent complex control circuits. This approach maintains ease of manufacture through integration while managing gain control through systematic switching strategies.
Data Source
AI summary
The present disclosure relates to a first active tunable low-noise RF bandpass filter that includes at least a first transistor element and a tunable frequency selective degeneration circuit coupled to a first non-inverting output of the first transistor element. The first active tunable low-noise RF bandpass filter combines low noise amplifier (LNA) and tunable bandpass filter functionalities into a single active RF bandpass filter. The tunable frequency selective degeneration circuit uses degeneration at frequencies outside of a passband of the active RF bandpass filter to increase feedback, thereby decreasing gain of the active RF bandpass filter. By decreasing the gain, linearity of the active RF bandpass filter may be improved in the presence of strong interfering RF signals, thereby enabling elimination of passive bandpass filter elements, such as surface acoustic wave (SAW) and bulk acoustic wave (BAW) filters, without degrading reception of in-band RF signals.