Variable Bandpass Filter Using Tunable Resonator Feedback
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Solution Overview
Problem
Current bandpass filters lack the ability to electronically adjust their pass-band center frequency and bandwidth effectively, limiting their versatility in signal processing applications, particularly in RF, microwave, and millimeter wave frequencies.
Innovation Solution
A variable filter design incorporating a signal loop with a frequency tunable resonator and an adjustable scaling block, controlled by a controller to achieve desired frequency responses, allowing for positive and negative gain adjustments and Q-enhancement or Q-spoiling of resonators.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If feedback gain is increased to achieve narrower bandwidth, then bandwidth is reduced, but the filter becomes an oscillator when loop gain exceeds unity
Solution Approach 1:
The patent implements feedback control where a portion of the output signal is fed back to the input through a controllable gain element. By adjusting the feedback gain factor, the system can achieve arbitrarily narrow bandwidth while maintaining stability as long as the loop gain remains below unity. This resolves the contradiction by providing continuous control over the feedback strength.
Solution Approach 2:
The patent changes the feedback gain parameter dynamically to control bandwidth. The gain factor can be adjusted continuously from zero to values approaching unity, allowing the bandwidth to be tuned from wide to arbitrarily narrow without crossing into oscillation. This parameter control mechanism resolves the stability-bandwidth tradeoff.
2Adaptability or versatility
If resonator selectivity is reduced to broaden pass band, then bandwidth increases, but control over center frequency and bandwidth becomes coarser
Solution Approach 1:
The feedback mechanism allows independent control of bandwidth and center frequency. By adjusting the feedback gain factor and phase, the system can achieve precise control over both parameters simultaneously, regardless of the resonator's inherent selectivity. This resolves the contradiction by decoupling the control precision from the resonator quality factor.
Solution Approach 2:
The patent introduces dynamic control elements (variable gain block, phase shifter) that allow real-time adjustment of feedback parameters. This dynamic control enables fine-tuning of center frequency and bandwidth independently, providing precise control even when using resonators with broader pass bands.
3Device complexity
If passive elements are used for tuning, then device complexity is reduced, but the ability to achieve arbitrary bandwidth and fine frequency control is limited
Solution Approach 1:
The feedback control system provides electronic tuning capability that surpasses passive element limitations. By using a controllable gain element and phase shifter in the feedback path, the system can achieve arbitrary bandwidth and precise frequency control with relatively simple circuit topology, resolving the contradiction between simplicity and versatility.
Solution Approach 2:
The feedback-based tuning mechanism serves multiple functions: it controls bandwidth, adjusts center frequency, and can compensate for resonator variations. This multi-functional approach provides superior adaptability while maintaining circuit simplicity, as a single feedback loop handles all tuning requirements.
Data Source
AI summary
A variable filter has a signal loop defined between a signal input and a signal output. A plurality of circuit elements connected in the signal loop, the plurality of circuit elements comprising a frequency tunable resonator, and an adjustable scaling block that applies a gain factor that is adjustable in a range that comprises a positive gain and a negative gain. A controller is connected to 1) tune the frequency tunable resonator; and to 2) adjust the gain factor of the adjustable scaling block between a negative gain factor to a positive gain factor providing for variable Q independent of frequency.