Tunable Analog Filter with Independent Q and Frequency Control
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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 flexibility in frequency filtering applications, especially in RF, microwave, and millimeter wave frequencies.
Innovation Solution
A controllable analog filter with a variable resonator and adjustable gain block, allowing for Q-enhancement and Q-spoiling, which enables precise control over the filter's center frequency and bandwidth, preventing spurious passband responses while maintaining the ability to tune over a broad range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
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 the output signal is fed back to the input through a controllable gain block. By adjusting the feedback gain to be slightly less than unity, the system achieves arbitrarily narrow bandwidth without becoming an oscillator. The feedback mechanism allows continuous adjustment of the loop gain to maintain stability while achieving the desired bandwidth.
Solution Approach 2:
The patent changes the feedback gain parameter to control the bandwidth. By varying the gain block's amplification factor, the system can achieve different bandwidths while maintaining stability. The key is to keep the loop gain slightly below unity, which prevents oscillation while allowing narrow bandwidth control.
2Adaptability or versatility
If resonator selectivity is reduced to broaden pass band, then bandwidth increases, but control over center frequency becomes coarser
Solution Approach 1:
The feedback path with controllable gain allows the system to achieve fine control over the center frequency even when the resonator has a broader passband. The feedback mechanism compensates for the reduced selectivity by providing additional control over the frequency response, enabling precise center frequency adjustment across a broader range.
Solution Approach 2:
The patent makes the feedback gain dynamic and adjustable, allowing the system to adapt its characteristics. By varying the feedback gain, the system can achieve different effective bandwidths and center frequencies, providing both broad tuning range and fine control precision through a single dynamic parameter.
3Device complexity
If passive elements are used for tuning, then device complexity is reduced, but electronic adjustability and control flexibility are limited
Solution Approach 1:
The patent introduces a feedback path with a controllable gain block, transforming a simple passive resonator into an active tunable filter. The feedback mechanism provides electronic control flexibility while maintaining relatively simple circuit structure. The gain block can be adjusted electronically to achieve different bandwidths and center frequencies without complex component switching.
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
The solution provides a flexible and precise frequency filtering capability, effectively avoiding spurious responses and allowing for broad frequency tuning, enhancing the filter's performance in RF, microwave, and millimeter wave applications.
Implementation Method 1
A BPF generally involves some form of resonator that stores energy in a given frequency band
Implementation Method 2
The energy storage of the resonator can also be arranged with feedback in which signal from the output coupling is fed back into the input coupling
Data Source
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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.