Feedback Capacitor Amplifier for Log-Linear Cutoff Frequency Control
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Solution Overview
Problem
Existing analog filters and amplifiers face inefficiencies in controlling cutoff frequency due to linear variations in resistance or capacitance according to digital codes, leading to inaccurate control, especially at high frequency bands, and inefficiencies in logarithmic scales.
Innovation Solution
An amplifier circuit with a feedback variable capacitor whose capacitance increases exponentially with a digital control code, allowing the cutoff frequency to vary linearly on a logarithmic scale, achieved through a logic circuit and specific capacitor segment connections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If variable resistance or capacitance varies linearly according to digital code, then control is simple, but accuracy deteriorates at high frequency bands
Solution Approach 1:
The patent changes the functional relationship between digital code and capacitance from linear to exponential. The capacitance value is controlled to vary exponentially with the digital code, which compensates for the logarithmic nature of frequency perception and achieves uniform frequency intervals across the entire control range, thereby maintaining high precision at all frequency bands.
Solution Approach 2:
The patent implements dynamic control of the capacitance value through digital coding. By using a digital control signal that exponentially modulates the capacitance, the system adapts to different frequency requirements dynamically, ensuring consistent control accuracy whether operating at low or high frequency bands.
2Ease of operation
If variable resistance or capacitance varies linearly according to digital code, then control is straightforward, but uniformity on logarithmic scale deteriorates
Solution Approach 1:
The patent transforms the control parameter relationship from linear to exponential to match the logarithmic scale characteristics. This parameter transformation ensures that equal steps in digital code produce equal intervals on the logarithmic frequency scale, achieving uniformity while maintaining digital control simplicity.
3Adaptability or versatility
If digitally controlled serial resistor connection uses binary structure, then resistance coverage is extended, but linearity deteriorates
Solution Approach 1:
The patent applies exponential weighting to the binary-weighted capacitor array instead of linear weighting. This allows the system to maintain the compact binary structure for extended control range while achieving linear response on a logarithmic scale, effectively resolving the linearity issue through parameter transformation.
4Adaptability or versatility
If digitally controlled parallel capacitor connection uses binary structure, then capacitance range is extended, but logarithmic scale linearity deteriorates
Solution Approach 1:
The patent modifies the binary-weighted parallel capacitor connection by applying exponential scaling to each capacitor's weight. This parameter change enables the capacitor array to produce exponentially varying total capacitance values, which directly translate to uniform intervals on the logarithmic frequency scale while maintaining the extended control range.
Data Source
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AI summary
An amplifier circuit is provided. The amplifier circuit includes an operational amplifier, a feedback resistor for changing gain and cutoff frequency characteristics of the operational amplifier, and a feedback variable capacitor for changing the cutoff frequency characteristics of the operational amplifier, wherein a capacitance of the feedback variable capacitor increases exponentially according to a digital control code, and the cutoff frequency of the operational amplifier is inversely proportional to the capacitance of the feedback variable capacitor and varies linearly on a logarithmic scale.