Active Filter Nonlinearity Cancellation for HD3 Distortion
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Solution Overview
Problem
Active filters introduce third harmonic distortion (HD3) due to non-linearities in passive components like capacitors, which are not effectively addressed by existing solutions that either require expensive materials or degrade signal quality.
Innovation Solution
A cancellation circuit is coupled to the active filter, using capacitors of the same type as the filter to generate a non-linear current of equal amplitude and opposite phase, canceling out the distortion caused by the filter's capacitors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If conventional active filters are used, then filtering function is provided, but third harmonic distortion (HD3) is introduced due to non-linearities in passive components
Solution Approach 1:
The cancellation circuit generates a counter-signal with equal amplitude and opposite phase to the distortion signal produced by the filter capacitors. This preliminary anti-action cancels out the third harmonic distortion before it affects the output signal, resolving the contradiction between maintaining filtering function and reducing distortion.
Solution Approach 2:
The invention utilizes the non-linear characteristics of the capacitor bank to generate the cancellation signal. By intentionally exploiting the non-linearity to create a beneficial counter-signal, the harmful distortion effect is converted into a useful cancellation mechanism, improving signal quality while maintaining the filter's operation.
2Object-affected harmful factors
If expensive materials or complex solutions are used to reduce distortion, then HD3 is reduced, but cost and device complexity increase
Solution Approach 1:
The cancellation circuit uses a capacitor bank with the same type and non-linear characteristics as the filter capacitors. By copying the non-linear behavior, the circuit generates an accurate cancellation signal that matches the distortion profile, achieving effective HD3 reduction without requiring expensive specialized materials or complex compensation networks.
Solution Approach 2:
The invention changes the capacitance value parameter by using a capacitor bank with equivalent capacitance rather than attempting to linearize the original capacitors. This parameter change allows the system to maintain the necessary filtering function while generating the required cancellation signal through controlled non-linearity.
Data Source
AI summary
A circuit includes an active filter, including an input, a first output, and a second output. The circuit includes a first capacitor having a first terminal and a second terminal. The first terminal of the first capacitor is coupled to the first output of the active filter, and the second terminal of the first capacitor is coupled to the input of the active filter. The first capacitor has a capacitance value. The circuit includes a capacitor bank having a first terminal and a second terminal. The first terminal of the capacitor bank is coupled to the second output of the active filter. The second terminal of the capacitor bank is coupled to the second terminal of the first capacitor and coupled to the input of the active filter. The capacitor bank has a capacitance that is equivalent to the capacitance value.