FET Voltage-Controlled Resistor Feedback for Low-Distortion Attenuation
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Solution Overview
Problem
Existing Field Effect Transistor (FET) circuits used in voltage controlled amplitude and waveform shaping applications suffer from significant distortion, particularly nonlinear distortion and intermodulation distortion, which are not effectively mitigated by conventional buffer amplifiers or feedback networks.
Innovation Solution
The implementation of a voltage controlled resistor circuit using a combination of FETs with feedback circuits and amplifier networks, specifically employing a voltage follower amplifier to isolate feedback resistors and reduce distortion, while also using a sinewave to triangle wave converter for improved linearity and frequency independence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a buffer amplifier is added to reduce distortion in FET circuits, then the linearity improves, but the device complexity increases
Solution Approach 1:
The patent applies feedback by connecting the output of the voltage controlled amplifier back to its input through a feedback network, creating a closed-loop system that automatically corrects nonlinear distortion. The feedback signal is combined with the input signal to produce an error signal that drives the amplifier, continuously minimizing the difference between desired and actual output, thereby improving linearity without requiring complex buffer amplifiers.
2Manufacturing precision
If feedback networks are used to reduce distortion, then the linearity improves, but the control voltage leakage increases
Solution Approach 1:
The patent segments the feedback network into distinct functional blocks: a feedback resistor network for signal sampling, a summing junction for error signal generation, and a control voltage isolation stage. This segmentation allows each component to perform its function optimally while preventing control voltage from leaking into the output path, as the summing junction mathematically combines signals without direct electrical connection between input and output control voltages.
3Device complexity
If conventional FET circuits are used for voltage control, then the device simplicity is maintained, but the intermodulation distortion increases
Solution Approach 1:
The patent introduces an intermediary error signal that mediates between the input signal and the amplifier output. This error signal, generated by the summing junction, contains only the difference between desired and actual output, allowing the amplifier to correct distortion without directly processing the full control voltage. This intermediary approach maintains device simplicity while effectively reducing intermodulation distortion through the feedback mechanism.
Data Source
AI summary
A number of field effect transistor circuits include voltage controlled attenuators or voltage controlled processing circuits. Example circuits include modulators, lower distortion variable voltage controlled resistors, sine wave to triangle wave converters, and or servo controlled biasing circuits.