Voltage-Controlled FET Biasing Circuits for Lower Distortion
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Solution Overview
Problem
Existing voltage controlled circuits, particularly those using FETs, face challenges in minimizing distortion and noise, especially when employing buffer amplifiers, as they often fail to provide substantial improvements in reducing harmonic and intermodulation distortion compared to feedback networks without amplifiers.
Innovation Solution
The implementation of enhanced voltage controlled resistor circuits using feedback networks with amplifiers, specifically voltage followers, to improve linearity and reduce distortion by isolating feedback resistors from the drain terminal and ground, thereby minimizing the leakage of control voltage and enhancing frequency response.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If buffer amplifiers are used in voltage controlled circuits, then noise and distortion should be reduced, but the improvement in reducing harmonic and intermodulation distortion is not substantial compared to feedback networks without amplifiers
Solution Approach 1:
The patent extracts the feedback resistors from direct connection to the drain terminal and ground, isolating them through a buffer amplifier. This separation removes the harmful interaction between feedback network and drain terminal that causes control voltage leakage and distortion, while maintaining the necessary feedback function.
Solution Approach 2:
The buffer amplifier serves as an intermediary element between the feedback resistors and the drain terminal. It mediates the feedback signal transmission while preventing direct harmful interactions, thereby reducing distortion and control voltage leakage without requiring complex circuit modifications.
2Device complexity
If feedback networks are connected directly to drain terminal and ground, then circuit simplicity is maintained, but control voltage leaks and frequency response is compromised
Solution Approach 1:
The feedback resistors are extracted from direct connection to drain terminal and ground, preventing control voltage leakage. This separation maintains circuit simplicity while eliminating the harmful direct path that compromises frequency response and control voltage stability.
Solution Approach 2:
The feedback network is segmented into separate components with the buffer amplifier isolating the feedback resistors from the drain terminal. This segmentation allows the feedback function to be maintained while preventing control voltage leakage and improving frequency response characteristics.
3Adaptability or versatility
If JFET or depletion mode FET is used, then voltage controlled resistance is achieved, but distortion reduction requires buffer amplifier which provides minimal improvement
Solution Approach 1:
The patent implements a feedback network with buffer amplifier that provides controlled feedback to the gate terminal. This feedback mechanism linearizes the voltage-controlled resistance characteristic and reduces nonlinear distortion by correcting deviations from the ideal transfer function.
Solution Approach 2:
The buffer amplifier acts as an intermediary that enables effective feedback control without the harmful direct connections. It mediates between the feedback resistors and drain terminal, allowing distortion reduction through proper feedback while preventing control voltage leakage.
4Manufacturing precision
If enhancement mode FET is used with feedback network isolation, then linearity and distortion reduction are improved, but circuit complexity increases
Solution Approach 1:
The buffer amplifier serves as an intermediary element that isolates the feedback resistors from the drain terminal and ground. This simple intermediary component achieves linearity improvement and distortion reduction without requiring complex circuit modifications, maintaining ease of implementation.
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
This approach significantly reduces nonlinear distortion and improves linearity in voltage controlled circuits, particularly when using enhancement mode FETs, by effectively isolating feedback networks and preventing control voltage leakage, leading to improved attenuation and frequency independence.
Implementation Method 1
a field effect transistor with a gate terminal, a source terminal and a drain terminal... the voltage between the source terminal and the drain terminal is controlled by a control voltage applied to the gate terminal
Data Source
AI summary
A number of biasing circuits for amplifiers including voltage controlled amplifier is presented. Also 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.