FET Voltage Controlled Resistor Feedback Circuit
Find Innovative SolutionsGenerate Solutions
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 the inclusion of buffer amplifiers in junction FET or MOSFET configurations.
Innovation Solution
The implementation of a feedback circuit with an amplifier, specifically a voltage follower amplifier, in conjunction with a feedback network, is used to reduce distortion in FET circuits, particularly in enhancement mode FETs, by isolating the feedback resistors from the drain terminal and ground, thereby improving linearity and attenuation characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a buffer amplifier is included in junction FET or MOSFET voltage controlled resistor circuits, then the circuit complexity increases, but the nonlinear distortion is not substantially reduced
Solution Approach 1:
The patent applies feedback by connecting the drain terminal to the gate terminal through a feedback network consisting of resistors. This feedback mechanism linearizes the transfer characteristic of the FET, reducing nonlinear distortion and intermodulation distortion without requiring buffer amplifiers. The feedback voltage opposes the control voltage, creating a linearizing effect that improves performance while maintaining circuit simplicity.
Solution Approach 2:
The patent changes the operating parameters of the FET by utilizing the relationship between drain current, gate-source voltage, and drain-source voltage. By establishing a specific feedback ratio (typically 0.5) and operating the FET in the saturation region with appropriate biasing, the circuit achieves linearized performance. This parameter optimization allows distortion reduction without adding complex buffer amplifier stages.
2Device complexity
If feedback resistors are directly connected to the drain terminal and ground, then the circuit is simpler, but control voltage leaks to the output reducing performance
Solution Approach 1:
The patent introduces an intermediary element - the feedback resistor network - that mediates between the control voltage source and the output. The feedback resistors are connected in a specific configuration where they provide the necessary feedback signal while blocking the direct leakage path of the control voltage to the output. This intermediary network allows the control voltage to influence the FET operation without directly appearing at the output terminal.
Solution Approach 2:
The patent segments the feedback path by using multiple resistors in the feedback network rather than a single direct connection. This segmentation allows different functions to be performed: one portion provides the feedback signal to linearize the transfer characteristic, while another portion isolates the control voltage from direct leakage to the output. The segmented approach maintains circuit simplicity while eliminating the harmful leakage effect.
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.