Voltage-Controlled Variable Resistor for Linear Large-Signal Attenuation
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Solution Overview
Problem
Existing voltage controlled variable resistor circuits are limited to small signal conditions and introduce distortion with large signal voltages, and they either lack linearity or have discontinuous resistance variation.
Innovation Solution
A voltage controlled variable resistor circuit design that includes a fixed attenuation circuit, operational amplifier, and transistors to provide continuous and linear resistance variation, capable of handling large signal levels by using a combination of fixed and variable resistive circuits and transistors, with an operational amplifier generating control signals for the transistors to adjust resistance in response to input signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a forward biased diode or MOS transistor is used as a voltage controlled variable resistor, then the circuit can provide voltage controlled resistance, but it can only be used in small signal conditions and introduces distortion with large signal voltages
Solution Approach 1:
The circuit is divided into multiple functional blocks: a differential amplifier stage that receives the control voltage and generates control currents, and a pair of transistors whose resistance is controlled by these currents. This segmentation allows each block to operate within its optimal range while collectively handling large signal levels without distortion.
Solution Approach 2:
The invention changes the operating parameters of the transistors by applying control voltages that modulate their channel resistance. The differential amplifier converts the control voltage into control currents that adjust the transistor operating points, enabling continuous resistance variation while maintaining linear operation even with large signal levels.
2Ease of operation
If a MOS transistor operating in triode region is used, then voltage controlled resistance can be achieved, but the voltage between source and drain must be kept very small to guarantee linearity
Solution Approach 1:
The differential amplifier configuration provides feedback mechanisms that automatically adjust the control currents to maintain linear operation. When large signal levels are applied, the feedback ensures that the transistors operate in a region where their resistance is properly controlled, eliminating the need to restrict the source-drain voltage to very small values.
3Reliability
If digital controlled switches are used to shunt resistors, then the circuit is suitable for large signal levels, but the resistance variation is discontinuous
Solution Approach 1:
The invention replaces static digital switches with dynamic transistor elements whose resistance can be continuously adjusted by analog control voltages. The differential amplifier dynamically adjusts the control currents in real-time, enabling smooth and continuous resistance variation while maintaining the ability to handle large signal levels, thus achieving both digital-like robustness and analog-like continuity.
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
The circuit achieves continuous and linear resistance variation, ensuring good linearity and effective operation with both small and large signal levels, reducing signal distortion and providing a scalable solution for variable resistance control.
Implementation Method 1
an operational amplifier circuit configured to receive the attenuated source signal and a feedback signal and generate a first control signal
Implementation Method 2
a first transistor having a control terminal configured to receive the first control signal, a first conduction terminal configured to generate an output signal and a second conduction terminal configured to generate the feedback signal
Data Source
AI summary
A voltage controlled variable resistor circuit is configured to variably attenuate a variable source signal. A fixed attenuation circuit is coupled to receive the variable source signal and output an attenuated variable source signal. The variable source signal is further applied across a variable resistive divider formed of a fixed resistive circuit and a variable resistive circuit. The variable resistive circuit has a first input configured to receive the attenuated variable source signal and a second input configured to receive a variable resistance control signal. The variable resistive circuit is configured to have a resistance which is variable in response to the attenuated variable source signal and the variable resistance control signal.