Variable Impedance Circuit With Parallel NMOS Transistors
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Solution Overview
Problem
Existing variable impedance circuits face limitations in achieving wide and continuous impedance variation, particularly when using MOS transistors, as they often result in non-linear resistance changes when transitioning between triode and saturation regions, and require complex circuit configurations with multiple control signals.
Innovation Solution
A variable impedance circuit comprising a fixed resistance and multiple NMOS transistors arranged in parallel, controlled by distinct voltage signals generated by a voltage generator, allowing for continuous impedance variation between terminals, with transistors switching on and off to maintain linear impedance characteristics across varying voltage conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a MOS transistor operates in triode zone to obtain linear impedance variation, then impedance linearity is improved, but impedance variation range is limited
Solution Approach 1:
The circuit segments the impedance control function across multiple MOS transistors (M1, M2, M3, M4) arranged in specific configurations. Each transistor operates in different regions (triode or saturation) under different control voltages, allowing the overall circuit to achieve both linear variation (when transistors are in triode) and wide variation range (by switching between different transistor states and regions).
Solution Approach 2:
The circuit dynamically switches transistors between triode and saturation regions by applying different control voltages (Vcon1, Vcon2, Vcon3). This dynamic operation allows the circuit to adapt its impedance characteristics: operating in triode region for linear variation and utilizing saturation region for extended impedance range, thus resolving the contradiction between linearity and variation range.
2Adaptability or versatility
If a circuit enables wide resistance variation by using transistor in saturation region, then impedance variation range is improved, but impedance linearity deteriorates
Solution Approach 1:
Different parts of the circuit (different transistors) have different operational characteristics assigned to them. Some transistors are designed to operate primarily in triode region for linear control, while others can operate in saturation region for extended range. The control voltages are specifically designed to keep certain transistors in linear region while others provide the range extension, thus achieving both linearity and wide variation range through local optimization.
3Adaptability or versatility
If multiple control signals are used to achieve continuous impedance variation, then impedance continuity is improved, but circuit complexity increases
Solution Approach 1:
The control voltages (Vcon1, Vcon2, Vcon3) are generated in a predetermined sequence and with specific timing relationships. The voltage generator applies these control signals in a coordinated manner to switch transistors on and off progressively, ensuring continuous impedance variation without requiring complex real-time control logic. This preliminary arrangement of control signals simplifies the overall circuit complexity while maintaining 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
Enables wide and continuous impedance variation while maintaining linear resistance characteristics, improving upon previous circuits by using a controlled voltage generator to manage transistor states and ensure consistent impedance across a range of signal values.
Implementation Method 1
a variable impedance circuit comprising a fixed resistance and a plurality of transistors, a first and a second terminal, wherein the transistors belonging to said plurality of transistors are arranged parallel to one another and parallel to said resistance
Data Source
AI summary
A variable impedance circuit includes at least one fixed resistance and a plurality of transistors between a first and a second terminal. The transistors belonging to the plurality of transistors are arranged parallel to one another and parallel to the resistance and are controllable by a plurality of control signals different from one another and configured in such a way as to obtain a total impedance between said first and second terminals that is substantially variable in a continuous manner.