Amplitude Modulation Circuit With Triode MOS for Low Distortion
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing amplitude modulation circuits suffer from low linearity, leading to increased third-order intermodulation distortion and incorrect signal detection, particularly when modulating signals with close frequency components.
Innovation Solution
An amplitude modulation circuit is designed with a specific configuration including bipolar transistors, resistive elements, and a Metal-Oxide-Semiconductor (MOS) transistor operating in a non-saturated region, with a drain-source resistance larger than the resistive elements, to enhance linearity and reduce distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional amplifier circuit is used for amplitude modulation, then the circuit structure is simple, but the linearity is poor causing third-order intermodulation distortion
Solution Approach 1:
The circuit is divided into two parallel branches: a first branch with a first transistor and first resistive element for processing one signal component, and a second branch with a second transistor and second resistive element for processing another signal component. This segmentation allows each branch to contribute to linear amplitude modulation while maintaining manageable circuit complexity.
Solution Approach 2:
The first MOS transistor is configured to operate specifically in a non-saturated region (triode region) with its resistance being larger than the resistive elements, creating a localized region of high linearity. This local quality improvement in the MOS transistor configuration enhances overall circuit linearity without requiring complete redesign of all circuit components.
2Reliability
If amplitude modulation is performed with low linearity, then the circuit operation is simple, but third-order intermodulation distortion increases causing incorrect signal detection
Solution Approach 1:
The first MOS transistor acts as an intermediary element between the input signals and the output, operating in the non-saturated region to provide a linear resistance that mediates the amplitude modulation process. This intermediary configuration ensures accurate signal detection by preventing distortion while integrating smoothly with the existing transistor structure.
3Reliability
If the MOS transistor resistance is made larger than the resistive elements, then linearity is improved, but the voltage gain may be reduced
Solution Approach 1:
The circuit operates by changing the resistance parameter of the MOS transistor dynamically as it switches between different resistance states during the amplitude modulation process. By configuring the MOS transistor to operate in the non-saturated region with resistance larger than the resistive elements, the circuit achieves optimal linearity while maintaining sufficient voltage gain through parameter optimization.
Data Source
AI summary
An amplitude modulation circuit includes: first, second, and third input terminals; first and second output terminals; a current source; first and second transistors including a base electrically connected to the first and second input terminals, a collector electrically connected to the first and second output terminals, and an emitter electrically connected to a grounding terminal via the current source; first and second resistive elements electrically connected between the first and second output terminals and a power line; and a first MOS transistor including a drain connected to the first output terminal, a source connected to the second output terminal, and a gate connected to the third input terminal. The MOS transistor is configured to operate in a non-saturated region, and a resistance between the source and the drain of the MOS transistor is larger than resistances of the first and second resistive elements.