Differential Amplifier Cross-Coupled Filtering for Higher Linearity
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Solution Overview
Problem
Conventional differential amplifier circuits and frequency mixers face challenges in achieving high linearity due to non-linear component generation, which is difficult to address with existing methods like feedback and pre-distortion, especially in mobile terminals where oscillation, complexity, and noise degradation are concerns.
Innovation Solution
A differential amplifier circuit configuration that includes a differential amplifying stage and a non-linearity filtering circuit with cross-circuit transistors and bias voltage sources, which filters non-linear signals to output only linear current components, improving linearity by offsetting non-linear components at the load side.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If feedback method or pre-distortion method is used to improve linearity, then linearity is improved, but device complexity increases and oscillation may occur
Solution Approach 1:
The circuit is divided into a differential amplifying stage and a non-linearity filtering circuit, where each stage performs a specific function. The differential amplifying stage handles signal amplification while the non-linearity filtering circuit separately handles non-linear component removal, allowing independent optimization of each stage without complex feedback loops.
Solution Approach 2:
The non-linearity filtering circuit extracts and removes non-linear components from the amplified signal. By separating the non-linear component removal function from the amplification function, the patent avoids the complexity of feedback methods while achieving improved linearity through selective extraction of harmful non-linear components.
2Manufacturing precision
If feedback method or pre-distortion method is used to improve linearity, then linearity is improved, but noise degradation occurs
Solution Approach 1:
The non-linearity filtering circuit specifically extracts non-linear components from the signal path without requiring feedback loops that would introduce additional noise. The filtering operation removes only the harmful non-linear components while preserving the linear signal components and avoiding the noise degradation associated with feedback methods.
Solution Approach 2:
The circuit converts the harmful non-linear components generated by the differential amplifying stage into removable filterable signals. By allowing non-linear components to be generated and then systematically removed by the non-linearity filtering circuit, the patent transforms the harmful effect into a manageable process that does not introduce additional noise.
3Manufacturing precision
If auxiliary differential amplifying stage is added to improve linearity, then second differential coefficient becomes negative, but device complexity increases
Solution Approach 1:
Instead of adding another differential amplifying stage to manipulate the second differential coefficient, the patent extracts non-linear components directly from the output of a single differential amplifying stage. This approach achieves the same linearity improvement goal with a simpler filtering circuit rather than a more complex multi-stage amplifying configuration.
Solution Approach 2:
The non-linearity filtering circuit acts as an intermediary between the differential amplifying stage and the output, removing non-linear components without requiring changes to the amplifying stage itself. This mediator approach simplifies the overall circuit by handling non-linearity correction in a separate, dedicated stage rather than complicating the amplifying stage configuration.
Data Source
AI summary
A differential amplifier circuit and a frequency mixer for improving linearity are disclosed. The disclosed differential amplifier circuit includes first and second loads, a first output terminal for the first load, a second output terminal for the second load, a differential amplifying stage including a differential stage for amplifying a voltage difference between a first input stage and a second input stage, and a biasing current source for biasing the differential stage, and a non-linearity filtering circuit for filtering a non-linear signal generated from the differential amplifying stage. The non-linearity filtering circuit includes a first cross circuit including a first transistor to connect the first and second output terminals, and a second cross circuit including a second transistor to connect the first and second output terminals. The differential amplifier circuit achieves an improvement in linearity, as compared to conventional differential amplifier circuits, by offsetting, at a load side, a non-linear component generated at an active element of the differential amplifier circuit, to output only a linear current component.