Downconversion Mixer IM2 Cancellation Using Scaled Distortion
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Solution Overview
Problem
Downconversion mixers in digital communication systems suffer from significant second-order intermodulation (IM2) distortion, which degrades receiver performance due to non-linear characteristics, and existing solutions fail to effectively mitigate this issue.
Innovation Solution
A downconversion mixer with IM2 cancellation is developed, incorporating a mixer, an IM2 generator, and a scaling unit. The IM2 generator uses first and second field effect transistors to generate IM2 distortion, and the scaling unit adjusts this distortion to cancel it out from the output baseband signal, achieving temperature compensation and improved noise performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a downconversion mixer is used to frequency downconvert the received RF signal, then the signal can be converted from RF to baseband, but IM2 distortion is generated that degrades receiver performance
Solution Approach 1:
The patent generates IM2 distortion intentionally in the IM2 generator circuit to match and cancel the harmful IM2 distortion produced by the mixer. By converting the harmful distortion into a useful cancellation signal, the system eliminates the adverse effects of mixer non-linearity while maintaining efficient signal conversion.
Solution Approach 2:
The patent applies preliminary anti-action by generating an opposing IM2 distortion signal before it combines with the baseband signal. The IM2 generator and scaling unit create a cancellation signal that is combined with the mixer output in advance, preventing the harmful distortion from degrading the receiver performance.
2Power
If the mixer operates with high gain to improve signal strength, then the output signal level increases, but IM2 distortion magnitude increases even more
Solution Approach 1:
The patent converts the harmful high-level IM2 distortion (which increases with mixer gain) into a beneficial cancellation signal. The IM2 generator replicates this distortion and the scaling unit adjusts it to perfectly cancel the harmful components, allowing the mixer to operate at high gain without performance degradation.
Solution Approach 2:
The system implements a feedback mechanism where the IM2 generator and scaling unit continuously provide an opposing signal that cancels the IM2 distortion produced by the mixer. This feedback loop ensures that even as mixer gain and corresponding distortion vary, the cancellation remains effective.
3Stability of the object's composition
If temperature compensation is implemented to maintain performance across temperature variations, then receiver stability improves, but device complexity increases
Solution Approach 1:
The IM2 generator and scaling unit serve multiple functions: they generate IM2 distortion for cancellation, provide temperature compensation, and maintain performance across varying conditions. By making these components multi-functional, the patent achieves temperature stability without proportionally increasing circuit complexity.
Solution Approach 2:
The system achieves temperature compensation through self-service mechanisms where the IM2 generator and scaling unit automatically adjust to maintain cancellation effectiveness across temperature variations, reducing the need for external temperature control circuits or manual calibration.
4Reliability
If IM2 distortion cancellation is added to the mixer, then receiver performance improves, but device complexity increases
Solution Approach 1:
The IM2 generator and scaling unit are designed to be multi-functional components that perform distortion generation, scaling, and cancellation simultaneously. This approach improves receiver performance while minimizing the increase in overall device complexity by avoiding separate dedicated circuits for each function.
Solution Approach 2:
The patent merges the IM2 cancellation functionality with the existing mixer structure by integrating the IM2 generator and scaling unit into the signal path. This combining of functions achieves performance improvement while reducing the incremental complexity compared to adding completely separate cancellation systems.
Data Source
AI summary
A downconversion mixer with IM2 cancellation includes a mixer, an IM2 generator, and a scaling unit. The mixer frequency downconverts an input RF signal with an LO signal and generates an output baseband signal. The IM2 generator includes first and second field effect transistors (FETs) that receive the input RF signal and generate an intermediate signal having IM2 distortion. The scaling unit scales the intermediate signal to generate a scaled signal and further combines the scaled signal with the output baseband signal to cancel IM2 distortion in the output baseband signal. The IM2 generator may further include first and second amplifiers coupled between the source and gate of the first and second FETs, respectively. Different amounts of IM2 distortion and different temperature variation patterns may be generated in the intermediate signal by using different gains for the amplifiers.