Squaring Unit for Second-Order Distortion Cancellation
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Solution Overview
Problem
In full-duplex wireless communication systems, transmit signal leakage causes interference and second-order distortion, degrading receiver sensitivity due to non-linearities in the mixer during down-conversion, which filters cannot fully eliminate.
Innovation Solution
A wireless receiver is equipped with a squaring unit that squares the combined signal carrying the desired RX signal and TX leakage signal, and a subtracting unit that cancels out the second-order distortion by subtracting the squared signal from the down-converted output, thereby reducing adverse effects on receiver sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If filtering is applied to remove TX signal leakage, then the amount of leakage is reduced, but residual leakage remains causing second-order distortion that degrades receiver sensitivity
Solution Approach 1:
The patent uses the non-linear mixing process that originally causes second-order distortion to instead generate a canceling signal. By intentionally creating second-order distortion products through mixing and then subtracting them, the harmful distortion is converted into a beneficial cancellation mechanism that improves receiver sensitivity while allowing filtering to reduce TX leakage.
Solution Approach 2:
The patent applies preliminary anti-action by generating the second-order distortion signal in advance through a separate mixing path and then subtracting it from the main receive path. This preemptive cancellation approach counteracts the distortion before it can degrade the desired signal, resolving the contradiction between leakage reduction and sensitivity maintenance.
2Object-affected harmful factors
If filtering is applied to remove TX signal leakage, then leakage is reduced, but device complexity increases due to additional filtering requirements
Solution Approach 1:
The patent substitutes mechanical/filter-based solutions with a signal processing approach. Instead of relying on complex physical filters to remove TX leakage and its distortion products, the invention uses mathematical subtraction of generated distortion signals, replacing physical filtering complexity with algorithmic signal manipulation.
3Reliability
If the mixer operates with high gain to amplify weak RX signals, then receiver sensitivity improves, but second-order distortion from TX leakage increases
Solution Approach 1:
The patent implements a feedback-like mechanism where the output of the mixer is fed back through a subtraction path. The second-order distortion components are extracted and subtracted from the main signal path, creating a closed-loop system that actively compensates for the distortion generated by high-gain mixing operations, thereby maintaining both sensitivity and low distortion.
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
This technique effectively reduces second-order distortion caused by TX signal leakage, enhancing receiver sensitivity by minimizing the masking of the desired RX signal and improving the reliability of signal detection.
Implementation Method 1
a mixer that down-converts an input signal to create a down-converted input signal
Implementation Method 2
a device that exhibits a strong, second order nonlinearity to, in effect, square the combined signal
Data Source
AI summary
This disclosure describes techniques for reducing adverse effects of TX signal leakage in a full-duplex, wireless communication system. In particular, the disclosure describes techniques for reducing adverse effects of second order distortion of TX signal leakage. To reduce or eliminate second order distortion of transmit signal leakage, a wireless device squares a combined signal that carries both a desired RX signal and a TX leakage signal. For example, the device may include a device that exhibits a strong, second order nonlinearity to, in effect, square the combined signal. The device subtracts the squared signal from the output of the mixer in the receive path, canceling out at least some of the second-order distortion caused by the mixer. In this manner, the device can reduce the adverse effects of second order distortion of TX signal leakage, and thereby enhance or maintain receiver sensitivity.