N-Path Gm-C Self-Interference Canceller for Close-Band Transceivers
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Solution Overview
Problem
Existing techniques for cancelling interference between closely operating transmitters and receivers in wireless devices are inefficient, particularly as frequencies approach each other, affecting receiver performance.
Innovation Solution
The development of transceiver self-interference cancellers using a plurality of second-order bandpass filters with variable resistances, capacitances, switches, and transconductors, along with local oscillators for tuning and calibration, to provide effective cancellation signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a transmitter and receiver operate simultaneously in close frequency bands, then communication efficiency is improved, but interference from the transmitter affects receiver performance
Solution Approach 1:
The interference cancellation is divided into multiple independent paths (first path with first and second cancellation signals, second path with third and fourth cancellation signals). Each path processes specific frequency components separately, allowing comprehensive cancellation across the entire frequency spectrum while maintaining high communication efficiency
Solution Approach 2:
Multiple cancellation signals act as intermediary elements between the interfering transmitter signal and the receiver. These cancellation signals are generated to replicate the transmitter signal characteristics and are subtracted from the receiver input, effectively mediating the interference problem without requiring physical separation of transmitter and receiver
2Adaptability or versatility
If frequencies of transmitter and receiver get closer together, then spectrum utilization is improved, but interference problem gets worse
Solution Approach 1:
The system dynamically adapts to different frequency configurations by generating multiple cancellation signals with different frequency shifts. The first cancellation signal targets the transmitter frequency, while the second cancellation signal targets a frequency shifted by a predetermined amount, allowing the system to effectively cancel interference across dynamically changing frequency relationships
Solution Approach 2:
The system changes frequency parameters by generating cancellation signals at different frequency offsets. The first cancellation signal operates at the transmitter frequency, while the second cancellation signal operates at a frequency shifted by a predetermined amount, enabling the system to handle varying frequency separations between transmitter and receiver
3Reliability
If multiple cancellation signals are generated at different frequency offsets, then interference cancellation effectiveness is improved, but circuit complexity increases
Solution Approach 1:
Multiple cancellation signal paths are merged into a single receiver input. The first cancellation signal (targeting transmitter frequency) and the second cancellation signal (targeting frequency-shifted components) are combined and subtracted together from the receiver input, achieving comprehensive interference cancellation while sharing common circuit resources
Solution Approach 2:
The cancellation signal generation circuit serves multiple functions: it generates cancellation signals for the transmitter frequency, generates cancellation signals for frequency-shifted components, and processes multiple frequency bands simultaneously. This multi-functionality reduces the need for separate dedicated circuits for each cancellation task
Data Source
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AI summary
Self-interference cancellers are provided. The self-interference cancellers can include multiple second-order, N-path Gm-C filters. Each filter can be configured to cancel self- interference on a channel of a desired bandwidth. Each filter can be independently controlled using a variable transmitter resistance, a variable receiver resistance, a variable baseband capacitance, a variable transconductance, and a variable time shift between local oscillators that control switches in the filter. By controlling these variables, magnitude, phase, slope of magnitude, and slope of phase of the cancellers frequency responses can be controlled for self- interference cancellation. A calibration process is also provided for configuring the canceller.