Digital Cancellation Circuit for IMD3 and Self-Interference
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Solution Overview
Problem
Existing communication systems face challenges with third-order intermodulation distortion (IMD3) and self-interference due to nonlinearities in power amplifiers, which cause interference across multiple radios and hinder efficient multichannel communications and frequency-division duplexing.
Innovation Solution
The implementation of fully digital cancellation circuits using digital-to-time converters (DTCs) and RF digital-to-RF converters to generate cancellation signals with a 180° phase difference, effectively canceling out interference signals by converting input sinewaves to digital square waves and back to analog RF signals with controlled gain, and utilizing binary search methods for calibration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If power amplifiers operate at high power levels, then transmission power and coverage are improved, but third-order intermodulation distortion and self-interference increase causing interference in multichannel communications
Solution Approach 1:
The patent converts the harmful intermodulation distortion signals into useful cancellation signals by processing them through digital signal processing. The distortion products are captured, digitally processed to generate anti-phase signals, and then subtracted from the original signal, transforming the harmful distortion into a beneficial cancellation mechanism that improves spectral purity while maintaining high power operation
Solution Approach 2:
The patent introduces digital signal processing circuits as intermediary elements between the power amplifier and the output. These intermediary circuits capture the distortion signals, process them digitally to generate cancellation signals, and inject them back to cancel the harmful components, acting as a mediator that eliminates interference while preserving the high-power transmission capability
2Productivity
If multiple radios operate concurrently on different frequency channels, then system capacity and productivity are improved, but receiver interference from transmit signals increases
Solution Approach 1:
The patent converts the harmful self-interference signals that leak from transmit to receive paths into useful cancellation signals. By capturing these interference signals, processing them through digital signal processing to generate anti-phase versions, and subtracting them from the receive signal, the system transforms the harmful interference into a beneficial cancellation mechanism that enables concurrent transmit-receive operation
Solution Approach 2:
The patent implements a feedback mechanism where the transmit signal is captured, processed to generate cancellation signals, and fed back into the receive path to cancel self-interference. This feedback loop continuously monitors and compensates for interference, enabling the system to maintain high productivity through concurrent operation while eliminating receiver interference
3Measurement precision
If digital to time converters are used to generate cancellation signals, then cancellation precision is improved, but device complexity increases
Solution Approach 1:
The patent replaces complex analog cancellation circuits with digital signal processing implementations. By using digital to time converters and digital signal processing to generate and control cancellation signals, the system achieves high precision cancellation while avoiding the complexity of precision analog components. The digital domain provides natural precision and ease of control, substituting mechanical/analog complexity with digital processing
Data Source
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AI summary
A cancellation circuit includes a limiter connected to an output of a first transmitter power amplifier that converts in input sinewave to a digital square wave and a digital to time converter (DTC) connected to the limiter. A RF digital to RF converter is connected to the DTC that converts the digital square wave input into an analog RF output. A cancellation amplifier with an input receives an output from the RF digital to RF converter and has an output connected to an output of a second transmitter power amplifier. The cancellation amplifier produces a cancellation signal to cancel an interference signal at the output of the second transmitter power amplifier from the output of the first transmitter power amplifier. A power detector is connected to the output of the second power amplifier that produces a power value detected at the output of the second power amplifier.