DTC Cancellation Circuit for IMD3 and Receiver Interference
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Solution Overview
Problem
Existing communication systems face challenges in filtering out third-order intermodulation distortion (IMD3) and receiver interference caused by transmit signals, which are difficult to eliminate due to their proximity to the carrier frequency and the impracticality of traditional filtering methods.
Innovation Solution
Implementing on-chip fully digital cancellation circuits using digital-to-time converters (DTC) to generate a cancellation signal with a 180° phase difference, effectively canceling out interference by converting input signals to digital square waves and adjusting gain through RF digital-to-RF converters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If traditional filtering methods are used to remove third-order intermodulation distortion (IMD3), then the distortion products can be eliminated, but the filtering becomes impractical because the distortion products are too close to the carrier frequency
Solution Approach 1:
The patent converts the harmful transmit signal into a beneficial cancellation signal by processing it through a digital-to-time converter (DTC) and RF digital-to-RF converter to generate an inverted replica that cancels the intermodulation distortion at the receiver input, transforming the problematic close-frequency distortion into a solvable interference cancellation problem
Solution Approach 2:
The patent introduces an intermediary cancellation signal path that includes a DTC and RF digital-to-RF converter between the transmit signal source and the receiver input, which processes the transmit signal to create an inverted replica that mediates the interference by canceling the IMD3 distortion products before they affect receiver operation
2Power
If transmit power is increased to improve communication range, then signal strength increases, but receiver interference from transmit signals injected into the receiver increases
Solution Approach 1:
The patent applies preliminary anti-action by generating an inverted replica of the transmit signal through the DTC and RF digital-to-RF converter before it reaches the receiver input, where this pre-prepared cancellation signal counteracts the harmful effects of high-power transmit signals injected into the receiver, enabling high-power operation without receiver desensitization
3Productivity
If frequency-division duplexing is implemented in systems with multiple radios to improve spectral efficiency, then communication capacity increases, but interference between transmit and receive signals becomes more complex
Solution Approach 1:
The patent segments the interference cancellation function into distinct modular components: a DTC for digital signal processing, an RF digital-to-RF converter for analog conversion, and a cancellation amplifier for signal inversion, allowing each component to be independently designed, calibrated, and optimized while managing the complexity of FDD interference cancellation in multi-radio systems
Data Source
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.