Feedforward Distortion Cancellation Using Phase-Offset Replica
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Solution Overview
Problem
Existing methods for eliminating out-of-band distortion in wireless communication signals are expensive, energy-inefficient, and require significant transmitter space due to the use of filters, while feedforward circuits face challenges in accurately canceling distortion without proper time alignment.
Innovation Solution
A feedforward distortion cancellation apparatus and method that generates a phase-offset replica of the analog RF modulated signal, combines it with the amplified signal to cancel out-of-band distortion, and uses an error amplifier to produce an amplified distortion cancellation signal, eliminating the need for additional filters by aligning the signals in time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If filters are used to eliminate out-of-band distortion, then distortion is reduced, but transmitter space and cost increase
Solution Approach 1:
The invention extracts and separates the distortion signal from the amplified signal using a coupler, then processes it independently through an error amplifier to generate a cancellation signal. This removes the need for physical filters by isolating the harmful distortion component for separate handling.
Solution Approach 2:
The invention converts the harmful distortion signal into a useful cancellation signal by amplifying it through the error amplifier and combining it with the main signal. The previously harmful out-of-band distortion becomes the basis for generating the cancellation signal that eliminates it when combined with the delayed main signal.
2Object-generated harmful factors
If filters are used to eliminate out-of-band distortion, then distortion is reduced, but energy consumption increases
Solution Approach 1:
The coupler extracts a portion of the amplified signal containing distortion, allowing the error amplifier to process only this extracted distortion component rather than the entire amplified signal. This selective processing reduces the energy burden compared to filtering the full signal.
Solution Approach 2:
The error amplifier creates a copy of the distortion signal that is then amplified and combined with the main signal path. This copying approach allows distortion cancellation without requiring the main signal path to pass through energy-intensive filtering components.
3Object-generated harmful factors
If feedforward circuits are used to cancel distortion, then distortion cancellation is achieved, but time alignment accuracy is compromised
Solution Approach 1:
The delay element is positioned to pre-align the main signal path with the distortion cancellation path before they are combined at the combiner. This preliminary time alignment ensures that when the amplified distortion cancellation signal is combined with the delayed main signal, they are properly synchronized for effective distortion cancellation.
Solution Approach 2:
The delay element acts as an intermediary that mediates the time alignment between the main signal path and the distortion cancellation path. By introducing a controlled delay to the main signal, it synchronizes the timing of both paths, enabling accurate distortion cancellation without requiring complex real-time adjustment mechanisms.
Data Source
AI summary
An apparatus and a method include receiving, by a transmitter integrated circuit (IC) having a serial data communications interface, a digital transmit signal, and generating a first signal that is an analog radio frequency (RF) modulated signal based on the digital transmit signal and a second signal that is a phase-offset version of the first signal. An amplified signal is generated by amplifying the first signal and includes an amplified version of the first signal and an out-of-band distortion signal. A reduced-power signal is generated from the amplified signal. The reduced-power signal is subtracted from the second signal to output a distortion cancellation signal. An amplified distortion cancellation signal is generated by amplifying the distortion cancellation signal using an error amplifier. The amplified distortion cancellation signal and a delayed version of the amplified signal are combined to output an amplified version of the first signal with reduced distortion.