RF Transceiver Digital Pre-Distortion Feedback Switch
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Solution Overview
Problem
Radio frequency (RF) transceivers face challenges in balancing size, power, and performance due to the costly and sparsely used hardware resources dedicated to digital pre-distortion (DPD) feedback systems, particularly in capturing feedback samples from the transmit power amplifier, which can interrupt the receive signal stream in frequency division duplexing configurations.
Innovation Solution
A digital pre-distortion feedback path is implemented using a switch to capture receive samples from the receive signal processing chain during feedback mode and route them to a DPD feedback processing unit, compensating for power amplifier non-linearity without impacting the receive signal stream, by puncturing the receive signal stream at predetermined times in frequency division duplexing configurations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional feedback circuitry is used to capture feedback samples from the transmit power amplifier, then digital pre-distortion performance is improved, but hardware resources are increased and power consumption is raised
Solution Approach 1:
The receive signal processing chain is designed to perform dual functions: normal receive signal processing and feedback sample capture for DPD. By configuring the receive chain to operate in different modes, the same hardware resources (LNA, ADC, signal processing units) serve both receive functionality and DPD feedback requirements, eliminating the need for separate dedicated feedback circuitry
Solution Approach 2:
The receive signal processing chain serves itself by capturing its own output signals and routing them to the DPD feedback path. The system uses its existing resources to generate the feedback information needed for pre-distortion, without requiring external or dedicated feedback hardware
2Measurement precision
If feedback mode is implemented in frequency division duplexing configuration, then power amplifier non-linearity compensation is achieved, but receive signal stream is interrupted
Solution Approach 1:
The feedback mode is implemented periodically at predetermined time intervals within the receive signal stream. The switch captures feedback samples at specific moments (periodic action) rather than continuously, allowing the receive chain to alternate between normal operation and feedback capture mode, thus maintaining receive signal integrity while providing periodic DPD feedback
Solution Approach 2:
A switch is introduced as an intermediary component that selectively routes the output of the ADC to either the normal receive signal processing path or the DPD feedback processing path. This mediator enables smooth transition between modes and prevents direct conflict between receive signal stream and feedback sampling
3Measurement precision
If hardware resources are dedicated to DPD feedback system, then pre-distortion accuracy is improved, but size and power consumption are increased
Solution Approach 1:
The same hardware resources (LNA, ADC, signal processing units) are shared between receive operations and DPD feedback functions. By configuring these universal resources to serve dual purposes, the system achieves accurate pre-distortion without adding dedicated feedback hardware, thus avoiding increased power consumption
Solution Approach 2:
The DPD feedback path is merged with the existing receive signal processing chain rather than being implemented as a separate system. The feedback samples are captured from the ADC output and processed through the same signal processing infrastructure used for receive operations, consolidating functionality and reducing overall power consumption
Data Source
AI summary
A radio frequency (RF) transceiver includes a transmitter portion configured to transmit RF signals at an output of a power amplifier (PA). A receiver portion has an input coupled to the output of the PA. The receiver portion includes a switch coupled to feedback first baseband signals to the transmitter portion during a feedback mode. The first baseband signals are based on the first RF signals received at the input of the receiver portion. A pre-distortion processing unit is coupled to receive the first baseband signals. In turn, the distortion processing unit provides pre-distortion feedback signals to the transmitter portion.