RF Transmitter Loopback Sampling for DPD and IQ Impairment Correction
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Solution Overview
Problem
RF transmitters and transceivers face challenges in compensating for transmit signal impairments such as PA nonlinearities, IQ mismatch, and LO leakage, which affect power efficiency and signal quality, and existing solutions like DPD and QMC have limitations in bandwidth and accuracy.
Innovation Solution
An RF transmitter and auxiliary receiver system with RF direct sampling, using an RF direct sampling ADC to convert loopback transmit RF signals to digital baseband signals, and digital downconversion to generate transmit signal data for impairment compensation, including DPD for PA linearization, QMC for IQ mismatch, and LOL correction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional DPD and QMC methods are used to compensate for transmit signal impairments, then power efficiency and signal quality are improved, but bandwidth requirements increase and system complexity increases
Solution Approach 1:
The patent combines the auxiliary receiver function with the main receiver, allowing a single receiver to perform both traffic reception and transmit impairment capture. This integration eliminates duplicate hardware components (ADCs, downconversion circuits, buffers) and reduces overall system complexity while maintaining the ability to compensate for PA nonlinearities, IQ mismatch, and LO leakage.
Solution Approach 2:
The main receiver is designed to serve dual purposes: receiving traffic signals and capturing transmit signal data for impairment compensation. By making the receiver universal, the patent eliminates the need for a separate dedicated auxiliary receiver, reducing hardware complexity while preserving the functionality needed for DPD, QMC, and LOL correction.
2Measurement precision
If separate auxiliary receiver is used to capture transmit signal data, then impairment compensation accuracy is improved, but device complexity and power consumption increase
Solution Approach 1:
The patent merges the transmit signal capture function into the main receiver by utilizing its existing ADC and downconversion circuitry. The receiver processes loopback transmit RF signals through the same signal path used for traffic reception, eliminating the need for separate measurement hardware while maintaining compensation accuracy through digital signal processing.
Solution Approach 2:
The receiver serves itself by using its own internal resources (ADC, downconversion circuitry, baseband processor) to capture and process transmit signal data for impairment compensation. This self-service approach eliminates the need for external dedicated measurement equipment, reducing overall device complexity while maintaining measurement precision.
3Device complexity
If RF direct sampling ADC is used to convert loopback transmit RF signals, then bandwidth requirements are reduced and hardware complexity is reduced, but conversion precision challenges increase
Solution Approach 1:
The patent replaces traditional superheterodyne RF downconversion hardware (mixers, local oscillators, multiple ADCs) with direct RF sampling using a single high-speed ADC. This substitution simplifies the hardware architecture by eliminating analog mixing stages and multiple LO PLLs, while the ADC's digital processing capabilities maintain the required conversion precision for impairment measurement.
Solution Approach 2:
The patent extracts the essential function of transmit signal capture from complex analog RF downconversion hardware and implements it through digital RF sampling. By taking out the analog mixing and multiple LO generation requirements, the system achieves simpler hardware while maintaining measurement precision through the ADC's direct sampling capability and subsequent digital processing.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution effectively compensates for transmit signal impairments, improving power efficiency and signal quality by accurately estimating and correcting PA nonlinearities, IQ mismatch, and LO leakage in real-time, while reducing bandwidth requirements and eliminating the need for additional LO PLL/synthesizers.
Implementation Method 1
an RF direct sampling ADC to convert the loopback transmit RF signals to digital transmit RF signals
Implementation Method 2
digital down conversion circuitry to downconvert the digital transmit RF signals to captured digital transmit baseband signals
Data Source
AI summary
A transmitter for an RF communications system, that includes an auxiliary receiver for capturing transmit signal data for use in compensating/correcting transmit signal impairments (such as for DPD, QMC, LOL). The transmitter (such as Zero IF) includes analog chain elements that introduce transmit signal impairments (such as PA nonlinearities). The auxiliary receiver is configured to receive loopback transmit RF signals, and includes an RF direct sampling ADC to convert the loopback transmit RF signals to digital transmit RF signals. Digital down conversion circuitry is configured to downconvert the digital transmit RF signals to captured digital transmit baseband signals, and data capture circuitry is configured to generate the transmit signal data based on the captured digital transmit baseband signals.