RF Transmitter DEVM Correction for Gain Drift and Nonlinearity
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Solution Overview
Problem
Modern IoT RF transmitters face challenges with complex nonlinearity and instantaneous gain variations due to low power design, leading to performance impairments such as DEVM degradation and reduced bit rates, which existing solutions fail to adequately address.
Innovation Solution
The implementation of a Dynamic Error Vector Magnitude (DEVM) correction module and baseband digital predistortion (DPD) circuits in RF transmitters to compensate for time-dependent gain variations and nonlinearity, using gain Look-Up Tables and calibration processes to adjust signal amplitudes and correct for impairments in both digital and analog components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If low power design is implemented in RF transmitters, then power consumption and silicon area are reduced, but linearity is impaired and instantaneous gain variation increases
Solution Approach 1:
The patent applies preliminary action by measuring and storing the instantaneous gain variation characteristics of the power amplifier before actual signal transmission. A calibration process is performed to characterize the gain variation over time, and this pre-acquired information is used to generate correction factors that compensate for the nonlinearity during normal operation, eliminating the need for real-time complex compensation circuits
Solution Approach 2:
The patent introduces an intermediary digital correction mechanism between the digital baseband and analog RF stages. A correction factor is generated based on pre-measured gain variation data and applied to the digital signal before DAC conversion, serving as a mediator that translates the complex analog nonlinearity problem into a simple digital multiplication operation, thus improving linearity without adding analog circuit complexity
2Power
If power amplifier gain is increased to improve transmission performance, then signal strength is improved, but temperature increases causing gain variation over time
Solution Approach 1:
The patent implements feedback by measuring the actual output signal of the power amplifier during calibration and using this information to generate correction factors. The system continuously monitors the gain variation caused by temperature effects and applies compensating correction factors to maintain stable gain characteristics, creating a closed-loop compensation mechanism that operates in the digital domain
Solution Approach 2:
The patent applies parameter changes by dynamically adjusting the digital correction factor based on the elapsed time since power amplifier turn-on. As temperature and gain characteristics change over time, the system selects appropriate correction factors from a pre-characterized set, effectively adapting to the changing operating conditions without requiring real-time temperature sensing or complex control circuits
3Reliability
If Digital Pre-Distortion is applied to compensate for power amplifier nonlinearity, then linearity is improved, but device complexity increases
Solution Approach 1:
The patent extracts the nonlinearity compensation function from the analog RF domain and relocates it to the digital baseband domain. By measuring the power amplifier characteristics once during calibration and storing the correction data in digital memory, the complex real-time analog compensation problem is transformed into simple digital lookup and multiplication operations, significantly reducing circuit complexity while maintaining compensation effectiveness
Solution Approach 2:
The patent uses copying by creating a digital model of the power amplifier's nonlinearity characteristics through calibration measurements. Instead of directly compensating for the physical analog nonlinearity, the system creates a digital replica of the gain variation behavior and uses this copy to generate correction factors, simplifying the compensation mechanism to digital signal processing operations
Data Source
AI summary
A radio frequency (RF) transmitter includes an analog RF power amplifier and a digital Dynamic Error Vector Magnitude (DEVM) correction module. The DEVM correction module compensates for time-dependent variations in an instantaneous gain of the RF power amplifier. The time-dependent variations may be variations that occur during a period the RF power amplifier is turned on. The RF transmitter may further include one or more analog baseband circuits, and one or more respective baseband digital pre-distortion (DPD) modules that compensate for amplitude modulation to amplitude modulation (AM2AM) nonlinearities in the analog baseband circuits. The digital DEVM correction module and baseband DPD modules may each include respective look-up tables having values determined by respective calibration operations.