Load-Modulated RF Amplifier Gain Shaping for DPD Linearity
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Solution Overview
Problem
Designing a satisfactory radio-frequency power amplifier for electronic devices is challenging due to the non-linear gain of load-line modulated radio-frequency power amplifiers, which exhibit gain expansion and abrupt transitions in gain profiles, making it difficult to design a digital predistortion circuit that operates effectively with these amplifiers.
Innovation Solution
The implementation of a load modulated radio-frequency amplifier circuit with an adjustable load component and a gain shaping circuit that tunes the load impedance to provide a smooth gain transition between unmodulated and modulated ranges, using a digital predistortion circuit to linearize the amplifier gain, and a method that includes predistorting baseband signals, upconverting, amplifying, and adjusting the load impedance based on instantaneous signal amplitudes to maintain continuous gain derivatives.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a load-line modulated radio-frequency power amplifier is used to achieve high power amplification, then the amplifier output power is improved, but the gain becomes non-linear with abrupt transitions and gain expansion
Solution Approach 1:
The digital predistortion circuit applies gain compression to the input signal before it enters the load-line modulated amplifier. This preliminary action pre-compensates for the expected non-linear gain expansion, so that the overall system maintains linear gain characteristics despite the amplifier's inherent non-linearity.
Solution Approach 2:
The system incorporates a feedback path that monitors the actual amplifier output and compares it with the desired output. The feedback signal is used to adjust the predistortion parameters, creating a closed-loop control system that continuously maintains gain linearity and compensates for variations in amplifier characteristics.
2Reliability
If digital predistortion is applied to linearize the amplifier gain, then the gain linearity is improved, but the device complexity increases due to additional circuits
Solution Approach 1:
The predistortion circuit dynamically adjusts its transfer function parameters based on the operating conditions and feedback measurements. By changing parameters such as compression depth and characteristic curves, the circuit maintains effective linearization across different power levels without requiring a completely different circuit architecture.
Solution Approach 2:
The digital predistortion circuit is designed to handle multiple functions: gain compression, phase compensation, and adaptation to different amplifier operating points. This multi-functionality reduces the need for separate dedicated circuits for each function, thereby limiting the increase in overall device complexity.
3Power
If the load impedance is made adjustable to modulate the amplifier, then the power amplification capability is improved, but the gain profile exhibits abrupt transitions between unmodulated and modulated ranges
Solution Approach 1:
The load impedance is made dynamically adjustable rather than fixed, allowing the amplifier to transition between different operating modes. The impedance modulation is controlled to track the input signal envelope, enabling the amplifier to maintain optimal efficiency across different power levels while avoiding abrupt gain transitions through smooth impedance transitions.
Data Source
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AI summary
An electronic device (10) may include wireless circuitry (24). The wireless circuitry (24) may include at least a digital predistortion circuit (64), an upconversion circuit (68), and a load-line modulated amplifier circuit (50). The digital predistortion circuit (64) can be configured to receive a reference baseband signal from one or more processors (26) and to selectively output a predistorted version of the reference baseband signal. The upconversion circuit (68) can be configured to receive a signal from the digital predistortion circuit (64) and to output a radio-frequency signal. The load-line modulated amplifier circuit (50) can be configured to amplify the radio-frequency signal. The load-line modulated amplifier circuit (50) can include an adjustable load component. The adjustable load component can have a constant impedance when an instantaneous signal amplitude of the reference baseband signal is within a first range and can be tuned to have a varying impedance when the instantaneous signal amplitude of the reference baseband signal is within a second range.