RF-DAC Variable Transformer Control for Linear Power Output
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Solution Overview
Problem
Developing modern power amplifier output stages for wireless mobile devices is challenging due to the complexity of calibration and non-linear behavior, especially for Class-E/F/D power stages, which require sophisticated digital multidimensional digital pre-distortion algorithms to reduce intermodulation products and achieve high efficiency and linearity.
Innovation Solution
The proposed solution involves a RF-DAC system using a combination of digitally controlled power amplifiers and a load-pull variable transformer to achieve a linear RF-DAC power curve, simplifying the calibration process and making parameters more robust over process, voltage, and frequency variations, by selecting and controlling single power amplifiers and transformers with coarse and fine resolution respectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a unary power cell array and a binary power cell array are used to amplify RF signals, then the amplifier can operate in highly efficient mode, but the RF-DAC power curve becomes very non-linear
Solution Approach 1:
The power amplifier is divided into multiple parallel branches, each containing a power cell with specific binary control signals. This segmentation allows independent control of each branch to achieve both high efficiency operation and linear power output by selectively activating appropriate branches based on the desired output power level.
Solution Approach 2:
The patent introduces a new dimension of control by adding parallel branches with different impedance values and binary control signals to the traditional unary/power cell architecture. This multi-dimensional control structure enables simultaneous optimization of efficiency (through selective cell activation) and linearity (through controlled impedance variation across branches).
2Manufacturing precision
If digital pre-distortion algorithms are applied to linearize the power amplifier, then intermodulation products are reduced, but the calibration process becomes complicated
Solution Approach 1:
The power amplifier structure itself provides the linearization function through its inherent multi-branch architecture with controlled impedance variation. By designing the parallel branches with specific impedance relationships and binary control mechanisms, the system achieves linear power output without requiring external digital pre-distortion calibration, making the system self-calibrating and simpler to implement.
3Power
If multiple power cells are activated concurrently to increase output power, then the power range is expanded, but the power curve becomes flat at high digital input values
Solution Approach 1:
Different branches of the power amplifier are assigned different local characteristics, specifically different impedance values and binary control signal configurations. This local quality variation ensures that each branch contributes differently to the total output power, maintaining precise control and resolution across the entire power range including high power levels, preventing the flattening effect.
Data Source
AI summary
There is provided a RF-DAC that may include (i) a first PAM that includes a first group of first power amplifiers of different amplifications, (ii) a second PAM that includes a second group of second power amplifiers of different amplifications; (iii) a load that includes an output port and a transformer; (iv) power amplifiers control units, and a transformer control unit. During a cycle of operation (i) each one of the first and second PAMs is configured to receive one or more power amplifiers digital control signals and activate a single power amplifier per each of the first and second PAMS, (ii) the transformer control unit is configured to receive a transformer digital control signal and control a transformer parameter of the transformer, and (iii) the transformer is configured to receive a first PAM output signal and a second PAM output signal, and output a transformer output signal that reflects digital information represented by the one or more power amplifiers digital control signals and the transformer digital control signal.