RF Power Amplifier Supply Control for Linearity at Power Back-Off
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Solution Overview
Problem
Existing RF power amplifiers for active antenna arrays face challenges in maintaining linearity and efficiency across a wide dynamic range, particularly when operating at different drive levels and temperatures, with existing techniques being limited in their ability to adjust bias conditions for Field Effect Transistors (FETs) and failing to track gain and phase effectively.
Innovation Solution
An amplifier system incorporating an Electronic Power Conditioner and a control section with a mixed analogue and digital electronic circuit, using control words stored in an EEPROM to adjust DC supply voltages and maintain linearity and efficiency by controlling gain compression, allowing for autonomous or telecommandable control of RF power amplifiers with FETs or other transistors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If amplifier drive is reduced, then linearity improves, but efficiency degrades
Solution Approach 1:
The patent implements dynamic bias adjustment that automatically adapts to varying drive levels. The bias circuit monitors the amplifier operating point and dynamically adjusts bias conditions to maintain optimal efficiency across the full dynamic range, transforming the static bias system into a dynamic one that responds to changing operating conditions.
Solution Approach 2:
The patent changes the bias parameters (Vbias, Ibias) as a function of drive level to maintain optimal operating conditions. By dynamically adjusting these parameters based on the amplifier's operating point, the system maintains both linearity and efficiency across varying drive levels, rather than being fixed at compromise values.
2Loss of energy
If bias conditions are optimized for a given RF output power, then efficiency is improved, but performance degrades at different drive levels
Solution Approach 1:
The bias circuit transitions from a static design optimized for a single operating point to a dynamic system that continuously adapts to varying drive levels. This enables the amplifier to maintain optimal efficiency whether operating at high power, back-off conditions, or varying temperatures.
Solution Approach 2:
The patent employs feedback mechanisms where the bias circuit monitors the amplifier's operating point and automatically adjusts bias conditions in response. This closed-loop approach ensures the amplifier maintains optimal efficiency and performance characteristics across the full dynamic range without manual intervention.
3Adaptability or versatility
If amplifiers operate at different drive levels and temperatures, then adaptability is improved, but gain and phase tracking becomes difficult
Solution Approach 1:
The patent uses feedback control where temperature sensors and drive level detectors provide information to the bias circuit, which then adjusts bias conditions to compensate for variations. This automatic compensation maintains consistent gain and phase characteristics across amplifiers operating at different conditions.
Solution Approach 2:
The bias parameters are dynamically changed based on temperature and drive level measurements. This allows each amplifier to maintain its optimal operating characteristics regardless of environmental conditions or drive level variations, ensuring consistent array performance.
4Loss of energy
If complex techniques like Chireax outphasing or Doherty amplifiers are used, then efficiency at back-off is improved, but device complexity increases
Solution Approach 1:
The patent extracts the efficiency enhancement function from complex external circuits (outphasing networks, Doherty structures) and implements it directly within the amplifier's bias system. This integration achieves back-off efficiency improvement without requiring additional complex signal paths or combining networks.
Solution Approach 2:
The patent introduces a simplified bias intermediary circuit that mediates between the power supply and the amplifier stages. This bias circuit provides the efficiency enhancement function that previously required complex signal processing architectures, using instead a straightforward voltage control approach.
Data Source
Figure 1~2
Figure 3~4
Figure 5.1~6
AI summary
A Solid State Power Amplifier (SSPA) for powering a single element of a multi-element antenna, the SSPA comprising: an RF amplifier, having a signal amplifying path that includes preamplifier, driver amplifier (16) and a power output stage (18) an Electronic Power Conditioner (EPC) for providing a variable value of DC voltage for powering the power output stage (18) of the RF amplifier; a control ASIC (40) for receiving an input power signal (46) of the RF amplifier for providing a voltage control signal to the EPC to determine the value of the DC voltage, the control ASIC addressing an EEPROM (42) holding a collection of control words that define output values of a control output signal for varying values of said input power, such that the value of the DC voltage (36) to the power output stage (18) is varied so as to control the gain compression of the RF amplifier for varying values of input power in order to maintain constant amplifier linearity.