Power Amplifier Bias Circuit for Gain Drift During Data Bursts
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Solution Overview
Problem
Power amplifiers in wireless communication systems face challenges in maintaining gain stability during long data bursts due to thermal effects, which can lead to increased Error Vector Magnitude (EVM) and dynamic EVM degradation, especially with newer standards requiring tighter EVM specifications and longer burst durations.
Innovation Solution
A temperature compensation circuit measures the power amplifier's temperature during data bursts and adjusts the gain by generating a bias compensation signal based on the temperature change and a temperature coefficient, using a bias circuit with a sampling circuit and a difference amplifier to control the bias current and stabilize the gain.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the power amplifier operates during long data bursts, then the productivity is improved, but the gain stability deteriorates due to thermal effects
Solution Approach 1:
The patent implements a feedback mechanism where the temperature of the power amplifier is continuously monitored during data bursts, and the bias circuit adjusts the gain based on the measured temperature to compensate for thermal effects. This closed-loop control maintains gain stability while allowing long burst operation.
Solution Approach 2:
The patent changes the bias parameters dynamically based on temperature measurements. By adjusting the bias current or voltage in response to temperature changes, the system compensates for thermal effects and maintains stable gain throughout the data burst duration.
2Stability of the object's composition
If temperature compensation is applied during data bursts, then the gain stability is improved, but the device complexity increases
Solution Approach 1:
The patent employs self-service principles by using an on-chip temperature sensor that automatically monitors the power amplifier's temperature and feeds this information to the bias circuit, which then autonomously adjusts the gain without requiring external intervention or complex control systems.
Solution Approach 2:
The patent merges the temperature sensing and gain control functions into a single integrated bias circuit. The temperature sensor, sampling circuit, and bias adjustment mechanisms are combined to work together as one unified system, reducing overall device complexity while maintaining effective temperature compensation.
3Stability of the object's composition
If the bias current is adjusted to compensate for gain droop, then the gain stability is improved, but the current consumption increases
Solution Approach 1:
The patent applies periodic action by sampling the temperature at specific intervals during the data burst (e.g., at the beginning and at predetermined times thereafter) rather than continuously. This allows the bias circuit to adjust gain periodically, maintaining stability while reducing overall current consumption compared to continuous adjustment.
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 approach effectively reduces gain droop and maintains stable EVM levels across varying temperatures, improving performance and reducing current consumption compared to previous DEVM compensation methods.
Implementation Method 1
Power amplifiers in wireless communication systems face challenges in maintaining gain stability during long data bursts due to thermal effects
Implementation Method 2
A bias circuit is disclosed that provides additional bias current for power amplifiers during data bursts to compensate for the gain droop caused by a rise in the power amplifier temperature during the data burst
Data Source
AI summary
A bias circuit provides additional bias current for power amplifiers during data bursts to compensate for the gain droop caused by a rise in the power amplifier temperature during the data burst. A bias circuit includes a difference amplifier and switches coupled to the difference amplifier. The switches operate the bias circuit in a first mode when a transmit data burst is detected and operate the bias circuit in a second mode after the bias circuit has operated in the first mode for a predetermined period of time. In the first mode, the bias circuit charges a storage capacitor and sets an output current to zero. In the second mode, the bias circuit outputs the output current that increases above the initial value of zero as the PA warms up, where the excursion of this increase of current is determined by a register. The switches disable the bias circuit when the transmit data burst ends.