Power Amplifier Bias Control Using Peak Collector Voltage Sensing
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Solution Overview
Problem
Conventional power amplifiers in CDMA systems face degradation in distortion characteristics due to changes in load, making it difficult to maintain desired performance without using isolators, which are costly and large.
Innovation Solution
A power amplifier design that includes a current mirror circuit to detect peak collector voltage and control bias current, allowing for dynamic adjustment to maintain distortion characteristics, implemented using HBTs and additional circuit components on a GaAs chip.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an isolator is provided after the power amplifier to prevent load variation influence, then the distortion characteristic is improved, but the device size and cost increase
Solution Approach 1:
The invention extracts the isolator from the system by implementing load variation compensation directly within the power amplifier circuit. The bias circuit now includes detection means for detecting load variation and control means for controlling the bias current based on the detected load variation, thereby eliminating the need for an external isolator while maintaining distortion characteristics
Solution Approach 2:
The invention introduces a bias circuit as an intermediary between the power amplifier and the load. This bias circuit detects load variation and adjusts the bias current accordingly, serving as a mediator that compensates for load changes without requiring an isolator. The bias circuit acts as a buffer that protects the power amplifier from load variations
2Reliability
If an isolator is provided after the power amplifier to prevent load variation influence, then the distortion characteristic is improved, but the manufacturing cost increases
Solution Approach 1:
The invention extracts the isolator from the system by implementing load variation compensation directly within the power amplifier circuit. The bias circuit now includes detection means for detecting load variation and control means for controlling the bias current based on the detected load variation, thereby eliminating the need for an external isolator while maintaining distortion characteristics
Solution Approach 2:
The power amplifier performs self-compensation for load variations through the bias circuit. The bias circuit detects load variation and automatically adjusts the bias current to compensate for the detected changes, enabling the system to self-regulate without external isolation components, thereby reducing cost
3Reliability
If the bias current is increased to compensate for load variation, then the distortion characteristic is improved, but the power consumption increases
Solution Approach 1:
The invention implements dynamic bias current adjustment based on detected load variation. The bias circuit continuously monitors load conditions and adjusts the bias current in real-time, increasing it only when load variation is detected and requiring compensation. This dynamic approach ensures distortion characteristics are maintained while minimizing unnecessary power consumption during stable operating conditions
Solution Approach 2:
The invention changes the bias current parameter dynamically in response to load variation. The control means adjusts the bias current level based on the detected load conditions, increasing the current only when necessary to compensate for adverse load changes and maintain distortion characteristics, thereby optimizing the trade-off between performance and power consumption
Data Source
AI summary
There are provided a power amplifying transistor, a bias circuit which supplies a bias current to the base of the power amplifying transistor, a current mirror circuit which detects a peak value of the collector voltage of the power amplifying transistor, and a control circuit which, when the peak value of the collector voltage becomes higher than a voltage set in advance, controls the bias circuit to increase the bias current.