Power Amplifier Bias Feedback for High-Power Linearity
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Power amplifier circuits in mobile communication terminals face linearity deterioration due to increased input power, as the base voltage of bipolar transistors falls excessively, leading to a mismatch in collector current amplitude and base current amplitude, which affects signal amplification linearity.
Innovation Solution
A power amplifier circuit design that includes an amplifier transistor, a resistance element in series with its base, a bias transistor to supply bias current, and a feedback circuit that adjusts the base voltage of the bias transistor to follow changes in bias current, using a detection circuit, current mirror circuit, offset circuit, and filter circuit to maintain stable base voltage and prevent linearity deterioration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a ballast resistor is inserted between the base of a bipolar transistor and a bias circuit to suppress temperature-induced collector current increase, then thermal stability is improved, but voltage drop across the resistor excessively increases when bias current increases, causing base voltage to fall more than needed and linearity of signal amplification to deteriorate
Solution Approach 1:
The patent applies feedback by detecting the bias current flowing through the ballast resistor and using this detected signal to dynamically adjust the operating point of the bipolar transistor. A detection circuit measures the bias current, and this measurement is fed back to control the base voltage or bias circuit operation, compensating for the excessive voltage drop across the ballast resistor and maintaining proper linearity while preserving thermal stability.
Solution Approach 2:
The patent introduces an intermediary detection circuit between the ballast resistor and the bias control system. This intermediary measures the actual bias current and translates it into a control signal that adjusts the base voltage or bias circuit parameters, mediating between the thermal stability requirement (ballast resistor) and the linearity requirement (base voltage control).
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
The feedback circuit effectively suppresses the decrease in base voltage and base-emitter voltage, maintaining power gain and improving linearity even at high output power levels, ensuring consistent signal amplification.
Implementation Method 1
voltage drop across the ballast resistor
Implementation Method 2
feedback circuit configured to change a base or gate voltage of the bias transistor to follow a change in the bias current supplied to the base of the amplifier transistor
Data Source
AI summary
A power amplifier circuit includes an amplifier transistor that amplifies an input signal, a resistance element coupled in series with the base of the amplifier transistor, a bias transistor that supplies a bias current from the emitter or the source of the bias transistor to the base of the amplifier transistor through the resistance element, and a feedback circuit that changes a base or gate voltage of the bias transistor to follow a change in the bias current supplied to the base of the amplifier transistor.