Stacked Power Amplifier Diode Biasing for High-Power Linearity
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Solution Overview
Problem
Power amplifiers with stacked transistors face challenges in maintaining linearity, especially at high input RF power levels, leading to reduced gain and poor performance.
Innovation Solution
The implementation of diode-based biasing circuits for power amplifiers, where diode-connected transistors rectify RF current leaks to generate variable gate-to-source voltages, increasing gain and improving linearity by dynamically adjusting bias voltages based on input RF power.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If stacked transistors are used in power amplifiers, then voltage breakdown resistance is improved, but linearity deteriorates at high input RF power levels
Solution Approach 1:
The bias voltage for each transistor in the stack is made dynamic rather than fixed. Diode-connected transistors are used to automatically adjust the bias voltage of each transistor based on the instantaneous RF power level, ensuring optimal operating points that maintain linearity across varying power conditions while preserving the voltage breakdown resistance benefits of stacked configuration
Solution Approach 2:
Diode-connected transistors are incorporated into the biasing circuitry to provide automatic feedback control. These diodes sense the RF power level and adjust the bias voltage accordingly, creating a closed-loop system that maintains optimal transistor operating points and linearity without external intervention
2Device complexity
If fixed bias voltages are applied to stacked transistors, then circuit simplicity is maintained, but gain and linearity are reduced at high input RF power
Solution Approach 1:
The biasing circuit uses diode-connected transistors that automatically adjust their own bias voltages based on the RF power level without requiring external control circuits. This self-adjusting mechanism maintains circuit simplicity while achieving dynamic optimization of gain and linearity, as each transistor's bias is autonomously regulated by its associated diode-connected transistor
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 enhances linearity metrics such as adjacent channel power ratio (ACPR) and maintains efficiency, allowing for improved performance across various output power levels.
Implementation Method 1
diode-connected transistors rectify RF current leaks to generate variable gate-to-source voltages
Data Source
AI summary
Techniques for improving linearity of amplifiers are described. In an exemplary design, an amplifier (e.g., a power amplifier) may include a plurality of transistors coupled in a stack and at least one diode. The plurality of transistors may receive and amplify an input signal and provide an output signal. The at least one diode may be operatively coupled to at least one transistor in the stack. Each diode may provide a variable bias voltage to an associated transistor in the stack. Each diode may have a lower voltage drop across the diode at high input power and may provide a higher bias voltage to the associated transistor at high input power. The at least one transistor may have higher gain at high input power due to the higher bias voltage from the at least one diode. The higher gain may improve the linearity of the amplifier.