Diode-Biased Stacked Amplifier for High-Power RF Linearity
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Solution Overview
Problem
Power amplifiers face challenges in maintaining linearity, especially at high input RF power, leading to reduced gain and poor performance, which is undesirable in wireless communication devices.
Innovation Solution
The implementation of a diode-based biasing circuit for stacked transistors, where diode-connected transistors rectify RF current 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
1Reliability
If conventional biasing circuits are used in power amplifiers, then the circuit complexity is low, but the linearity deteriorates at high input RF power
Solution Approach 1:
The biasing circuit transitions from a static configuration to a dynamic one by incorporating diode-connected transistors that automatically adjust bias voltages in response to input RF power levels. The diode-connected transistors (M2, M4, M6) create voltage drops that dynamically modulate the gate-source voltages of the stacked transistors, enabling the biasing to adapt to varying signal conditions and maintain linearity across different power levels.
Solution Approach 2:
The diode-connected transistors provide implicit feedback by sensing the input RF power level and automatically adjusting the bias voltages accordingly. The voltage drops across the diode-connected transistors are proportional to the input power, creating a feedback mechanism that compensates for gain compression and maintains consistent linearity without requiring external control circuits.
2Reliability
If stacked transistors are used to improve linearity, then the gain increases, but the bias voltage control becomes difficult
Solution Approach 1:
The biasing circuit is designed to be self-regulating, where the diode-connected transistors automatically generate the appropriate bias voltages based on the input RF power level. The circuit uses its own operating conditions (input power) to control its biasing, eliminating the need for external control mechanisms and simplifying the overall system while maintaining precise bias voltage control across varying conditions.
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 the linearity of power amplifiers, as evident by improved adjacent channel power ratio (ACPR) metrics, and allows for increased gain at high input RF power without sacrificing efficiency.
Implementation Method 1
diode-connected transistors rectify RF current to generate variable gate-to-source voltages
Data Source
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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.