Bulk-Biased Power Amplifier for Linearity at High Output Power
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Solution Overview
Problem
Power amplifiers in wireless communication systems face challenges in achieving high linearity and compression points due to nonlinear transfer functions, which result in intermodulation products and harmonic distortion, and existing methods like predistortion require known nonlinearity.
Innovation Solution
A power amplifier is designed with a dynamic bias voltage applied to the bulk node of the input transistor, which varies as a nonlinear function of the input signal's envelope, allowing for improved linearity and increased compression point without introducing gain expansion at lower input powers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a power amplifier operates at high power levels, then output power is improved, but linearity deteriorates due to nonlinear transfer function creating intermodulation products and harmonic distortion
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the bulk terminal voltage of the transistor as a control parameter. By varying this voltage based on the input signal envelope, the transistor's threshold voltage and transfer function are modified in real-time, allowing the amplifier to maintain linearity across different output power levels. This resolves the contradiction by enabling high power operation without sacrificing linearity through continuous parameter optimization.
2Manufacturing precision
If predistortion is used to linearize the amplifier, then linearity is improved, but the method requires known nonlinearity characteristics which increases device complexity
Solution Approach 1:
The patent implements self-service by using the amplifier's own input signal envelope to control the bulk terminal voltage. The system automatically adjusts its own operating parameters based on the signal characteristics without requiring external feedback or complex predistortion algorithms. This simplifies the device by eliminating the need for separate nonlinearity characterization and compensation circuits, achieving linearity through self-regulation.
3Power
If dynamic bias voltage is applied to the bulk node, then the 1dB compression point is enhanced, but gain expansion may occur at lower input powers
Solution Approach 1:
The patent applies dynamics by implementing a dynamic bias voltage that continuously adapts to the input signal envelope rather than using a fixed bias. The bulk terminal voltage is modulated in real-time according to the signal amplitude, which dynamically adjusts the transistor's operating point. This dynamic control allows the amplifier to maintain optimal gain and linearity across the entire input power range, preventing gain expansion at low powers while enhancing the compression point at high powers.
Data Source
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AI summary
A power amplifier (20) for a transmitter circuit (10) is disclosed. The power amplifier (20) comprises at least one field-effect transistor (100, 100n, 100p) having a gate terminal (110, 110n, 110p) and a bulk terminal (120, 120n, 120p), wherein the at least one field-effect transistor (100, 100n, 100n) is configured to receive an input voltage at the gate terminal (110, 110p, 110n) and a dynamic bias voltage at the bulk terminal (120, 120n, 120p). Furthermore, the power amplifier (20) comprises a bias- voltage generation circuit (130). The input voltage is a linear function of an input signal. The bias- voltage generation circuit (130) is configured to generate the dynamic bias voltage as a nonlinear function of an envelope of the input signal.