Power Amplifier Bias Equalization Near the 1 dB Compression Point
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Solution Overview
Problem
Existing power amplifiers face challenges in achieving good amplitude-to-amplitude (AM-AM) and amplitude-to-phase (AM-PM) metrics while maintaining high power added efficiency (PAE), linearity, and error vector magnitude (EVM) performance.
Innovation Solution
The solution involves a new equalization approach that compensates for AM-AM and AM-PM variations by controlling bias conditions, such as bias voltage, versus output power to alter the AM-AM and AM-PM profiles. This approach is applicable to all frequencies, technologies, and types of amplifiers, including power amplifiers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If operation is performed further away from the 1 dB compression point to reduce AM-AM and AM-PM distortion, then linearity and EVM performance are improved, but power added efficiency (PAE) performance is significantly degraded
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the bias voltage of the amplifier based on the output power level. The bias voltage is modulated to compensate for AM-AM and AM-PM distortions, allowing the amplifier to operate near the 1 dB compression point while maintaining improved linearity and EVM performance. This dynamic parameter adjustment resolves the contradiction by enabling high efficiency operation without sacrificing linearity.
2Manufacturing precision
If digital pre-distortion (DPD) is used to improve linearity and EVM performance, then AM-AM and AM-PM metrics are improved, but feedback loop complexity and circuit complexity increase
Solution Approach 1:
The patent extracts and eliminates the complex feedback loop requirement of traditional DPD by using a feedforward bias modulation approach. Instead of requiring output feedback and complex digital processing, the invention uses a simpler circuit that directly modulates the bias voltage based on the input signal power level, achieving similar linearization results without the complexity of feedback loops and digital processors.
3Manufacturing precision
If high current density is used in IC FET fabrication to achieve good AM-AM and AM-PM metrics, then linearity is improved, but power added efficiency and thermal performance are degraded
Solution Approach 1:
The patent changes the operating parameters by implementing dynamic bias voltage modulation that allows the amplifier to operate at high current density near the 1 dB compression point while maintaining good AM-AM and AM-PM metrics. The bias modulation compensates for the distortions that would otherwise result from high current density operation, enabling both high efficiency and good linearity metrics simultaneously.
Data Source
AI summary
Circuits and methods for achieving good AM-AM and AM-PM metrics while achieving good power, PAE, linearity, and EVM performance in an amplifier. Embodiments provide an equalization approach which compensates for AM-AM and AM-PM variations in an amplifier by controlling bias voltage versus output power to alter the AM-AM and AM-PM profiles imposed by the amplifier. Differential amplifier embodiments include cross-coupled common-gate transistors that generate an equalization voltage that alters the gate bias voltage of respective main FETs in proportion to a power level present at the respective drains of the main FETs. Single-ended amplifier embodiments include an equalization circuit that alters the bias voltage to the gate of a main FET in proportion to a power level present at the main FET drain. Embodiments may also include a linearization circuit which alters the AM-PM profile of an input signal to compensate for the AM-PM profile imposed by a coupled amplifier.