RF Amplifier Nonlinearity Compensation for AMAM and AMPM Distortion
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Solution Overview
Problem
Designing satisfactory radio-frequency amplifier circuitry for electronic devices with wireless communications capabilities is challenging due to non-linearities that cause amplitude modulation to amplitude modulation (AMAM) and amplitude modulation to phase modulation (AMPM) distortion, leading to errors in error vector magnitude (EVM) and adjacent channel power ratio (ACPR).
Innovation Solution
Incorporating AMAM or AMPM distortion compensation circuits, which are differential circuits biased with a tail current source, to cancel out third-order intermodulation distortion without impacting gain performance by using higher order non-linearities produced by auxiliary transistors coupled in-phase and out-of-phase with the main amplifier.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If radio-frequency amplifier circuitry is designed to amplify signals for wireless transmission, then signal power is increased for long-distance transmission, but non-linearities cause AMAM and AMPM distortion leading to EVM and ACPR errors
Solution Approach 1:
The patent converts the harmful non-linearities of the main power amplifier into beneficial effects by using auxiliary amplifiers that intentionally introduce opposite non-linearities. The auxiliary amplifiers are designed with transistors coupled in-phase and out-of-phase to generate distortion components that cancel the third-order intermodulation distortion produced by the main amplifier, thereby transforming the harmful distortion into a useful cancellation mechanism that improves EVM and ACPR performance
Solution Approach 2:
The patent implements a counterweight approach by introducing auxiliary amplifiers that produce equal and opposite distortion effects to balance the non-linearities of the main amplifier. The auxiliary circuits generate compensating signals with inverted polarity that act as an 'anti-weight' to the distortion products, effectively neutralizing the harmful effects on signal fidelity while maintaining the high power output capability
2Manufacturing precision
If distortion compensation circuits are added to cancel third-order intermodulation distortion, then EVM and ACPR performance is improved, but circuit complexity increases with additional transistors and current sources
Solution Approach 1:
The patent merges the distortion compensation function with the existing power amplifier structure by integrating auxiliary amplifiers that share common elements with the main amplifier. The auxiliary circuits use transistors whose gate terminals are coupled to the same input terminals as the main amplifier, and they share common current sources and biasing networks, thereby combining multiple functions into a unified circuit architecture that reduces overall complexity
Solution Approach 2:
The auxiliary amplifiers are designed to serve multiple functions simultaneously: they provide distortion compensation through their non-linear transfer characteristics, maintain signal amplification capability, and generate the necessary out-of-phase and in-phase components for complete distortion cancellation. This multi-functionality reduces the need for separate compensation circuits and simplifies the overall system design
Data Source
AI summary
An electronic device may include wireless circuitry. The wireless circuitry can include an amplifier with first and second input transistors and at least one non-linearity distortion compensation circuit that includes a third transistor having a gate terminal coupled to a gate terminal of the first input transistor, a fourth transistor having a gate terminal coupled to a gate terminal of the second input transistor, and a tail current source coupled to a source-drain terminal of the third transistor and to a source-drain terminal of the fourth transistor. The amplifier may be coupled to one or more additional non-linearity distortion compensation circuit. The non-linearity distortion compensation circuit may be coupled out-of-phase with the amplifier, whereas the additional non-linearity distortion compensation circuit may be coupled in-phase with the amplifier.