RF Amplifier Circuit with Third-Order Non-Linearity Cancellation
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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-linear characteristics of transistors, which generate third-order intermodulation distortion, degrading signal-to-noise and distortion ratio (SNDR) and error vector magnitude (EVM).
Innovation Solution
Implementing a third-order non-linearity cancellation circuit that cross-couples input transistors with non-linearity cancellation transistors, utilizing a feedforward loop for common mode signal biasing and tail current control to reduce amplitude modulation to amplitude modulation (AMAM) and amplitude modulation to phase modulation (AMPM) distortion, while maintaining linear performance across process, voltage, and temperature variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If traditional radio-frequency amplifier circuitry is used, then the circuit can amplify signals, but third-order intermodulation distortion is generated that degrades signal quality
Solution Approach 1:
The patent applies preliminary anti-action by introducing a non-linearity cancellation circuit that generates cancellation signals with opposite polarity to the intermodulation distortion products. These cancellation signals are injected into the amplifier output to preemptively neutralize the distortion before it degrades the signal quality, thereby resolving the contradiction between maintaining amplification capability and eliminating harmful distortion.
Solution Approach 2:
The patent converts the harmful non-linear characteristics of the amplifier transistors into a beneficial effect by deliberately exploiting the same non-linearity to generate cancellation signals. The non-linearity cancellation circuit uses the amplifier's own non-linear behavior to create distortion products that are then inverted and fed back to cancel the original distortion, transforming the harmful effect into a solution.
2Object-affected harmful factors
If non-linearity cancellation circuitry is added, then intermodulation distortion is reduced, but circuit complexity increases
Solution Approach 1:
The patent merges the non-linearity cancellation function with the existing amplifier circuitry by integrating the cancellation transistors into the same circuit block and sharing common biasing networks and tail circuits. This consolidation allows the cancellation functionality to be added without proportionally increasing overall circuit complexity, as multiple components serve dual purposes in both amplification and distortion cancellation.
Solution Approach 2:
The patent implements multi-functionality by designing the non-linearity cancellation circuit to share resources with the main amplifier. The bias circuitry serves both the input transistors and cancellation transistors, the tail circuits provide current sourcing for multiple transistor pairs, and the overall structure allows a single circuit block to perform both signal amplification and distortion cancellation functions simultaneously.
Data Source
AI summary
An electronic device may include wireless circuitry. The wireless circuitry can include first and second input transistors, a third transistor having a gate terminal coupled to a gate terminal of the first input transistor and having a drain terminal coupled to the second input transistor, a fourth transistor having a gate terminal coupled to a gate terminal of the second input transistor and having a drain terminal coupled to the first input transistor, one or more tail circuits coupled to source terminals of the third and fourth transistors, and a bias circuit configured to output a bias voltage that is conveyed to the gate terminals of the first and second input transistors and to the one or more tail circuits. The bias circuit can be coupled to the input transistors via a coil and to the one or more tail circuits via a feedforward path.