Power Amplifier Neutralization Circuit for Memory Distortion
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Solution Overview
Problem
Power amplifier circuits in 5G and 5G-NR systems suffer from memory distortion due to unwanted remodulation terms caused by the leakage of modulated current from collector nodes into input nodes, which degrade the adjacent channel leakage ratio (ACLR) and are difficult to compensate with digital predistortion.
Innovation Solution
Incorporation of neutralization circuits in the power amplifier circuit to inject neutralization currents that cancel the leaked modulated currents, thereby suppressing unwanted remodulation terms and improving ACLR performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If digital predistortion is used to compensate for distortion, then some distortion can be corrected, but memory distortion with memory effect cannot be effectively compensated
Solution Approach 1:
The patent introduces a neutralization circuit as an intermediary component between the amplifier stages. This circuit captures the leaked modulated current from the collector node and injects a neutralization current into the input node, acting as a mediator to cancel the harmful leakage current that digital predistortion cannot address.
Solution Approach 2:
The neutralization circuit extracts the harmful modulated current component from the collector node through a coupling capacitor, separating it from the main signal path. This extracted current is then processed and injected back as a neutralization current to cancel the leakage effect at the input node.
2Power
If amplifier stages are used to amplify RF signal, then signal power is increased, but modulated current leaks from collector node to input node creating unwanted remodulation terms
Solution Approach 1:
The patent converts the harmful leaked modulated current into a beneficial neutralization current. The same current that causes remodulation distortion is captured, processed, and injected back in a controlled manner to cancel the distortion, turning the harmful leakage into a useful cancellation mechanism.
Solution Approach 2:
The neutralization circuit performs preliminary anti-action by capturing the modulated current before it completes the harmful feedback loop from collector to input. By injecting the neutralization current in advance, the circuit prevents the remodulation distortion from occurring in the first place.
3Reliability
If neutralization circuit is added to suppress leaked current, then ACLR performance is improved, but capacitive loading increases
Solution Approach 1:
The neutralization circuit uses a coupling capacitor to partially extract the modulated current rather than attempting to capture the entire current. This partial action approach provides sufficient distortion cancellation while limiting the capacitive loading effect on the amplifier stages.
Data Source
AI summary
Memory distortion neutralization in a power amplifier circuit (58) is provided. The power amplifier circuit (58) includes one or more amplifier stages (40, 42) each configured to amplify a radio frequency (RF) signal based on a time-variant modulated voltage received at a respective collector node. Notably, each of the amplifier stages (40, 42) can inherently cause a derivative of the time-variant modulated voltage (a.k.a. a modulated current) to be leaked from the respective collector node into a respective input node, which can create unwanted remodulation terms that can degrade an adjacent channel leakage ratio (ACLR) of the power amplifier circuit (58). Herein, a neutralization circuit (54, 60) is configured to inject a neutralization current to the respective input node to cancel at least a portion of the leaked modulated current.