Source-Follower Bias Circuit for Power Amplifier ACLR Linearity
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Solution Overview
Problem
The nonlinearity of power amplifiers in wireless communication systems affects the adjacent channel leakage ratio (ACLR) performance, primarily due to 3rd order inter-modulation, which is not effectively addressed by existing technologies.
Innovation Solution
A bias circuit with a source follower that generates a bias voltage for the power amplifier, providing low output impedance and rejecting power amplifier kick-back harmonic interference, thereby stabilizing the bias voltage and improving ACLR performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a bias circuit is used to provide bias voltage to the power amplifier, then the power amplifier can operate stably, but the bias circuit has high output impedance which makes it sensitive to power amplifier kick-back harmonic interference
Solution Approach 1:
The patent changes the output impedance parameter of the bias circuit from high to low by using a source follower configuration. This parameter change makes the bias circuit less sensitive to harmonic interference while maintaining stable bias voltage, directly resolving the technical contradiction between reliability and harmful factor sensitivity.
2Power
If the power amplifier operates with high gain, then the signal amplification is improved, but the 3rd order inter-modulation increases which degrades ACLR performance
Solution Approach 1:
The patent employs feedback mechanisms where the stable bias voltage provided by the low output impedance bias circuit compensates for nonlinearities in the power amplifier. This feedback approach allows the power amplifier to operate at high gain while the feedback loop corrects for 3rd order inter-modulation effects, improving ACLR performance.
Solution Approach 2:
By changing the bias voltage stability parameter through the source follower configuration, the patent enables the power amplifier to maintain optimal operating conditions that reduce 3rd order inter-modulation. The stable bias point ensures symmetric operation that minimizes inter-modulation distortion while preserving signal amplification capability.
Data Source
AI summary
A power amplifier system includes a differential power amplifier and a bias circuit. The differential power amplifier is arranged for receiving a differential input pair to generate an output signal. The bias circuit is arranged for generating a bias voltage to bias the differential power amplifier, and the bias circuit comprises a source follower for receiving a reference voltage to generate the bias voltage.