Envelope-Tracking Bias Circuit for Low-Distortion Power Amplifiers
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Solution Overview
Problem
Existing power amplifier modules (PAMs) face high current consumption due to fixed bias current settings, leading to increased current consumption even when RF signal power is low, and AM-PM distortion, which degrades ACPR performance.
Innovation Solution
An envelope tracking current bias circuit that generates a first bias current based on a reference voltage and a second bias current based on an envelope voltage, with a bias current generator summing these currents to provide an envelope tracking bias current to the power amplifier, reducing AM-PM distortion by dynamically adjusting bias current levels in response to signal power variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fixed bias current is set to a high level to prevent biasing deterioration, then the reliability of the power amplifier is improved, but the current consumption increases even when RF signal power is low
Solution Approach 1:
The bias current is changed from a fixed value to a dynamically adjustable value that varies with the envelope voltage of the RF signal. The bias current generator produces a first envelope tracking bias current that is proportional to the envelope voltage, allowing the bias current to adapt to changing signal conditions and reduce consumption when signal power is low while maintaining reliability when signal power is high.
Solution Approach 2:
The bias current parameter is changed from a constant fixed value to a variable parameter that tracks the envelope voltage. By making the bias current proportional to the envelope voltage through the bias current generator, the system optimizes the trade-off between reliability and current consumption by adjusting the bias current parameter according to the actual signal conditions.
2Device complexity
If a fixed bias current is used to simplify the circuit design, then the device complexity is reduced, but the AM-PM distortion increases which degrades ACPR performance
Solution Approach 1:
The bias current generator uses the envelope voltage as feedback to dynamically adjust the bias current. The envelope voltage, which represents the signal power variations, is fed back to the bias current generator to produce a corresponding bias current that compensates for AM-PM distortion, thereby improving ACPR performance without excessive circuit complexity.
Solution Approach 2:
The bias current generator acts as an intermediary component that processes the envelope voltage and generates the appropriate bias current. This intermediary element enables the system to reduce AM-PM distortion by introducing a controlled relationship between the envelope voltage and bias current, achieving performance improvement with minimal added complexity.
Data Source
AI summary
An envelope tracking current bias circuit of a power amplifier circuit including a power amplifier includes a first current source circuit configured to generate a first bias current based on a reference voltage, a second current source circuit configured to generate a second bias current based on an envelope voltage of an input signal, and a bias current generator configured to generate a first envelope tracking bias current based on the first bias current and the second bias current, and supply the first envelope tracking bias current to the power amplifier circuit to reduce amplitude modulation-phase modulation (AM-PM) distortion of the power amplifier circuit.