Envelope-Tracked Bias Circuit for Multiband Power Amplifiers
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Solution Overview
Problem
Existing power amplifier modules for multiband communications systems face challenges in reducing current consumption and maintaining efficiency, as they often supply a fixed bias current, leading to high current consumption and AM-PM distortion, especially when handling varying signal powers across different frequency bands.
Innovation Solution
A power amplifier apparatus with an envelope tracking (ET) current bias circuit that generates a first ET bias current by calculating direct and ET currents based on a reference voltage and ET voltage, respectively, and adjusts their ratio using a control circuit to maintain a constant average current, thereby optimizing performance across different frequency bands.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fixed bias current is supplied to the power amplifier, then the amplifier can maintain stable operation across different frequency bands, but the current consumption increases and AM-PM distortion occurs when signal power varies
Solution Approach 1:
The patent applies dynamics by transitioning from a fixed bias current to a dynamically adjustable bias current that adapts to signal power levels. The bias current is modulated according to the envelope of the RF signal, allowing the power amplifier to maintain optimal operating conditions across varying signal powers and frequency bands, thereby reducing current consumption while preventing AM-PM distortion.
Solution Approach 2:
The patent changes the parameter of bias current from a fixed value to a variable value that tracks the signal envelope. By adjusting the bias current parameter dynamically based on signal conditions, the system achieves both energy efficiency and operational stability across different frequency bands and signal powers.
2Device complexity
If a fixed bias current is supplied to the power amplifier, then the circuit design is simplified, but AM-PM distortion and ACPR performance deterioration occur when the amplifier is coupled in a phase opposite to the output signal
Solution Approach 1:
The patent implements feedback by using the envelope of the RF signal to control the bias current. The envelope detector extracts the signal envelope, which then feeds back to modulate the bias current, creating a closed-loop system that automatically compensates for phase opposition effects and maintains optimal performance across different operating conditions.
Solution Approach 2:
The dynamic adjustment of bias current based on signal envelope feedback enables the system to adapt to phase opposition conditions, reducing AM-PM distortion and improving ACPR performance without requiring complex additional circuitry.
3Reliability
If a high bias current is supplied to prevent deterioration, then the amplifier maintains linearity at high signal power, but current consumption increases unnecessarily at low signal power
Solution Approach 1:
The patent uses dynamic bias current adjustment that tracks the signal envelope, allowing the bias current to be high when signal power is high (maintaining linearity) and low when signal power is low (reducing current consumption). This dynamic adaptation eliminates the need to maintain a constantly high bias current, achieving both linearity and energy efficiency.
Solution Approach 2:
The bias current parameter is changed from a fixed high value to a variable value that adapts to signal power levels, achieving optimal linearity only when needed while reducing current consumption during low-power operation.
Data Source
AI summary
A power amplifier apparatus, includes an envelope tracking (ET) current bias circuit configured to generate a first ET bias current by calculating a direct current DC, based on a reference voltage, and an ET current, based on an ET voltage, according to an envelope of an input signal; and a power amplifier circuit having a bipolar junction transistor supplied with the first ET bias current and a power voltage to amplify the input signal, wherein an average current of the first ET bias current is controlled to be substantially constant.