RF Power Amplifier Bias Circuit for Memory Effect Suppression
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Solution Overview
Problem
The challenge of designing RF power amplifiers for 5G NR systems with wider bandwidths is the increased memory effect causing asymmetrical third-order intermodulation distortion and deteriorating Adjacent Channel Power Ratio (ACPR), which is not effectively addressed by existing bias circuits, leading to poor performance and high power consumption.
Innovation Solution
A bias circuit with a control loop and regulation circuit that adjusts loop bandwidth using the Miller effect to ensure stability and noise suppression, providing a low baseband impedance path and compensating for base current changes, thereby reducing memory effects and improving ACPR.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the bandwidth of modulation signal is increased to achieve higher data transmission rate, then the data transmission rate is improved, but the memory effect increases causing asymmetrical third-order intermodulation distortion and deteriorating ACPR
Solution Approach 1:
The bias circuit performs preliminary action by adjusting the base current of the power amplifier transistor before the RF signal is amplified. The control loop proactively compensates for the memory effect by dynamically adjusting the bias current based on the input signal conditions, preventing the intermodulation distortion from occurring in the first place rather than correcting it after amplification.
Solution Approach 2:
The patent implements a feedback mechanism where the control loop continuously monitors the base current and adjusts the bias current accordingly. The regulation circuit uses feedback to detect changes in the base current caused by memory effect and automatically compensates by adjusting the bias current to maintain proper amplifier operation and minimize intermodulation distortion.
2Device complexity
If existing bias circuits are used without adjustment, then the circuit complexity is kept low, but the ACPR performance deteriorates due to unaddressed memory effects
Solution Approach 1:
The patent introduces an intermediary control loop and regulation circuit between the existing bias circuit and the power amplifier. This intermediary structure mediates the relationship by adding minimal complexity components (transistor, capacitor, resistor) that actively compensate for memory effects without requiring complete redesign of the bias circuit, thus achieving ACPR improvement with limited increase in circuit complexity.
3Speed
If the loop bandwidth is increased to improve response speed, then the response speed is improved, but the stability and noise suppression degree deteriorate
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the loop bandwidth based on operating conditions. The regulation circuit modifies the bandwidth parameter of the control loop to optimize the balance between response speed and stability. By changing the bandwidth parameter adaptively rather than using a fixed value, the system achieves fast response when needed while maintaining stability under normal operating conditions.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The proposed bias circuit enhances RF power amplifier performance by reducing ACPR deterioration and AM-AM distortion, ensuring stability and noise suppression, even with increased input signal bandwidths, without increasing circuit complexity or cost.
Implementation Method 1
the regulation circuit adjusts a loop bandwidth of the control loop based on Miller effect when it is determined that the bias current output by the control loop can meet a first condition
Implementation Method 2
the regulation circuit adjusts a transmission zero of the control loop by the second resistor so that the stability of the control loop meets the third condition; the transmission zero is introduced by the parallel connection of the first transistor and the first capacitor
Data Source
AI summary
A bias circuit includes a control loop, configured to output a bias current to the input end of the RF power amplifier; a regulation circuit, configured to adjust loop bandwidth of the control loop based on Miller effect when it is determined that the bias current output by the control loop can meet a first condition, so that stability and noise suppression degree of the control loop can meet a second condition.