RF Transmitter Bias Filtering for WLAN Output Linearity
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Solution Overview
Problem
Conventional Wireless LAN devices face decreased output linearity due to power noise amplification when a large current is supplied, leading to reduced data transmission rates and efficiency, as the switching power supply's output voltage drops and noise is not effectively reduced.
Innovation Solution
Incorporating a low-pass filter between the voltage generator and power amplifier to stabilize the bias and reduce power noise, using a combination of resistors and capacitors to filter the control voltage and provide a stable bias for the power amplifier, thereby enhancing output linearity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a switching regulator operates at high frequency to provide regulated DC power, then power consumption is reduced and efficiency is improved (80%-90% efficiency), but output voltage drops when large current is supplied, causing operation voltage of the power amplifier to drop and decreasing output linearity
Solution Approach 1:
The patent introduces a low-pass filter as an intermediary component between the switching regulator and the power amplifier. This filter mediates the interaction by filtering the control voltage to remove switching noise while maintaining the DC component, thus preventing noise from reaching the power amplifier input and degrading linearity, while allowing the switching regulator to continue operating efficiently at high frequency
2Power
If the switching regulator supplies large current to the Wireless LAN device, then power delivery is improved, but output voltage drops and noise is amplified by the power amplifier, decreasing output linearity
Solution Approach 1:
The patent converts the harmful switching noise generated during high-current operation into a beneficial situation by using the low-pass filter to selectively remove the noise frequency components while preserving the useful DC control voltage. The filter transforms what would be harmful noise into a clean control signal, allowing the power amplifier to operate with high linearity even when large current is supplied
3Productivity
If the power amplifier amplifies the RF signal, then data transmission rate is improved, but noise generated during transmission-reception transition is also amplified, decreasing output linearity
Solution Approach 1:
The patent applies preliminary action by filtering the control voltage before it reaches the power amplifier. The low-pass filter is positioned upstream to pre-remove switching noise from the control signal, preventing the noise from being amplified by the power amplifier along with the RF signal, thus maintaining output linearity while preserving high data transmission capability
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 solution effectively reduces signal errors caused by power noise, improving output linearity and data transmission efficiency, as evident from the reduction in error vector magnitude from -29.3 dB to -32 dB in OFDM 64-QAM constellations.
Implementation Method 1
a low-pass filter coupled between the voltage generator and the power amplifier, for low-pass-filtering the control voltage to form the bias
Data Source
AI summary
An RF transmitter for a Wireless LAN device for enhancing an output linearity of the Wireless LAN device includes an RF processing unit for generating an RF signal, a voltage generator for generating a control voltage, a power amplifier coupled to the RF processing unit and driven by a bias, for amplifying power of the RF signal, and a low-pass filter coupled between the voltage generator and the power amplifier, for low-pass-filtering the control voltage to form the bias.