Analog RF Pre-Distortion Bias Circuit for WLAN Linearity
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Solution Overview
Problem
In WLAN Front-End Module products, achieving linearity with error-vector-magnitude (EVM) levels below -47dB is challenging due to gain expansion and gain compression issues in RF amplification, which are not adequately addressed by existing technologies.
Innovation Solution
An analog amplitude pre-distortion circuit with a bias circuit that detects RF signal amplitudes and applies bias voltages at specific frequency ranges and impedances to the amplifier stage, using a detector stage and a bias application stage with variable reactance components to control gain expansion and compression.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional RF amplification is used, then amplification gain is achieved, but gain expansion and compression occur causing poor linearity and high EVM levels
Solution Approach 1:
The bias circuit applies amplitude-dependent bias voltages to the amplifier stage input before the RF signal is amplified, pre-compensating for the nonlinear gain characteristics. The detector stage monitors the RF signal amplitude and the bias application stage adjusts the bias voltage accordingly, preventing gain expansion and compression before they occur during amplification.
Solution Approach 2:
The invention dynamically changes the bias voltage parameter applied to the amplifier stage input based on the detected RF signal amplitude. By varying the bias voltage in response to amplitude changes, the circuit compensates for gain nonlinearities and improves linearity, achieving EVM levels below -47dB as required by WiFi-6 and WiFi-7 standards.
2Manufacturing precision
If bias voltage is applied across all frequency ranges, then linearity improves, but impedance mismatch occurs at different frequency ranges
Solution Approach 1:
The bias application stage applies different impedances to different frequency ranges: lower impedances at lower frequencies (first range) and higher impedances at higher frequencies (second range). This frequency-dependent impedance adaptation allows the circuit to maintain both linearity improvement through biasing and proper impedance matching across the operating bandwidth, preventing signal reflection and distortion.
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 significantly improves the linearity of RF amplification by reducing gain expansion and compression, achieving lower EVM levels and enhancing the performance of WLAN Front-End Module products.
Implementation Method 1
a detector stage for detecting an amplitude of the RF signal, and for producing a correction signal based on the amplitude of the RF signal
Implementation Method 2
a bias application stage coupled to the amplifier stage input, wherein the bias application stage is operable to: apply, according to the correction signal, a bias voltage at a first range of frequencies at first impedances to the amplifier stage input
Implementation Method 3
an amplifier stage comprising an amplifier stage input for receiving the RF signal from the RF input, wherein the amplifier stage is operable to amplify the RF signal to produce an amplified RF signal
Data Source
Figure 1
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AI summary
An analog amplitude pre-distortion circuit and method. The circuit includes a Radio Frequency, RF, input for receiving an RF signal. The circuit also includes an amplifier stage comprising an amplifier stage input for receiving the RF signal from the RF input, wherein the amplifier stage is operable to amplify the RF signal to produce an amplified RF signal. The circuit further includes a bias circuit. The bias circuit includes a detector stage for detecting an amplitude of the RF signal, and for producing a correction signal based on the amplitude of the RF signal. The bias circuit also includes a bias application stage coupled to the amplifier stage input.