Varactor-Biased Amplifier Input for 5G AM-PM Linearization
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Solution Overview
Problem
Modern 5G power amplifiers face challenges in achieving high-accuracy amplitude modulation-phase modulation (AM-PM) phase linearization due to dependencies on power amplifier temperature, supply voltage, process variations, and frequency band, necessitating complex calibration processes and large memory requirements for digital pre-distortion (DPD) coefficients.
Innovation Solution
An amplifier system with a dynamically biased varactor and push varactor bias circuitry directly integrated on the power amplifier die, adjusting input capacitance to reduce signal distortion through analog phase pre-distortion, providing accurate phase correction across varying conditions without complex alignment or calibration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If baseband digital pre-distortion (DPD) is used to correct power amplifier AM-PM distortion, then phase linearization is achieved, but large memory is required to store DPD coefficients for each operation condition
Solution Approach 1:
The patent replaces the digital DPD approach with an analog pre-distortion (APD) circuit implemented directly in the bipolar power amplifier process. This analog circuit uses a varactor diode with dynamic bias control to provide continuous phase correction, eliminating the need for large memory tables while achieving comparable or superior linearity performance.
Solution Approach 2:
The APD circuit is implemented using the same bipolar process and devices as the power amplifier itself, providing automatic tracking of process, temperature, and device variations without requiring external calibration or large lookup tables. The circuit serves its own calibration needs through direct integration.
2Measurement precision
If different DPD coefficient sets are used for all parameters impacting AM-PM distortion, then correction accuracy is improved, but memory requirements grow exponentially
Solution Approach 1:
The patent changes the approach from storing discrete coefficient sets for different parameters to using a continuous analog circuit whose behavior naturally adapts to process, temperature, and device variations. The varactor diode's capacitance continuously adjusts with bias voltage, providing real-time correction without discrete lookup tables.
Solution Approach 2:
The analog pre-distortion circuit provides universal correction across all operating conditions using a single circuit topology implemented in the bipolar process, eliminating the need for multiple coefficient sets for different frequency bands, power levels, and temperature conditions.
3Measurement precision
If analog pre-distortion is implemented in the front-end module, then accurate phase correction is achieved, but process tracking and device tracking become more difficult
Solution Approach 1:
The patent merges the analog pre-distortion circuit with the power amplifier by implementing both in the same bipolar process on the same die. This integration ensures automatic tracking of process, temperature, and device variations since both circuits experience identical environmental conditions and manufacturing variations.
4Measurement precision
If complex alignment circuits or calibration circuits are added to achieve high-accuracy phase correction, then linearity is improved, but device complexity increases
Solution Approach 1:
The integrated APD circuit provides self-calibration through its direct implementation in the bipolar process with the power amplifier. The circuit automatically tracks process and temperature variations without requiring external alignment circuits or complex calibration procedures, achieving high accuracy through inherent process matching.
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 achieves high-accuracy phase correction with strong process and temperature tracking, reducing signal distortion and improving power amplifier linearity, particularly in 5G applications, by implementing analog pre-distortion directly on the power amplifier die, enhancing phase correction accuracy and reducing memory requirements.
Implementation Method 1
a varactor with a capacitive output that is coupled to the signal input for adjusting input capacitance
Implementation Method 2
push varactor bias circuitry with a bias level output that is coupled to a tuning input, and a bias control input. The push varactor bias circuitry is configured to adjust bias voltage at the tuning input and thereby adjust the capacitance at the signal input
Data Source
AI summary
The present disclosure relates to an amplifier system having an output amplifier stage with a signal input and output, and a varactor with a capacitive output that is coupled to the signal input for adjusting input capacitance. The amplifier system also includes push varactor bias circuitry with a bias level output that is coupled to a tuning input, and a bias control input. The push varactor bias circuitry is configured to adjust bias voltage at the tuning input and thereby adjust the capacitance at the signal input by way of the varactor and reduce signal distortion at the signal output in response to a distortion compensation signal received at the bias control input.