RF Power Amplifier BIST Using Subharmonic Mixing for Predistortion
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Solution Overview
Problem
Current testing methods for nonlinear digitally-controlled radio frequency (RF) power amplifiers in cellular handsets are costly, power inefficient, and require external equipment, making them impractical for high production yields and low defect rates, especially for non-constant amplitude modulation schemes like 8-PSK in EDGE technology.
Innovation Solution
A built-in self-testing (BIST) mechanism using subharmonic mixing for predistortion calibration, which temporarily couples the RF power amplifier output into the frequency reference input, allowing for phase error measurement and analysis without external test equipment, thereby detecting distortions and nonlinearities within the power amplifier.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional external RF test equipment is used for power amplifier testing, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The transmitter performs self-testing by using its own receiver chain to measure power amplifier distortion. The receiver chain acts as an integrated measurement tool, eliminating the need for external test equipment. The system measures AM-AM and AM-PM distortions internally through signal processing of transmitted and received signals.
Solution Approach 2:
The receiver chain serves dual purposes: normal signal reception and power amplifier distortion measurement. By making the receiver chain multi-functional, the system eliminates dedicated test equipment while maintaining measurement capabilities using existing hardware resources.
2Measurement precision
If both transmit and receive chains are used for BIST, then measurement capability is improved, but power consumption increases
Solution Approach 1:
The system uses time-division multiplexing where the transmitter and receiver operate in alternating time slots. During measurement phases, the transmitter transmits test signals and the receiver measures distortions. This periodic operation allows both chains to be utilized for BIST while managing power consumption through controlled activation periods.
3Productivity
If simplified testing methods are used, then productivity is improved, but measurement precision deteriorates
Solution Approach 1:
The system implements feedback-based distortion measurement where the receiver chain captures the actual transmitted signal and compares it against expected characteristics. This feedback mechanism enables accurate measurement of AM-AM and AM-PM distortions using standard transceiver components, achieving both productivity and precision requirements.
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
This approach reduces test time and power consumption, eliminates the need for external hardware, and allows for internal characterization and compensation of distortions, enhancing production efficiency and reducing defective units, while maintaining compatibility with various wireless standards.
Implementation Method 1
A built-in self-testing (BIST) mechanism using subharmonic mixing for predistortion calibration
Implementation Method 2
generating a phase error signal as a function of the frequency reference input and the RF signal
Data Source
AI summary
A novel and useful apparatus for and method of predistortion calibration and built-in self testing (BIST) of a nonlinear digitally-controlled radio frequency (RF) power amplifier (DPA) using subharmonic mixing. The RF power amplifier output is temporarily coupled into the frequency reference (FREF) input and the phase error samples generated in the phase locked loop (PLL) are then observed and analyzed. The digital predistortion and BIST mechanisms process the phase error samples to calibrate and test the DPA in the transmitter of the Digital RF Processor (DRP). The invention enables the characterization of nonlinearities, the configuration of internal predistortion, as well as the testing of the transmitter's analogRF circuitry, thereby eliminating commonly employed RF performance testing using high-cost test equipment and associated extended test times.