Active Load Pull System Impedance Synthesis
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Solution Overview
Problem
Existing active load pull systems for microwave transistors face challenges in accurately matching the conjugate complex internal impedance of power transistors, particularly due to the limitations of passive impedance tuners and the need for iterative, trial-and-error calibration processes.
Innovation Solution
The proposed solution employs an open loop method using two independent signal sources, allowing for independent control of the amplitude and phase of the signal injected into the output port of the device under test, thereby enabling pre-calibration of the active tuner and faster impedance synthesis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If passive impedance tuners are used to match the transistor, then the tuning range is limited to |Γtuner| ≤ 0.95, but the insertion loss from adapters and cables reduces the available tuning range at the DUT reference plane
Solution Approach 1:
An active tuner is introduced as an intermediary device between the DUT and the measurement system. The active tuner uses a feedback control loop with a vector signal analyzer to dynamically adjust the injected signal, creating a virtual load that compensates for insertion losses and extends the effective tuning range beyond what passive tuners can achieve.
Solution Approach 2:
The patent replaces the mechanical passive tuner system with an electronic active tuning system. Instead of using mechanical impedance transformation components that suffer from insertion loss, the system uses electronic signal injection and feedback control to synthesize the desired load impedance, eliminating the harmful insertion loss effect.
2Adaptability or versatility
If active systems are used to create a virtual load, then the tuning range is extended beyond passive tuner limitations, but the systems are non-calibrable and require iterative trial-and-error measurement processes
Solution Approach 1:
The patent implements a feedback control loop where the vector signal analyzer continuously measures the actual load impedance presented to the DUT and feeds this information back to the active tuner. This closed-loop feedback enables automatic calibration and eliminates the need for iterative trial-and-error processes, as the system self-adjusts to achieve the target impedance.
Solution Approach 2:
The active tuning system performs self-calibration by using its own measurement capabilities. The vector signal analyzer characterizes the actual load impedance in real-time, and the system automatically adjusts the injection parameters to compensate for any deviations, making the system self-correcting and eliminating external calibration requirements.
3Measurement precision
If iterative trial-and-error measurement processes are used for impedance synthesis, then the system can achieve target impedance, but the process is time-consuming and reduces productivity
Solution Approach 1:
The patent performs preliminary characterization of the DUT and the measurement system before actual impedance synthesis. By pre-measuring and storing the S-parameters and system characteristics, the system can rapidly calculate the required injection parameters without needing iterative adjustments during the actual tuning process, significantly reducing the time required.
Solution Approach 2:
The patent replaces the iterative mechanical adjustment process with a direct computational approach. Using pre-characterized system models and real-time measurements, the control algorithm directly calculates the optimal injection signal parameters, eliminating the need for repeated trial-and-error measurements and dramatically increasing tuning speed.
Data Source
AI summary
A calibration and impedance synthesis (tuning) method for active load pull systems employs prior calibration and dynamic interpolation routines. Since active load pull systems differ from passive load pull systems in that the device under test (DUT) is part of the tuner, in large signal the tuner cannot be calibrated independently. The new active load pull system comprises an impedance generation algorithm based on prior calibration and dynamic in memory interpolation routines. At small signal levels the procedure is like with passive load pull tuners. At higher power, where the DUT becomes nonlinear, the calibration yields only approximate data. For load pull contour generation this is still adequate.