Open Loop Load Pull Measurement for Wideband Reflection Control
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Solution Overview
Problem
Existing load-pull measurement systems are limited in controlling reflection coefficients for wideband modulated signals, particularly at higher frequencies and harmonic frequencies, due to electrical delay and non-linearity issues, restricting their application range and accuracy.
Innovation Solution
An open-loop load-pull measurement approach using frequency-binned optimization of reflection coefficients, with synchronized and coherent digital-to-analog and analog-to-digital conversion, allows for independent control of reflection coefficients across a large modulation bandwidth, compensating for electrical delay and non-linearities, and enabling accurate measurement and control of reflection coefficients at baseband, fundamental, and harmonic frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If closed-loop feedback control is used to control reflection coefficients, then real-time control is achieved, but electrical delay and phase shift across bandwidth limit the maximum controllable bandwidth
Solution Approach 1:
The patent segments the frequency spectrum into multiple discrete frequency bins and processes each bin independently through parallel computation. This allows the system to handle wide bandwidth by dividing it into manageable segments that can be optimized separately, eliminating the bandwidth limitation imposed by electrical delay in continuous feedback systems.
Solution Approach 2:
The patent performs preliminary optimization computation offline to determine the optimal injection signal parameters for each frequency bin before actual measurement. This pre-computation approach eliminates the need for real-time feedback adjustment during measurement, thereby removing the constraint of electrical delay and phase shift that limits closed-loop bandwidth.
2Measurement precision
If single reference frequency is used for signal generation, then accuracy is improved, but application range to higher frequencies and broadband signals is limited
Solution Approach 1:
The patent extends the single reference frequency approach by adding a frequency multiplication dimension. Multiple signal frequencies are generated by multiplying the reference frequency by different integer factors (harmonics), allowing the system to cover a wide frequency range while maintaining the accuracy benefits of a single reference source.
Solution Approach 2:
The patent makes the measurement system universal by enabling it to handle both single-tone and wideband modulated signals through the same apparatus. The system can selectively apply appropriate reflection coefficients for different signal types and frequency ranges, making it adaptable to various application scenarios from narrowband to broadband measurements.
3Adaptability or versatility
If conventional active load pull systems are used, then broadband active loads are achieved, but non-linearity of amplifiers limits measurement accuracy
Solution Approach 1:
The patent implements an optimization loop that iteratively adjusts injection signal parameters based on measured reflection coefficients. This feedback mechanism compensates for amplifier non-linearities by continuously refining the control signals until the desired reflection coefficients are achieved, thereby maintaining measurement accuracy despite the non-linear behavior of broadband amplifiers.
Data Source
Figure 1~2b
Figure 2c~3
Figure 4
AI summary
Measurement arrangement and method for active load pull measurements of a device under test (1). A wideband analog-to-digital conversion block (3) is provided for obtaining measurement data. First and second injection signal generators (7, 8) are connected to a source side and a load side of the device under test (1). This set up allows to create predetermined reflection coefficients at reference planes of the device under test (1). Injection signal parameters as determined are converted into the injection signals at the source and load side by digital-to-analog conversion. The wideband analog-to-digital conversion block (3) is further arranged for analog-to-digital conversion of the intermediate frequency signals to obtain the actual measured reflection coefficient versus frequency functions with a first frequency resolution. The first frequency resolution applied in the analog-to-digital conversion is equal to or better than a second frequency resolution applied in the digital-to-analog conversion.