Load pull (LOADPULL) technology is a very effective test solution for power amplifier design optimization. The active harmonic LOADPULL can evaluate and measure the harmonic characteristics of the power amplifier more efficiently and accurately, and then optimize the power efficiency of the power amplifier. This is especially important for the design of LDMOS and GaN power amplifiers.
R&S's network analyzer ZVA24/40/67, with four internal excitation sources, and FOCUS' MPT multi-harmonic TUNER, can build the industry's most advanced and compact active harmonic LOADPULL solution without the need for an additional signal source. Active load traction can be applied to the fundamental, second harmonic and third harmonics to achieve comprehensive and efficient test optimization of the power amplifier.
Introduction of load traction systemThe LOADPULL system is used to optimize the parameters of the power amplifier, which can accurately determine the optimal DC operating point, maximum output power, maximum efficiency, optimal linearity, optimal noise matching and optimal power matching point of the power amplifier. In general, the load traction system is composed of an impedance tuner (TUNER), an auxiliary device and a test instrument. For the on-chip test of the power amplifier, a probe station system is also required to be jointly constructed. From the test method, the load traction system can be divided into two types: traditional load traction and modern load traction. The traditional passive load traction is mainly composed of signal source, TUNER, power meter and spectrum analyzer. With the load traction test software, the power amplifier can be optimized. For passive test accessories and TUNER, network analyzers are also needed for calibration. In addition to the above devices, modern load traction requires a harmonic receiver, usually implemented by a network analyzer, which can further test the PAE and simplify the configuration of the system. Further, a more efficient and advanced system can be built.
The role of load traction:
Due to the small signal and large signal characteristics of the power amplifier, the small signal characteristics measured by the vector network analyzer are difficult to optimize the various indicators of the power amplifier in the case of large signals, making the entire debugging work extremely complicated. And cumbersome, it is difficult to achieve optimal performance. Through the scanning test of the load traction system, the impedance load of the input and output of the power amplifier is changed, and the optimal matching impedance under the indexes of maximum power and efficiency is found, thereby realizing the optimal design of the amplifier.
Different responses of large and small signals
Harmonic load tractionWhether it is satellite, radar, or base station, mobile phone applications, the requirements for power amplifier efficiency are very high, and it can be said that the higher the better. Therefore, improving the efficiency of the power amplifier, especially the power added efficiency, has become the top priority of power amplifier design optimization. Harmonic impedance, especially for secondary and tertiary harmonic impedance optimization, has been widely recognized by power amplifier designers, but how to optimize harmonic impedance is a problem, using harmonic impedance tuners, scanning to change impedance and Phase characteristics are a very effective solution.
Harmonic TUNER optimizes harmonic impedance and boosts power amplifier PAE
Traditional LOADPULL test system and its shortcomingsThe impedance tuner of the traditional LOADPULL system is directly connected to the input and output terminals of the power amplifier. The power that is actually excited by the signal source to the input end of the power amplifier is unknown, so the power added efficiency PAE cannot be accurately measured, and the PAE is a very important indicator of the power amplifier. Therefore, a new solution is needed.
Vector LOADPULL test system
The vector LOADPULL system utilizes a vector network analyzer, TUNER, dual directional coupler and DUT. No additional signal source is needed here, and the spectrum analyzer, signal excitation and measurement are all done by the vector network. At the same time, due to the addition of the directional coupler, the incident and reflected power that is actually excited to the input end of the power amplifier can be measured by the vector network, and the output power can also be measured by the receiver of the vector network, so that the PAE test can be accurately performed. At the same time, the test speed of the system is several times faster than the traditional LOADPULL system.
Vector load traction system
Insertion lossFor the load traction system, due to the insertion loss of the cable, connector, probe, etc. between the DUT and the TUNER, the tuning range of the impedance tuner becomes smaller, that is, the threshold value becomes smaller and cannot be tuned to The outermost periphery of the SMITH chart achieves very small impedance tuning. However, for high-power amplifiers, the optimal impedance for achieving maximum power and efficiency is usually small. If the tuning range is not large enough, the optimum performance of the amplifier cannot be tested. Therefore, the impact of insertion loss must be addressed.
Insertion loss reduces impedance tuning range
Active load traction and pre-matching technologyIn order to reduce the influence of insertion loss and increase the threshold, a method of reverse active power injection, that is, an active load pulling method, is usually employed. To get enough devaluation, a large reverse injection power is needed. Usually, the power provided by one signal source is not enough, and an extra high power amplifier is needed to amplify the power. Therefore, the whole solution requires a signal source and filtering. Devices, isolators, amplifiers, TUNER, etc., greatly increase the cost and complexity of the system. A better solution is to use a pre-matching technique, which combines mechanical TUNER and active power injection into a hybrid load pull. The mechanical TUNER provides a large initial Γ value, on which power injection is performed. With a small injection power, a very close to 1 Γ value can be achieved, eliminating the need for additional power amplifiers, reducing system complexity and cost.
Pre-matching technology reduces the required reverse injection power
Vector active harmonic load traction systemCombined with the above-mentioned load traction, vector load traction, harmonic load traction, and active load traction, we can achieve a very advanced, more powerful, more accurate, more compact, and more compact load. The traction system, the vector active harmonic load traction system, tunes the fundamental and harmonic impedance of the power amplifier over the entire range of the SMITH chart, measures the maximum power, PAE and other indicators, and optimizes the design of the power amplifier in all aspects.
Vector active harmonic load traction
R&S advanced vector active harmonic load traction technologyR&S network analyzer ZVA24/40/67, with 4 excitation sources inside, can realize the active signal generation of fundamental wave, second harmonic and third harmonic, and cooperate with FOCUS's unique MPT multi-harmonic TUNER. Active impedance tuning of the fundamental, second and third harmonics can be performed simultaneously, plus FOCUS's pre-matching technique, which greatly reduces the required reverse injection power, eliminating the need for external amplifiers and external signal generation. Reduces system complexity and improves test efficiency and accuracy. Since the built-in 4-source vector is unique to R&S, the entire solution is the industry's only simplest and most efficient system for simultaneous three-harmonic vector active load pull, enabling the most complete impedance tuning and optimization of the power amplifier.
R&S advanced vector active harmonic load traction technology
With this technology, it is very efficient to optimize the efficiency of the power amplifier, improve the performance of the entire amplifier, and save a lot of time cost, which is a very effective solution for high-performance power amplifier design.
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