IVCAD Suite Measurement Standard

Load Pull is an essential technique for characterizing RF transistors, especially when operating in the nonlinear or large-signal region. S parameters provide valid results only in the linear region, where RF transistors are inefficient and output minimal power.

Load Pull accurately measures devices under real-world, high-power conditions, making it the preferred choice for assessing transistors in RF Power Amplifier applications. When a transistor operates with a large signal, Load Pull is the only reliable method to simulate application-like conditions and predict key RF specifications. 

By using a software-controlled Load Pull setup, engineers can quickly characterize a Device Under Test (DUT), identify the optimum operating conditions, and design power amplifiers in a fraction of the time, dramatically reducing the design cycle and ensuring maximum performance.

For RF Power Amplifier designs, Load Pull measurements can be performed under Continuous Wave (CW) or Pulsed CW conditions, depending on the DUT power and thermal dissipation. Pulsed CW measurements help mitigate thermal effects, allowing for more accurate assessments of device performance under extreme conditions.

The key to effective Load Pull measurements is selecting the right configuration, balancing frequency coverage, power handling, accuracy, and ease of operation to meet specific testing requirements.

Traditional Load Pull, or Scalar Load Pull, was the first system to measure device performances automatically under various source and load impedances. The scalar setup can use coaxial or waveguide tuners. These test benches use pre-characterized passive tuners for impedance matching and scalar power detectors for measurements. Based on the pre-characterization of the impedance tuners, the measurements rely on the set of measured or interpolated s-parameters at different impedance conditions. 

Raw measurements from scalar instruments (power meters) are de-embedded, in real-time, to the DUT reference plane using the loss calculation of tuners and other components in the setup. The accuracy of the measurements relies entirely on the calibration quality and the tuners’ mechanical repeatability. Therefore, building a mechanical tuner requires a high level of expertise.

The scalar load-pull architecture is cost-effective and can be advantageously driven using IVCAD Suite Measurement Standard (IVT).

With the advent of new Vector Network Analyzer technologies, device characterization benches shifted to Vector Receiver Load Pull (VRLP) for a much more complete characterization technique. It allows extracting parameters not possible to measure with a Scalar Setup, like AMPM curves. Therefore, most of the load pull setups built nowadays are Vector based.

The IVCAD IVT module offers a modern and efficient methodology for load-pull measurements using low-loss couplers, inserted between the tuners and DUT. The VNA allows real-time measurement of a and b-waves at the DUT reference plane, enabling vector information not normally made available with traditional setups.

This setup architecture measures the load impedance presented to the DUT without prior assumptions of tuner characterization, positioning, or losses. Extremely accurate transistor input impedance derived from the a-and b-waves results in properly defined delivered input power, power added efficiency, and power gain measurements. At fundamental and harmonics, Output powers are made available along with multi-tone carrier and intermodulation products.

Load Pull measurement data can be challenging to handle for several reasons, primarily due to the complexity of the measurements themselves and the need for precise interpretation of the results.

Load Pull testing involves sweeping various parameters (such as frequency, power, impedance, and bias conditions) and can generate large datasets. Finding the key information among this huge quantity of data that can be overwhelming. Incorrect analysis can lead to misleading conclusions about the transistor's performance.

• Interpolation: The first need is to ensure that the data can be interpolated under a wide variety of test conditions to learn how the transistors perform under conditions that were not used during the test campaign.
• In-depth Analysis: Based on the daily support provided to customers worldwide for decades by the AMCAD Engineering teams, IVCAD offers ready-to-use measurement analysis templates that will reveal the optimal performance that a transistor can deliver when correctly matched.

Analyzing the data to determine the optimal operating point for a given RF device or amplifier design requires detailed, methodical interpretation. In addition to the Whiteboard tool provided with the Front-End module (IVF), the load pull analysis templates provided with IVCAD Suite Measurement Standard (IVT) will secure and speed-up the handling of your load pull measurement data.