To meet the growing demands of transistor users, the power density of active devices continues to rise. Commercial wireless communications, avionics, broadcasting, industrial, and medical systems are pushing for smaller output stage devices that can deliver higher power. For Freescale Semiconductor, delivering high-performance RF and microwave transistors for these applications is not a challenge, as their products offer significant advantages in terms of features, packaging, and application engineering support.
Freescale has a strong presence in the production and sale of discrete and integrated RF semiconductor devices. The company’s seventh-generation silicon RF out-of-band diffusion metal oxide semiconductor (LDMOS) with HV7 technology delivers excellent output power and linearity for WiMAX infrastructure at 3.8 GHz. Freescale’s high-voltage HV7 process supports 48V operation for industrial, scientific, and medical (ISM) applications. Additionally, the company extends the operating frequency of its high-power GaAs PHEMT devices up to 6GHz for WiMAX amplifier applications.
Recently, Freescale announced the first two-stage radio frequency integrated circuit (RF IC) capable of delivering 100W output power. When paired with the company’s cost-effective MMG3005N general-purpose amplifier (GPA), the MWE6IC9100N and MW7IC18100N RF ICs provide a complete solution for 100W power amplifiers used in wireless base stations operating at 900 and 1,800 MHz frequencies.
While the performance of these RF power devices is impressive, putting them into the hands of customers is just the start. Every delivery is supported by Freescale’s technical team, offering assistance in testing, modeling, packaging, and application engineering throughout the product lifecycle.
RF Power CharacteristicsLoad pull measurement techniques have gained popularity in recent years, especially for characterizing RF power amplifiers under various complex load conditions. These methods are widely used to measure key parameters such as peak output power, gain, and efficiency. In addition, the use of complex modulation signals in the same environment is becoming more common. For high-power RF semiconductor manufacturers, accurately characterizing these devices remains challenging, requiring large peripheral equipment that typically operates at less than 0.5Ω impedance and has a quality factor (Q) between 8 and 10.
Freescale’s RF department has developed advanced techniques to improve measurement accuracy and automated custom solutions. The division has a high-reflection (high gamma) load-pull lab covering test frequencies from 250MHz to 8GHz and up to 100W continuous power (CW) or 500W pulse power for GaAs, GaN, and LDMOS devices. This lab supports modeling, applications, and other functional groups. Freescale has also developed specialized test equipment to optimize impedance conversion ratios, converting 50Ω system characteristic impedances into the low-impedance requirements for high-power transistor load pull measurements.
In addition to fixture-based systems, Freescale uses on-wafer load-pull systems based on commercial wafer probe test equipment, primarily for device research, development, and modeling. These systems incorporate a unique three-dimensional anti-vibration mechanism to minimize tuning vibrations and reduce damage to the probe-to-wafer contact.
Freescale’s load-pull system is highly accurate, with a maximum gamma value of 0.93 to 0.95 (Smith chart edge), sensor differential gain ΔGt less than 0.25dB, and less than 0.1dB in the measurement region. This level of precision is achieved using high-precision 7mm coaxial connectors across all measurement reference planes. These connectors have a voltage standing wave ratio (VSWR) of typically 1.008:1 at 2 GHz. Additional features include center contact impedance below 0.1mΩ, good correction characteristics, cell-to-cell impedance variation less than 0.1%, and phase transition of less than 0.21 degrees at 18GHz.
A combination of a vector network analyzer (VNA), load-pull system, and a penetration-reflection-line (TRL) correction method can achieve source matching better than 45 dB. Compared to traditional VNA correction methods like short-open-load-penetration (SOLT), TRL is less affected by parasitic components at high frequencies, making it ideal for precise measurements.
Typically, 5,000 to 6,000 impedance points are tested per tuner to ensure even distribution across the source and load impedance planes. For devices with very low termination impedance, small changes in impedance can significantly impact performance, requiring high-density test points. However, when evaluating devices with high package-matching impedance, fewer test points may be sufficient, allowing for sparse load pull testing in those cases.
A typical load pull setup is shown in Figure 2. Freescale uses its load pull systems to evaluate peak pulse compression, AM-AM and AM-PM conversion, frequency response, and input impedance of large signal devices. The system also supports composite signal measurements, including average and peak power, adjacent channel power (ACP), dual-tone and polyphonic intermodulation distortion (IMD), and EDGE signal behavior under different load conditions. CCDF analysis is another key feature, commonly used in 2G and 3G wireless measurements. The varying thermal loads generated by CW, pulse, and modulated signals require different load impedance optimizations, as shown in Figure 3.
Beyond its extensive measurement capabilities, Freescale has developed valuable data entry and post-processing tools that allow users to quickly analyze device behavior in 2D or 3D formats, providing deeper insights into device performance under various conditions.
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