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Optimizing an RF/microwave amplifier demands a fair bit of knowledge, and can require a healthy rack of test equipment. Fortunately, Freescale Semiconductor has taken a major step toward helping engineers in need of optimizing a high-frequency amplifier with its RF Power Tool. In spite of measuring only 4 × 10 × 13 in. and weighing a mere 6 lbs., this offering is capable of making all the key amplifier measurements, including gain, efficiency, bandwidth, and bias requirements.

RF Power Tool

The RF Power Tool plugs into a Freescale evaluation board, and requires only a few external components (principally a DC power supply and dummy load), effectively forming a “bench in a box.” It allows designers to completely evaluate and optimize the performance of an amplifier circuit on a Freescale evaluation board.

Freescale’s RF Power Tool (Fig. 1) includes the instrument; a power supply (with adapters for use in the United States, Australia, Europe, and the United Kingdom); a flexible microwave cable with SMA connectors; a pair of cables that connect to the evaluation board, a Universal Serial Bus (USB) cable for connecting the instrument to a personal computer (PC); and Microsoft Windows software that runs on any version of the operating system (OS) from Windows XP forward. To work with the RF Power Tool, a user selects an evaluation board suitable for an amplifier under test, a high-power DC supply, a dummy load (termination), heat sink, and a coaxial cable to connect the amplifier to the dummy load (Fig. 2).

Evaluation boards are available for power levels from 50 W to 125 kW for various applications. The boards are equipped with the required sensors and other connectors that mate with the RF Power Tool. For users wishing to design their own test routines, the instrument supports SCPI-compliant command sets (also available from Freescale), and is compatible with LabVIEW test software from National Instruments.

RF Power Tool measurement system

The RF Power Tool includes a full range of RF and DC sources and sensors as needed for amplifier testing. The core capability is a continuous-wave (CW)/pulse signal generator with 1-Hz tuning resolution from1 MHz to 2.5 GHz and a digital step attenuator with maximum range of 0 to 31.5 dB in 0.5-dB steps to adjust RF output levels to +30 dBm. The compact test set provides three 150-mW output ports—from 1 to 400 MHz, 300 to 1200 MHz, and at 2.4 GHz—with an additional 2.4-GHz port with 1-W output level. This is needed for such applications as industrial heating, where at least 350-mW drive must be supplied.

The test instrument offer flexible pulsed signal capabilities, generating pulse widths from 0.5 μs to 5 ms in 0.1-μs steps and pulse widths from 5 ms to 1 s in 1-ms steps across a duty-cycle range of 0.1 to 99.9%. It includes internal triggering circuits and an input for external triggering. It also features four watt meters with directional couplers and the capability to measure forward and reflected power levels from 1 mW to 2 kW across its frequency range.

The RF Power Tool also includes multiple voltmeters and ammeters, as well as four bias supplies and an RF driver amplifier. The four-channel bias supply delivers voltages from 0 to 5 VDC with 10-mV resolution, and DC measurement capability ranges from 0 to 100 VDC and 0 to 250 A (see table).

Table

The RF Power Tool is by no means a replacement for a full rack of test gear, and does not offer the performance levels needed for checking low-noise amplifiers (LNAs). Nevertheless, it does provide the capabilities necessary for evaluating and optimizing a wide range of amplifiers (through 2.5 GHz). For example, appliance manufacturers that employ solid-state RF power sources; RF subsystem design companies and their suppliers; and manufacturers of systems that employ RF power for various purposes (including heating, drying, and sealing) may have limited solid-state RF power design experience and RF test equipment. They might even be making a transition from vacuum tubes to solid-state power. and might benefit from having simple measurement capabilities.

Others likely to benefit from this simplified approach include medical equipment manufacturers, distributors, universities, and even hobbyists (such as ham-radio operators). Since the entire optimization process can be accomplished using this single instrument, a PC, a DC power supply, and a dummy load, it can be performed anywhere where AC power is available.

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This file type includes high resolution graphics and schematics when applicable.