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Harwin Gecko EETImes Europe third page Sept 14.qx High Reliability in a compact package Harwin’s Gecko connectors provide high reliability under extreme conditions. - Pin spacing 1.25mm - 2A per contact and up to 1000 operations - Four-finger BeCu contact system (Patent Published) - Pick and Place to optimise production - Comprehensive selection of cabling options available - Locking latch with board retention features For evaluation samples, CAD models and technical specifications go to: www.harwin-gecko.com RF power amplifier evaluation…In a box By David Lester For veteran design enginers with years of experience and a rack of test equipment at their disposal, making the choices required to optimize the performance of an RF power amplifier circuit in an evaluation board is a relatively routine and frequent task. However, Fig. 1: The RF Power Tool. that’s not the case in companies such as manufacturers of RF heating systems where RF and microwave test equipment and RF design engineers are rarely present. The latter situation is increasingly encountered by Freescale’s technical staff as high-power systems transition from vacuum tube to solid-state RF power generation. To understand the challenges these companies face, it’s important to look at the optimization and validation process, the equipment needed to perform it, and a solution that potentially circumvents the problem. Like digital design at low frequencies, RF power amplifier validation and optimization requires trade-offs between various parameters. Metrics such as gain, efficiency, operating bandwidth, RF drive level, biasing, and amplifier architecture all may be affected when values of one of them is changed. However at microwave frequencies those parameters are complicated by factors that aren’t encountered at baseband / low frequencies, but nevertheless must be effectively dealt with. Watching from behind someone changing these values on multiple pieces of test equipment looks a lot like a mad scientist perfecting his or her “creation”. The analogy isn’t that far-fetched, as breathing life into a “dumb” evaluation board requires external resources from RF amplifiers to drive circuit to signal generators, wattmeters, voltmeters, ammeters, thermometers, power supplies, and interconnects. A reasonable solution to the problem of simplifying the use of RF and microwave evaluation boards, and making them more than simply “dumb” hardware has eluded vendors of RF and microwave power transistors for years. In addition to the problems this presents to designers, it puts the onus on device manufacturers to somehow solve customer problems remotely. To address the issue, Freescale recently introduced an instrument that is as close to a “bench in a box” as it could be while keeping the cost as low as possible ($5,500), combining nearly every function required to evaluate an RF power transistor in a circuit in a single enclosure. The RF Power Tool system –see figure 1, which measures 10x25x33cm and weighs 2.7kg, incorporates the following major functions: • A CW and pulse signal generator covering 1 to 2500 MHz, with 1Hz resolution, a digitally-variable step attenuator with a range of 0 to 31.5 dB in 0.5-dB steps, and adjustable RF output of +30 dBm. It has three 150 mW outputs (1 to 400 MHz, 300 to 1200 MHz, and 2.4 GHz) and an additional 2.4 GHz output that delivers the 1 W necessary for industrial heating and other applications that require more drive. • RF driver amplifier • Four wattmeters with directional couplers (1 mW to 2 kW) • Four DC bias supplies (0 to 5 VDC with resolution of 10 mV) • Voltmeters and ammeters (0 to 100 VDC and 0 to 250 A) • Thermometers • USB 2.0 port and DC and RF connections to the evaluation board • LabVIEW-based software that effectively becomes the user’s “cockpit”, allowing all capabilities of the system to be visually orchestrated, data offloaded to Excel for analysis, and many other functions. What remains to be supplied by the user is a high-power DC supply, termination (dummy load), heat sink, and A cable for connection between the amplifier and the load. Probably at least as important as the hardware, the system is designed to keep users from making mistakes that could damage the device by making it nearly David Lester is Analog Design Engineer at Freescale Semiconductor – www.freescale.com 28 Electronic Engineering Times Europe October 2014 www.electronics-eetimes.com


EETE OCT 2014
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