Microwave Engineering Europe - October 2008 - (Page 32)

32 RF ATE Enabling the state-of-the-art in automatic test equipment By: Mark Schrepferman, Peregrine Semiconductor, www.psemi.com T he challenges facing the RF test and measurement industry are classic chicken and egg problems. In order to make more efﬁcient automatic test equipment (ATE), better RFICs are required, and, in order to make better RFICs, test equipment must be able to test the limits of the IC under development. As a result, top performing RFICs push the capabilities of the “state-of-the-art” test equipment used to develop them, in turn enabling the next generation of instrumentation that will be used to push the limits once again. This scenario invites a cooperative relationship between the top-performing IC design centers and industry-leading ATE manufacturers. One of the key building block components in any piece of high-end RF ATE solution is a single-pole, double-throw (SPDT), RF switch. These devices are used in many of the critical circuits and can have a profound impact on the overall performance of the ATE solution. Among other important functions, switches are used to construct high performance digital step attenuators (DSAs; Figure 1), ﬁlter bank switching (Figure 2), and RF signal path selection within the ATE instrumentation. The limitations of GaAs and SiGe in providing repeatable switching performance in these applications across a wide frequency range are well known. As a result, test equipment manufacturers have turned to highly-reliable CMOS semiconductor technology with expectations for higher performance. Their key expectations of silicon-based devices is that they will achieve fast settling times, superior low frequency performance, high linearity, high electrostatic discharge (ESD) performance, and consistent quality from chip to chip and lot to lot. Switching transients and fast settling time One of the most important aspects for ATE is fast settling time, because this allows the instrumentation to perform measurements faster, increasing throughput, usability and reducing manufacturing test costs. All of these improvements add up to measurable product advantages for ATE manufacturers who need to succeed in an extremely competitive environment. The well-known challenge here is that a typical GaAs-based switch demonstrates gate lag in settling time (see Figure 3), resulting in a phase and insertion loss drift. As a general rule, ATE manufacturers specify switch insertion loss to be within 0.05 dBm in 20 µs. Simply put, the faster the switch settles to within this 0.05 dBm limit, the faster the ATE can report a measurement. Figure 3 shows a typical GaAs MESFET switch with a ﬁnal settling time of 83 µs. Note also that this GaAs switch also has a ~1 dB overshoot after a switching event. This overshoot means that the transient power can be up to 26 percent higher than the ﬁnal value, and if multiple switches are used, the transient power will be even higher. ATE engineers have had to compensate for these transients in their designs for many years. In contrast, Figure 4 shows the performance of the PE42552 UltraCMOS™ switch from Peregrine Semiconductor. Note that this part settles to within 0.05 dBm insertion loss within 13 µs (faster than the ATE manufacturer speciﬁcation of 20 µs). And, it has no overshoot. In applications where switches are used to make attenuators (Figure 1) switching transient settling time delay (such as in Figure 3) can translate into errors in Figure 1: Multiple switches are required to perform digital step attenuation (DSA) within ATE. Figure 2: Switches are used in ﬁlter bank switching in ATE. Figure 3: This GaAs MESFET switch took 83 µs to achieve a 0.05 dB ﬁnal settling time, which is 63 µs longer than ATE manufacturers require. Microwave Engineering Europe ● October 2008 ● www.mwee.com 032-035_MWEE.indd 32 2/10/08 13:42:31 http://www.psemi.com http://www.mwee.com

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Microwave Engineering Europe - October 2008 Contents Comment News Cover Feature: AWR's AXIEM Software Brings 3D Planar Electromagnetic (EM) Simulation "Up Front" RFID: Augmented Reality: Beyond RFID and QR Codes for Mobile Phone Platforms Filters & Frequency Synthesis ZigBee Goes Green with Support for Smart Energy Simplify Mobile Data Applications and Services Test Enabling the State-of-the-Art in Automatic Test Equipment National Physical Laboratory Test Facility Aids Development of Next-Generation Antennas Selecting the Synthetic Test Environment for Transmit-Receive (T-R) Modules in a Phased Array Radar System Products Calendar

Microwave Engineering Europe - October 2008

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