Microwave Engineering Europe - October 2008 - (Page 34)

34 RF ATE limit the circuit performance (power and dynamic range) and degrade the instrument’s overall performance. The integration advantages of silicon make it possible to include ESD protection devices within the silicon switch. UltraCMOS switches, for instance, provide class 1C performance on the RF pins (1000 V to 2000 V) HBM. Consistent performance Precision is a key metric in ATE design. To achieve the required performance levels, ATE manufacturers need to minimize the variation in the performance of the switches they use. One inefﬁcient way to do this is to screen each lot of switches, discarding the ones that are out of spec. Alternatively, MEMS switches can be used, but that technology is still challenged by reliability and repeatability issues as well. Readily available CMOS switches offer repeatable performance from lot to lot, due to the very nature of silicon processing. When they are conﬁdent in the consistency of switch performance, ATE manufacturers can eliminate the prescreening step and speed up production and delivery. Besides the consistent broadband performance and linearity mentioned above, Figure 5: A view of the linearity performance of an UltraCMOS switch as compared to that of a typical GaAs MESFET switch across the 10 kHz to 10 MHz low frequency range of interest. another important RF parameter for switches used in state-of-the art test equipment is consistent insertion loss performance. Insertion loss is important because, when there are many switches in the signal path, the loss of each switch becomes multiplied. The total loss, especially in higher power paths, results in higher power consumption. The insertion loss (and, therefore, noise ﬁgure) of switches can also limit the dynamic range in a receive path. Figure 6 shows that the typical insertion loss for an UltraCMOS broadband switch is <1 dB at 7.5 GHz, which is nearly 50 percent lower than comparable GaAs switches. Insertion loss performance can be closely tied to linearity. For instance, GaAsbased RF switches tend to demonstrate increased insertion loss and die size with linearity improvements. This is because the conventional circuits need multi-stacked FETs or multi-gate FETs and large gate width to achieve low distortion, which results in large parasitic off-capacitances Microwave Engineering Europe ● October 2008 ● www.mwee.com 032-035_MWEE.indd 34 2/10/08 13:44:37 http://www.lpkf.com http://www.lpkf.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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