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TEST & MEASUREMENT Mixed-signal boundary-scan I/O: reducing cost of test JTAG boundary-scan provides such structural test method at lowest cost. What’s more, when SMD is used JTAG boundary-scan is the only way to get access to pins, specifically in Ball Grid Array (BGA) packages for example. JTAG boundaryscan requires only a minimum number of probes and enables low cost fixtures reducing the cost of test even further. Furthermore, by combining mixed-signal test capabilities with boundary-scan a structural test of boards is sufficient to detect manufacturing defects and minimize the slip-through. Far more expensive functional tests to find manufacturing defects at individual board level are now minimized or no longer needed. The JT 5705 / USB from JTAG Technologies as shown in figure 1 is a mixed-signal boundary scan I/O controller which has both analog and digital test capabilities in combination with boundary-scan. The controller has two JTAG ports to control the boundary-scan chain(s) of the Unit Under test (UUT). In addition the module contains 64 digital I/O channels that operate from 1 to 3.6 volt. Eight I/O’s can be used as analog channels that can measure and generate Fig. 1: the JT 5705 / USB mixedsignal boundary-scan I/O controller. Fig. 2: Use of the JT 5705 in a fixture at tbp electronics. analog voltages from -16 to +16 V or from 0 to +32 V. Tbp electronics, a Dutch EMS, uses the JT 5705 to minimize the percentage of slip by means of structural testing. They have mounted a JT 5705 on a special carrier board inside a fixture as shown in figure 2 to create a compact test configuration. The carrier board can hold two JT 5705 modules enabling a compact test configuration with 128 channels, 16 of which can used as analog. An extension module can be mounted on the carrier board to later add additional functionality. Via a data and power connector the three modules on the carrier board are connected to an exchangeable cassette with probes. The carrier board also contains an analog matrix. This enables the channels of the three modules to be connected to the first connector of the cassette. Via the matrix a channel can get one of seven functions: digital input or output, analog input or output, pull-up or pull-down, or oscilloscope line. These functions can be switched on the fly. Frequency measurements are also possible. The configuration with two JT 5705 modules and a cassette with probes can measure and stimulate both digital and analog circuits via the boundary-scan program. This combined method saves one test step. Thanks to the increased coverage a functional test is no longer needed in most cases. Using DfM tbp electronics increased the first pass yield for a particular board with 20% to almost 93%. Using the Mixed-Signal Boundary-Scan I/O Controller to test the boards resulted in a fault coverage of over 97% and a slip of less than 0.2%. Tools and techniques for the electrical characterization of biosensors By Jonathan Tucker The field of bioelectronics has the potential to revolutionize personal healthcare, strengthen security systems, and help safeguard the environment, as well as protect food and water supplies. Emerging semiconductor and nanoscale technologies are making advances in noninvasive physical biosensors, lab-on-a-chip tools, prosthetics/implants, and medical telematics systems possible. At their simplest, biosensors are devices used to detect an analyte, i.e., a substance or chemical constituent of interest. Essentially, they can allow for understanding bio-composition, structure, and function by converting a biological response into an electrical signal. Proper testing of the electrical portions of these sensors is essential to support their development. Biosensors are devices that do one or more of the following: detect, record, convert, process, and transmit information regarding a physiological change or process; use biological materials to monitor the presence of various chemicals in a substance (analyte); combine an electrical interface (transducer) with the biologically sensitive and selective element. More specifically, a biosensor contains a bioreceptor—a biomolecule that recognizes the target analyte. The transducer portion of the biosensor converts the recognition event into a measurable signal that correlates with the quantity or presence of the chemical or biological target of interest. Figure 1 illustrates a generalized biosensor model. Performance criteria for a biosensor system include the speed and ease of use by non-technical personnel, its selectivity to a target analyte, sensitivity and resolution, it linearity, the accuracy and repeatability, the dynamic range. High analyte concentrations should not degrade sensor usability and the biosensor should be relatively insensitive to temperature, electrical noise, physical shock or vibration to exhibit a usable lifetime. Last but not least, it should be safe to use. Jonathan Tucker is a Senior Marketing and Product Manager for Keithley Instruments, which is part of the Tektronix test and measurement portfolio - www.keithley.com 30 Electronic Engineering Times Europe April 2014 www.electronics-eetimes.com


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