| Introduction
Traditionally, we have tested pacemakers by simulating the operation and observing the circuit response under some specific condi-tions, such as changes in battery status and heart behavior. With the growing complexity of these circuits, this testing approach began to require some 40 to 45 minutes, when it once took only 10 to 15 minutes for a complete test.
Automating the Tests
To remove this bottleneck in the production flow, we needed to automate testing of the circuit, despite its small size and the consequent poor availability of test points. To make automated testing possible, our first step was to insert a scan chain inside the digital controller IC of the pacemaker to add some test points on the hybrid. With these changes, we can now control and observe the whole circuit.
Our next step was to assemble the necessary test equipment. To control the scan chain structure inside the IC, we built a small microprocessor-based scan controller board, which exchanges data and commands through a 16-bit parallel port to the 8255 PIO of a National Instruments AT-MIO-16DE-10 DAQ board. With this new interface, we drastically increased the speed of the hardware and software debugging of the scan controller. By working on a single PC, we could run the C remote debugger for the scan controller software and LabVIEW for data and command exchange through the PIO port in multitasking mode.
We developed a complete LabVIEW command set for the scan controller to be used as a Plug and Play component in the final test program. We also needed to develop the test algorithms. After the implementation of the DFT structures, we partitioned the circuit into a set of well-defined, fully controllable, and observable functional blocks. We can test each one separately with a special LabVIEW program written specifically for that functional block. We can also debug and optimize each functional block program before including it in the main test program. The extensive measurement resources built into the DAQ board - 16 analog inputs, eight programmable function inputs for triggering, two analog outputs, and so on - drastically reduce the requirements for custom test interface circuitry. We needed only a set of analog buffers, logic-level shifters, and multiplexers for arbitrary signal and DC voltage generation through one of the two DACs.
We use a digital multimeter (DMM) controlled over the IEEE 488 bus by LabVIEW for parametric measurements on discrete components such as diodes, resistors, zeners, and transistors. The LabVIEW instrument driver for the DMM greatly simplifies setup of this process.
Using the DAQ board, we can do the following: - Take timing measurements - gated/ nongated frequency, period, and pulsewidth - with the DAQ-STC ASIC
- Test transient response to an arbitrary stimulus of filters and amplifiers by sampling analog signals that we have suitably triggered and/or synchronized to the inputs
- Test analog comparators for several reference voltage values - we find the 12-bit DAQ board accurate for such characterization
- Verify the frequency response and CMRR of filters and amplifiers
- Make analog time-constant estimates through analog signal sampling and postprocessing
- Measure DC voltage
The Resulting System
The figure on the front side shows a simplified block diagram of the resulting ATE. We structured the main test program to run the functional block virtual instruments (VIs) in sequence; we can separately enable or disable any of them. The figure above shows the main front panel. For each functional block VI, we can edit a set of pass or fail limits right from the main front panel. Each element of the set contains a minimum value, a maximum value, and a comment string that we typically use to describe the test and to specify the measurement unit. For each functional block, the screen displays a pass/fail indicator; we can also request more detailed results. With the functional block VI enabling or disabling capability, we can easily rerun a subset of the tests for rework or single block characterization, as necessary.
We can easily implement data management procedures, such as operator and serial number input, report printing, and data collecting for statistics, through the variety of LabVIEW library functions available.
Conclusions
Usually a new test approach requires a long development time and a high ATE cost. With National Instruments products, we quickly developed an ATE system to comprehensively perform fault detection and isolation, test time, and so on, within a very short time and at low cost. The resulting equipment maintains a high level of flexibility and expandability for both hardware and software thanks to the variety of National Instruments DAQ board resources and their ease of use with LabVIEW.
For more information, contact: Jacopo Costella MEDICO SpA, Via Pitagora 15 35030 Rubano (PD) ITALY Tel: 39 049 8976755 Fax: 39 049 8976788 E-mail: medico.red@interbusiness.it |
