A new class of test instrument: The FPGA based module

Testing involves applying stimulus to a device, called the Unit Under Test (UUT), and evaluating the measured response against the expected values. Traditional systems use discrete instruments to supply the stimulus and measure the response, but most devices are part of a larger system and may be a component of a closed control loop. Many devices are designed to respond to the inputs by generating outputs that are dependent on some part of the output being fed back to the inputs through the rest of the system. To be comprehensive, a test of such a device must include stimulus and response that matches, as closely as possible, the way the device is used in the full system. This requires test equipment that can alter the stimulus in response to the UUT's outputs. For low speed systems, software can often accomplish this, which is the traditional approach, but systems that require much faster response than practically accomplished in software are simply not tested in this fashion unless custom test hardware is designed to do it. This drives up the cost of test station and test program design, development, and maintenance, making it prohibitive except where crucial. Recent advancements in Field Programmable Gate Array (FPGA) technology have made a new class of instrument available to the test market. Modules based on standard interfaces that provide a large FPGA with external memory, multiple ADC and DAC channels with the digital side interfaced to the FPGA, and a large number of digital I/O pins plus programming interfaces that are fairly easy to use are now available at low cost. These modules can replace custom electronics that were required to achieve satisfactory test results in “Hardware in the Loop” test scenarios at very low acquisition and development cost. FPGA based test instruments allow rapid development of complex control systems without custom hardware development. The future impact of such implementations will be reduced station and test program maintenance cost and problems since the “custom hardware” is contained in the test program and the hardware it runs on is a commercially available standard part number.