Innovations in infrared scene simulator design

Richard Lane, Jeffery L. Heath, Robert Lee Murrer, Jr.
1998 Technologies for Synthetic Environments: Hardware-in-the-Loop Testing III  
The MIRAGE (Multispectral Infrared Animation Generation Equipment) Dynamic Infrared Scene Projector, is a joint project developed by Santa Barbara Infrared, Inc. and Indigo Systems Corporation. MIRAGE is a complete infrared scene projector, accepting 3-D rendered analog or digital scene data at its input, and providing all other electronics, collimated optics, calibration and thermal support subsystems needed to stimulated a unit under test with high-fidelity, dynamic infrared scenes. At the
more » ... rt of MIRAGE is a 512 x 512 emitter array, with key innovations that solve several problems of existing designs. The read-in integrated circuit (RIIC) features "snapshot" updating of the entire 512x512 resistive array, thus solving synchronization and latency problems inherent in "rolling-update" type designs, where data is always changing somewhere on the emitter array at any given time. This custom mixed-signal RIIC also accepts digital scene information at its input, and uses on-board D/A converters and individual unit-cell buffer amplifiers to create analog scene levels, eliminating the complexity, noise, and limitations of speed and dynamic range associated with external generation of analog scene levels. The proprietary process used to create the advanced technology micro-membrane emitter elements allows a wide choice of resistor and structure materials while preserving the dissipation and providing a thermal time constant of the order of 5ms. These innovations, along with a compact electronics subsystem based on a standard desktop PC, greatly reduce the complexity of the required external support electronics, resulting in a smaller, higher performance dynamic scene simulator system. 1 Emitter issues and problem areas that the MIRAGE design team identified include: 1. Difficulties of emitter signal interfaces. 2. The limited selection of array resistor material. 3. Stability of un-annealed resistors 4. Scene dependent image non-uniformity. System issues include: 1. Lack of standardized Non-Uniformity Correction. 2. Synchronization of emitter frame production and unit under test (UUT) imaging. Emitter Issues The present generation of very large array infrared scene simulators are all based on arrays of small resistors driven by a read-in integrated circuit. While the sizes of the resistors, the circuit details of the RIICs, and the manufacturing processes vary from supplier to supplier, these systems all have one thing in common. The emitter arrays must be driven with analog voltages, in fact, multiple channels of analog voltages. The analog inputs are sampled by circuits in the RIIC pixel cells at the appropriate time to update individual scene elements. Another common feature of current generation scene simulators is that they must work with digital scene input. The scenes that these devices project are quite often fabricated artificially, using specially adapted 3-D imaging technology, based on high-speed computers. Thus, the interface between the scene projector and the system that generates the images it projects is a digital interface. Since current emitter arrays are inherently analog devices, digital to analog converter (DAC) circuits must be incorporated into scene projector systems. Another fact of life for infrared scene projectors is that virtually all of today's IR simulators are installed in Hardware in the Loop (HWIL) test systems. These systems provide for movement between the unit under test (UUT) and the projected image with multi-axis full-motion simulation systems. Often test requirements dictate that that the emitter projection assembly must be mounted on one motion simulation system while the UUT is mounted on a separate motion system. The requirement for use in the HWIL laboratory is in direct conflict with the analog nature of present emitters. As with any high-resolution DAC application the DAC output and the emitter analog input are ideally placed in extremely close proximity to avoid noise pickup and grounding errors. Since mass must be limited on motion platforms, the system integrator is faced with somehow reducing the mass or number of multiple, bulky DAC circuits, or carefully cabling multiple highresolution signals from remotely-mounted DACs up to the emitter. The problem becomes more severe at higher frame rates as present generation emitter technology requires more and more analog inputs to support higher frame rates. Thus the system integrator is faced with driving up to 64 analog inputs 3 to get the maximum frame rate performance from the latest arrays. Scaling of arrays to ever-larger formats demanded by the increasing number of pixels in new infrared detectors increases the integrator's challenge exponentially. While the size and complexity issues may be the most obvious drawbacks of present projector systems there are issues with the arrays themselves that hinder high performance projection. Emitter resistor material has been a subject of considerable development and discussion. The ideal emitter resistor would operate over an extremely wide temperature range with no temperature coefficient. It would also be very durable and possess very high long-term stability, that is, its resistance value would remain constant after many temperature cycles. Current emitter fabrication schemes place formidable
doi:10.1117/12.316358 fatcat:akvxxa4x2bd6nmyqvqdlunbiuq