AGH University of Science and Technology is one of the leading technical universities in Poland. In the Department of Measurement and Electronics we perform research on application-specific integrated circuits (ASICs) designed in deep sub-micron CMOS process (like 40nm) and 3D CMOS, which are today’s cutting-edge technologies. In one of our research areas, X-ray detection, we want to build a novel, fast X-ray camera that can count each photon reaching the sensor. The heart of the camera is a hybrid pixel detector containing an ASIC, which is a prime object of our research interest. The ASIC is much different from conventional charge-coupled device sensors. It works in single-photon counting mode with many blocks inside each pixel, which allows for photon-by-photon amplification, shaping and counts depending on its energy. The main problems, besides the design itself, include the leading concept verification and further validation of the chip and the whole camera.
Since the ASIC design stage is time consuming and its fabrication is costly, designers like to know early if their idea will meet the final requirements of the product, or if there are some improvements that need to be taken into consideration before the design begins. Designers usually make predesign simulations of an idea using the Monte Carlo (MC) method. In the case of a pixel matrix, which should accumulate thousands of photons in each pixel, such simulations require a lot of time, even for very fast computers. Using the NI LabVIEW FPGA Module, we increased the speed of the calculations 4,000 times compared to using a standard Windows-based solution in different environments such as Mathematica and NI LabVIEW software running on an Intel i7 processor. This helped us discover the critical points of our solution before the design stage and made the solution better. We presented the achievement at IEEE conferences as well as NI Days in Warsaw, Poland.
When fabricating an IC, we must verify that it matches the design. In the beginning, we had to perform functional tests, which helped us find the optimum values of the circuit biasing. Since the ASIC is specific, we have to build the virtual device (Figure 2) that will measure the chip parameters at this stage.
First, we implement communication with the ASIC using an NI PXI-6562 digital waveform generator/analyzer. It is much easier, compared to an FPGA, to debug and correct the digital waveforms, which need to be changed often during the optimization process. Additionally, the device needs to control certain currents in the range of a few nanoamperes. We can set the analog voltage in the range of a few volts using any multifunctional DAQ device for the control, but the current measurement requires dedicated instruments.
We chose the NI PXI-4071 digital multimeter (DMM) because it best met our requirements for current range sensitivity of 1 pA. Before this, we used a traditional precise microampere meter, which was more difficult than the PXI modular instruments to integrate into the system. It is a time-consuming task and the triggering is much more difficult. The time for preparing the software is short, and the tests take us no more than two weeks or two months for the most complicated ICs. With this setup, we can quickly verify the chip and go to the second stage of tests using the automatic probing of pure ICs on the wafer placed at the probe station. Those tests include well-known biasing lines and verified communication and can be fixed in the FPGA. For those tests, the best option was the NI FlexRIO device used for the MC simulations. This time we equipped it with certain I/O modules that offer interfacing with the circuit.
Further tests of the detectors operating in a real-world environment for synchrotron radiation showed that the device needed to work in a hard environment with dedicated synchronization for different, highly specialized systems. Since the measuring time at the synchrotron facility is costly, rapid prototyping of the systems is the next crucial requirement. Generally, there is almost no time for system debugging. We used an NI PXI system for tests at different synchrotron facilities so we could do all the necessary tests in two days and implement the necessary synchronization functionality. This would not be possible using any other approach.
The tests of prototype device proved the camera was almost ready to be presented to the client. The only things missing were the device software driver and the end user software (if required). At this stage, the device software drivers could be built in any programming environment. However, since we already built all the functionality necessary for camera operation during previous stages of the project, we reused those components and easily reduced development time. The software drivers built in LabVIEW were fast and fully functional, and we could connect to the device from any environment since the interface is the Ethernet connection. The final product, called HyPix-3000, was released by Japanese Rigaku Co. in April this year as a novel, next generation two-dimensional X-Ray detector, which brings the cutting-edge technology to commercial usage. It introduce the new quality in the resolution, speed and easiness of use and is expected to be one of most popular equipment for in-house X-Ray diffraction and non-destructive test.
The whole process described above seems to be common in many companies. However, in our case, while working at the university on the designs and verification of the cutting-edge technology circuits, we teach hundreds of young engineers every year how to do what we are doing. Of course this applies for both integrated circuit design and programming of control-measuring applications. We are an NI LabVIEW Academy, which we extend for teaching programming of control-measuring applications and LabVIEW advanced programming. Not only does this help us efficiently teach practical programming, but it also get students ready to be involved in our projects. Some of our best students formed a company, which after just one year became an NI Alliance Partner, hired six certified developers, and is involved in international projects very close to our area of research.
AGH University of Science and Technology
al. Mickiewicza 30