There’s more to data acquisition systems than just data acquisition. In a previous post, I discussed how Nutaq’s tools can be used to acquire multiple signals, using a single FPGA to process them. Obtaining the signals from the sensors for processing is only one part of a complete data acquisition system. Another important part is the control component.
Parts Of A Data Acquisition System
Data acquisition systems always include sensors that transform a stimulus (for example, a gamma ray in a PET scanner) into an electrical signal that can then be converted by an ADC into a digital signal for processing. In addition, these systems often need a way to adjust different parameters of their sensors (gain, offset, and so on). Some systems also contain mechanical parts (motors) to control the position of sensors or reflectors. A complete data acquisition solution should be able to address this sub-system as well as the analog to digital conversion of the signals. Nutaq provides such a solution in the form of an FMC (FPGA Mezzanine Card) called the LVDS-16In-16Out.
Nutaq’s Solution for DAQ Front-End Control
The LVDS-16In-16Out (URL2) is an FMC module designed by Nutaq that interfaces 32 LVDS signal pairs from the FMC connector to the outside world through high-speed buffers. The LVDS-16In-16Out takes advantage of Nutaq’s “Double-stack” implementation to make it a LVDS-32In-32Out FMC stack. It can be used either in GPIO mode or synchronous mode. GPIO mode is a simple asynchronous interface using each LVDS signal pair as a GPI or GPO. Synchronous mode transforms each group of 16 LVDS pairs in a synchronous interface with 1 clock signal, 1 data valid signal and 14 data signals. In its current implementation, this interface works at a frequency of up to 100MHz.
Nutaq provides another solution for controlling front-ends, the Mestor interface. The Mestor, when used with its breakout box, makes 32 GPIOs available to the Nutaq AMC card, the Perseus 601X. It also adds four 250 KSPS ADCs available to monitor analog signals, such as power signals or even feedback signals for control purposes. This interface is less versatile than the LVDS FMC, but since it isn’t connected to the FMC connector of the Perseus, it can be used with an FMC on the same board. For example, you could use a MI125-32 (MI125 in “Double-stack” configuration) on a Perseus and control the enable signal of each of the 32 sensors connected to the ADC channels using the Mestor and its breakout box.
Example of an LVDS-Breakout Box System Using the Synchronous Mode
For simplicity, let’s consider a scenario where a system needs to control an analog front end by using 700 GPIOs and also has to monitor the status of 700 more. The status of all these GPIOs needs to be updated at least once every microsecond. A Perseus with an LVDS-16In-16Out FMC daughter card connected to a system-specific breakout box makes this possible.
The following diagram illustrates this system. Note that the 16 input signal pairs of the LVDS-16In-16Out FMC daughter card are assigned similarly to the 16 output signal pairs (1 clock pair, 1 frame sync pair, 14 signal pairs).
We have 14 LVDS output signal pairs available for updating 700 GPOs with this setup, which means that each signal pair needs to handle 50 multiplexed GPIO signals. To update at least every microsecond, the FPGA design needs to be clocked at 50MHz or faster. The same mathematics apply to the monitoring of the GPIs in the input direction.
On the Perseus side, a System Generator for DSP™ model using the MBDK from Nutaq makes it easy to generate the bitstream that handles the multiplexing and demultiplexing of the signals. In addition to the complete support provided for this FMC in Nutaq’s software tools, a reference design is available for the ML605 platform, which is the Virtex-6 evaluation board from Xilinx.
Nutaq in the Front End Controller
A complete data acquisition system includes more than just ADCs and a processing unit. In a lot of cases, it should also address the need for controlling a front end. Nutaq’s LVDS-16In-16Out FMC fits in beautifully in the front-end controller component of a data acquisition system. Its GPIO-based high-speed interface control can handle high throughput, and the addition of the MBDK makes it easy to design the multiplexing/demultiplexing application.