Data acquisition and digital pulse processing systems require hardware that’s able to acquire data simultaneously from multiple sensors. To be able to properly interpret the data received, all the channels need to be precisely synchronized. The alignment of the signals received from the sensors is critical to obtaining good quality in the reconstructed image. With that in mind, Nutaq pushed the idea further by offering a tightly synchronized, but also very cost-efficient solution using FPGA mezzanine cards (FMCs) that allow up to 32 channels of analog data to be received and processed per FPGA device.

Obtaining Optimal Sampling Synchronization

In a multichannel data acquisition system, the synchronization of the reception channels is essential to obtaining a precise measurement of the position where an event occurred to reconstruct an image. Channels acquired on the same processing unit are more easily synchronized and calibrated than channels acquired on different processing units. Nutaq’s MI125 FMC paired with a Perseus advanced mezzanine card (AMC) allows up to 32 channels to be acquired simultaneously on a Virtex®-6 FPGA from Xilinx®. Trace length matching present on the MI125 ensures that the clock signals of each analog-to-digital converter (ADC) module on the board are in synch, resulting in optimal sampling synchronization. The MI125 FMC was designed based on LTM®9012 ADC modules from Linear Technology®. On top of its great analog specification, this ADC module discloses the length of the internal path of the analog input signals, allowing us to precisely match the length of the path taken by the data from the connector to the silicon.

Nutaq’s MI125 Is Perfectly Suited For Multichannel Applications Like Small Animal Imaging

The base MI125 FMC has sixteen 14-bit ADC channels running at a maximum sampling frequency of 125 MHz. This number of channels is enough for several multichannel applications, such as small animal imaging PET applications which require 8 to 16 channels. For applications requiring more channels, like full-body PET, radio astronomy, air cargo scanners, beam position monitoring for linear accelerators, and others, the MI125 FMC can be expanded to 32 channels without compromising accuracy or synchronisation thanks to Nutaq’s “Double-Stack” FMC implementation. Using Nutaq’s MI125-32 attached to a Perseus AMC allows the number of channels to be increased even more by placing multiple instances of this combination inside a chassis with multiple slots, making it possible to create systems with many more inputs (64, 128, 256, and so on). On top of this, our PCIe real-time communication tool enables data transfer through the fat pipes of a MicroTCA chassis, thus providing low-latency, high-bandwidth inter-board data communication.

How Nutaq’s Double-Stack FMC Works

Nutaq developed its “Double-Stack” FMC with channel density in mind. It takes advantage of the MicroTCA full-size form factor, allowing the use of two FMCs on a single AMC carrier. The trick to implementing “Double-Stack” FMC is to design a board that needs only the signals available on an LPC connector to function. Instead of using an LPC connector to connect this board to a carrier, an HPC connector is used. Signals destined to both FMCs of the stack will go through this connector to the “extender” FMC; signals for the “extender” FMC will use the LPC signals, and signals for the “top” FMC will use the extra signals available from the HPC. The extra signals from the HPC connector are then rerouted to an LPC connector installed on the “extender” FMC to be connected to the “top” board. The MI125 is an example of an FMC implementing Nutaq’s “Double-Stack” standard. The figure below shows how the signals are propagated through the stack to connect the carrier board to both MI125 boards. The “top” board is called MI125-16 and the “extender” board is called MI125-16-E.

Nutaq Double-Stack FMC MI125
For a more detailed explanation of how Nutaq’s “Double-Stack FMC” is implemented, please refer to this presentation.