In this blog post, I give a sneak preview of Nutaq’s upcoming MO1000 FPGA mezzanine card (FMC). This new FMC will expand on our massive MIMO offerings by adding high-density digital-analog converter (DAC) channels to our solutions. It is currently still under development as we have just finished working on the first prototypes.
The MO1000 FMC is an 8 channel phase-aligned D/A card designed around the high-performance ADI AD9148 quad-DAC from Analog Devices. It takes advantage of Nutaq’s “double-stack” FMC design, which enables it to become part of a 16 channel phase-aligned D/A card.
Here’s a high-level functional overview of the MO1000’s design. Each AD9148 handles 4 DAC channels; hence the 8 channels on a single board. All the control signals for these chips (e.g. clocks and frame synchronization signals) are carefully routed to allow for maximum synchronization between both DAC devices.
MO1000 block diagram
Not only is the routing of every signal carefully targeted to maximize synchronization between the channels of a single MO1000 FMC, the clocking scheme and board layout is also designed with the idea to maximize the synchronization of 16 channels when two MO1000 FMCs are used together in a double-stack configuration.
People familiar with the design of other Nutaq FMCs, like the Radio420, the MI125 and the LVDS-xIn-xOut, are already familiar with the double-stack concept. But for those of you who aren’t, I’ve included some diagrams showing how the signals are routed on a MO1000 system when it’s used as a double-stack FMC with 16 DAC channels as well as when it’s used as a normal single FMC with 8 DAC channels.
Channels routing in a MO1000-8 FMC
Channels routing in a MO1000-16 FMC
Here’s the setup we used to measure the performance of our first batch of units. We used different equipment arrangements to perform our measurements and validate them: one with a spectrum analyser; the other with an MI125 in a wideband configuration using the record feature of our software tools to perform data capture and post-processing.
We obtained good analog performance on the first prototypes. The following figure shows the spectrum of a 40 MHz tone generated by a MO1000-AC-SE in 4x interpolation mode (1 GHz sampling rate) and captured by a MI125. In this configuration, we measured a total harmonic distortion (THD) of -72.8 dBc and a spurious-free dynamic range (SFDR) of 64.1 dBc.
With the testing and characterization of our first prototypes near completion, we are on the verge of going forward with the next version of the MO1000 FMC. Some modifications to the design are needed to meet our design objectives and to add features for future uses of this FMC in massive MIMO systems. For example, we are adding the ability to clock a MO1000 system from a MicroTCA backplane through the FMC bidirectional clocks. I look forward to presenting the initial results of the bring-up of the new MO1000 version to you a few weeks from now.
For more information on Nutaq’s double-stack FMC, please see this presentation.