Configuration of all the different elements is performed via a simple SPI interface into the control logic. Each element is programmed by loading a 16-bit word that can be static or -- for more sophisticated applications -- the parameters can be changed on the fly (more on this later).
The configuration is set up using a simple GUI (graphical user interface) that allows control of the features described above, as well as test and loopback modes. This GUI is illustrated below:
GUI for controlling the FPRF device.
here to see a larger image.)
Thus far we've considered a simplified description of the mechanics of the device -- but what can you use it for? Well, the chip was designed to be highly flexible, because one of the key applications is for cellular femto and pico cells, as I'll explain. These boxes act as local base stations for cell phones, and link into the internet to provide fast connectivity inside the home or small office. For example, the nearest tower to where I live is on the other side of a hill, so my reception is patchy at best. A femto cell would free me from reliance on signals from the tower.
The challenge in designing an RF chip for these applications is that cellular systems are different around the world -- with potentially over 40 different combinations needed on 4G or LTE phones to produce a truly global coverage. So the designers of the FPRF had to make it programmable so it wasn't restricted to a single market.
As soon as you have a chip that encompasses all the cellular frequencies, you also cover many other applications. For example, changing TV transmissions from analog to digital has freed up a bunch of spectrum for new wireless services. This is called "white space" and companies are working on a huge range of products as diverse as domestic appliances, smart metering, machine-to-machine (M2M) and rural broadband.
One application that Lime uses as a demonstration is a spectrum analyzer. The receiver in the chip is swept across the band to listen to all frequencies and the instantaneous output is displayed as the spectral plot. This demonstrates the ability of the FPRF chip to rapidly and dynamically change. Manufacturers of military systems were quick to grasp this, and are busily designing software defined radio (SDR) systems.
The spectrum analyzer uses a low-cost Myriad-RF evaluation board that is available to buy on an open-source website (sponsored by the company). Click here to find details of the board, data sheets, a user forum, downloads that include the FPRF configuration software, and a growing number of project ideas which will be added to the site over the coming months.
But the fun really begins when you combine an FPGA and an FPRF. All modern wireless systems owe a massive debt to digital processing to condition the signals and recover the data from amongst the noise. The Myriad-RF board can be connected to an Altera DE0-Nano board from TerAsic and to FPGA Mezzanine Card (FMC) Xilinx boards, including the whole Series-7 product range of Artix, Kintex, and Virtex All Programmable FPGAs and Zynq All Programmable SoCs. Appropriate Myriad-RF interface boards for the above can be ordered through Azio.
Combining FPGA and FPRF boards
here to see a larger image.)
Access to both programmable RF and programmable logic opens up a world of new opportunities. For example, I've been looking into the possibilities for using FPRF devices in university teaching and research, which has uncovered a bewildering range of applications. Researchers are thinking about using the device for cellular applications where they can implement a particular algorithm in the logic domain and see the results in the RF output. Alternatively, the FPRF can receive weak signals, and researchers can try out different error correction schemes in the FPGA. Other possibilities involve using the chip for evaluating resource management algorithms for self-organizing networks, ground penetrating radar, or car-to-car communications.
The FPRF allows both professionals and hobbyists access to a flexible wireless transceiver, that will find its way into many new products over the coming years. Of course, it goes without saying that If you are planning to transmit wireless signals, don't forget to check your local regulations on permitted power levels and frequencies.
This article first appeared on All Programmable Planet, which was devoted to all things programmable.