"FPGAs -- A revolutionary technique for realizing high flexible FFT spectrometers at Bonn"
Bernd Klein;
In the last few years FGPAs (Field Programmable Gate Arrays) have become very popular for building fast and reconfigurable hardware. State of the art chips are built which consist of up to 96 dedicated 18-bit x 18-bit multipliers. These process more than 19 billion multiplications per second. This features makes it possible to implement real time FFTs with at least 1024 channels and a dynamic range of 26 bits, which ensures, that data is taken and processed continously and that the sensitivity of the spectrometer is much higher than currently used auto-correlators and AOSs.
Because an FPGA can be configured by downloading an image file to it, maintenance, even via Internet, is very easy. In addition, upgrading to multiple receiver channels is straight forward once one channel has been set up.
In combination with fast and high resolution samplers (ADCs), as well as DDCs (Digital Down Converters) and a fast PCI communication, very fast and flexible spectrometers with a high resolution in both frequency and power domain can be built. By undersampling the signal, every IF band within the response range of the ADC can sampled directly. When using the DDCs, online tunable sub-bands can be observed with much higher frequency resolution. The power spectrum generated by the FFT can be pre-integrated in the FPGA to reduce PCI communication, but also read out in short time intervals.
First measurements show very stable baselines, and stability tests give an Allan time of 300 seconds or more. Expectedly the frequency linearity is better than 0.01 percent and the power linearity is around 1%.
Our presentation will conclude with a live demonstration of a prototype of this new kind of spectrometer.