25-m Urumqi, China → 6-cm Galactic Plane Survey 12-m APEX, Chile → Continuum / Pointing

1. A new generation ofField Programmable Gate ArrayBackends for RadioastronomyBernd KleinRichard Wielebinski

2. 25-m Urumqi, China → 6-cm Galactic Plane Survey • 12-m APEX, Chile → Continuum / Pointing • 30-m Pico Veleta, Spain → Pulsar-Observation • 100-m Effelsberg → Continuum Observation

3. analog spectrometer • digital spectrometer Autocorrelator 0.5 GHz, 1024 channels AOS 0.8 GHz, 1024 channels Filter spectrometer 0.1 GHz, 8-64 channels Review:Spectrometer in Radioastronomy 2005 FFTS 1 GHz, 32768 channels Number of channels ~1965 ~1980 Monolithic bandwidth

4. The „Wiener-Khinchin-Theorem“orhow an autocorrelator works FFT spectrometers implement the direct approach, calculating the frequency spectrum in „real-time“ which is then transformed to a power spectrum. Due to the lack of processing power, autocorrelators take the indirect way. calculating the autocorrelation function (ACF) which can be summed up, followed by the computation of the FFT triggered in time intervals of seconds.

5. A D FFT Spectrometer:FPGA -- Signalprocessing Time domain Frequency domain analog digital Accumulated Power Spectrum FPGA: Field Programmable Gate Array

6. Trend in the Development of Digital Logic Field Programmable Gate Arrays • high integration rate • re-programmable • low price; mass products • defined specifications • short and low risk design cycle Makimoto Wave FFT Spectro- meter standardized semiconductors today Time [year] customer specific semiconductors Application Specific ICs • custom made microchips • expensive • designed for one specific task • high risk of errors Autocorrelator

7. General Advantages of DigitalFPGA based FFT Spectrometers small dimensions; no sensitive mechanical parts inside • use in moving and vibrating telescope insensitive to environmental variations • temperature • humidity low power consumption • less than30 Watts • easy cooling fully remote operational safe to use at high altitude sites ! more than 32000 channels sample rate 2x 1GS/s • 1GHz bandwidth modular design, simple reproducibility • almostmaintenance free • easy to replace in case of failure • upgrades through software 8 bit resolution cf. autocorrelators • higher sensitivity • higher dynamic range • no additional cal through total power measurements

8. FFTS installed at the 100-m Effelsberg telescope The broad-band FFTS installed at the Effelsberg telescope is able to cover a frequency-bandwidth of up to 2 x 500 MHz using to commercially available ADC/FPGA digitizers.

9. FFTS– Technical Details • Monolithic bandwidth: 500 MHz – 1 GHz • Frequency channels: 32768 • ADC sample rate: 2 x 1 GS/sec, 8-bit quantization • ADC Nonlinearity: ±0.8 LSB • Time base: better ±2 ppm, sampling jitter: <1 ps • Signal input (programmable): -22, -16, -10, -2, +4, +10 and +18 dBm • Power consumption: < 30 W / GHz bandwidth • Dimensions: 233mm x 160mm x 20mm • Costs: < 20.000 € / GHz bandwidth

10. NGC 253 CO(7-6) IRC+10216 CO( 7-6) FFTS at the APEX telescope:First Results and Stability Allan Plot Measured Allan Variance of the FFTS, showing high stability resulting in possible integration times of up to 1000 seconds. Almost twice the time of good autocorrelators.

11. Advantages of digital FPGA based FFTSpectrometer • High monolithic bandwidth (currently, up to 1 GHz) • Full signal sampling due to 8-/10-bit ADCs • FFT with up to 32768 frequency channels with current FPGA chips • No additional spectra calibration through implicit power measurements • Higher sensitivity and stability in comparison to traditional spectrometers • Modular design and simple reproducibility • Low space and low power requirements  thus safe to use athigh altitudes (e.g. APEX, ~5100 m) • Decreasing costs per GHz bandwidth due to commercial digital design  Future perspective:Increasing bandwidth with decreasing costs

12. Thank you!!! • Is this not great? • A&A436,391(2005)