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Overview of DDC Personality Status and Improvements in PFB Systems

This document provides an overview of the DDC (Digital Down Converter) Personality status as of October 2011, detailing various versions and their progressive improvements. It outlines specific problems identified in version 1.0, including issues with large spurious tones, insufficient filter sharpness, and limited bandwidth support. Subsequent versions (1.1 and beyond) have introduced enhanced architectures, improved filter responses, and expanded bandwidth options. Future advancements are discussed, highlighting ongoing developments for complete support and correction of existing limitations.

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Overview of DDC Personality Status and Improvements in PFB Systems

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  1. DDC Personality Status October 2011 – Matt Luce

  2. Overview • Block Diagram • Version 1.0 Problems • Version 1.1 • PFB • Weaver • Future Improvements • Version 1.2 and beyond

  3. DDC Block Diagram

  4. 1.0 Typical Spectrum

  5. 1.0 Problems w/PFB • PFB is generating large spurious tones • PFB sub-band edges are too soft • >32MHz dead-zones between sub-bands to avoid aliasing

  6. 1.0 Problems w/down-converters • Weaver IR filter is not sharp enough and is creating aliases. • Cleanup/weaver filters are creating too many ripples in the pass-band.

  7. 1.0 Problems w/Decimation • Limited BW support • 64MHz and 16MHz are the only completely functional • CIC output truncation is critical!

  8. What is version 1.1? • Architecture: 2 down-converters • Improved filter responses • Poly-phase • Weaver image reject • CIC cleanup • Improved down-converters • Supported Bandwidths: 64MHz, 32MHz, 16MHz…62.5kHz • Mark5B • Format select: 1 or 2 streams • Bug fixes!

  9. Large Spurious Signals 1.0 (append) 1.1 (sign extend)

  10. Improved Poly-phase Filter Bank 1.0 (80) 1.1 (128)

  11. Improved Weaver IR Filter Old (20) New (128)

  12. SB-SB Aliasing (1.1) 636MHz 650MHz

  13. Improved CIC Cleanup Filter 1.0 (40) 1.1 (128)

  14. DSP Slice Budget: 640 Available • Channelization (2) • 128 per IF • DC (2): • Mixers (DDS + multipliers) • 6 per DC • Image reject FIR • 68 per DC • CIC & cleanup FIR: • 34per DC • 216 total • TOTAL: 472 (~70%)

  15. Spectrum: 488 FFT Bench

  16. Spectrum: Bench 0Baseline

  17. Spectrum: VLBA Single station auto-correlationsTD023C

  18. The Future • 1.1.1 (Experimental version) • Hilbert SSB • 1.2 • Partial support for128MHz BW • 512-640MHz • 896-1024MHz • Tsys (w/ quantizer) • 1.3 • Full support for 128MHz BW • Pipeline delay correction

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