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Readout mode of the Photometer

Readout mode of the Photometer. Koryo Okumura, Marc Sauvage, Nicolas Billot, Bertrand Morin DSM/DAPNIA/SAp. Direct and DDCS readout mode. DDCS : Double differencial correlated sampling V_out = (VH_blind – V_ref) – (V_bolo – V_ref). Direct mode : V_out = VH_blind – V_bolo.

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Readout mode of the Photometer

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  1. Readout modeof the Photometer Koryo Okumura, Marc Sauvage, Nicolas Billot, Bertrand Morin DSM/DAPNIA/SAp

  2. Direct and DDCS readout mode DDCS : Double differencial correlated sampling V_out = (VH_blind – V_ref) – (V_bolo – V_ref) Direct mode : V_out = VH_blind – V_bolo - Koryo Okumura - PACS Science Verification Review (Phase 3 @ MPE Garching) : Readout mode of the Photometer

  3. Low frequency noise spectral densityof the blue detector Direct mode DDCS mode - Koryo Okumura - PACS Science Verification Review (Phase 3 @ MPE Garching) : Readout mode of the Photometer

  4. Low frequency noise spectral densityof the red detector Direct mode DDCS mode - Koryo Okumura - PACS Science Verification Review (Phase 3 @ MPE Garching) : Readout mode of the Photometer

  5. Can we improve the performance of DDCS mode? • Some dedicated tests were carried out in order to investigate a possible improvement of DDCS mode • Check the behaviour with slower readout • Use the new sequencer • Explore CKRL and VDECX parameter space - Koryo Okumura - PACS Science Verification Review (Phase 3 @ MPE Garching) : Readout mode of the Photometer

  6. Influence of the readout frequency on the noise - Koryo Okumura - PACS Science Verification Review (Phase 3 @ MPE Garching) : Readout mode of the Photometer

  7. Influence of the readout frequency on the noise (1) • The goal is not to try to use a lower readout frequency • The goal is to check that DDCS mode has a lower noise level with a slower readout sequence, which confirms that the higher noise in DDCS is due to the stabilisation of the signal. • Usually the readout frequency is 40 Hz • 20 Hz readout was tested with navg=2 • 10 Hz readout was in the trials, but the command never passed through - Koryo Okumura - PACS Science Verification Review (Phase 3 @ MPE Garching) : Readout mode of the Photometer

  8. Readout sequence CKRL VDECX OFF OFF ON CKRL t DVECX OFF ON ON - Koryo Okumura - PACS Science Verification Review (Phase 3 @ MPE Garching) : Readout mode of the Photometer

  9. Influence of the readout frequency on the noise (2)Direct mode - Koryo Okumura - PACS Science Verification Review (Phase 3 @ MPE Garching) : Readout mode of the Photometer

  10. Influence of the readout frequency on the noise (3)DDCS mode - Koryo Okumura - PACS Science Verification Review (Phase 3 @ MPE Garching) : Readout mode of the Photometer

  11. Influence of the readout frequency on the noise (4)How the spectral noise changes? - Koryo Okumura - PACS Science Verification Review (Phase 3 @ MPE Garching) : Readout mode of the Photometer

  12. Influence of the readout frequency on the noise (5) • For low biases up to 1.8 V, the noise is lower by a factor of 2 • But, for the nominal bias of 2 V, the noise level stays unchanged • This is consistent with the hypothesis that the high noise in DDCS is at least partly due to the stabilisation of the signal in the readout sequence - Koryo Okumura - PACS Science Verification Review (Phase 3 @ MPE Garching) : Readout mode of the Photometer

  13. Changing the sequencer - Koryo Okumura - PACS Science Verification Review (Phase 3 @ MPE Garching) : Readout mode of the Photometer

  14. Readout sequence CKRL VDECX OFF OFF ON CKRL t DVECX OFF ON ON - Koryo Okumura - PACS Science Verification Review (Phase 3 @ MPE Garching) : Readout mode of the Photometer

  15. Noise level with the new sequencer - Koryo Okumura - PACS Science Verification Review (Phase 3 @ MPE Garching) : Readout mode of the Photometer

  16. Response with the new sequencer - Koryo Okumura - PACS Science Verification Review (Phase 3 @ MPE Garching) : Readout mode of the Photometer

  17. NEP with the new sequencer - Koryo Okumura - PACS Science Verification Review (Phase 3 @ MPE Garching) : Readout mode of the Photometer

  18. Results • This is a global change for all the detectors • The bias setting for a given flux level is “different” from the original sequencer setting • New calibration measurements are needed • We can achieve a NEP 20% lower than the original sequencer • This is still above the specification, but it is important to improve this mode and keep it as an alternative mode • It is then necessary to use a different bias settings for the new sequencer in DDCS mode and another bias settings for the old sequencer in direct mode - Koryo Okumura - PACS Science Verification Review (Phase 3 @ MPE Garching) : Readout mode of the Photometer

  19. Influence of 2 parameters VDECX and CKRLX on the noise in DDCS mode - Koryo Okumura - PACS Science Verification Review (Phase 3 @ MPE Garching) : Readout mode of the Photometer

  20. OFF OFF ON CKRL t DVECX OFF ON ON Readout sequence CKRL VDECX - Koryo Okumura - PACS Science Verification Review (Phase 3 @ MPE Garching) : Readout mode of the Photometer

  21. VDECX and CKRL parameters (1)Explored values of dCKRL and dVDECX • How can we improve the performance of DDCS mode? • CKRL and VDECX voltage could change something in the way the bolometer reponds • Let us try to explore them in a systematic way to measure the NEP - Koryo Okumura - PACS Science Verification Review (Phase 3 @ MPE Garching) : Readout mode of the Photometer

  22. OFF OFF ON CKRL t DVECX OFF ON ON VDECX and CKRL parameters (2)What do these parameter mean and do? - Koryo Okumura - PACS Science Verification Review (Phase 3 @ MPE Garching) : Readout mode of the Photometer

  23. VDECX and CKRL parameters (3)NEP in this 2D parameter space (Red matrix 9) - Koryo Okumura - PACS Science Verification Review (Phase 3 @ MPE Garching) : Readout mode of the Photometer

  24. VDECX and CKRL parameters (4)NEP in this 2D parameter space (Red matrix 10) - Koryo Okumura - PACS Science Verification Review (Phase 3 @ MPE Garching) : Readout mode of the Photometer

  25. VDECX and CKRL parameters (5)Different settings of CKRL and VDECX on the red array - Koryo Okumura - PACS Science Verification Review (Phase 3 @ MPE Garching) : Readout mode of the Photometer

  26. VDECX and CKRL parameters (6)Noise spectral density does not vary significantlyRed array - Koryo Okumura - PACS Science Verification Review (Phase 3 @ MPE Garching) : Readout mode of the Photometer

  27. VDECX and CKRL parameters (7)Conclusion • Promising, because… • About 30 % NEP improvement • Promising, but… • Need a bit more verification for characterisation • We covered a limited parameter space to characterize this mode • This improvement is not likely to cumulate with the improvement by the new sequencer - Koryo Okumura - PACS Science Verification Review (Phase 3 @ MPE Garching) : Readout mode of the Photometer

  28. Global conclusions • DDCS mode can be improved by about 20% by using the new sequencer • It is also improved by fine tuning 2 parameters • These 2 possibilities will certainly not be a cumulative improvements • Combination of these 2 possibilities can be the best solution, but we will need more data to conclude • Improved DDCS should be kept as an alternative of the direct mode - Koryo Okumura - PACS Science Verification Review (Phase 3 @ MPE Garching) : Readout mode of the Photometer

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