Slide 1

CEA DSM Dapnia SAp Readout mode of the Photometer Koryo Okumura, Marc Sauvage, Nicolas Billot, Bertrand Morin DSM/DAPNIA/SAp Slide 2 CEA DSM Dapnia SAp November 8th 2007- Koryo Okumura - PACS Science Verification Review (Phase 3 @ MPE Garching) : Readout mode of the Photometer2 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 Slide 3 CEA DSM Dapnia SAp November 8th 2007- Koryo Okumura - PACS Science Verification Review (Phase 3 @ MPE Garching) : Readout mode of the Photometer3 Low frequency noise spectral density of the blue detector Direct modeDDCS mode Slide 4 CEA DSM Dapnia SAp November 8th 2007- Koryo Okumura - PACS Science Verification Review (Phase 3 @ MPE Garching) : Readout mode of the Photometer4 Low frequency noise spectral density of the red detector Direct modeDDCS mode Slide 5 CEA DSM Dapnia SAp November 8th 2007- Koryo Okumura - PACS Science Verification Review (Phase 3 @ MPE Garching) : Readout mode of the Photometer5 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 Slide 6 CEA DSM Dapnia SAp November 8th 2007- Koryo Okumura - PACS Science Verification Review (Phase 3 @ MPE Garching) : Readout mode of the Photometer6 Influence of the readout frequency on the noise Slide 7 CEA DSM Dapnia SAp November 8th 2007- Koryo Okumura - PACS Science Verification Review (Phase 3 @ MPE Garching) : Readout mode of the Photometer7 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 Slide 8 CEA DSM Dapnia SAp November 8th 2007- Koryo Okumura - PACS Science Verification Review (Phase 3 @ MPE Garching) : Readout mode of the Photometer8 Readout sequence VDECX CKRL DVECX ON OFF ON OFF ON OFF t Slide 9 CEA DSM Dapnia SAp November 8th 2007- Koryo Okumura - PACS Science Verification Review (Phase 3 @ MPE Garching) : Readout mode of the Photometer9 Influence of the readout frequency on the noise (2) Direct mode Slide 10 CEA DSM Dapnia SAp November 8th 2007- Koryo Okumura - PACS Science Verification Review (Phase 3 @ MPE Garching) : Readout mode of the Photometer10 Influence of the readout frequency on the noise (3) DDCS mode Slide 11 CEA DSM Dapnia SAp November 8th 2007- Koryo Okumura - PACS Science Verification Review (Phase 3 @ MPE Garching) : Readout mode of the Photometer11 Influence of the readout frequency on the noise (4) How the spectral noise changes? Slide 12 CEA DSM Dapnia SAp November 8th 2007- Koryo Okumura - PACS Science Verification Review (Phase 3 @ MPE Garching) : Readout mode of the Photometer12 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 Slide 13 CEA DSM Dapnia SAp November 8th 2007- Koryo Okumura - PACS Science Verification Review (Phase 3 @ MPE Garching) : Readout mode of the Photometer13 Changing the sequencer Slide 14 CEA DSM Dapnia SAp November 8th 2007- Koryo Okumura - PACS Science Verification Review (Phase 3 @ MPE Garching) : Readout mode of the Photometer14 Readout sequence VDECX CKRL DVECX ON OFF ON OFF ON OFF t Slide 15 CEA DSM Dapnia SAp November 8th 2007- Koryo Okumura - PACS Science Verification Review (Phase 3 @ MPE Garching) : Readout mode of the Photometer15 Noise level with the new sequencer Slide 16 CEA DSM Dapnia SAp November 8th 2007- Koryo Okumura - PACS Science Verification Review (Phase 3 @ MPE Garching) : Readout mode of the Photometer16 Response with the new sequencer Slide 17 CEA DSM Dapnia SAp November 8th 2007- Koryo Okumura - PACS Science Verification Review (Phase 3 @ MPE Garching) : Readout mode of the Photometer17 NEP with the new sequencer Slide 18 CEA DSM Dapnia SAp November 8th 2007- Koryo Okumura - PACS Science Verification Review (Phase 3 @ MPE Garching) : Readout mode of the Photometer18 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 Slide 19 CEA DSM Dapnia SAp November 8th 2007- Koryo Okumura - PACS Science Verification Review (Phase 3 @ MPE Garching) : Readout mode of the Photometer19 Influence of 2 parameters VDECX and CKRLX on the noise in DDCS mode Slide 20 CEA DSM Dapnia SAp November 8th 2007- Koryo Okumura - PACS Science Verification Review (Phase 3 @ MPE Garching) : Readout mode of the Photometer20 Readout sequence VDECX CKRL DVECX ON OFF ON OFF ON OFF t Slide 21 CEA DSM Dapnia SAp November 8th 2007- Koryo Okumura - PACS Science Verification Review (Phase 3 @ MPE Garching) : Readout mode of the Photometer21 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 Slide 22 CEA DSM Dapnia SAp November 8th 2007- Koryo Okumura - PACS Science Verification Review (Phase 3 @ MPE Garching) : Readout mode of the Photometer22 VDECX and CKRL parameters (2) What do these parameter mean and do? CKRL DVECX ON OFF ON OFF ON OFF t Slide 23 CEA DSM Dapnia SAp November 8th 2007- Koryo Okumura - PACS Science Verification Review (Phase 3 @ MPE Garching) : Readout mode of the Photometer23 VDECX and CKRL parameters (3) NEP in this 2D parameter space (Red matrix 9) Slide 24 CEA DSM Dapnia SAp November 8th 2007- Koryo Okumura - PACS Science Verification Review (Phase 3 @ MPE Garching) : Readout mode of the Photometer24 VDECX and CKRL parameters (4) NEP in this 2D parameter space (Red matrix 10) Slide 25 CEA DSM Dapnia SAp November 8th 2007- Koryo Okumura - PACS Science Verification Review (Phase 3 @ MPE Garching) : Readout mode of the Photometer25 VDECX and CKRL parameters (5) Different settings of CKRL and VDECX on the red array Slide 26 CEA DSM Dapnia SAp November 8th 2007- Koryo Okumura - PACS Science Verification Review (Phase 3 @ MPE Garching) : Readout mode of the Photometer26 VDECX and CKRL parameters (6) Noise spectral density does not vary significantly Red array Slide 27 CEA DSM Dapnia SAp November 8th 2007- Koryo Okumura - PACS Science Verification Review (Phase 3 @ MPE Garching) : Readout mode of the Photometer27 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 Slide 28 CEA DSM Dapnia SAp November 8th 2007- Koryo Okumura - PACS Science Verification Review (Phase 3 @ MPE Garching) : Readout mode of the Photometer28 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