.. index:: Flatband voltage shift .. _calobs-block-pv-vis-flatbandvoltage: **CALBLOCK-PV-026:** VIS Flatband Voltage Shift ================================================= .. include:: definitions.rst Parent requirement ------------------ P-R-NI-CAL-PV-001 in |RD2a| Observation configuration file ------------------------------ | :download:`ocf_CALBLOCK-PV-026.csv ` Scheduling ---------- Once, during PV. In case of failure, repeat at next possible opportunity. Time-critical ------------- No Dependencies ------------ None Objective --------- Ionizing radiation causes charge accumulation in the oxide of the MOS capacitors, and with that an increase of effective voltage potential under that particular gate (flatband voltage shift). Any shift will change the operating point at drain-to-gate interfaces, which are the charge injection structure, the serial register dump, and the output amplifiers. Due to the thin-gate oxide process used for the CCD273 the expected flatband voltage shift is only about 0.1V for an End-of-Life (EoL) Total Ionising Dose (TID) of about 2.8 Krad(Si), e.g. about 0.04V/Krad(Si). This figure is so low that no adjustments to the voltage set points for the CCDs are foreseen, also not for the output amplifiers. Nevertheless, these are predictions and a simple monitoring procedure is required to trace possible shifts on a yearly cadence starting in PV. Observations ------------ The procedure is based on the CHINJ02 test during the VIS ground calibration campaign (VGCC): With a fixed voltage setting for IG1 and IG2, the IDL voltage is stepwise increased from the nominal setting that ensures charge injection up to and beyond the point when injection stops. The IDL voltage for this charge injection turn-on/off point increases with accumulated flatband voltage shift and is therefore a tracer for the received ionising radiation dose. After each change to the IDL voltage some lines need to be injected and the image acquired. All data is taken with the RSU closed, and therefore no dedicated pointing is needed. The VIS sequence VOGC8026 (Execute Charge Injection Sequence) is used for voltage shift monitoring. In particular, * the injection timing is as in nominal readout (e.g. it takes 72s to inject into the full CCD) * it allows injection for less than 2066 lines * it allows windowing for readout IDL voltage steps: 10.5, 10.7, ... step size 0.05 V ..., 12.2, 12.3, 12.5 Fulfilling ---------- :ref:`calobs-vis-flatbandvoltage` Targets and pointing constraints -------------------------------- :command:`Pointing`: Straylight suppression as per MOCDA-SYS-003. Instrument configuration ------------------------ Instrument: Wide survey Methodology / Uplink procedure ------------------------------ :command:`Entity`: VIS :command:`Commanding Method`: None :command:`Dither Sequence`: None Sequence and parameters for VOGC8026: * CHG_INJ_ON/_OFF: 100/1 (100 injected lines) * VSTART_INJ/VEND_INJ: 1966/2066 (Pattern stops after 100 lines) * VSTART/VEND: 1966/2086 (120 lines read) * IDL: see above * ID_WIDTH: 60 µs (Default) * TOI_CHINJ: 1000 µs * ID_DELAY: 1500 µs (VGCC CONF2 with TOI_IMAGE: 1000 µs) * IG1: 4V (VGCC default) * IG2: 6V (VGCC default) * 30µs DWELL (CHINJ_RoDly) = OFF Inter-operability constraints ----------------------------- None In-orbit duration ----------------- :command:`In-orbit Duration`: ``34*40s = 0.4 h`` The VOGC8026 sequence has the following timings: * Flushing: 4.5s * Injection into 100 lines (CR rejection, averaging, etc.): 3.5s * Window readout 120 lines (CI image + 20 postscan): 4.1s * Compression and transfer (max.): 16.6s * Total time per IDL setting: 29s (+11s buffer) (plus an additional 5s buffer for the first of the 34 sequence, to set the filename) * Total number of IDL steps: 34 Data volume ----------- ``34*46.0 MB = 1564 MB`` The VOGC8026 sequence has the following memory usage: 120 lines per quadrant, compressed by a factor 1.5, yields about 46.0 MB Processing input ---------------- :command:`Ground Processing Input Data`: :command:`Data Description`: Processing method ----------------- TBW Processing output ----------------- TBW Required accuracy, constraints ------------------------------ TBW Processing tools ---------------- TBW Validation ---------- TBW Recovery -------- TBW Quality control parameters -------------------------- DataModel: ``_ Contact person -------------- VIS instrument scientist .. raw:: latex \clearpage