The questions Is detector material limiting noise performance? Is this a property of the 1.7 m cutoff material/process, or the higher operating temperature? Is the problem with the noise floor or the starting CDS noise? Requirement / Goal = 8e- / fowler ~16...yes …both …CDS too high
Confusing effects Is detector noise floor masked by dark current, mux glow, or particle hits? Is mux degrading detector noise? Is controller degrading mux noise? …slightly. Upgradeable, but not urgent. …not now. RTS may intrude later. …particle hits in substrate are a concern.
How do we know detector material limits noise performance? Image pixel noise >> bare mux, ref pixels Dependence on T, not seen in ref pixels. Excess noise goes away when reset switch is closed.
Temporal noise map shows reference pixels are much quieter than image Need >400 samples to see intrinsic width of histogram
Temporal Noise Histograms vs. T
Fowler Noise at 140K Excess noise goes away when reset switch is closed.
Is it just the temperature?
At 77K CDS noise is still much higher than for 2.5 m HgCdTe. True fowler limit may be due to mux glow, dark current, drift or Cosmic Rays.
Dark current vs. Temperature Modal dark current is negligible. ~0.2e-/read mux glow has small effect at Fowler 64. Dewar showed no light leak previously, but this has not been tested recently.
Sample Up the Ramp Average of all channels is quite linear but individual channels sho considerable scatter. ….Drifts? ….Cosmic ray hits?
K Hot pixels frozen out Dark images vs T Movie 140K lots of hot pixels Many diffuse cosmic ray hits
Cosmic Rays ? Difference of successive 300s dark images 100K Fowler 32 Some are very diffuse Movie
Long darks show flat field pattern Movie Dark Flat
e-/ADU vs T 4% rise from 85 to140K Inverse Gain
Bare mux performance ….Not currently a limitation.
Bare mux 006, ch 1, optimum biases CDS noise (ADU) Reset modeImage pixels spatial temporal Reference pixels spatial temporal Line, Pulsed Global Global + dummy before reset Global + dummy after reset Line, Continuous gain = 1.1 to 1.4 e-/ADU PREVIOUS RESULTS
To reduce bias sensitivity… V load VoVo Column bus CellDrain V reset RG Row Sel Col Sel BiasGate BiasPower CiCi R load OutputDrain VddA BG tracks BP so bias current ~constant. [Can use 32 ch readout] VddA = BP eliminates body effect, but… …. VddA still acts like phantom gate connection here so VddA=BP increases net effect of VddA drift. Vishay J mA, 700K, 0.05%/C 375
Bare mux CDS noise ConfigurationSpatial noise min.exp 300s Temporal (mode) min.exp 300s BG = BP VddA = BP BG = BP Independent VddA ANU bias board BG= BP, VddA=BP ANU bias board Separate BP, BG, VddA Mux030, SDSU biases, BG= BP, Noise in ADU, gain = 1.1 to 1.4 e-/ADU Continuous line reset, all pixels on ch 1, ~1 sec/read. BP=3.3V, BG=2.4V, VR=0.6,
DRIFTS in CDS frames ConfigurationDrift (ADU) RMS of means for 200 frames Min.exp 300s SDSU biases BG= BP, VddA=BP ANU bias board BG= BP, VddA=BP ANU bias board Separate BP, BG, VddA Mux030, SDSU biases, BG= BP, RMS variation of mean in ADU. gain = 1.1 to 1.4 e-/ADU Continuous line reset, all pixels on ch 1, ~1 sec/read. BP=3.3V, BG=2.4V, VR=0.6 Drift reduced by shield installation? …less convection around JFET currrent source?
ANU bias loopback tests ANU drift and noise are dominated by the Leach 8 channel video board drift and noise, so they are indeed very good. We plan to improve the drift of the Leach board by a factor of two by a component change, and will then remeasure.