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2005-05-25 1
HAWAII-2RG NOISE
SNAP Collaboration Meeting
M.Bonati, D.Guzman, R.Smith
Caltech
2005-05-25 2
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- / 5e- @ fowler ~16
...yes
…both
…CDS too high
2005-05-25 3
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.
2005-05-25 4
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.
2005-05-25 5
Temporal noise map shows
reference pixels are much quieter than image
• Need >400 samples to see intrinsic width of histogram
2005-05-25 6
Temporal Noise Histograms vs. T
2005-05-25 7
Fowler Noise at 140K
Excess noise goes away when reset switch is closed.
2005-05-25 8
Is it just the temperature?
2005-05-25 9
• At 77K CDS noise is still much higher than for 2.5m HgCdTe.
• True fowler limit may be due to mux glow, dark current, drift or Cosmic Rays.
2005-05-25 10
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.
2005-05-25 11
Sample Up the Ramp
• Average of all channels is quite linear but individual channels sho considerable scatter.
• ….Drifts?
• ….Cosmic ray hits?
2005-05-25 12
115K
Hot pixels frozen out
Dark images vs TM
ovie
140K
lots of hot pixels
Many diffuse cosmic ray hits
2005-05-25 13
Cosmic Rays ?
• Difference of successive 300s dark images
• 100K
• Fowler 32
Some are very diffuse
Mov
ie
2005-05-25 14
Long darks show flat field patternM
ovie
Dark Flat
2005-05-25 15
e-/ADU vs T
4% rise from 85 to140K
Inverse Gain
2005-05-25 16
Bare mux performance
….Not currently a limitation.
2005-05-25 17
Bare mux 006, ch 1, optimum biases
CDS noise (ADU)
Reset mode Image pixels spatial temporal
Reference pixels spatial temporal
Line, Pulsed 16.8 7.2
Global 10.1 11.8 6.3 8.8
Global + dummy before reset
10.2 6.8
Global + dummy after reset
9.7 6.2
Line, Continuous 5.8 6.8 5.8 6.8
gain = 1.1 to 1.4 e-/ADU
PREVIOUS RESULTS
2005-05-25 18
2005-05-25 19
To reduce bias sensitivity…
Vload
Vo
Column bus
CellDrain
Vreset
RGRow Sel
Col Sel
BiasGate
BiasPower
Ci
Rload
OutputDrain
VddABG 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 J5082.4mA, 700K,
0.05%/C
375
2005-05-25 20
Bare mux029 -- CDS noise
Configuration Spatial noise min.exp 300s
Temporal (mode)
min.exp 300s
BG = BPVddA = BP
5.2 5.7 6.0
BG = BPIndependent VddA
5.25 5.6
ANU bias boardBG=BP, VddA=BP
5.8 6.0 5.4
ANU bias boardSeparate BP, BG, VddA
6.4 7.1 5.9 6.1
Mux030,SDSU biases, BG=BP,
4.9 5.0 4.6
Noise in ADU, gain = 1.1 to 1.4 e-/ADUContinuous line reset, all pixels on ch 1, ~1 sec/read. BP=3.3V, BG=2.4V, VR=0.6,
2005-05-25 21
DRIFTS in CDS frames
Configuration Drift (ADU)RMS of means for 200 frames
Min.exp 300s
SDSU biasesBG=BP, VddA=BP
4.3 36
ANU bias boardBG=BP, VddA=BP
1.4 16
ANU bias boardSeparate BP, BG, VddA
0.9 1.6
Mux030,SDSU biases, BG=BP,
1.5 4.9
RMS variation of mean in ADU. gain = 1.1 to 1.4 e-/ADUContinuous 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?
2005-05-25 22
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.