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READ 1 to 1000 Hz for a 2.5µm cutoff Teledyne H2RG Roger Smith Caltech 2012-07-03, Tue 10:50am SPIE 8453-35 H2RG noise to 1kHz2012-07-03 1 Slides.

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Presentation on theme: "READ 1 to 1000 Hz for a 2.5µm cutoff Teledyne H2RG Roger Smith Caltech 2012-07-03, Tue 10:50am SPIE 8453-35 H2RG noise to 1kHz2012-07-03 1 Slides."— Presentation transcript:

1 READ 1 to 1000 Hz for a 2.5µm cutoff Teledyne H2RG Roger Smith Caltech , Tue 10:50am SPIE H2RG noise to 1kHz Slides containing shading such as this box (marked as “Redacted”) contain information concealed by the shading which **may** be ITAR sensitive and if determined as such could incur severe penalties if distributed to non US persons (citizens or Legal Permananent Residents). Therefore it is recommended that this presentation only be distributed to non “US Persons” in PDF format so that the redactions remain in place. Note that the responsibility lies with the person passing the data onwards, not the creator of the information.

2 Abstract (for reference only) A camera operating a Teledyne H2RG in H and Ks bands is under construction to serve as a near- infrared tip-tilt sensor for the Keck-1 Laser Guide Star Adaptive Optics system. After imaging the full field for acquisition, small readout windows are placed around one or more natural guide stars anywhere in the AO corrected field of view. Windowed data may be streamed to RAM in the host for a limited time then written to disk as a single file, analogous to a “film strip”, or be transmitted continuously via a second fiber optic output to a dedicated computer providing real time control of the AO system. The various windows are visited at differing cadences, depending on signal levels. We describe a readout algorithm, which maximizes exposure duty cycle, minimizes latency, and achieves very low noise by resetting infrequently then synthesizing exposures from Sample up the Ramp data. To illustrate which noise sources dominate under various conditions, noise measurements are presented as a function of synthesized frame rate and window sizes for a range of detector temperatures. The consequences of spatial variation in noise properties, and dependence on frame rate and temperature are discussed, together with probable causes of statistical outliers. SPIE H2RG noise to 1kHz

3 H2RG The application Tip tilt sensing for LGS AO on Keck 1, with OSIRIS integral field spectrograph, Reimage 120 arcsec diameter AO corrected 50 milliarcsec/pixel. H or K bands; dichroic or annular mirror pickoff. Multiple guide stars, No moving probes. SPIE H2RG noise to 1kHz arcsec For calibrations and acquisition 4ch readout of Band of Interest 105 arcsec For fast tip-tilt correction multiple windows, typically 4x4, read sequentially through 1 ch. Black pixels have low QE

4 The Camera SPIE H2RG noise to 1kHz 4 Lens barrel, removable through rear hatch Light tight detector housing, removable through rear hatch Wheel carries pupil stops + filters, and diagnostic apertures 0.5mm thick fiberglass cylinders cold bench with intermediate stage for floating shields Window is tilted to compensate for astigmatism due to dichroic pick off. Articulated fold mirror, manual at present, motorize later.

5 Tip Tilt Sensor for Keck-1 AO Laser guide star is insensitive to wavefront tilt. –Laser light follows same paths upwards as upon return. –So need natural guide star. Better to sense in in NIR than present optical camera (STRAP): –Higher strehl in K band = better sensitivity = more guide stars. –Higher strehl = better centroiding accuracy for given S/N. –Access to regions obscured by dust. –Frame rate is fast enough that thermal background does not overwhelm above benefits Keck AO NIR Tip-Tilt Sensor 5

6 Modeling says K band is best if < 30arcsec off axis. Strehl vs separation of science target and guide star… Keck AO NIR Tip-Tilt Sensor 6

7 When off axis, multiple stars help Keck AO NIR Tip-Tilt Sensor 7

8 Sky fraction improvement Keck AO NIR Tip-Tilt Sensor 8

9 Zenith angle improvement Keck AO NIR Tip-Tilt Sensor 9

10 NIR Tip Tilt Concept Pick off mechanism selects dichroic or annular mirror to pass K (or H) band to TRICK. Re-image full AO FoV onto 2K*2K 2.5µm cutoff H2RG sensor Multiple guide stars possible. No mechanisms: –fast capture, and –offsets are precise. Nyquist sampling in Ks band Keck AO NIR Tip-Tilt Sensor 10

11 TRICK location on AO bench Keck AO NIR Tip-Tilt Sensor 11 TRICK dewar Pick off goes here

12 TRICK location - detail Keck AO NIR Tip-Tilt Sensor 12 TRICK OSIRIS PICK OFF MECHANISM

13 Mechanical Keck AO NIR Tip-Tilt Sensor 13

14 Simplified block diagram For field acquisition & calibration: Full frame or band of interest readout, only to host. For guiding: Multiple ROIs, typically 4x4 pixels. Different visitation rates for each. Raw data streamed to –2 nd fiber link indefinitely, or –Buffered in host RAM then written as single FITS file = “film strip”. 2 nd data link is unidirectional (no handshaking) since timing is slaved to readout. Configuration descriptor packet is sent on video link (2 nd fiber) at every reset. Readout configuration commands accepted in real time, but take effect at next reset. SPIE H2RG noise to 1kHz Camera System

15 READOUT MODES Optimize for high exposure duty cycle, thus best SNR SPIE H2RG noise to 1kHz 15

16 Correlated Double Sampling Exposure delay = p dummy reads for constant self heating Subtract first frame from last frame Equivalent to Fowler sampling with m = SPIE H2RG noise to 1kHz 16 Ignore p scans e = 1 = number of exposures to do …. not shown here r = number of reset scans between exposures m = 1 = number of scans to coadd then store. p = 10 = number of dummy scans between coadded groups k = 2 = number of store cycles per exposure At least one reset between frames Reset while idling Initial scan Final scan Exposure time Frame time Let’s review common readout timing options…. Duty cycle = Exposure time Frame time

17 Fowler “m” Exposure delay is multiple of dummy read time but need not be multiple of m SPIE H2RG noise to 1kHz 17 Coadd m Ignore p scansCoadd m e = 1 = number of exposures to do …. not shown here r = number of reset scans between exposures m = 3 = number of scans to coadd then store. p = 6 = number of dummy scans between coadded groups k = 2 = number of store cycles per exposure Exposure time Frame time Duty cycle < 1 Subtract means

18 Sample Up the Ramp (SUR) Store every scan (no real time coadd) Use post facto least squares fit to measure slope with best S/N Effective exposure duty cycle due to weighting of shot noise by least squares ~ 90%; reduce this to include effect of the reset overhead. Equivalent MultiAccumulate with m= SPIE H2RG noise to 1kHz 18 e = 1 = number of exposures to do …. not shown here r = number of reset scans between exposures m = 1 = number of scans to coadd then store. p = 0 = number of dummy scans between coadded groups k = 12 = number of stores per exposure

19 Multi-Accumulate (JWST terminology, variant of SUR) Coadd in real time, store every m scans, total exposure duration is multiple of m scan times. Least squares fit of stored (coadded) scans is used to estimate noise. Advantage of coadd over single samples with gaps is lower noise and better cosmic ray detection ( which appears as jump in ramp). One or more reset scans between exposures SPIE H2RG noise to 1kHz 19 Coadd m Reset r scans e = number of exposures to do …. not shown here r = 2 = number of reset scans between exposures m = 3 = number of scans to coadd then store. p = 0 = number of dummy scans between coadded groups k = 4 = number of stores per exposure Coadd m

20 Readout mode used in the noise tests presented hereafter Differential Multi-Accumulate Sparse reset allows us to use end of previous frame as baseline for next so duty cycle ~100%, except for a gap when reset occurs. For tip-tilt control interpolating over this data gap is ok since sample rate is typically ten times servo’s closed loop bandwidth. Can use global reset (least overhead) or line by line (least thermal transient) SPIE H2RG noise to 1kHz 20 Coadd m Reset Coadd m Difference = frame 1 Difference = frame 2 Difference = frame 3 Difference = frame 4 Occasional gap ! Exposure time

21 SPIE H2RG noise to 1kHz 21 Pixel timing optimization for ARC Inc. 8ch IR video card 10 µs/pixel is standard but can go faster with no penalty. …by reducing overheads to 2.16µs, and overlapped this with signal settling. For 3µs dwell, pixel time is halved sample twice as often with same noise BW

22 SPIE H2RG noise to 1kHz 22 Pixel Time Optimization 22 Is SNR improved more by: – increasing settling time above 2µs, or – adding more dwell time (noise BW limiting), or – coadding more frames ? At low frequency, more coadds are better than more dwell time. More dwell time is better at high frequency, with most gain by 4us Moderately small window for fast readout RMS noise (temporal per pixel) mean in 16x16 window(e-) Choose 2µs settle + 4µs dwell = 6µs/pixel Conventional 10µs pixel

23 SPEED-NOISE CURVES MEAN NOISE AT DIFFERENT TEMPERATURES Skip through slides to animate. SPIE H2RG noise to 1kHz

24 T=80K Mean in window for per pixel RMS (temporal) noise (e-) SPIE H2RG noise to 1kHz ,000 Synthesized frame rate (Hz)

25 T=90K Mean in window for per pixel RMS (temporal) noise (e-) SPIE H2RG noise to 1kHz ,000 Synthesized frame rate (Hz)

26 T=100K Mean in window for per pixel RMS (temporal) noise (e-) SPIE H2RG noise to 1kHz ,000 Synthesized frame rate (Hz)

27 T=110K Mean in window for per pixel RMS (temporal) noise (e-) SPIE H2RG noise to 1kHz ,000 Synthesized frame rate (Hz)

28 T=120K Mean in window for per pixel RMS (temporal) noise (e-) SPIE H2RG noise to 1kHz ,000 Synthesized frame rate (Hz)

29 T=130K Mean in window for per pixel RMS (temporal) noise (e-) SPIE H2RG noise to 1kHz ,000 Synthesized frame rate (Hz)

30 T=140K Mean in window for per pixel RMS (temporal) noise (e-) SPIE H2RG noise to 1kHz ,000 Synthesized frame rate (Hz)

31 SPIE H2RG noise to 1kHz Deliberately left blank.

32 NOISE MECHANISMS Same plots again but now identify effects of dark current, RTS, 1/f, white SPIE H2RG noise to 1kHz 32

33 T=80K Mean in window for per pixel RMS (temporal) noise (e-) ,000 Synthesized frame rate (Hz) Mux glow, not dark current since depends on # reads not frame rate Smaller ROI = more coadd at given frame rate CDS noise, i.e. no coadds SPIE H2RG noise to 1kHz 33

34 T=90K Mean in window for per pixel RMS (temporal) noise (e-) Hot pixels included Mux glow dominates when hot pixels excluded SPIE H2RG noise to 1kHz ,000 Synthesized frame rate (Hz)

35 T=100K Mean in window for per pixel RMS (temporal) noise (e-) Hot pixels? climbing as T increases Mux glow not increasing with T SPIE H2RG noise to 1kHz ,000 Synthesized frame rate (Hz)

36 T=110K Mean in window for per pixel RMS (temporal) noise (e-) Must be RTS noise Since rises and falls again with T as characteristic frequency changes. At high frequency noise is white, so scales as ~1/√(coadds) SPIE H2RG noise to 1kHz ,000 Synthesized frame rate (Hz) Prevent this turn up at low frame rates by putting time delay between samples instead of reading more often

37 T=120K Mean in window for per pixel RMS (temporal) noise (e-) RTS noise kink SPIE H2RG noise to 1kHz ,000 Synthesized frame rate (Hz)

38 T=130K Mean in window for per pixel RMS (temporal) noise (e-) White noise drops very slightly at higher temperature Dark current starts to manifest itself at longer exposure times SPIE H2RG noise to 1kHz ,000 Synthesized frame rate (Hz)

39 T=140K Mean in window for per pixel RMS (temporal) noise (e-) Dark current dominates: Depends mostly on frame rate not # reads Scales faster than 1/√(frame_time) …why? SPIE H2RG noise to 1kHz ,000 Synthesized frame rate (Hz)

40 SPIE H2RG noise to 1kHz 40 Mux glow 2.5µm 80K 40 I dark = e-/s (SUR at 2s/sample) Greater for fast read of small windows due to self heating … see next slide. Frame number Time (s) Mux glow= e-/read at 6µs/pixel. Change x axis 4x4 32x32 8x8 16x16

41 SPIE H2RG noise to 1kHz 41 Self-heating can masquerade as mux glow As window size is reduced same power is concentrated in smaller area so temperature rises: dark current increases with number of reads rather like mux glow, but more steeply than mux glow. 8x8 window After160,000 frame SUR in 75s 8x8 Hot spot in next readout 5e-/s or e-/read 32x32 window After 10,000 frame SUR in 75s …weaker since thermal footprint of previous 8x8 window is decaying. Glow ~0.0035e-/read

42 Noise model SPIE H2RG noise to 1kHz *(coadds) Model parameters 1/f floor=2.4e e-/read Low noise ground based astronomy recipe At 80K, for pixels with negligible RTS XX*

43 Noise model – 1/f suppressed SPIE H2RG noise to 1kHz *(coadds) Model parameters 1/f suppressed e-/read Low noise ground based astronomy recipe XX*

44 NOISE MAPS AT DIFFERENT TEMPERATURES SPIE H2RG noise to 1kHz

45 Noise Maps, sparsely sampled 4x4 windows evenly spaced across detector –128 pixels in from edge –256 pixel inter-ROI separation. Packed into 32x32 pixel array

46 Noise maps vs. Frame rate and Temperature SPIE H2RG noise to 1kHz Hz 10Hz 1kHz 80K 110K 130K 140K Redacted

47 Histograms vs. Frame rate and Temperature SPIE H2RG noise to 1kHz 47 80K 110K 130K 140K 100Hz 10Hz 1kHz

48 Using data from noise maps on previous slide: Noise Histograms vs. Frame rate and Temperature SPIE H2RG noise to 1kHz Hz10Hz1kHz 80K Redacted

49 Using data from noise maps on previous slide: Noise Histograms vs. Frame rate and Temperature SPIE H2RG noise to 1kHz Hz10Hz1kHz 110K Redacted

50 Using data from noise maps on previous slide: Noise Histograms vs. Frame rate and Temperature SPIE H2RG noise to 1kHz Hz10Hz1kHz 130K Redacted

51 Using data from noise maps on previous slide: Noise Histograms vs. Frame rate and Temperature SPIE H2RG noise to 1kHz Hz10Hz1kHz 140K Redacted

52 SPEED-NOISE CURVES FOR SELECTED PIXELS AT DIFFERENT TEMPERATURES Differentiate RTS and hot pixels. SPIE H2RG noise to 1kHz

53 16x16 ROI, single pixel speed-noise curves SPIE H2RG noise to 1kHz K 120K Speed-noise curve Column 1 pixels 1e- 10e- 100e- 1000e- 1e- 10e- 100e- 1000e- Redacted

54 Random Telegraph Signal Gain of the pixel buffer MOSFET is bistable when there is a single electron trap located in or near the channel SPIE H2RG noise to 1kHz 54

55 RTS frequency vs. T SPIE H2RG noise to 1kHz K 110 K Same pixels Normal RTS

56 Fixed patterns –Dominated by self heating –Power dissipation (only) when pixel addressed. –Addressing one pixel continuously when idle creates hot spot. –Starting up at a new window location, setup overheads exceed thermal settling time. Settling is benign provided that you idle the way you read! –Effect of moving window Must move window –to compensate for atmospheric dispersion differential w.r.t. science target, –or for non-sidereal science target. Self heating profile across window changes…. SPIE H2RG noise to 1kHz

57 Jog 4x4 window 2 pixels to left 100Hz synth frame last frame before move Time Repeat s First frame after move

58 Jog 4x4 window 2 pixels to left 1kHz synthesized frame rate last frame before move exponential decay Time Repeat s First frame after move

59 Transients settle in 6 milliseconds 6 ms 1kHz synthesized frame rate Column 2 Column 1 Columns 3 and 4

60 ANOMALIES These may be skipped due to lack of time. SPIE H2RG noise to 1kHz

61 Column offset where window addressed Entire column is offset while ROI is addressed during full frame readout Full frame CDS image of field of spots after global reset of single 64×64 window. Before the “fix” SPIE H2RG noise to 1kHz 61

62 Fixed by changing window address Offset goes away when ROI pointers are moved to lower left corner. Full frame CDS image of field of spots after global reset of single 64×64 window. After the “fix” SPIE H2RG noise to 1kHz 62

63 Race condition for window reset. Spurious resets due to race condition in mux column select logic for window reset. To illustrate the effect 3 windows on diagonal are reset sequentially in the sequence {1,2,1,3,1}, then full frame is read out SPIE H2RG noise to 1kHz 63

64 Reset “ghosts” fixed SPIE H2RG noise to 1kHz 64 Window ghosts are moved to line 1 after each target window is reset, by resetting a second time with window start and end at (1,1) The ghost still occurs but in line one, where it can be ignored.

65 Line skip fault in engineering grade mux Scan bottom to top, H2RG-222 Scan top to bottom, H2RG-222 Pinhole grid imaged onto detector with pixel pitch in X and Y No change when clocking direction is reversed Vertical skips occur when addressing these lines Line advances two or more lines per vertical clock pulse when a particular range of lines is addressed. Which lines are affected depends on temperature, supply voltages and number of channels being read out. Pixels in windows not overlapping with affected bands are addressed correctly so the band of ~100 lines can be treated as bad pixels for window mode but in full frame all trailing lines are effectively lost SPIE H2RG noise to 1kHz 65

66 ADDITONAL SLIDES SPIE H2RG noise to 1kHz 66

67 SPIE H2RG noise to 1kHz 67 Raw pixel values vs Time (no coadding) Noisiest pixels exhibit “Random Telegraph Signal” a bimodal noise distribution due to single traps in or channel near buffer FET. Number of such traps and distance from channel produce a spectrum of amplitudes. Characteristic time constants vary widely. All silicon transistors suffer from this to some extent. In big transistors many traps are in play and it accounts for 1/f noise. In small transistors one or a few traps produce RTS noise. Cooling increases the time constant. Slow traps become so slow they become invisible, but fast traps which would average to zero now move into signal passband. Quiet pixel Excess noise is due to RTS in mux Raw value minus 1st frame (ADU) Frame number Noisy pixel

68 SPIE H2RG noise to 1kHz 68 Histogram of RTS noise for the nasty case of two traps about the same size Time series

69 SPIE H2RG noise to 1kHz 69 Same after coadd and subtract (100 coadds) For time series on previous slide Differencing turns steps into spikes. Coadding helps but noise is still significantly degraded by RTS. Better to reject outliers than try to average them away


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