COROT WEEK Liège 4-7/12/2002

CorotWeek 3, Liège 4-7/12/2002 1

(working on Saturday!!!)

The CCD flight models Miss Pernelle BernardiMr Vincent Lapeyrere

Mr Tristan Buey

and the CCD team at work From Meudon : Régis Schmidt, Bertrand le Ruyet, Jêrome Parisot, Didier Tiphène

From CNES : Olivier Gilard, Guy Rolland (for irradiation test)

Funding by CNES.

COROT WEEK Liège 4-7/12/2002.


What’s up??PAST.

Test of electrical model on 4 chips are finished:---> Constraints for flight electronic readout and processing.

Irradiation test are finished:---> Performances for the end of life.

Present and future.Test and calibration of the 10 CCDs flight models:

---> Selection for the flight camera.---> Delivery of the CCDs in March 2003.

Test of the CCD mechanical models:---> Delivery for the MIQ Camera in December 2003.

Bench dedicated to scientist for photometric experiment:---> From May 2003.


Results on the flight models2 CCDs flight models have already been tested on the bench.A third one is under test at that time.We test one CCD every 3 weeks.High homogenety between the CCDs (7 EM and 2 FM).We have about 20Go of raw images per CCD and 1Go of reduced images.2 steps to reach the performances of the CCDs:

* Measurements of the characteristics on the bench.Working point, Dark current, PRNU, Gain, Coeff Temp, Saturation…

* Software models (expected system performances and CCD characteristics).

Happiest flying mascot!!!

????

CCD information


Working point (1)

• Optimize 3 bias voltages VOD, VRD, VOG

• Measurement of the video signal for different values of the bias voltages:

• Same working range for the 3 CCDs FM:

Video Signal vs Vod

35000

45000

55000

65000

75000

85000

95000

105000

1800 2000 2200 2400 2600 2800 3000 3200 3400 3600

Vod (ADU)

Video signal (e-)

Left output

Right output

CCD N° VOD VRD VOG

056 26.5 0.2 V 13.2 0.2 V -1.9 0.2 V

071 26.5 0.2 V 13.2 0.2 V -1.9 0.2 V

076 26.5 0.2 V 13.2 0.2 V -1.9 0.2 V


Working point (2)• Sensitivity of the video signal to the bias voltages : static measurement, in dynamic it

will depend on the frequency and some compensations exist.• About same order at worst frequency (100kHz, readout frequency).

• Higher sensitivities = 4e-/mV

• Specification for the electronics: 1mV peak to peak ---> equivalent noise of few e -.

Video signal vs Vod

y = -3,8385x + 49668

y = -4,0153x + 49998

41000

41200

41400

41600

41800

42000

42200

42400

42600

42800

43000

1800 1850 1900 1950 2000 2050 2100 2150 2200

Vod (ADU)

Video signal (ADU)

CCD N° VOD VRD VOG

056 2.6 1.0 1.9

071 3.9 1.8 2.0

076 3.7 1.2 2.5

Sensibility is given in e-/mv.


Dark at –40°C• Dark mean value: Spec: < 0.5e-/px/s at –40°C

• No cosmetic (all pixels < 100e-/px/s)

CCD N° Mean value (e-/px/s) Local max (e-/px/s) 80% of windows<

056 0.11 0.23 0.13

076 0.11 0.42 0.13

Histogram of the mean value of 32*32 pixels windows

over the CCD

Mean value

80% of windows


PRNU (Pixel response Non Uniformity) (1)

= 420nm, = 10nm = 700nm, = 10nm = 950nm, = 10nm

Obtained with flat illumination

Give the uniformity of the state surface and AR coating ---> Surface Pattern

Give the uniformity of the physical characteristics---> High homogeneity

Give the uniformity of the thickness---> Fringing Pattern


PRNU (Pixel response Non Uniformity) (2)

• Global PRNU = dispersion of the mean values of the windows, standard deviation of the mi,j.

The Global PRNU is not a relevant parameter.

• Local PRNU = dispersion of the pixels values inside each window, mean value of the i,j.

• 64*64 windows of 32*32 pixels (no side effects by removing pixels).

• In each window (i,j), we calculate - the mean value mi,j

- the standard deviation i,j

Local PRNU vs wavelength

0,00

0,50

1,00

1,50

2,00

2,50

400 500 600 700 800 900

Wavelength (nm)

Local PRNU

5676


CCD Gain (µV/e-)• The CCD is illuminated with white LEDs at several time flashes• Calculation of the mean value: m the variance of the difference of 2 images with the same flash:

Calculation of the gain

0

5000

10000

15000

20000

25000

30000

35000

40000

45000

0 10000 20000 30000 40000 50000 60000

Mean (ADU)

Variance (ADU)

Right output

Left output

TGm2= GT is the gain of the complete

video chain (e-/ADU)Telec

CCD GGG *3,76=

CCD N° Left side Right side

056 4.33 4.28

076 3.97 4.15

Results at –40°C:

1 ADU of the ADC = 76.3V


CCD Gain versus temperature

• Global gain (e-/ADU) measured at different temperatures from –45°C to 30°C• The electronics gain is constant the variation of the global gain is the same

than the variation of CCD gain.

CCD Gain vs temperature

y = -0,0048x + 4,1152y = -0,0046x + 4,0982

3,90

4,00

4,10

4,20

4,30

4,40

4,50

-52 -42 -32 -22 -12 -2 8 18 28

T (°C)

CCD gain (µV/e-)

Left output

Right output

fit (left output)

fit (right output)

CCD N° Temperature coefficient of the CCD Gain (ppm/K)

056 -4700

076 -3700


Full Well Capacity in Flat Field

Calculation of the gain

0

5000

10000

15000

20000

25000

30000

35000

40000

45000

0 10000 20000 30000 40000 50000 60000

Mean (ADU)

Variance (ADU)

Right output

Left output

Image pixel Saturation

CCD N° FWC (ke-)

056 87

076 110

E2V data: 2 groups of CCDs

- 3 CCDs with a FWC < 90ke-

- 7 CCDs with a FWC > 100ke-


Full Well Capacity with a PSF

Right output

Left output

2 sizes of PSF 3 positions on the CCD

= 20 pixels

= 50 pixels

First results:

* Saturation occurs at lower values when the PSF is far from the output.

* Depends on the PSF size.

Traps? Results soon… in CorotWeek4


Temperature Coefficient of Quantum Efficiency• Measure of the flux at: - different wavelengths from 400nm to 950nm - different temperatures from –45°C to –30°C• Correction by the temperature coefficient of the CCD gain (G ~ -4000ppm/K)

111*)2(

)2( −+−+=

GR

RQ

R = temperature coefficient of the CCD response

G = temperature coefficient of the CCD gain

Q = temperature coefficient of the quantum efficiency

But the temperature coefficient of the CCD response is about 1500ppm/K

Temperature Coefficient of the Quantum Efficiency

0

2000

4000

6000

8000

10000

12000

400 500 600 700 800 900 1000

Wavelength (nm)

Qe/Qe (pp/°)

5676


Results of the irradiation tests (1).

3 chips tested (4210) with protons at 4 different energies (30 to 60Mev).

Tested characteristics :• Working point.• Gain and Full Well Capacity.• Dark Current (mean value, defect).• Pixel Response Non Uniformity.

No transient were visible due to the too high proton flux (more than one impact on a single pixel on each image).


Results of the irradiation tests (2).

Unless the dark current all the other characteristics of the CCD will not be degraded enough to impact on the system performances.

Irradiation will induce in the dark current : Local defect (spatial and temporal). Global evolution

<0.5e-/s ---> 3 to 10e-/s

Rapid evolution with the temperature gives strong constraint on the CCD operational temperature

---> Under -40°C.

Defect are less than 1/10000 pixels.No possible recovering on board… Aïe!!


Selection of the flight models

Could avoid random choice if more than 4 CCDs are still alive after the test campaign!!!

The aim of this work is to develop methods to :– Determine if all CCDs are able to fly– Find criteria for each program

By software models using :–The expected performances of the system (PSF, pointing, thermal stability…). –The characteristics of the CCDs measured on the bench and also at E2V.

4 CCDs have to be selected, the parameters of choice have to be optimized for the asteroseismology et exoplanets.


CCD parameters• Should be used for sorting :

– Dark current• Noise• White pixels

– Pixel response non uniformity• Cosmetic defects• Function of the wavelength

– Gain• Function of the temperature

– Quantum efficiency• Number of electron collected• Function of temperature

– Pixels capacity

• Shouldn’t be used :– Non linearity

• Dominated by the electronic

– Transfer efficiency

– Read out noise• Dominated by the electronic

– Irradiation sensitivity


Map of the dark noise• Dark noise is due to the poissonian statistic of the dark current :

( )∑∈

×=maski

iNTσ

Psf Mask for photometry

Value of the dark current

We obtain an image, each pixel indicates the dark noise at that position

Here each pixel indicates the max value in the 32*32 pixels windows


Map of the jitter noise• 3 different flat fields for 3 different parts of the bandwidth• Each flat field is convolved with the corresponding PSF• The jitter noise is calculated with the sum of the 3 images

350-550 nm

550-750 nm

750-950 nm

Flat fields Convolution with the PSF

sum Computation of the jitter noise

Each pixel indicates the max value of the jitter noise inside the 32*32 pixels windows


Jitter and dark noise

Average value calculated over all the CCD surface

Unit : ppm

Unit : e-

Photon noiseSpecification (1/10 photon noise)Dark noiseJitter noise

Jitter noiseAverage ~ 7.5 ppm

Dark noiseAverage ~ 11 e-

On the curve we plot :• Photon noise versus the star magnitude.• Noise specification.• Average Value of the jitter and dark noises.


Jitter and dark noise

Jitter default

Unit : ppm

Unit : e-

Photon noiseSpecification (1/10 photon noise)Dark noiseJitter noise

Jitter noiseAverage ~ 7.5 ppm

Dark noiseAverage ~ 11 e-


Other parameters• Variation of global CCD response with temperature

(Gain and quantum efficiency) – Coefficient ~ 1500 ppm/K

=> Variation of about 10 ppm (with T=5.10-3K)

• Quantum efficiency– Values (E2V data):

• Pixel capacity– Values (E2V data)

N° CCD 060 076 045 071 032 067 062 056 055 033 Capacity (ke-/pix.) 111 110 108 104 102 102 102 87 86 85

N° CCD 056 032 055 060 062 033 071 045 067 076 Average Qe (en %) 64,3 64,5 64,1 62,7 62,1 61,9 61,3 61,3 60 60 Diff. in % off max 0 0,10 0,78 2,56 3,47 4,49 4,63 4,78 7,14 7,16


Parameters priority

• For seismology :1. Pixel capacity2. Quantum efficiency3. Temperature coefficient4. Jitter noise map

• For exoplanets :1. Dark noise (strong defects, will

evolve with radiations!)2. Jitter noise map (strong defects)3. Quantum efficiency4. Pixel capacity5. Temperature coefficient


CCD quality

• All important parameters on the same diagram

• Compare CCDs between them

=> Example of 2 CCDs (seismology PSF) :

Best CCD


Conclusion

• Methods are developed to sort the CCDs

• Now :

– Applied these methods on the bench data

– Choose 2 CCDs for each scientific program

Documents

COROT WEEK Liège 4-7/12/2002