The Loral Maxplanck Ccd Detector

The DISR CCD was designed and produced in the early nineties at Loral [2] under contract from MPS, formerly the Max-Planck-Institut fur Aeronomie. The design was optimized for the DISR application in respect to the rigid limitations in mass, power and data rate allocations provided by the Huygens probe.

The CCD is a buried channel front side illuminated frame transfer device with 256 active lines and 512 (+ 8 dark) columns. The detector is employed 2 phase MPP clocking and gated anti-blooming primarily used as an electronic shutter, but also used to remove excessive charge from overexposure. As shown in Table 1, the pixels are 17x23 ^m2 on 23 ^m centers leaving 6 ^m for anti-blooming on the side of each pixel. The pixel capacity of more than 150 000 e_ is set to a full well of 125 000 e_ by the anti-blooming gate potential. The quantum efficiency is up to 50% at 600 and 800 nm.

Table 1. Summary of the Loral Max Planck chip specification.

Parameter

Specification

Device technology

Buried channel, Frame Transfer, FI

Clocking architecture

2 phase MPP clocking

No. of active pixels

256 lines, 512 (+8 dark) columns

Pixel size

17 ^mx23 ^m; 23 ^m pixel pitch

Pixel capacity

>150 000 e"; 125 000 e" used

QE

up to 50% (600 and 800 nm)

CTE

0.999 999 (at the beginning)

Line transfer time

2 ^s/line

Output amplifier

One single stage, 5-8 e" noise at 70 kHz

Anti-blooming

Gated anti-blooming incl. el. shutter function

Temperature sensor

2 AD590 dice on ceramic substrate

Fast line transfer of 2 ^s/line allows rapid image shift into the memory zone with minor image smear during the charge transfer. Highest shuttering effect (up to 7% at the top of the images) occurred only in the early phase of the observations with 7 ms exposure times, but can be effectively removed.

As shown in Fig. 1, the CCD die was bonded to a ceramic substrate, which provides excellent electrical isolation to the metal package ground. Such isolation allows the operation of the detector from up to several meters, even in the noisy environment of a spacecraft. The DISR CCD imaging system could therefore be suitably used for the Imager for Mars Pathfinder (IMP, 1997) and further Mars camera applications [3].

A number of manufacturing lots were required to perfect the design. The flight detector, CCD #093, received gold metallization on the back side of the die substrate to establish reliable substrate grounding [4].

Figure 1. Front view to the DISR CCD on the top end of the Sensor Head Board (SHB).

Two AD590 sensors visible on top of the CCD allow precise temperature measurements.

Figure 1. Front view to the DISR CCD on the top end of the Sensor Head Board (SHB).

Two AD590 sensors visible on top of the CCD allow precise temperature measurements.

Figure 2 shows the arrangement of the optical channels on the imager as projected by the fiber bundle:

• HRI High resolution down looking imager, 160^ 256 pixels

• SLI Side looking imager 128 x 256 pixels

• MRI Medium resolution imager 176 x 256 pixels

• ULVS Upward looking visible spectrometer 8 x 200 pixels

• DLVS Down. looking visible spectrometer 20 x 200 pixels

• SA1, SA2, SA3, SA4; Solar Aureole 1-4, 4 x 6 x 50 pixels.

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