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Implementation of two multi-channel ASICs for CCD readout

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					  Implementation of two multi-channel
        ASICs for CCD readout

                ASPIC (DSI design, LSST camera baseline)
                   CLASSIC (Clamp & Sample design)


                 ASICs designers : H. Lebboloa , R. Sefria , V. Tocutb
Tests & Characterization : Pierre Antilogusa, S. Baileya, P. Baillya, J. Jeglotb, C.Juramya,,
                          D. Martina , M. Moniezb ,F. Wicekb

                              a IN2P3/LPNHE    , b IN2P3/LAL
                                  LSST Focal Plane
                                                                                   189 Science CCD
                                                                                    4k X 4k 10mm pixels
                                                                                      = 3 x109pixels
                                                                                        for a focal plane of
                                                                                           - 64 cm de diameter
                                                                                           - 9.6 Deg 2




                                                3X3
                                               CCD
                                              “RAFT”




                                                                                          The CCD are split in 16
Science Rafts (9 CCD):                                                                    segments of 1 M pixels :
autonomous, fully                                                                         2s readout time for the
testable 144 Mpixel camera.                                                               full focal plane => 500kHz
1 Raft ~ 1/2 Megacam at CFHT
                                                                               Corner rafts :
LSST camera = 21 rafts
                                                                               guiding and wavefront sensing

    15/10/09 - Detectors for Astronomy 2009            ASICs for CCD readout                                     2
                     LSST camera readout system




                         189 Science CCD x 16 outputs = 3024 readout channels
                          Request a compact readout chain inside the cryostat
                           The topic of this talk : ASIC for FE CCD readout


15/10/09 - Detectors for Astronomy 2009   ASICs for CCD readout                  3
     LSST Front End : ASIC for CCD readout specifications

Requirements :
• CCD readout at 500 kHz (nominal) to 250 kHz
• Noise : ~5nV / √Hz (or 7µV rms noise for 500ns integration )
( ~2 e- to be compared to 5 e- read noise for the whole CCD Chain)
• Power dissipation at cryo temperature : 20-25 mW/channel
• Crosstalk : 10-4 level ( 0.01% (goal) - 0.05% (max) )
• 90Keˉ Full Well capacity (150Keˉ max)
• 0.5% linearity ( defined over 0 to 100 000 eˉ full well )
• Differential outputs
• Output Load : 50pF // 1 k Ω
• Power Supply 0/5V with respect to reference = 2.5 V
• Running temperature 173K
                           Our initial worry :
   Does a 8 channels ASIC will have the required low level crosstalk

  15/10/09 - Detectors for Astronomy 2009   ASICs for CCD readout   4
          Analog signal processing of CCD : DSI or C&S

The standard technique for analog                        Vout
signal processing of CCDs, is
“Correlated Double Sampling”. It has
been commonly implemented using
one of the following schemes:
• “Dual Slope Integrator” (DSI )
                                                        reset feedthrough                                t
• “Clamp & Sample” (C&L) .
                                                                    Reference level       signal level

                                                                            Charge dump



The first prototype implemented for LSST , the Analog Signal Processing
ASic , (ASPIC I ), was a 8 channels ASIC with :
• 4 DSI channels : The reference design for LSST is DSI.
• 4 C&S channels : As we had a C&S design almost “ready” and
considering the higher complexity of the DSI design and the R&D/unknown
related to the crosstalk.



 15/10/09 - Detectors for Astronomy 2009   ASICs for CCD readout                                         5
   Analog signal processing of CCD : Dual Slope Integrator (DSI)




                 Noise % 1/ sqrt (Tintegration)




                                           5K
                                                                          100pF
                           5K
                                       -        5K          outp                  "diff DSI" outp
                                       +
                                                      inp
                 +                              10K
                 -
                            Vref
                                                                   Vref
              8k 2p
                                                        CDS
            8p
                                                      (switches)
            2k                                  10K
                                                                          100pF
Vref Vref                                        5K
                                   -                  inm   outm                  "diff DSI" outm

                                   +




                                                                   Vref


 Clamp                 1 gain , 2 integration constant time

        15/10/09 - Detectors for Astronomy 2009                             ASICs for CCD readout   6
 Analog signal processing of CCD : Clamp and Sample (C&S)




      clamp Switch




Noise % 1/ sqrt (Tau)
With Tau = filter at the output of the C&S
The “usage wants” Tau to be of the order 1/10 of the CCD signal width
On ASPIC I , we had no filtering at the output of the C&S ( Tau ~ 35 ns )



   15/10/09 - Detectors for Astronomy 2009   ASICs for CCD readout          7
               Analog signal processing of CCD :ASPIC I
                                                                               •Techno : CMOS 0.35µ 5V
                                                                               •Vendor : AMS
                                                                               •Package : CQFP100
  TEST          Require            DSI                      C&S


Crosstalk       0.05 %          0.007 %                     0.02 %
               Goal 0.01%

                                                                               4 DSI channels
Linearity       0.5 %          +/-0.2 %                     ~0.5%


Power           25 mW          48.5 mW (22o C)           24.3 mW
per




                                                                                                             3.8mm
channel
Noise           7 µV           19.04µV (Tint=500ns) 12µV (22o C)
              ( -100oC)                             10µV (-100o C)

Cold          Works at -                     Tested down to -170oC
              100oC
                                                                               4 C&L channels
   15/10/09 - Detectors for Astronomy 2009             ASICs for CCD readout                             8
                                                                                                2.7mm
   Analog signal processing of CCD : ASPIC I Conclusion


                            The first prototype has demonstrated
      DSI and C&S : implementation in a multi channel Integrated Circuit work at
      low temperature with low crosstalk
      DSI : Good fit between measurements and simulations (based on an equivalent
      circuit using a linearized schematic to replace CDS switches)
      C&S : gave competitive results

                           ASPIC II  optimise Noise & Power and add functionalities

                             Proto 1 - Noise density simulations & Measurements

                  50

                  45
                  40
                                                         DSI
                  35
                  30                                                              Noise measurement LPNHE
             µV




                  25                                                              Noise measurement LAL
                  20                                                              Noise simulation

                  15
                  10
                  5

                  0
                       0           0,05                  0,1             0,15
                                          1/SQRT(Tint)
15/10/09 - Detectors for Astronomy 2009                   ASICs for CCD readout                             9
            Analog signal processing of CCD :ASPIC II
   3 input amplifier gains : 2.5 – 5 – 7.5
       to deal with CCD gain spread.
                                                                        •Techno : CMOS 0.35µ 5V
   3 integration time constants : 500ns – 1µs – 1.5µs                  •Vendor : AMS
      to deal with CCD readout frequency.
                                                                        •Package : CQFP100
   Idle mode : DC current reduction by a factor of 1.000               • 8 DSI channels
         baseline : { gain 5 + 500ns integration time}




15/10/09 - Detectors for Astronomy 2009         ASICs for CCD readout                       10
                   ASPIC II : Layout and improvement


LVDS inputs : 1.2V +/- 200mV terminated
with 100 ohms
     CDS clocks: clamp + integrator
     reset + signal integration + reference
     integration
CMOS inputs: 0V / +5V (compatible with
3.3V signals)
    input gain and integration time select
Improvement compared to ASPIC I :
    Noise:
         1/f noise reduced : amplifier first
         stage optimization
         RC Input gain : noise source
    Power consumption :
         Source identified : amplifier
         output stage.



   15/10/09 - Detectors for Astronomy 2009   ASICs for CCD readout   11
                               ASPIC II : Simulation


Noise simulations of ASPIC 2 @ -100°C
6µV RMS noise for an Integration Time of 500ns



                                                 Noise            0.1%     Linearity




                                                               -0.15%




   15/10/09 - Detectors for Astronomy 2009         ASICs for CCD readout        12
                           ASPIC II : first results




                  TEST          Require           DSI                  DSI
                                               (simul)               (measure)

               Crosstalk         0.05 %          -                        0.02 %
                               Goal 0.01%


               Linearity         0.5 %      +/-0.1 %                     +/-0.1%


               Power            25 mW       25 mW (27o C)            26 mW (22o C)
               per             Goal 20 mW   20 mW(-100o C)
               channel
               Noise            7µV           8 µV (27o C)               9 µV (22o C)
                               ( -100oC)       (Tint=500ns)




15/10/09 - Detectors for Astronomy 2009          ASICs for CCD readout                  13
           “study on the side” : C&S version II ( CLASSIC )
•   Pin to pin compatible with ASPIC 2
                                                                      •Techno : CMOS 0.35µ 5V
•   3 bit programmable gain input amplifier
                                                                      •Vendor : AMS
•   4 bit programmable output time constant filter to                 •Package : CQFP100
    match the readout frequency (tau = 8ns to 392ns )                 • 8 C&S channels
•   Two differents C&S topologies (simulated noise ~ 1 e-
    for a power < 20 mW/channel and 500 kHz CCD
    readout)
•   Idle mode




    15/10/09 - Detectors for Astronomy 2009   ASICs for CCD readout                       14
                                       Conclusion

-   We made a 8 channels ASICs with low crosstalk ,
    low noise , low power, fast readout, for analog
    signal processing of CCD using CMOS 0.35µ 5V:
      - Such ASICs are needed for a large focal
         plane like the LSST one
      - If you are tired of fighting against « setup
         noise » , such ASIC with differential output
         directly in your cryostat could make your life
         so easier ….
-   If you were expecting a “3 sigma effect” between
    DSI and C&S (or C&S and DSI) …looks like it
    was the wrong talk … still the difference is
    always in the detail ( crosstalk vs time , ultimate
    readout speed, connection to CCD …) , and we
    are far to have completed the characterization of
    our second generation of prototypes .
-   For LSST, we now look forward to plug a LSST
    prototype CCD on our ASPIC II …

    15/10/09 - Detectors for Astronomy 2009         ASICs for CCD readout   15

				
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