6 Feb. 2003 (update) A.P.Kashchuk (LNF/INFN, on leave from PNPI) 2

Remarks for further improvements of the Triple GEM detector w.r.t. M0 prototype tested in October 2002

1.Cdet must and can be reduced from 50pF to 5pF (change design), then ASDQ chip can be used effectively (better than ASDQ++ and CARIOCA): ENC=1200+70e/pF=1550e (RMS) x 4 =>>> 1fC (threshold) compare: at present design with ASDQ++ (CARIOCA will be similar) ENC=2000+40e/pF=4000e (RMS) x 4 =>>> 3fC (threshold);2.Further S/N improvement if double signal by OR-ing on the amplifier input (instead to readout single detector to own amplifier, one can use 2 amplifiers for reliability, but read double signal to each one, output select by DIALOG);3.As it is needed for GEM, ASDQ chip has discharge protection on the negative input: 550pF at 3kV, 1.5mJ. CARIOCA will need external protection, and additional noise of the protection board will be added: 10pF and 15 Ohm =>> 500e;4.Guard traces must be added between readout pads to reduce crosstalks from pad to pad (ASDQ has Rin=300 Ohm);5.Full charge (50fC in average from 6mm gas gap) will be collected by ASDQ. It is equivalent to gas gain 104.

6 Feb. 2003 (update) A.P.Kashchuk (LNF/INFN, on leave from PNPI) 3

Where this ‘blocking’ capacitor?

6 Feb. 2003 (update) A.P.Kashchuk (LNF/INFN, on leave from PNPI) 4

smallesttheCeq _

Cathode

Drift gap

GEM1

GEM2

GEM3

Anode

Transfer1

Transfer2

Induction gap

‘Blocking’ capacitor (defines the current return path)

in chain

To be cancelled

or minimizedTo be maximized

6 Feb. 2003 (update) A.P.Kashchuk (LNF/INFN, on leave from PNPI) 5

Time

0s 10ns 20ns 30ns 40ns 50ns-I(R31) -I(R37) -I(R38)

-4.0uA

-2.0uA

0A

2.0uA

Cdet=5pF, Cbl=100pF

Time

0s 10ns 20ns 30ns 40ns 50ns-I(R31) -I(R37) -I(R38)

-4.0uA

-2.0uA

0A

2.0uA

Cdet=50pF, Cbl=100pF Time

0s 10ns 20ns 30ns 40ns 50ns-I(R31) -I(R37) -I(R38)

-4.0uA

-2.0uA

0A

2.0uA

Cdet=5pF, Cbl=1000pF

Time

0s 10ns 20ns 30ns 40ns 50ns-I(R31) -I(R37) -I(R38)

-40nA

-20nA

0A

20nA

Zoomx100

‘Blocking’ capacitor (defines crosstalks)

x1 x1

x1

SimplifiedGEM

(induction gap)spice-model

Signal (green)

Crosstalk

(blue/red)

at various

conditions

Neighbor pads 2D array

Time

0s 10ns 20ns 30ns 40ns 50ns-I(R31) -I(R37) -I(R38)

-2.0uA

-1.0uA

0A

1.0uA

Cdet=5pF, Cbl=0

High crosstalk (even with

opposite polarity) bad!

Crosstalks are equal

on all pads!

tr=100um/nstf=RampCin

6 Feb. 2003 (update) A.P.Kashchuk (LNF/INFN, on leave from PNPI) 6

Cdet=5-50pF, Rin=300, Cbl=1000pF

x10

Cdet=5-50pF, Rin=30

x10

Time

0s 10ns 20ns 30ns 40ns 50ns-I(R31) -I(R37) -I(R38)

-4.0uA

-2.0uA

0A

2.0uA

Time

0s 10ns 20ns 30ns 40ns 50ns-I(R31) -I(R37) -I(R38)

-400nA

-200nA

0A

200nA

Time

0s 10ns 20ns 30ns 40ns 50ns-I(R31) -I(R37) -I(R38)

-4.0uA

-2.0uA

0A

2.0uA

Time

0s 10ns 20ns 30ns 40ns 50ns-I(R31) -I(R37) -I(R38)

-400nA

-200nA

0A

200nA

Signal (green/ red)

Crosstalk

(blue)

at various

conditions

One can see from here, that Triple GEM has to be optimized

Time

0s 10ns 20ns 30ns 40ns 50ns-I(R31) -I(R37) -I(R38)

-4.0uA

-2.0uA

0A

2.0uA

Cdet=5pF, Rin=300, Camp=5-50pF, Cbl=500pF

Time

0s 10ns 20ns 30ns 40ns 50ns-I(R31) -I(R37) -I(R38)

-40nA

-20nA

0A

20nA

x100

6 Feb. 2003 (update) A.P.Kashchuk (LNF/INFN, on leave from PNPI) 7

Time

0s 20ns 40ns 60ns 80ns 100ns-I(R31) -I(R37) -I(R38)

-10uA

-5uA

0A

5uA

Time

0s 20ns 40ns 60ns 80ns 100ns-I(R31) -I(R37) -I(R38)

-8.0uA

-4.0uA

0A

4.0uA

Time

0s 20ns 40ns 60ns 80ns 100ns-I(R31) -I(R37) -I(R38)

-8.0uA

-4.0uA

0A

4.0uA

Cbl=1000pF

Cdet=Camp=5pF, Ramp=300

Attention: crosstalks to pads from the GEM-foil

Cbl=100pF

Cbl=10pF

Noise source on GEM-foil (e.g.history)

Qin=50fC

Noise=blue/top

Signal=green/bottom