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RSH Front End Electronic. R. Beaujean, S. Böttcher. Kiel Nov 07, 2005. CSA. Detector FET + OpAmp shaping amp. Feed back. Front End Electronic Block Diagramm. Feed back network: C f and R f (parallel)

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rsh front end electronic

RSH Front End Electronic

R. Beaujean, S. Böttcher

Kiel Nov 07, 2005



Detector FET + OpAmp shaping amp

Feed back

Front End Electronic Block Diagramm

Feed back network: Cf and Rf (parallel)

Cf (pF) defines sensitivity : (44/Cf ) mV/MeV (for Si)

Rf (MegOhm) defines time constant of discharging (pile up)

shaping amplifier: signal level conditioning for ASIC input

improves signal to noise ratio

can select fast charge collection


CSA Noise considerations:

increasing with:

detector capacitance (e.g. 85 pF @ 300 um, 2 cm²)

detector dark current ~ SQRT(Id)

(doubles every 8 degree K)

decreasing with: increasing FET current

noise ~ 1/SQRT(gm); gm~SQRT(Id)

gm (mutual conductance, forward transfer admittance)

is the parameter we can influence by selecting the type of FET

and the FET drain current (--> power consumption).


Range of Energy Deposit Measurements in Si

The minimum detectable energy deposit must be ~ 60 keV (well below 115 keV of MIPs in 300 um Si)

assuming a dynamic range of 10k for the analogue section,

this gives an upper limit of 600 MeV energy deposit

Maximum output voltage of the CSA is ~3 Volt

--> Cf = 44 mV * 600 MeV / 3V = 8.8 pF

the CSA output for 60 keV energy deposit is then 0.3 mV


How to improve the resolution for required energy deposit range at given ADC resolution

For CsI and BC430M:

Photodiode1+ CSA1 with low Cf for lowE events (high gain)

Photodiode2+ CSA2 with med. Cf for med.E events (med. gain)

Photodiode3+ CSA3 with high Cf for highE events (low gain)

For SSD (A, B, C detectors) :

only 1 block of SSD-detector + CSA

behind the CSA two independent shaping amplifiers with low (x1) and high (x16) gain respectively (the CSA defines the dynamic range).



small size, SMD active components required

1. FET: BF862 SOT23-3 plastic package

equivalent noise input voltage 0.8 nV/Hz

input capacitance 10 pF

transfer admittance gm 45 mS typ.

2. OpAmp: AD8005 SOT23-6 plastic package

low quiescent current ~ 400 uA

low noise, high slew rate,

plastic packages have to be qualified for flight


Quiescent Power consumption

CSA: FET drain Id~ 4mA @ 3V; amplifier 0.5 mA@ +-5V

noise critical FETs may be operated with Id>4 mA,

less critical FETs may be operated with Id<4 mA

shaping amplifier: 0.5 mA@ +-5V

Interface to ASIC

positive output signal, shaping time TBD (1-5 us)