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RSH Front End Electronic
R. Beaujean, S. Böttcher
Kiel Nov 07, 2005
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
Detector FET + OpAmp shaping amp
Feed back
CSA
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).
CSA noise versus input capacitance (typical FET)
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
0
1x103
2x103
3x103
0 200 400 600
11/04/05
Cf =2 pF
Cf= 10 pF
11/04/05
energy deposit in Si /MeV
CS
A o
utpu
t /m
V
CSA output with Si detector
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).
Layout of typical CSA (Kiel) for PIN2774
0
2x103
4x103
6x103
8x103
10 20 30 40
eqn: y=c*exp(-0.5*(x-a)2/b2), R:305,a=29.6739, b=1.50803, c=5578.24
59.5 keV AM241
11/04/05
channel
coun
ts
PIN2744
Kiel-CSA + 2 cm² detector: rms noise ~ 3 keV
Components
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@ +-5Vnoise 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)
Recommended