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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

slide2

CSA

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

slide3

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).

slide5

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

slide7

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).

slide10

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

slide11

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)