Amptek CoolFET A250CF Manual - Halaman 3

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Halaman Cetak
300 M
DC or AC Coupling
Input Protection
Jumper
Input
49.9
Test
Figure 2. Bock Diagram of A250CF "CoolFET."
2.2
CoolFET Hybrid
The CoolFET hybrid contains three (3) FETs that are
placed on top of a thermoelectric cooler and enclosed in a
TO-8 package. There are two main advantages to cooling
the FET: it reduces the leakage current and increases the
transconductance, both of which reduce the electronic noise
of the system. The increased transconductance provides a
much improved noise slope (eV/pF) over un-cooled
systems, which is especially important for large capacitance
detectors.

3 Specifications

3.1
Performance
Noise at 0 pF (keV)
(2 s shaping)
CoolFET
DC
coupled
Type
Low C
0.670
iss
High C
0.850
iss
Table 1. Typical noise data for A250CF.
depends on (1) the detector capacitance, (2) input
configuration (AC vs DC coupling, use of input protection),
and (3) which CoolFET is used.
Gain: With a 0.5 pF feedback capacitor and a gain of 2 in
the output buffer.
176 mV/MeV (Si)
220 mV/MeV (Ge)
144 mV/MeV (CdTe)
Amptek A250CF CoolFET User Manual –Rev. A5
Charge Sensitive Preamplifier
Bias
SHV
Drain
Jumpers
Gate
Jumpers
Thermoelectric
Cooler
Noise
Slope
(eV/pF)
300 M
Bias
1.00
13
1.20
11.5
The noise
A250CF CoolFET
Drain Current
Jumpers
A250
CoolFET
Hybrid
2 G
0.5
pF
152 mV/MeV (HgI2)
4 V/pC
0. 64 µV/electron
FET Capacitance (C
FET 1 and 2 Low C
FET 3 High C
Rise Time: 2.5 nsec at 0 pF, no output buffer
Integral Nonlinearity: < 0.03%
3.2
Inputs
Detector Input: Positive or negative input signals from
semiconductor detectors.
Bias: Detector bias voltage, maximum 1 kV, from a power
supply.
Test: Input voltage pulses for system test and calibration.
3.3
Outputs
Energy (E): Provides an output voltage step proportional
to the input charge. Nominal gain is 176 mV/MeV (Si).
Polarity and DC offset are adjustable. Output Impedance is
50 Ω.
Dynamic Range: ± 4 V, offset adjustable to ± 6 V
Timing: Provides a tail pulse (1 s decay) for system
timing measurements. Polarity is adjustable. (see below).
Amplitude equal to E output. Output Impedance is 50 Ω.
Offset
Energy
Gain of 2
Adjust
Optional Invert
Timing
Gain of 2
Optional Invert
+/- 8V
+3.3V
Power
Supply
+/- 5V
TEC Pwr
):
iss
: 8 pF
iss
: 60 pF
iss
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