Charge Sensitive Preamplifier
A2 50
STATE-OF-THE-ART
• External FET allows matching to detector
• FET can be cooled
• Noise at room temperature ~ 100 electrons RMS
• Low power (19 mW typical)
Features
•
•
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•
•
•
•
•
•
Ultra low noise
Low power
Fast rise time (2.5 ns at 0 pF)
External FET (allows selection or cooling)
Positive or negative signal processing
Pin selectable gain
Small size (14 pin hybrid DIP)
High reliability screening
One year warranty
Applications
•
•
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Aerospace
Nuclear physics
Portable instrumentation
Nuclear monitoring
Particle, gamma, and x-ray imaging
Medical and nuclear electronics
Electro-optical systems
Overview
The A250 is a hybrid state-of-the-art Charge Sensitive Preamplifier for use with a wide range of detectors
having capacitance from less than one, to several thousand picofarads. Such detectors include silicon, CdTe, CZT,
and HgI2 solid state detectors, proportional counters, photomultiplier tubes, piezoelectric devices, photodiodes,
CCD’s, and others.
To permit optimization for a wide range of applications, the input field effect transistor is external to the
package and user selectable. This feature is essential in applications where detector and FET must be cooled to
reduce noise. In all applications, it allows the FET to be matched to the particular detector capacitance, as well
as to noise and shaping requirements. In larger quantities, the A250 may be specially ordered with an internal
FET.
The noise performance of the A250 is such that its contribution to FET and detector noise is negligible
in all charge amplifier applications, i.e., it is essentially an ideal amplifier in this respect.
The internal feedback components configure the A250 as a charge amplifier; however, it may be used as
a high performance current or voltage preamplifier by choice of suitable feedback components.
While these preamps were designed for multidetector satellite instrumentation, their unique characteristics make them equally useful in a broad range of laboratory and commercial applications.
Figure 1: Typical Application
COOLING (OPTIONAL)
FET
A250
A275
DETECTOR
CHARGE SENSITIVE
PREAMPLIFIER
AMPTEK INC.
Tel: +1 (781) 275-2242
PULSE HEIGHT
ANALYZER
OR A/D
SHAPING
AMPLIFIER
14 DeAngelo Drive, Bedford, MA 01730-2204 U.S.A.
Fax: +1 (781) 275-3470 e-mail: sales@amptek.com www.amptek.com
A250 Specifications (Vs = ±6 V, T = 25 °C unloaded output)
INPUT CHARACTERISTICS
Sensitivity
(Cf = 1 pF)
44 mV/MeV (Si)
55 mV/MeV (Ge)
36 mV/MeV (CdTe)
38 mV/MeV (HgI2)
1 V/pC
0.16 µV/electron
Sensitivity can be reduced by connecting Pin 2 and/or 3 to Pin
1, thus providing Cf = 3, 5, or 7 pF. Additional external capacitors can be added for further reduction of gain. In general,
the sensitivity is given by A = 1/Cf (pF) V/pC. For silicon, the
sensitivity is A = 44/Cf (pF) mV/MeV.
Noise
Input FET dependent. See Figure 2.
Noise slope
Input FET dependent. See Figure 2.
Data presented in Figure 2 is representative of results obtained
with recommended FETs, and is characteristic of the FET and
shaping time constants, rather than the A250, which is effectively noiseless. In general, the choice of input FET is based
on its noise voltage specification (ηV/√Hz) and its input capacitance (Ciss).
For low capacitance detectors, a FET with small Ciss should be
chosen, such as 2N4416 or 2SK152.
For very high capacitance detectors, two or more matched high
Ciss FETs such as the 2N6550 may be paralleled to achieve the
best noise performance.
Dynamic Input Ca- >40,000 pF with two 2SK147 FETs and
pacitance
Cf = 5 pF
Polarity
Negative or positive
Power Dissipation
14 mW + 6[Ids]
Variation of Sensitivity with Supply < 0.15%/V at ±6 V.
Voltage
Temperature Sta- < 0.1% from 0 to +100 °C < 0.5% from -55
bility
to +125 °C
Operating Temper-55 to +125 °C
ature
Storage Tempera-65 to + 150 °C
ture
Screening
Amptek High Reliability
Package
14 Pin hybrid DIP (metal)
Weight
3.8 g
Warranty
One year
Test Board
PC-250
Options
RC Feedback Kit (1 GΩ resistor, 0.1 pF capacitor)
Internal FET (consult factory)
NASA GSFC S-311-P-698 screening
Amptek High Reliability Screening
A250F with internal FET (SIP Package)
Other ConfiguraA250F/NF with external FET (SIP Packtions (Package)
age)
Pin Configuration (14 pin hybrid DIP)
Pin 1
300 MΩ resistor in parallel with 1 pF feedback capacitor. Connect this pin to the
detector and the gate of the FET.
Pin 2
2 pF feedback tap
Pin 3
4 pF feedback tap
Pin 4
-6 V direct
Pin 5
-6 V through 50 Ω
Pin 6
Compensation (0 - 30 pF to ground) for
low closed loop gain configuration
(where a large feedback capacitor is
used together with small detector capacitance).
Pin 7
Ground and case
> +2.8 V
Pin 8
Output through 100 Ω
Negative Clipping
< -4.6 V
Level
Pin 9
Output direct
Pin 10
+6 V through 50 Ω
GENERAL
Pin 11
+6 V direct
f > 300 MHz with 2N4416 FET
Gain-Bandwidth T
fT > 1.5 GHz with two 2SK147 FETs
Product
See Figure 7.
Pin 12
Ground and case
Pin 13
Provide 2.75 mA drain current to the external FET by connecting Pin 13 to 14.
(See operating current specifications.)
Pin 14
Input. Should be connected to the drain
of the FET. This pin is held internally at
+ 3 Volts.
OUTPUT CHARACTERISTICS
Polarity
Inverse of input
Rise Time
2.5 ns at 0 pF input load with 2SK152
4.5 ns at 100 pF input load with 2N6650
or 2SK152. See Figures 3 and 4.
Output Impedance Pin 8: 100 Ω; Pin 9: < 10 Ω.
Integral Nonlinear- < 0.03% for 0 to +2 V unloaded
ity
< 0.006% for 0 to -2 V unloaded
Decay Time Con- 300 MΩ x Cf = 300 µs, 900 µs, 1.5 ms,
stant
2.1 ms. User selectable T=Rf Cf
Positive
Level
Clipping
Operating Voltage
±6 V, (±8 V maximum)
Operating Current
±1.2 mA plus the FET drain current (Ids).
Where: Ids (mA) = 3/R (kΩ) - 0.25. As
a special case, the internal 1 K resistor
may be used for R, by connecting Pin 13
to 14, giving Ids = 2.75 mA.
A250 Specifications (con’t)
Figure 2: A250 Noise Characteristics
Figure 6: A250 Configured as a Low Noise Voltage Amplifier
+6V
VI
13 1K
FET
D INPUT
G
RI
20 μF
S
10
A250
14
9
1 300M
1pF
7,2
Vo
OUTPUT
5
-6V
RF
Typical RF = 1M, RI = 10K; GAIN: Vo = VI(RF/RI)
Noise as a function of detector capacitance, input FET, feedback capacitor, and shaping times
Figure 7: A250 Small Signal Phase & Amplitude vs. Frequency
Figure 3: A250 Rise Time
For low capacitance FET: 2N4416 (Ciss = 4 pF, Ids = 3 mA)
For high capacitance FET: 2 x 2SK147 (Ciss = 180 pF, Ids = 1.5 mA each)
Output rise time versus detector capacitance and FET
Figure 8: A250 Connection Diagram
R
Figure 4: A250 Output Response
11
12
EXTERNAL FET D
G S 14
INPUT
Output response with A250 configured as a charge sensitive
preamplifier; 2SK152/3mA, Rf = 300 MΩ, Cf = 1 pF, Cd = 0 pF
2
3
Figure 5: A250 Output Response
A250
OUTPUT
9
1K
300M
1
DETECTOR
50
0.047
13
+6V
10
Cf
8
100
1 pF
2 pF
50 0.047
4 pF
4
5
-6V
6
COMP.
7
Figure 9: A250 Mechanical dimensions.
0.100

0.500












0.870
Output response with A250 configured as a Transimpedance
Amplifier (current to voltage); 2N4416/3mA, Rf = 60 kΩ, Cf = 0 pF, Cd = 0 pF
0.185

14 8
1 7
TOP VIEW
0.300
0.250
0.018
(inches)
SIDE VIEW
A250 Applications
Figure 10: A Two Detector Telescope System.
A150
PULSE SHAPING
FET
A250
DETECTOR
A275
D400
QUAD
COUNTER
A150
A275
A150
A150
BLR1
COINCIDENCE LOGIC
OPTIONAL COOLING
A150
BASELINE RESTORER
FAST TIMING
A150
A150
A150
PULSE SHAPING
FET
A250
DETECTOR
A275
μP
D400
QUAD
COUNTER
A150
A275
OUTPUT DEVICE
A150
OPTIONAL COOLING
STACKED
DISCRIMINATORS
BLR1
BASELINE RESTORER
Figure 11: The A250 Connected to a Solid State Detector.
+HV
1 Meg
3 POLE SHAPING
100 nF
(HV)
44 mV/MeV
+6V (pole zero)
3 Meg
1
>100 Meg
13
13
14
14
A250
FET
10 nF
(HV)
7
10
10
9
-6V
+6V
12 1213131414+6V
2
100 pF
(NPO)
5
200 ns
1.5 V/MeV
440 mV/MeV
1
+
-
A275
7
1.07k
10
10
+6V
10
10
+6V
121213131414+6V
9
5
47 uH 866
1
9k
9
k
-6V
+
-
168 pF
(NPO)
1.1k
Solid State Detector
2
A275
7
10
10
5
1
8
9
2
9k
9k
-6V
Ref V1
1k
1.1k
12
12
7
8
BLR1
-6V
Figure 12: The A250 Connected to a Proportional Counter.
+
-
4
Active Baseline
Restoration
HV
1NF, HV
Optional Input
Protection
1M, HV
Proportional
Counter
300 Ohm
1NF, HV
1
13
14
FET
7
+
A150
Ref V2
8
9
6
-6V
Figure 13: The A250 Connected to a DP5/PX5 DPP & MCA.
+6V
10
9
A250
+6V
To other A150s,
ADC or MCA
+6V
1M, HV
-6V
5
9
9
6
10
10
2
6
8
5
1
+6V
A150
+
Detector
5
1
13
14
FET
10
A250
7
-6V
9
5
-6V
DP5
or PX5
Computer
Digital Pulse
Processor
and MCA
For more information, please see http://www.amptek.com
AMPTEK INC.
14 DeAngelo Drive, Bedford, MA 01730-2204 U.S.A.
Tel: +1 (781) 275-2242 Fax: +1 (781) 275-3470 e-mail: sales@amptek.com www.amptek.com