RAMP

A225

TEK

ULTRA LOW NOISE: <280 electrons RMS
Model A225 is a high performance thin film hybrid charge sensitive
preamplifier and shaping amplifier developed especially for highresolution systems employing solid state detectors, proportionalcounters, photomultiplier tubes and other charge producing detectors
in the pulse height analysis or A/D mode of operation.
While these units were specifically designed for satellite instrumentation, the following unique characteristics make them equally useful forspace, laboratory and commercial applications:Features

Applications• Operates from -55 to +125 ºC.
• Small size (14 pin hybrid DIP) allows
mounting close to the detector.
• Ultra low power (as low as 10 mW)• Wide range single supply voltage(+4 to +25 VDC)
• Pole-zero cancellation (internal)• Two outputs available (timing pulseand shaped unipolar)• High reliability screening• One year warranty• Aerospace• Portable instrumentation• Nuclear monitoring• Particle, x-ray, and gamma detection• Imaging• Research experiments• Medical and nuclear electronics• Electro-optical systems

TYPICAL APPLICATION
DiscriminatorandGating Logic

DETECTORA225

MultichannelAnalyzer
or ADC

Amptek High Reliability Screening••••••••••••

Precap Visual: MIL-STD-883, Method 2017, low magnification, high magnification
Sealing: Welded, Hermetic Seal
Stamping: Date Code and Serial Number
Stabilization Bake: MIL-STD-883, Method 1008, Condition C. +150 °C, 24 hours minimum
Temperature Cycle: MIL-STD-883, Method 1010, Condition C. Min. T=-65 °C to +150 °C, 10 minutes each extreme, 5 minutes maximum transfer time
Centrifuge: MIL-STD-883, Method 2001, condition B. YI axis; 10,000 G’s
Electrical Test: As per Specifications
Burn-In Test: MIL-STD-883, Method 1015, 160 hours at +125 °C
Fine Leak Test: MIL-STD-883, Method 1014, Condition A. Rejection if leak rate in excess of 5x10-7 cc/sec.
Gross Leak Test: MIL-STD-883, Method 1014, Condition C. Perflourocarbon
Electrical Test: As per Specification
External Visual: MIL-STD-883, Method 2009

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

SPECIFICATIONS(Vs = +5 V, T = 25 ºC, RLOAD = 10 K)

Input Characteristics
Sensitivity:

240 mV/Mev (Si)
300 mV/Mev (Ge)
195 mV/Mev (CdTe)
206 mV/Mev (HgI2)
5.2 V/pC
0.83 µV/electron

Noise:

2.5 keV FWHM (Si)
2.0 keV FWHM (Ge)
3.1 keV FWHM (CdTe)
2.9 keV FWHM (HgI2)
4.5 x 10-17 C rms
280 electrons rms

Noise Slope:

50 eV/pF (Si)40 eV/pF (Ge)62 eV/pF (CdTe)
58 eV/pF (HgI2)
9 x 10-19 C/pF
5.6 electrons/pF

Dynamic Input Capacitance: > 7,000 pF
Polarity:

Negative

Detector Capacitance:

Up to 1,000 pF

Output Characteristics
1) Shaping Amplifier (Pin 8)
Polarity:
Positive
Peaking Time:
2.4 µsIntegral Nonlinearity:< 0.04% for 0 to 10V
output pulse
Pole-Zero Compensation: Internal
Dynamic Range:(Vs - 1.25) Volt
DC Level:
0.8 V nominal
2) Timing Pulse (Pin 12)
Polarity:
Sensitivity:

Risetime:

Positive
44 mV/Mev (Si)
55 mV/Mev (Ge)
1.0 V/pC
18 ns (unloaded)

GeneralWeight:.14 oz, 4 g

Operating Voltage:

Vs = +4 to +25 VDC

Operating Current:

2.3 mA independent of Vs

Variation of Sensitivity
with Supply Voltage:< 0.07% /Volt, 4 to 10 Volts< 0.005% /Volt, 10 to 25 VoltsOPERATING NOTESGeneralDue to its hermetic seal and small size, the A225 is well suited for use inspace or within a vacuum chamber. In such applications care should betaken to avoid electrical discharge near the input which can damage theunit and VOID WARRANTY. Use care in soldering leads - avoid
overheating.
For laboratory usage, the A225 can be mounted on its PC-25 test
board (see below) and enclosed in a small metal box with appropriate
cable connectors. A high voltage coupling capacitor should be added at
the input as well as a small hole in the metal box in order to provide
screwdriver adjustment to the gain control potentiometer.

Package and Pin Configuration
0.100
0.500

141

87
0.870

0.185
0.300

0.250
0.018
(inches)TOP VIEW Input
SIDE VIEW
Pin 1
Pin 2, 9Case
Pin 3, 6, 7, 10, 13NC
Pin 4
Input GND and Case
Pin 5
Output GNDPin 8
OutputPin 11
Vs = +4 to +25 VDC
Pin 12
Timing Pulse
Pin 14Compensation (see notes)

Circuit Layout
Due to the high sensitivity and ultra low noise of the A225, care should
be taken in circuit layout. The PC-25 Test Board may be used as an
example of appropriate layout technique. In general, ground plane
construction is recommended. Input and output lines should be kept well
separated and in most cases shielding will be necessary.
Particular attention should be paid to the detector ground connection
to avoid oscillation due to feedback. The supply voltage is internallydecoupled. While this is normally adequate, in some applications
external bypassing may be helpful.
To facilitate noise minimization in certain applications, two separate
ground connections are provided. Pin 4 is the ground connection for theinput stage and is also connected to the case. Pin 5 is ground for theremainder of the circuit. In most applications Pin 4 and 5 may beconnected to the same ground (preferably a ground plane under the unit)
along with Pins 2,3,6,7,9,10 and 13.
The A225 may also be used in applications where the input from thedetector is positive by connecting Pin 5 (output ground) to a negative
supply voltage instead of ground. This voltage can range from 0 to -10 V.
A negative output pulse at Pin 8 will result from a positive input. The
dynamic range in this case will be approximately 0.5 Volts greater thanPin 5. For example, with Pin 5 operated at -5 Volts, negative pulses of up
to 5.5 Volts amplitude can be obtained. This mode of operation will
result in increased operating current. The A225 is not specified in thismode and critical parameters should be verified by the user.

Temperature:-55 to +125 ºC Operational

Temperature Stability:

0.02% / ºC at 25 ºC typical±2% from -25 to +75 ºC

Screening:

Amptek High Reliability

Power Supply

Package:

14 pin hybrid DIP (metal)

Radiation Resistance:

100k rad(Si)Warranty:

One year

While specifications are given for operation at +5 V, the characteristics of
the A225 are relatively unaffected by changes in supply voltage from +4
to +25 VDC. Parameters critical to a particular application should bechecked at the actual operating voltage.

Test Board:

PC-25

For more information visit www.amptek.com

OPERATING NOTES (Continued)
Input
In order to minimize noise, the A225 input (Pin 1) has nointernal protection. External protection may be added to Pin 1
by connecting two back-to-back diodes to ground.
Typical Protective Circuit
C (HV)
DETECTOR

1

A225

NOTE: The input protection circuit provides a limited amountof protection against transients generated in the detector and bias
network. Any circuit capable of providing absolute protection
would cause intolerable degradation of noise performance. For
this reason, care must be exercised in the use of any preamp withhigh voltage detectors. Specifically, damage may result fromdetector breakdown, breakdown of the high voltage coupling
capacitor or other component, excessively rapid rise or fall ofdetector bias voltage, or the addition of uncharged capacitanceacross the input with bias voltage applied.
In some applications, increased protection will justify anincreased noise level. In this case, a resistor may be added inseries with the input - normally a few hundred ohm will suffice.
Outputs
Pin 8
The shaping amplifier of the A225 produces a unipolar pulse atPin 8 suitable for high resolution, high rate pulse height analysis.
This output has an AC impedance of approximately 30 Ω andwill drive 1 kΩ loads as well as several feet of unterminatedcable. In applications requiring highest linearity, load resistanceshould be greater than 5 kΩ. This output has a quiescent D.C.
output level, or Baseline, of approximately 0.8 V. In mostapplications the pulse should be capacitively coupled to external
circuitry.
Pin 12The output at Pin 12 is a timing pulse with an unloaded risetimeof approximately 20 ns and a falltime of 2.8 µs capable ofdriving a load of 500 Ω. This output has approximately the same
linearity characteristics as the shaped output at Pin 8. Grounding this pin could damage the unit.
Bipolar Pulse
In applications requiring a bipolar pulse, the unipolar output canbe differentiated with an RC differentiator. The time constantshould be approximately 1.8 µs, suggested values are: C = 1 nF,
R = 1.8 kΩ. In most cases this pulse should be buffered in orderto drive subsequent circuitry.
Test Circuit
The A225 can be tested with a pulser by using a small capacitor(usually 1 to 2 pF) to inject a test charge into the input. The unit
will respond to the negative-going edge of the test pulse, whichshould have a transition time of less than 20 ns. This negative
going edge should be followed by a relatively flat part of thewaveform so that it appears as a step function.
For example, a square wave is a good test waveform. (Keepthe square wave frequency low enough that the response to thepositive-going edge can be ignored.) Alternately, a “sawtooth”
waveform or a tail pulse with long fall time (> 100 µs) may beused. Charge transfer to the input is according to Q = Ct·V,
where Q = total charge, Ct = value of test capacitor, and V =amplitude of voltage step. DO NOT connect the test pulser tothe input directly or through a large capacitor (> 100 pF) as thiscan produce a large current in the input FET and cause irreversible damage.
Typical Test Circuit+5 V

Fast RisePulser

Ct2 pF50 Ω

111A225

8Scope2, 3, 4, 5, 6,7, 9, 10, 13

Negative going pulse
Rise Time < 20 ns, fall time > 10 µs, or square wave.
Amplitude: 22 mV = 1 MeV (Si)
1 MeV (Si) = (1 x 106 eV x 1.6 x 10-19 C / 3.6 V = 0.044 x 10-12 C
V = Q / Ct = (0.044 x 10-12 C) / (2 x 10-12 F) = 22 mV
Hence, a 22 mV step into 2 pF test capacitor will simulate thecharge of a 1 MeV energy deposition into a silicon detector.

CompensationThe A225 is internally optimized for detector capacitance up toapproximately 50 pF. In applications with large detector
capacitance and requiring short timing pulse risetime, a compensation capacitor from 0 to 250 pF may be connected from Pin 14to ground. The exact value should be experimentally determinedwith the detector connected to the input. Note that this compensation will not normally be necessary if the timing pulse is not
used, or its risetime is not critical.

PC-25 TEST BOARD for the A225/A206

The PC-25 is a printed circuit board which accepts theA225 charge sensitive preamplifier and shaping amplifier
and the A206 voltage amplifier and discriminator. It is
designed to be used for two purposes: to facilitate testing ofthese devices, together or separately, and to simplify theiruse in many applications. The board provides input test
circuitry, gain adjustment, voltatge reference to the A206,
and convenient access to all active device pins. Groundplane construction minimizes noise pickup.

For more information visit www.amptek.com

APPLICATION NOTESThe A225/A206 Complete High Resolution System and Typical Waveforms
10 nF(HV)

1Detector Input

Ct2 pF

Vs = +4 V to +15 V

Vs = +15 V Vr

114, 58

A225
4, 51610k12

Gain Adjust

Timing Pulse

TestVv

1110A206

91312Low Level
Discriminator

Discriminator andGating Logic

Upper:
A225, Pin 8(Vertical: 50 mV/div;
Horizontal: 2 μs/div)

CounterPulse
Counting
Mode

Multichannel
Analyzeror ADC

Pulse
HeightAnalysis

Upper:
Amplifier Output
A206, Pin 13(Vertical: 500 mV/div;
Horizontal: 2 μs/div)

Lower:
A225, Pin 12(Vertical: 20 mV/div;
Horizontal: 2 μs/div)Lower:
Discriminator Output
A206, Pin 9(Vertical: 5 V/div;Horizontal: 2 μs/div)

Connection of the A225 to a Solid State Detector+HV Bias

1M.01 μF

Vs = +5 V

10 M

111

S.S. Detector

8A225

10 nF(HV)4, 5

12

To Pulse Height
Analysis or A/DTiming Pulse

Connection of the A225 to a Proportional Counter+HV Bias

1M.01 μF

Vs = +5 V

1M

111

Proportional Counter

8A225

10 nF(HV)4, 512

To Pulse Height
Analysis or A/DTiming Pulse

A225F
The A225F is a high density version of the Amptek A225 and features a Single
In-line Package (SIP).
Please visit our web site at www.amptek.com for complete details.

AMPTEK INC.

RAMP

TEK

Tel: +1 (781) 275-2242

14 DeAngelo Drive, Bedford, MA 01730-2204 U.S.A.
Fax: +1 (781) 275-3470 e-mail: sales@amptek.com

www.amptek.com