Preamplifier - A250

This preamp is from Amptek Inc at a price of $475.

It has been designed for multidetector satellite instrumentation, which obviously makes it an ideal choice for CubeSat.

Main features

  • Ultra low noise
  • Low power
  • Fast rise time (4nS at 0pF)
  • External FET
  • Positive or negative signal processing
  • Pin selectable gain
  • Small size (14 pin hybrid DIP)
  • There’s a one year warranty also included, which is nice!

The preamp has been designed alongside the A275 shaping amplifier (which we are also using) also made by Amptek. Since the two components are made by the same manufacturer, they should communicate well.


(Supply voltage = ± 6V, Temperature = 25°C) unloaded output

Input characteristics

Sensitivity (Cf = 1pF) Dynamic input capacitance Polarity
44 mV/MeV (Si)
55 mV/MeV (Ge)
36 mV/MeV (CdTe)
38 mV/MeV (HgI2)
0.16 μV/electron
Sensitivity can be reduced by connecting PINS 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.
> 40,000 pF with 2X2SK147 FETS and Cf = 5pF Negative or positive

Output characteristics

Polarity Rise Time Output Impedance Integral Nonlinearity Decay Time Constant Positive Clipping Level Negative clipping level
Inverse of input 3.8nS at 0pF input load with 2SK152
4.5nS at 100pF input load with 2N6550 or 2SK152
100Ω < .03% for 0 to + 2V unloaded
< .006% for 0 to -2V unloaded
300 MΩ XCf = 300μS, 900μS, 1.5mS, 2.1mS > +2.8V < –4.6V


Gain-bandwidth product Operating voltage Operating current Power dissipation Variation of sensitivity with supply voltage Temperature stability Operating temperature Storage temperature
fT>300 MHz with 2N4416 FET
fT>1.5 GHz with two 2SK147 FETs
± 6V (± 8V maximum) ± 1.2 mA plus the FET drain current (IDS)
IDS (mA) = 3/R(kΩ) –0.25.
As a special case, the internal 1K resistor may be used for R,
by connecting Pin 13 to 14, giving IDS = 2.75 mA.
14mW + 6[IDS] < .15%/V at ± 6V < .1% from 0° to + 100°C
< .5% from –55°C to + 125°C
–55°C to + 125°C –65°C to + 150°
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