STATE-OF-THE-ART
| Features | Applications |
| ? Ultra low noise | ? Aerospace |
| ? Low power | ? Nuclear physics |
| ? Fast rise time (2.5 ns at 0 pF) | ? Portable instrumentation |
| ? External FET (allows selection or cooling) | ? Nuclear monitoring |
| ? Positive or negative signal processing | ? Particle, gamma, and x-ray imaging |
| ? Pin selectable gain | ? Medical and nuclear electronics |
| ? Small size (14 pin hybrid DIP) | ? Electro-optical systems |
| ? High reliability screening | |
| ? One year warranty | |
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
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 basedon 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 FETssuch asthe 2N6550 may be paralleled to achieve the best noise performance. | |
| Dynamic Input Capacitance | >40,000 pF with two 2SK147 FETs and Cf = 5 pF |
| Polarity | Negative or positive |
| OUTPUT CHARACTERISTICS | |
| Polarity | Inverse of input |
| Rise Time | 2.5 ns at 0 pF input load with 2SK1524.5 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 Nonlinearity | < 0.03% for 0 to +2 V unloaded < 0.006% for 0 to -2 V unloaded |
| Decay Time Constant | 300 MΩ x Cf = 300 μs, 900 μs, 1.5 ms,2.1 ms.User selectable T=Rf Cf |
| Positive Clipping Level | > +2.8 V |
| Negative Clipping Level | < -4.6 V |
| GENERAL | |
| Gain-Bandwidth Product | f T > 300 MHz with 2N4416 FET f T > 1.5 GHz with two 2SK147 FETs See Figure 7. |
| 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. |
| Power Dissipation | 14 mW + 6[Ids] |
| Variation of Sensitivity with SupplyVoltage | < 0.15%/V at ±6 V. |
| Temperature Stability | < 0.1% from 0 to +100 °C < 0.5% from -55 to +125 °C |
| Operating Temperature | -55 to +125 °C |
| Storage Temperature | -65 to + 150 °C |
| 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 |
| Other Configurations (Package) | A250F with internal FET (SIP Package) A250F/NF with external FET (SIP Package) |
| 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 ca pacitance). |
| Pin 7 | Ground and case |
| Pin 8 | Output through 100 Ω |
| Pin 9 | Output direct |
| Pin 10 | +6 V through 50 Ω |
| Pin 11 | +6 V direct |
| 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. |
Noise as a function of detector capacitance, input FET, feedback capacitor, and shaping times
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)
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