A101 Charge Sensitive Preamplifier & Discriminator
Model A101 is a hybrid charge sensitive preamplifier, discriminator, and pulse shaper developed especially for instrumentation employing photomultiplier tubes, channel electron multipliers and other low capacitance charge producing detectors in the pulse counting mode. The A101 is widely used in laboratory and commercial applications for mass spectrometers, laboratory and research experiments, aerospace instrumentation, medical electronics, and electro-optical systems.
Product Details
- Small size (TO-8 package) allows mounting close to collector of multiplier.
- Power required is typically 15 mW.
- Single power supply voltage.
- Outputs interface directly with CMOS and TTL logic.
- Input threshold is externally adjustable.
- Output pulse width is variable with external trim capacitor.
- High reliability process.
- One year warranty.
Input Characteristics
Test Conditions: Vs = +5 V, T = +25 °C
| Threshold | Model A101 has a nominal threshold referred to the input of 1.6 x 10-13 coulomb. This is equivalent to 106 electrons. The threshold can be increased by the addition of a resistor between Pins 9 and 12. See Figure 1, “Input threshold as a function of external resistance” in Operating Notes. |
| Stability | < 1.5% of threshold, 0 to +50 ºC. See Figure 3, “Threshold vs. Temperature” in Operating Notes. |
| Noise | RMS noise level < 0.4% of threshold. |
| Protection | Back-to-back diodes to ground. |
| Detector Capacitance | 0 to 60 pF |
Output Characteristics
1) Pin 5 provides a positive 5 volts output pulse capable of interfacing directly with CMOS.
2) Pin 6 is an open collector output and with an external pullup resistor provides a negative going pulse (the complement of Pin 5). This output can drive TTL and can be wire-ored with other units. Pullup resistor may be connected to Vs or to other positive supply up to +15 V.
Pulse Characteristics
| Risetime | 6 ns |
| Falltime | 20 ns |
| Width | 220 ns nominal. May be increased to greater than 1 µs by the addition of a capacitor between Pins 3 and 4. See Figure 2, “A101 pulse width as a function of detector capacitance” in Operating Notes. |
| Amplitude | 5 volts |
General
| Count Rate | 4 x 106 CPS, Periodic |
| Pulse Pair Resolution | 250 ns |
| Operating Voltage | +4 to +10 VDC |
| Operating Current | 3 mA quiescent, 4 mA @ 105 CPS |
| Temperature | -55 to +70 ºC operational |
| Warranty | One year |
| Package | 12-Pin, TO-8 case. |
| Screening | Amptek High Reliability |
| Mean Time Between Failure (MTBF) | 0.4/106 hrs @ +125 °C |
| Test Board | PC-11 |
Vacuum
Due to its hermetic seal and small size, the A101 is well suited for use within a vacuum chamber. In such applications the mounting should provide adequate heat dissipation and care should be taken to avoid electrical discharge near the input, which can damage the unit and void the warranty.
Use care in soldering leads – avoid overheating.
Pin Assignments
| Pin 1 | Ground |
| Pin 2 | Vs (+4 to +10 VDC) |
| Pin 3 | Pulse Width Adjust |
| Pin 4 | Pulse Width Adjust |
| Pin 5 | Positive Output |
| Pin 6 | Open Collector Output |
| Pin 7 | No Connection |
| Pin 8 | No Connection |
| Pin 9 | Threshold Adjust |
| Pin 10 | No Connection |
| Pin 11 | No Connection |
| Pin 12 | Input |
Power Requirements
All device specifications apply to operations at +5 V. The unit can be operated up to +10 V with increased power dissipation and threshold. Supply is internally bypassed. Care should be taken in the circuit layout and in some applications power supply decoupling may be helpful.
The case is internally connected to Pin 1, ground.
Input
The detector is normally capacitively coupled to Pin 12 with a capacitor of adequate voltage rating. Alternately, the detector anode can be direct coupled to the input if the cathode is at negative potential. The A101 is sensitive to a negative charge pulse of at least 0.16 picocoulomb. This threshold may be increased by the connection of a resistor between Pins 9 and 12. Approximate values are given in Figure 1, “Input threshold as a function of external resistance” above.
The A101 can be tested with a pulser by using a small 2 pF test capacitor to inject a test charge into the input. The unit will trigger on the negative-going edge of the pulse which should have a much longer fall time (> 1 µs) or a square wave may be used. (If a square wave is used, triggering on the positive-going edge will occur for large pulses.)
Charge transfer in the test circuit is according to Q = C · V where Q = total amount charge, C = capacitance, and V = voltage. Use only a small capacitor in this circuit (1 to 10 pF). DO NOT connect a low impedance pulser through 500 pF when testing as this will produce a large pulse through the input transistor and may cause irreversible damage.
Outputs
The output at Pin 5 is a positive, 220 ns wide pulse.
Pin 6 is an open collector output and should be left unconnected if not used. A negative going output can be obtained by connecting a pullup resistor (typically 1 kohm) between Vs and Pin 6. The pullup resistor may be tied to any positive voltage up to 15 V (as required for example, in interfacing with particular logic families.) In multi-detector systems, where more than one preamp drives the same counter, the open collector outputs of several A101s can be connected together to the counter input with a single pullup resistor. DO NOT CONNECT THIS PIN DIRECTLY TO Vs (PIN 2) AS THIS MAY DAMAGE OUTPUT STAGE AND VOID WARRANTY.
The output pulse can be increased by the connection of a capacitor between Pins 3 and 4. See Figure 2, “A101 pulse width as a function of detector capacitance” below for typical values.
Line Driver for A101
The PC-11 is a printed circuit board designed to facilitate testing of the A101. In addition to testing circuitry, it provides component locations for use with detectors. Ground plane construction minimizes external pick-up.
Inputs
| IN | Detector Input; Pin 12; should be AC coupled with a high voltage capacitor (500-1000pF) |
| DET | Provides post to connect the detector and input capacitor |
| TEST IN | Input to test circuit as described in specifications |
| Vs | Pin 2; supply voltage (+4 to +10 VDC) |
| H.V. | Provides post to connect the detector to the high voltage supply through a resistor |
Outputs
| +OUT | Positive, TTL type output from Pin 5 |
| O.C. OUT | Negative; open collector output from Pin 6 (must be connected through 1 kohm to Vs) |
| BUF OUT | Positive output through a Buffer/Line Driver IC from Pin 5 |
Components
| Cv | Filter capacitor (1uF) |
| Rp | Pullup resistor (1 kohm) |
| C | Test capacitor (2 pF) |
| R | Test pulse termination resistor (50 ohm) |
| Rt | Threshold adjust resistor |
| Cw | Pulse width adjustment capacitor |
| Cd | High voltage detector coupling capacitor (user supplied) |
| Rb | Detector Bias resistor (user supplied) |
| U2 | Line driver TPS2829 |
Connection of a photomultiplier tube to the A101 Using + High Voltage
Connection of a Channel Electron Multiplier to the A101
Connection of a photomultiplier tube to the A101 Using – High Voltage
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