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
Figure 1. Input threshold as a function of external resistance.
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.
A101 test circuit
Tr < 20 ns, Tf > 1 µs
Negative going
Amplitude: 0.25 V = 0.5 picocoulomb
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.
Figure 2. A101 pulse width as a function of external capacitance
If the standard pulse width is adequate Pins 3 and 4 must be left unconnected.
Figure 3. Threshold vs. Temperature
Line Driver for A101
Line driver for the A101