Operating Notes
The A206 has two parts:
1) A matching Voltage Amplifier (VA) to the A203 or A225
2) A Lower Level Discriminator (LLD)
The output of the VA is NOT internally connected to the LLD. Pin 13 MUST be connected to Pin 12 if the LLD is to be used.
Power to the VA and LLD is provided separately in order to provide maximum flexibility for independent operation. However, for normal operation Pins 4 and 5 should be connected to Vs.
The VA has an internal input coupling capacitor and no other external capacitor is needed when connecting to either unipolar or bipolar outputs of the A203 or the A225.
If the output of the VA (Pin 13) is to be connected to external circuitry it MUST be coupled with an external capacitor. This output can drive several feet of unterminated coaxial cable.
For bipolar input pulses to the VA connect a 330 kohm resistor from Pin 3 to ground. This biases the amplifier for maximum dynamic range.
The LLD requires a reference voltage Vr and a variable voltage Vv. Set Vr at a level between +4.5 and +5.5 Volts and Vv to a lower voltage than Vr. The Difference, Vr-Vv, is the discrimination level at which the unit will trigger. For example, if Vr = +5 V and Vv = +3.5 V, any pulse of amplitude greater than +1.5 V will trigger the discriminator.
The LLD output pulse is typically a 5 µs wide positive pulse. A wider pulse can be obtained by connecting a capacitor (1 to 10 pF) between Pins 6 and 8. Leave these Pins unconnected if the standard pulse width is acceptable.
A typical circuit to provide bias to the LLD is shown below.
A temperature stable voltage reference should be used.