The A111F is a high density version of the Amptek A111 Charge Sensitive Preamplifier and Discriminator. The A111F features a Single In-line Package (SIP).
A111F THRESHOLD ADJUSTMENT
A) Increasing the Threshold of the A111F:
Increasing the threshold of the A111F beyond the x10 provided by shorting out Pins 3 & 4 can be achieved by an RC feedback as shown below.
Apart from unit to unit variation, the discrimination levels will be as follows:
1) Shorting out Pins 3 and 4 will result in x10 increase of nominal threshold: (5 x 104 electrons) x 10 = 5 x 105 electrons.
2) Shorting out Pins 3 and 4 plus feedback:
R = 50 k C = 2.2 pF : x 17
R = 20 k C = 3.3 pF : x 23
R = 5 k C = 4.7 pF : x 40
R = 2 k C = 6.8 pF : x 88
Intermediate values can be obtained by adjusting the value of R.
B) Decreasing the Threshold of A111F:
Decreasing the threshold of the A111F beyond the nominal 5 x 104 electrons can be achieved by
adding a resistor from Pin 4 to ground. A 300 ohm resistor will approximately double the sensitivity
resulting in a threshold of 2.5 x 104 electrons.