External protection may be added to pin 1 by

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Unformatted text preview: e noise, the A225 input (Pin 1) has no internal protection. External protection may be added to Pin 1 by connecting two back-to-back diodes to ground. Typical Protective Circuit C (HV) DETECTOR 1 A225 NOTE: The input protection circuit provides a limited amount of protection against transients generated in the detector and bias network. Any circuit capable of providing absolute protection would cause intolerable degradation of noise performance. For this reason, care must be exercised in the use of any preamp with high voltage detectors. Specifically, damage may result from detector breakdown, breakdown of the high voltage coupling capacitor or other component, excessively rapid rise or fall of detector bias voltage, or the addition of uncharged capacitance across the input with bias voltage applied. In some applications, increased protection will justify an increased noise level. In this case, a resistor may be added in series with the input - normally a few hundred ohm will suffice. Outputs Pin 8 The shaping amplifier of the A225 produces a unipolar pulse at Pin 8 suitable for high resolution, high rate pulse height analysis. This output has an AC impedance of approximately 30 Ω and will drive 1 kΩ loads as well as several feet of unterminated cable. In applications requiring highest linearity, load resistance should be greater than 5 kΩ. This output has a quiescent D.C. output level, or Baseline, of approximately 0.8 V. In most applications the pulse should be capacitively coupled to external circuitry. Pin 12 The output at Pin 12 is a timing pulse with an unloaded risetime of approximately 20 ns and a falltime of 2.8 µs capable of driving a load of 500 Ω. This output has approximately the same linearity characteristics as the shaped output at Pin 8. Grounding this pin could damage the unit. Bipolar Pulse In applications requiring a bipolar pulse, the unipolar output can be differentiated with an RC differentiator. The time constant should be approximately 1.8 µs, suggested values are: C = 1 nF, R = 1.8 kΩ. In most cases this pulse should be buffered in order to drive subsequent circuitry. Test Circuit The A225 can be tested with a pulser by using a s...
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This note was uploaded on 01/15/2012 for the course AAE 490 taught by Professor Andrisani during the Fall '09 term at Purdue.

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