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A206 Voltage Amplifier/Low Level Discriminator

Model A206 is a Voltage Amplifier/Low level Discriminator developed especially for instrumentation employing solid state detectors, proportional counters, photomultipliers or any charge producing detectors in the pulse height analysis or pulse counting mode of operation.


  • Small Size (16 Pin Dual In-Line Package) allows mounting close to the detector.
  • Power required is typically 12 mW.
  • Single power supply voltage.
  • Low noise.
  • Both Pulse Height Analysis and Pulse Counting mode of operation.
  • High Reliability.
  • One year warranty.


Typical Application


  • Specifications +

    Specifications (Vs = +15 V, T = +25 ºC)

    Voltage Amplifier

    Gain 10x nominal, non inverting
    Input polarity 1) Positive Unipolar; Dynamic range: 85% of Vs
    2) Bipolar; If a bipolar input is used, an external resistor (Rb = 330 K ) must be connected between Pin 3 and ground. Dynamic range: 65% of Vs
    Dynamic range 65% of Vs
    Ac Output Impedance 20 ohm
    Integral Nonlinearity at full output < 0.5%


    Input Polarity Positive or Bipolar
    Output pulse Positive; 5 µs wide; 90% of Vs.
    The output pulse width can be increased by the addition of an external capacitor (1 to 10 pF) between Pins 6 and 8.
    Rise time 20 ns
    Reference voltage Pin 11, Vr; Range: +4.5 to +5.5 VDC (impedance > 2 Mohm)
    Variable voltage Pin 10, Vv; (Vv < Vr)
    Discrimination Level Vr – Vv (impedance > 2 Mohm)


    Operating Voltage +10 to +18 VDC
    Operating Current 0.8 mA quiescent @ 15 V
    Temperature -55 to +70 ºC operational
    Package 16 Pin Dual In-Line (Metal)
    Screening Amptek High Reliability
    Mean Time Between Failure (MTBF) 1.6/106  hrs @ +60 °C
    Warranty One year

    Pin configuration

    Pin 1 Ground and Case
    Pin 2 No Connection
    Pin 3 Bipolar Input Bias
    Pin 4 Vs Amplifier (+10 V to +18 V)
    Pin 5 Vs Discriminator (+10 V to +18 V)
    Pin 6 Discriminator Pulse Width Adjust
    Pin 7 No Connection
    Pin 8 Discriminator Pulse Width Adjust
    Pin 9 Discriminator Output
    Pin 10 +Vv variable (Vv < Vr)
    Pin 11 +Vr reference (+4.5 to +5.5 VDC)
    Pin 12 Discriminator Input
    Pin 13 Amplifier Output
    Pin 14 No Connection
    Pin 15 No Connection
    Pin 16 Amplifier Input
  • Operating Notes +

    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.

  • Test Boards +

    PC236 Test Board for the A203 with the A206

    The PC236 is a printed circuit board designed to facilitate testing of the A203/A206 system. It provides the test circuit for the charge sensitive preamplifier, as well as the voltage references for the discriminator. All components are laid out on a ground plane in order to minimize noise and external pickup.

    PC236 Test Board Layout
    PC236 Test Board Schematic

    PC25 Test Board for use with the A206 and A225

    PC25 test board for the A225 with the A206. 2.625 in x 1.750 in (6.67 cm x 4.45 cm)

  • Typical Waveforms +

    THE A-203/A-206 Complete System and Typical Waveforms

    A203/A206 Complete System

    Horizontal Scale: 10 µs/div
    Vertical Scale: 10 mV/div
    Top Trace: Input to test capacitor -22mV = 1 MeV(Si)
    Bottom Trace: Output of CSP (A203, Pin 13)

    Horizontal Scale: 500 ns/div
    Top Trace: Unipolar output of SA (A203, Pin 8)
    Vertical Scale: 50 mV/div
    Bottom Trace: Bipolar output of SA (A203, Pin 9)
    Vertical Scale: 100 mV

    Horizontal Scale: 5 V
    Vertical Scale: 2 µs
    LLD Output-Positive (A206, Pin 9)

    The A225/A206 High Resolution System and Typical Waveforms

  • Mechanicals +

    A206 Mechanical Diagram

  • Documentation +