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A203 Charge Sensitive Preamplifier & Shaping Amplifier

Model A203 is a Charge Sensitive Preamplifier/Shaping Amplifier 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 18 mW.
  • Single power supply voltage.
  • Low noise.
  • Pole-zero cancellation (external).
  • Unipolar and bipolar output.
  • High Reliability.
  • One year warranty.

Typical Application
  • Specifications +

    Input Characteristics


    For positive unipolar output (Pin 8) 210 mV/MeV (Si);
    262 mV/MeV (Ge);
    4.8 x 1012 V/coulomb;
    0.76 µV/electron
    For bipolar output (Pin 9) 115 mV/MeV (Si);
    144 mV/MeV (Ge);
    2.6 x 1012 V/coulomb;
    0.42 µV/electron.

    Noise (nominal)

    Unipolar 8 KeV FWHM (Si);
    6.4 KeV FWHM(Ge);
    1.4 x 10-16 coulomb rms;
    875 electrons rms
    Bipolar 12 KeV FWHM (Si);
    10 KeV FWHM (Ge);
    2.2 x 10-16 coulomb rms
    Noise Slope (typical) 100 eV/pF (Si);
    80 eV/pF (Ge);
    1.81 x 10-18 coulombs/pF
    Dynamic Input Capacitance 3,500 pF
    Polarity Negative
    Protection Back-to-back diodes to ground

    Output Characteristics

    Charge Sensitive Preamplifier Output – Pin 13:

    Rise time 50 ns
    Fall time 30 µs
    AC Output impedance 50 ohm

    Shaping Amplifier

    Time constants 250 ns
    Positive Unipolar, Pin 8 AC output impedance: 85 ohm
    Dynamic range: 75% of Vs
    Pole-zero cancellation: External 1 Mohm between Pins 12 and 13
    Bipolar, Pin 9 AC output impedance: 2 kohm
    Dynamic range: 35% of Vs


    Operating Voltage +10 to +18 VDC
    Operating Current 1.4 mA quiescent @ 15 V
    Temperature -55 ºC 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 Charge Sensitive Preamplifier Input
    Pin 2 No connection
    Pin 3 No connection
    Pin 4 Ground and case
    Pin 5 Ground and case
    Pin 6 No connection
    Pin 7 No connection
    Pin 8 Unipolar shaping Amplifier Output
    Pin 9 Bipolar Shaping Amplifier Output
    Pin 10 No connection
    Pin 11 Vs Shaping Amplifier (+10 V to +18 V)
    Pin 12 Shaping Amplifier Input
    Pin 13 Charge Sensitive Preamplifier Output
    Pin 14 Vs C.S. Preamplifier (+10 V to +18 V)
    Pin 15 No connection
    Pin 16 No connection
  • Operating Notes +

    Operating Notes

    The A203 has two parts:
    1) A Charge Sensitive Preamplifier (CSP)
    2) A Shaping Amplifier (SA).

    The output of the CSP is internally connected to the input of the SA.

    Power to the CSP and SA are provided separately in order to provide maximum flexibility for independent operation. However, for normal operation Pin 11 and Pin 14 should be connected to Vs. Supply is internally bypassed. Care should be taken in circuit layout and in some applications power supply decoupling may be helpful. If the leads of the A203 are left long or the unit is socketed, the unconnected Pins 2, 3, 6, 7, 10, 15, and 16 should be grounded in order to minimize pick-up.

    The sensitivity of the CSP is defined by: G = 44/C in mV/MeV (Si), where C is the feedback capacitor (in pF). The feedback capacitor in the A203 is 2 pF. If a lower sensitivity is desired, an external capacitor may be added between Pins 1 and 13. A capacitor with good temperature stability should be used and the leads should be kept short.

    The detector must be capacitively coupled to Pin 1 with a capacitor of adequate voltage rating.

    If the output of the CSP (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.

    The SA has two outputs: 1) Unipolar (Pin 8) which is single integration – single differentiation. 2) Bipolar (Pin 9) which is single integration – double differentiation. Either output can drive the A206, which has an input coupling capacitor. If the unipolar output (Pin 8) is to be connected to other external circuitry it MUST be capacitively coupled.

    If pole-zero cancellation is required at the unipolar output in order to minimize the baseline shift, a 1 Mohm resistor must be externally added between Pins 12 and 13.

    The A203 can be tested with a pulser by using a small capacitor to inject a negative test charge into the input. The unit will respond to the negative-going edge of either a square wave or a tail pulse with long fall time (> 10 µs). In either case the negative-going transition should be less than 20 ns. Charge transfer in the circuit is according to Q = C·V, where Q = total amount of charge delivered to input, C = test capacitor and V = amplitude of the pulse. Use only a small capacitor in this circuit (1 to 10 pF). DO NOT connect a low impedance pulser through a large capacitor when testing as this will overdrive the input and may damage the unit. Example: A 22 mV tail pulse across a 2 pF test capacitor is equivalent to 1 MeV energy loss in silicon (3.5 eV/pair) and will produce a 210 mV unipolar pulse at Pin 8.

    Test Circuit

    Negative going pulse
    Rise Time < 20 ns, fall time > 10 µs, or square wave
    Amplitude: 22 mV = 1 MeV (Si)

    EXAMPLE: To simulate 1 MeV in silicon detector:

    1 MeV (Si) = 0.044 pC
    Ct = 2 pF
    V = Q / Ct = 0.044 pC / 2 pF = 22 mV
    i.e. a 22 mV step into 2 pF test capacitor simulates 1 MeV in silicon.

  • PC236 Test Board +

    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
  • 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)

  • Applications +




  • Mechanicals +

     A203 Mechanical Diagram

  • Documentation +