Gain Stage Stabilizer
A dc stabilizer (schematic sheet 2) is provided around the gain stage amplifiers to
maintain the dc output at gain AMP 4 near zero volts over a wide range of tempera-
tures and count rates. Transconductance amplifier A23 monitors the output of gain
AMP 4 with respect to zero volts and generates a correction voltage that is summed in
at the input of gain AMP 2. The stabilization loop time constant is determined by the
transconductance current programming resistors R14 and R276 and capacitors C2 and
C26 resulting in a time constant sufficiently long so as not to have an effect on the
overall amplifier shaping transfer function.
Active Filters
Three active filter stages, A4, A5 and A6 (schematic sheet 4), produce complex pole
pairs providing a near Gaussian pulse shape and a sharp cutoff frequency characteristic
for optimal signal to noise ratio. The filter time constant is selected by the shaping
switch and associated resistors and capacitors. The output signal from the third inte-
grator is normally negative and drives the unipolar output amplifier.
Unipolar Output
The signal provided by the third complex pole integrator drives the unipolar output
amplifier (schematic sheet 5) and associated driver, A8 and transistors Q21, Q22 and
Q31. The unipolar output amplifier includes a single pole filter provided by feedback
resistor R163 and capacitors C81 through C86; the time constant is selected by the
shaping switch. For Gaussian shaping the unipolar output provides a semi-Gaussian
pulse shape. However, if the triangular shaping is selected, relays K2 and K3 are acti-
vated which allow the signals from complex pole integrators A4, A5, and A6 to be
summed at the input of the unipolar output amplifier, in the correct proportion, produc-
ing a semi-triangular output signal.
Baseline Restorer
The baseline restorer (schematic sheet 5) maintains the unipolar output signal baseline
at ground reference, with precision, over a wide range of count rates.
Transconductance amplifier A10 monitors the unipolar output signal and develops a
correction voltage, having the correct amplitude and polarity, which is summed at the
input of the unipolar output amplifier to reference the unipolar output signal baseline
at zero volts. The baseline restorer is gated and operates only in the absence of or in
between output pulses providing superior baseline control over a very wide range of
count rates.
Restorer symmetry is selectable is selectable by ASYM/STM jumper plug W7. For the
symmetrical restorer mode, positive and negative restoration slew rates are equal.
When the asymmetrical is selected, the negative restorer slew rate is reduced substan-
tially providing a softer restorer response for positive output signals
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Circuit Description
