Pyramid CR10 User Manual page 22

PSI System Controls and Diagnostics
The shaping amplifier is a Cremat CR-200 module with one of a choice of time constants
between 100 nsec and 4 µsec. Generally, a longer time constant gives better signal to noise ratio
at the expense of degraded count rate capability. The full width half maximum of the Gaussian
output pulses is 2.35 times the shaping time. The pole-zero adjustment compensates the pole in
the response caused by the charge sensitive preamplifier feedback resistor. It is adjusted during
manufacturing test to give a clean, symmetric pulse shape.
The optional CR-210 baseline restoration module prevents downward shift of the DC baseline at
high count rates. It requires the shaped pulses to have positive polarity. If it is not fitted, a
jumper passes the signal to the output stage.
Since the charge-sensitive pre-amplifier stage is inverting, a negative incoming charge pulse will
give a positive output, and no further inversion is required to give a positive final pulse. If the
incoming charge pulse is positive, then the inverting stage of the intermediate amplifier should be
enabled by fitting the POL jumper to give positive output pulses.
The final output stage is a unity gain line driver with 47 ohm series output impedance. A trimpot
allows residual DC offset in the output to be removed.
Incoming +/-12 V power is filtered and Zener diodes with transistor regulators produce the
additional +/- 6.8 V and +/- 6.1 V rails required. A LED confirms that the +12 V supply is
present.
CR10 User Manual CR10_UM_180115 Page 22 of 40