Introduction
ComTec GmbH
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1.
Introduction
FAST ComTec’s CSP10...13 is a single channel charge sensitive preamplifier module intended
for use with various types of radiation detectors including semiconductor detectors (e.g. Si, CdTe
and CZT), P-I-N photodiodes, avalanche photodiodes (APDs), and various gas-based detectors.
The CSP10...13 is one of a series of four charge sensitive preamplifiers offered by FAST
ComTec, which differ from each other most notably by their gain. A guide to selecting the best
charge sensitive preamplifier for your application can be found on the next page or at our web
site:
http://www.fastcomtec.com
. As with all FAST ComTec’s preamplifier modules, the
CSP10...13 is housed in a small shielded metal case with a D-sub 9 connector for power supply.
The FAST ComTec Model CSP10...13 Charge Sensitive Preamplifier is designed for optimum
performance with Silicon Surface Barrier (SSB) detectors. Operating as a charge to voltage
converter, the unit accepts charge carriers produced in the detector during each absorbed
nuclear event. The output then provides a voltage in direct proportion to the collected charge at
the rate of 1.4V per picocoulomb. This translates to a gain of 62mV per MeV (see table) for room
temperature silicon detectors.
For typical use with positively biased SSB detectors, the extremely linear energy output provides
a negative polarity pulse ideal for energy spectroscopy.
The high charge rate capability of the design is evidenced by an energy rate capacity of greater
than 10
5
MeV per second when used with silicon detectors. In order to take full advantage of such
a high count rate capabilty, a main amplifier with a correspondingly high count rate ability, such
as the FAST ComTec Model CSA4, should be used.
The basic operation of the preamplifier is indicated in the functional schematic diagram below.
The first stage acts as an operational integrator which produces an output potential proportional
to the accumulated charge on the feedback capacitor Cf. The integrator drives the output buffer
with a gain of +2.
The noise contribution of the preamplifier is only 1.7 KeV, FWHM, (Si) with an increase of less
than 34 eV for each picofarad of additional source capacitance. To reduce noise injected through
the HV input, a decoupling network is utilized for filtering the detector bias voltage.
To reduce the possibility of transmission line reflections when using long lengths of coaxial cable,
the energy output is provided with a series resistor, eliminating the necessity of terminating the
line at the receiving end.
For those applications utilizing lower voltage detectors with vacuum chamber feedthrough
connectors or direct detector cabling inside a chamber, the Model CSP10...13-1B provides a BNC
for the detector and HV bias input. Necessary power is provided by any FAST ComTec main
amplifier through the five foot compatible cable furnished with the preamp.
Tables to the CSP10...13
