Signal processing Preamplifier

In general the premultiplexing function of the CID readout is very attractive in that it physically separates the detection and signal processing functions and allows a preamplifier to be introduced before input to the CCD. With the CID, the signal processing function has no chip area constraint and noise problems associated with direct injection are avoided. However the CID approach requires more preamplifier gain and power dissipation than those approaches which introduce TDI before preamplification. 

Analog electronics. The number of electron-hole pairs produced in the absorption of gamma photons is in the order of hundred thousands. The induced extremely low current has to be amplified before further signal processing. There are two types of preamplifiers ... 

Figure Bl.10.2. Schematic diagram of a counting experiment. The detector intercepts signals from the source. The output of the detector is amplified by a preamplifier and then shaped and amplified friitlier by an amplifier. The discriminator has variable lower and upper level tliresholds. If a signal from the amplifier exceeds tlie lower tlireshold while remaming below the upper tlireshold, a pulse is produced that can be registered by a preprogrammed counter. The contents of the counter can be periodically transferred to an online storage device for fiirther processing and analysis. The pulse shapes produced by each of the devices are shown schematically above tlieni.

A linear amplifier is required to process the output signals from the preamplifier. 

Dead time, or resolving time, of a counting system is defined as the minimum time that can elapse between the arrival of two successive particles at the detector and the recording of two distinct pulses. The components of dead time consist of the time it takes for the formation of the pulse in the detector itself and for the processing of the detector signal through the preamplifier-amplifi-er-discriminator-scaler (or preamplifier-amplifier-MCA). With modern electronics, the longest component of dead time is that of the detector, and for this... 

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