P.F. Manfredi

A time-over-threshold machine: the readout integrated circuit for the BABAR Silicon Vertex Tracker

A low-noise, mixed-signal, 128-channel CMOS integrated circuit containing the complete readout electronics for the BABAR Silicon Vertex Tracker has been developed. The outstanding feature of the present implementation is the ability to perform simultaneously low-level signal acquisition, derandomizing data storage, sparsification and data transmission on a single monolithic chip. The signals from the detector strips are amplified, shaped by a CR-RC/sup 2/ filter with digitally selectable peaking time of 100 ns, 200 ns, 300 ns, or 400 ns, and then presented to a time-over-threshold processor to implement a compression type analog-to-digital conversion. The digital information is stored, sparsified and read out through a serial link upon receipt of a command. The digital section operates from a 60 MHz incoming clock. Noise measurements at 200 ns peaking time and 3.5 mW total power dissipation per channel yield an equivalent noise charge of 600 el. rms at 12 pF added source capacitance. The chip measures 5.7 mm/spl times/8.3 mm and contains 330 k transistors. The first full-scale prototype was fabricated in a radiation soft 0.8 /spl mu/m, 3-metal CMOS process. The same circuit is now being fabricated in an analogous radiation hard technology.

Status of the KEDR detector

Abstract KEDR is a general-purpose detector for experiments at the VEPP-4M e + e − -collider in the energy range 2 E =2.0– 12 GeV . All detector subsystems (except the aerogel Cherenkov counters) have been installed into the detector at VEPP-4M. Some preliminary data have been taken in the energy region of the J/Ψ meson. The tuning of the detector and the VEPP-4M collider is in progress. Preliminary results on the detector performance are presented. The future experimental program for the KEDR detector is discussed.

Noise limits in a front-end system based on time-over-threshold signal processing

Abstract An analog signal processor based on the Time-over-Threshold (ToT) range compression is employed in the front-end section of the readout chip of the microstrip vertex detector for the BaBar experiment. The paper, after describing the circuit solutions that have been adopted to optimize the ToT operation, focuses on the noise aspects of the ToT processor. Comparisons are made between the signal-to-noise ratio in the linear processor preceding the ToT circuit and that obtained at the output of the entire analog channel including the ToT function.

Front-end electronics for pixel sensors

Abstract This paper discusses the criteria that underlie the design of front-end systems for pixel sensors of different types in a highly diversified fields of application. In the pixel front-end systems, low level analog signals coexist with digital activities and the design must comply with severe limitations in the area and in the power allotted to the single pixel cell. Noise and radiation hardness issues are of utmost importance in several applications. Some ways to arrive at a design which suits specific application requirements are discussed and the impact of the most advanced monolithic processes is evaluated.

Noise in CdZnTe detectors

Noise in CdZnTe devices with different electrode configurations was investigated. Measurements on devices with guard-ring electrode structures showed that surface leakage current does not produce any significant noise. The parallel white noise component of the devices appeared to be generated by the bulk current alone, even though the surface current was substantially higher. This implies that reducing the surface leakage current of a CdZnTe detector may not necessarily result in a significant improvement in noise performance. The noise generated by the bulk current is also observed to be below full shot noise. This partial suppression of shot noise may be the result of Coulomb interaction between carriers or carrier trapping.

Optimization of front-end design in imaging and spectrometry applications with room temperature semiconductor detectors

This paper addresses the optimization of front-end design in position sensing, imaging and high-resolution energy dispersive analysis with room temperature semiconductor detectors. The focus is on monolithic solutions able to meet the requirements of high functional densities set by multielectrode, finely segmented detectors. Front-end architectures featuring additional functions besides charge measurements, as demanded by the need of acquiring and processing multiparametric information associated with the detector signals will be discussed. Noise will be an issue of dominant importance in all the following analysis. The advent of CMOS processes featuring submicron gate length and gate oxide thicknesses in the few nanometers region is overturning some of the classical criteria in the choice of the front-end device. The achievement of the limits in resolution requires a strict control of the noise contribution from the current amplifier which ordinarily follows the front-end element in the charge-sensitive loop. This aspect becomes more crucial in designing front-end systems with submicron processes.

Development of a detector for bunch by bunch measurement and optimization of luminosity in the LHC

The front IR quadrupole absorbers (TAS) and the IR neutral particle absorbers (TAN) in the high luminosity insertions of the LHC each absorb approximately 1.8TeV of forward collision products on average per pp interaction (~;;235W at design luminosity 1034cm-2s-1). This secondary particle flux can be exploited to provide a useful storage ring operations tool for optimization of luminosity. Novel segmented, multi-gap, pressurized gas ionization chambers are proposed for sampling the energy deposited near the maxima of the hadronic/ electromagnetic showers in these absorbers. The system design choices have been strongly influenced by optimization of signal to noise ratio and by the very high radiation environment. The ionization chambers are instrumented with state of the art low noise, fast, pulse shaping electronics capable of resolving individual bunch crossings at 40 MHz. Data on each bunch are separately accumulated over multiple bunch crossings until the desired statistical accuracy is obtained. At design luminosity approximately 2x103 bunch crossings suffice for a 1percent luminosity measurement.

Noise degradation induced by /spl gamma/-rays on P- and N-channel junction field-effect transistors

This paper compares the effects of /spl gamma/-rays on the noise behaviour of P- and N-channel JFETs intended as front-end elements in radiation detector preamplifiers. It will be shown that exposure to /spl gamma/-rays affects the noise spectral density in a way which is substantially different for the two types of devices. As a result of the noise analysis it is suggested that in preamplifiers exposed to /spl gamma/-rays the P-channel JFET should be preferred at processing times in the 1-to-10 /spl mu/s range, while the N-channel device remains superior in applications involving processing times below 0.1 /spl mu/s.

JFET-PMOS technology, in the design of monolithic preamplifier systems for multielectrode detectors

Some basic steps in the development of a low-noise monolithic preamplifier system for multielectrode detectors are reviewed. Some of these steps refer to the realization of an effective filter on the monolithic chip. Others were oriented toward arriving at a technology suitable for a low-noise design. A nonhomogeneous monolithic process combining N- and P-channel JFET and N- and P-channel MOS on the same substrate meets the objective. Radiation hardening considerations restricted the design to two device categories only, NJFET and PMOS. As a preliminary result of the effort in the areas of filter design and technology development, a 64-channel preamplifier system for microstrip detectors is described. >

Liquid krypton electromagnetic calorimeter

Abstract A calorimeter using 30 tons of liquid krypton for the KEDR detector is being constructed. The main effects which determine the energy and space resolution have been studied. An energy resolution of 1.7% at 1.2 GeV was obtained with the prototype. A space resolution of 0.4 mm for relativistic particles has been reached with the prototype.