Front-end electronics for pixel sensors Manfredi, P.F.; Manghisoni, M.
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
06/2001, Letnik:
465, Številka:
1
Journal Article
Recenzirano
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.
This paper discusses the present trends in the design of low-noise front-end systems for room temperature semiconductor detectors. The technological advancement provided by submicron CMOS and BiCMOS ...processes is examined from several points of view. The noise performances are a fundamental issue in most detector applications and suitable attention is devoted to them for the purpose of judging whether or not the present processes supersede the solutions featuring a field-effect transistor as a front-end element. However, other considerations are also important in judging how well a monolithic technology suits the front-end design. Among them, the way a technology lends itself to the realization of additional functions, for instance, the charge reset in a charge-sensitive loop or the time-variant filters featuring the special weighting functions that may be requested in some applications of CdTe or CZT detectors.
During the past 15 years, the CMOS technologies have provided the most widely followed approach to signal processing with microstrip detectors. In more recent times, CMOS front-end systems have been ...developed to acquire and process signals from pixel detectors. During the past few years, the favor toward CMOS processes in their applications in the broad area of detector signal processing has been enhanced by the technological advancement known as
device scaling and by two aspects connected to it. One is the shrinking in channel length
L into the deep submicron region. The second one is the related reduction in the gate-oxide thickness
t
ox to a few nm. The reduction in
t
ox has, as a consequence of primary importance, a decreased 1/
f-noise contribution to the equivalent noise charge (ENC). The thinner gate-oxide and the shrinking in gate length, in some regions of operations, concur to increase the transconductance of the device, which results in a smaller ENC contribution from channel thermal noise. The goal of the present paper is to address the question of whether or not the most advanced CMOS processes may meet the requirements set by high resolution, high dynamic range applications like the energy-dispersive photon analysis with solid-state detectors of comparatively large capacitance.
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.
A chip has been developed for reading out the silicon strip detectors in the new BTeV colliding beam experiment at Fermilab. The chip has been designed in a 0.25 /spl mu/m complementary ...metal-oxide-semiconductor (CMOS) technology for high radiation tolerance. Numerous programmable features have been added to the chip, such as setup for operation at different beam crossing intervals. A full size chip has been fabricated and successfully tested. The design philosophy, circuit features, and test results are presented in this paper.
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.
Noise in CdZnTe detectors Luke, P.N.; Amman, M.; Lee, J.S. ...
IEEE transactions on nuclear science,
06/2001, Letnik:
48, Številka:
3
Journal Article
Recenzirano
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. Devices with coplanar strip electrodes were observed to produce a 1/f noise term at the preamplifier output. Higher levels of this 1/f noise were observed with decreasing gap widths between electrodes. The level of this 1/f noise appeared to be independent of bias voltage and leakage current but was substantially reduced after certain surface treatments.
We report on bipolar NPN phototransistors fabricated at ITC-IRST on thick high-resistivity silicon substrates. The phototransistor emitter is composed of a phosphorus n+ implant, the base is a ...diffused high-energy boron implant, and the collector is the 600–800
μm thick silicon bulk, contacted on the backplane. We have studied the current amplification for two different doping profiles of the emitter, obtaining values of
β ranging from 60 to 3000. For various emitter and base configurations, we measured the static device characteristics and extracted the leakage currents and the base resistance, verifying the fundamental relationship between them and the total base capacitances. The use of such phototransistors to detect ionizing particles is exploited and discussed.
CVD diamond shows promising properties for use as a position-sensitive detector for experiments in the highest radiation areas at the Large Hadron Collider. In order to study the radiation hardness ...of diamond we exposed CVD diamond detector samples to 24
Gev/
c and 500
Mev protons up to a fluence of 5×10
15
p/cm
2. We measured the charge collection distance, the average distance electron–hole pairs move apart in an external electric field, and leakage currents before, during, and after irradiation. The charge collection distance remains unchanged up to 1×10
15
p/cm
2 and decreases by ≈40% at 5×10
15
p/cm
2. Leakage currents of diamond samples were below 1
pA before and after irradiation. The particle-induced currents during irradiation correlate well with the proton flux. In contrast to diamond, a silicon diode, which was irradiated for comparison, shows the known large increase in leakage current. We conclude that CVD diamond detectors are radiation hard to 24
GeV/
c and 500
MeV protons up to at least 1×10
15p/cm
2 without signal loss.
This paper compares the effects of 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 ...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 gamma-rays the P-channel JFET should be preferred at processing times in the 1-to-10 mus range, while the N-channel device remains superior in applications involving processing times below 0.1 mus
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