As a result of a cooperation between Brookhaven National Laboratory and eV Products a generation of high performance readout ASICs was developed. The ASICs, realized in CMOS 0.5 /spl mu/m technology, are available in several different versions, single or multi-channel and with unipolar or bipolar shaper, in view of their use in research, spectroscopy, medical, safeguard and industrial applications. Four innovative circuit solutions are implemented in the ASICs: (i) a high linearity compensated continuous reset system which self-adapts to a wide range of detector leakage currents with minimum noise contribution; (ii) a high order shaper realized by using the follow-the-leader feedback (FLF) approach; (iii) a class AB rail-to-rail output stage with high driving capability; (iv) a baseline holder (BLH) for the baseline stabilization. The basic structure of the ASICs, a description of the novel circuit solutions and the preliminary experimental results are reported.

http://www.inst.bnl.gov/~poc/publications/N15-21.pdf

A generation of CMOS readout ASICs for CZT detectors

The field of pixel detectors has grown strongly in recent years through progress in CMOS technology, which permits many hundreds of transistors to be implemented in an area of 50–200 μm2. Pulse processing electronics with noise of the order of 100 e− RMS permits to distinguish photons of a few kilo-electron-Volts from background noise. Techniques are under development, which should allow single chip systems (area ∼1 cm2) to be extended to larger areas. This paper gives an introduction into the concept of quantum imaging using direct conversion in segmented semiconductor arrays. An overview of projects from this domain using strip, pad and in particular hybrid pixel detectors will be presented. One of these projects, the Medipix project, is described in more detail. The effect of different correction methods like threshold adjustment and flat field correction is illustrated and new measurement results and images are presented.

/pdf/development-of-segmented-semiconductor-arrays-for-quantum-jtxvwjr0wn.pdf

Development of segmented semiconductor arrays for quantum imaging

We report on the multichannel IC (RX64DTH) designed for position sensitive X-ray measurements with silicon strip detectors and dedicated to medical imaging applications. This integrated circuit has a binary readout architecture with a double threshold allowing on selection energy window for measured signals. The design was realized in a 0.8 /spl mu/m CMOS process. The core of the RX64DTH IC consists of 64 readout channels. The single channel is built with four basic blocks: charge sensitive preamplifier, shaper, two independent discriminators, and two independent 20-bit counters. Each readout channel counts pulses which are above the low discriminator threshold and counts pulses independently above the high discriminator threshold. The energy resolution in such architecture is limited by the noise of a single channel and by channel to channel threshold spread. We present the noise and matching performance of a 384-channel module built with a silicon strip detector and six RX64DTH ICs. In the 384-channel module an equivalent noise charge of about 200 el. rms is achieved for the shaper peaking time of 0.8 /spl mu/s and strip capacitance of 3 pF. The deviation of discriminator thresholds for the whole system is only 87 el. rms. The obtained results show that the energy resolution and uniformity of analog parameters (noise, gain, offset) are sufficient for medical diagnostic applications such as dual energy mammography and angiography.

RX64DTH -a fully integrated 64-channel ASIC for a digital X-ray imaging system with energy window selection

The paper describes the development of a multichannel readout system for X-ray measurements using silicon strip detectors. The system comprises two application-specific integrated circuits (ASICs), a front-end chip, and a digital data storage chip. In the front-end ASIC, a binary readout scheme is employed. The binary data are stored in the asynchronous counters and read out serially at the end of the measurement sequence. The front-end circuit is designed such that it can work with direct current coupled detectors with a leakage current up to few nanoamperes. The size of the input device is optimized for a detector capacitance in the range from 2-5 pF per strip. An equivalent noise charge of 110 electrons rms has been achieved for the total strip capacitance of 2.5 pF at the peaking time of 1 /spl mu/s. Low noise performance and high counting-rate capability have been demonstrated by measurements of X-ray spectra.

Development of a fully integrated readout system for high counting rate position sensitive measurements of X-rays using silicon strip detectors

Since diagnostic X-rays have been proven to be a cause of cancer, some precautions are essential to reduce the dose delivered to patients. In this paper, an idea to reduce the dose by a new type of X-ray computed tomography (CT) using silicon strip detectors is discussed. Thin tungsten plates placed between edge-on silicon strip detectors are the key element to reduce the background of scattered X-rays and improve the image contrast with low dose. The initial results of a feasibility study are also reported.

Application of silicon strip detectors to X-ray computed tomography

Characterization results are given for an original ASIC allowing continuous acquisition of ionising radiation images in spectroscopic mode. Ionising radiation imaging in general and spectroscopic imaging in particular must primarily be guided by the attempt to decrease statistical noise, which requires detection systems designed to allow very high counting rates. Any source of dead time must therefore be avoided. Thus, the use of on-line corrections of the inevitable dispersion of characteristics between the large number of electronic channels of the detection system, shall be precluded. Without claiming to achieve ultimate noise levels, the work described is focused on how to prevent good individual acquisition channel noise performance from being totally destroyed by the dispersion between channels without introducing dead times. With this goal, we developed an automatic charge amplifier output voltage offset compensation system which operates regardless of the cause of the offset (detector or electronic). The main performances of the system are the following: the input equivalent noise charge is 190 e rms (input non connected, peaking time 500 ns), the highest gain is 255 mV/fC, the peaking time is adjustable between 200 ns and 2 μs and the power consumption is 10 mW per channel. The agreement between experimental data and theoretical simulation results is excellent.

An important step forward in continuous spectroscopic imaging of ionising radiations using ASICs

A new X-ray radiology system has been devised that significantly reduces the dose of radiation administered to patients in spinal X-ray examinations. The apparatus scans the patient, using a high-efficiency linear solid-state detector and highly sensitive electronics, operating in counting mode. Two specific integrated circuits were developed, one of which contains an automatic offset correction. The detection system characterization data will be briefly presented. Data is acquired in real time by a high-speed computer-controlled VME system. The scan parameters and image filtering are also computer-controlled. The first images recorded using this new apparatus are given, along with the preliminary comparative dosimetric analysis.

New quantum detection system for very low dose X-ray radiology

The paper entitled “New Quantum Detection System for Very Low Dose X-ray Radiology”, presented at the talk session, discusses the preliminary data obtained using a new quantum X-ray radiology system with a high-efficiency solid-state detector and highly sensitive electronics, making it possible to reduce significantly the dose adiministered to a patient in X-ray radiology examinations. The present paper focuses more on the technological aspects of the apparatus, such as the integration of the detector with the two Asics, and the computer system. Namely, it is shown how the computer system calibrates the detection system, acquires the data in real time, and controls the scan parameters and image filtering process.

The quantum X-ray radiology apparatus

The aim of this paper is to describe a very general readout system for one-dimensional ionizing particle detectors. This system is based on a VME (Versa Module Eurocard, IEEE P1014, Mar. 12, 1987) bus which allows us to read and store up to 1000 channels in 1 ms. Thus, two-dimensional images can be recorded in a short time, for example by moving the measurement device composed of the detectors and their onboard electronics. This concept has been applied to a new low-dose X-ray radiology apparatus. A direct numerical radiographic image obtained with this system is presented.

High-speed data acquisition system for spectroscopic imaging of ionizing particles

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An important step forward in continuous spectroscopic imaging of ionising radiations using ASICs

New quantum detection system for very low dose X-ray radiology

The quantum X-ray radiology apparatus

High-speed data acquisition system for spectroscopic imaging of ionizing particles