Improved Dynamic Range Charge-Sensitive Amplifier

Wide band-gap CdZnTe material, which is widely used in the detection of the hard X-ray and the Gamma ray irradiation, has great advantages in the energy resolution and the detection efficiency. In the design of the conventional nuclear spectroscopy system using CdZnTe crystal, the requirement to eliminate the influence of the electric noise and improve the energy resolution has high priority consistently. The crucial part of the detector processing is to convert the signal which is generated by the CdZnTe detector into a Gaussian-pulse which has smaller enough pulse-width. Generally, the transient current signal which comes from the CdZnTe detector needs to be amplified by using a Charge Sensitive Amplifier (CSA) because the nA magnitude signal (Dozens of nA). The application of the CSA can also improve the system SNR and decrease the influence of the external interference in the signal transmission. Based on the theory of the nuclear electronics, researches of the CSA and the pseudo-Gaussian shaping-filter for the CdZnTe spectroscopy detector were accomplished. On the classic theory of the traditional CSA, we present a new CSA circuit structure. the time constant of attenuation can be altered without changing the value of RF and CF. In addition, there was no obvious influence on the rising time and the noise characteristics of the output-pulse of the CSA simultaneously. Moreover, we demonstrated the application of our CSA improved the sensitivity of the CdZnTe detector that we used in previous experiment. In the simulation of this paper, the optimal parameters of each component were determined according to the analysis of the functional characteristics of the CSA and the pseudo-Gaussian shaping-filters. Experiment results show that the rising time of the CSA output signal is 20ns approximately, the falling time is 150μs and the output pulse of the two stage pseudo-Gaussian shaping filter has minimum 200ns pulse width (FWHM). Based on the performance in our experiment, the designed CSA and the multi-stage pseudo-Gaussian shaping-filter can improve the energy resolution of our CdZnTe detector for the hard X-ray radiation effectively, and the energy resolution for the 137Cs(the source of Gamma) can reach up to 3.5%.

The increasing demand for performance improvements in radiation detectors, driven by cutting-edge research in nuclear physics, astrophysics and medical imaging, is causing not only a proliferation in the variety of the radiation sensors, but also a growing necessity of tailored solutions for the front-end readout electronics. Within this work, novel solutions for application specific integrated circuits (ASICs) adopted in high-resolution X and $$\upgamma $$ γ ray spectroscopy applications are studied. In the first part of this work, an ultra-low noise charge sensitive amplifier (CSA) is presented, with specific focus on sub-microsecond filtering, addressing the growing interest in high-luminosity experiments. The CSA demonstrated excellent results with Silicon Drift Detectors (SDDs), and with room temperature Cadmium-Telluride (CdTe) detectors, recording a state-of-the-art noise performance. The integration of the CSA within two full-custom radiation detection instruments realized for the ELETTRA (Trieste, Italy) and SESAME (Allan, Jordan) synchrotrons is also presented. In the second part of this work, an ASIC constellation designed for X-Gamma imaging spectrometer (XGIS) onboard of the THESEUS space mission is described. The presented readout ASIC has a highly customized distributed architecture, and integrates a complete on-chip signal filtering, acquisition and digitization with an ultra-low power consumption.

A wide swing charge sensitive amplifier for a prototype Si–W EM calorimeter

In this article, we present the study and the experimental results of a charge sensitive amplifier (CSA) for the mini-silicon drift detector (SDD) pixel sensors of the DEPleted Field-Effect Transistor (DEPFET) sensor with signal compression (DSSC) detector for photon science applications at the European X-ray free electron laser (XFEL) GmbH in Hamburg area. The DSSC detector must be able to cope with an image frame rate up to 4.5 MHz and with a dynamic range up to 104 photons/pixel/pulse for a photon energy of 1 keV. These goals will be pursued with the adoption of the DEPFET detector strategy. For the first camera prototype, a simpler solution based on a mini-SDD array read out by a conventional CSA has been adopted. We present here the CSA solution with a very simple V-to-I converter stage, which allows the self-canceling of the offset current flowing between the CSA and the filter, without the need of an intermediate stage. The CSA is compatible with the same application-specified integrated circuit (ASIC) architecture and readout chain already designed for the DEPFET detector. We present two versions of the CSA: one with a linear response and another with a nonlinear output characteristic. The nonlinear version provides increased input dynamic range preserving single-photon sensitivity. The experimental measurements have demonstrated the functionality of the proposed self-canceling solution and good noise performance with an equivalent noise charge (ENC) of 65 e- rms at the 4.5-MHz frame rate and a linearity error lower than 0.25% of the complete channel. In addition, the functionality of the nonlinear version (signal compression version) of the CSA has been demonstrated, without penalty in noise performance in the linear region of the CSA response.

Semiconductor strip sensors applied as solid-state radiation or particle detectors can be used in radiation detection and measurement for various applications in particle physics experiments, X-ray imaging (e.g. medical), or material science. The X-ray imaging devices with spectroscopic and position resolution features are a very important research topic at many institutes and companies worldwide. Short strip silicon detectors are good candidates for X-ray spectroscopy, because of their relatively small capacitance and leakage current. If additionally, strip pitch is below 100 μm, then the high spatial resolution is also possible. In this paper, the analysis and noise optimization of the read-out electronics for short silicon strip detectors with Charge Sensitive Amplifier (CSA) and shaping amplifier (shaper) is presented. The CSA is optimized for the detector capacitance of around 1.5 pF, and the shaper nominal peaking time is about 1 μs (controlled by the sets of switches). We take into account the sources of noise in a radiation imaging system (current parallel noise, voltage series noise, and 1/f or flicker series noise) both internal (related to the front-end electronics itself) but also external, stemming from a sensor, interconnect, or printed circuit board parasitic components. We target the noise level below 40 el. rms, considering low power consumption (a few mW) and limited channel area.

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Noise and crosstalk models of the particle detector with zero-pole transformation charge sensitive amplifier

A front-end ASIC for semiconductor radiation detectors is presented. It is composed of a Charge Sensitive Amplifier (CSA), a pulse shaper, and a Peak Detect and Hold (PDH) circuit. Poly-resistor is used as source degeneration component to reduce the noise of current source in the CSA. The ASIC has been designed in a 0.5 ?m CMOS DPTM technology and tested with Verigy 93000. The gain (PDH excluded) is 78.5 mV/fC and the Equivalent Noise Charge (ENC) with detector disconnected is 800-900 e. The power dissipation without the output buffer is about 2.6 mW.

The Charge Sensitive Amplifier (CSA) is the key module of the front-end electronics of various types of Silicon detectors and most radiation detection systems. High gain, stability, and low input noise are the major concerns of a typical CSA circuit in order to achieve amplified susceptible input charge (current) for further processing. To design such a low-noise, stable, and low power dissipation solution, a CSA is required to be realized a complementary metal-oxide-semiconductor (CMOS) technology with a compact design. This research reports a low-noise highly stabile CSA design considerations for Silicon detectors applications, which has been designed and validated in TSMC 0.35um CMOS process. In a typical CSA design, the detector capacitance and the input transistor’s width are the most dominating parameters for achieving low noise performance. Therefore, the Equivalent Noise Charge (ENC) with respect to those parameters has been optimized, for a set of detector capacitance from 0.2pF – 2pF. However, the parallel noise of the feedback was removed by adopting a voltage-controlled NMOS resistor, which in turn helped to achieve high stability of the circuit. The simulation results provided a baseline gain of 9.92mV/fC and show that ENC was found to be 42.5e – with 3.72 e – /pF noise slope. The Corner frequency exhibited by the CSA is 1.023GHz and the output magnitude was controlled at -56.8dB; it dissipates 0.23mW from with a single voltage supply of 3.3V with an active die area of 0.0049 mm 2 .

In this paper, equations for signal processing and noise analysis were derived for a realistic radiation detector model, and simulations were performed under various conditions. Realistic radiation detector model was composed of silicon PIN diode detector, Charge Sensitive Amplifier (CSA), and CR-RC2 shaper. For the realistic CSA model, a finite bandwidth model with a single pole response amplifier was presented and related equations were derived. Through realistic CSA model, it was possible to calculate the signal distortion phenomena such as charge transfer loss and ballistic deficit of the actual circuit and the noise value of the CSA output stage. For the realistic shaper model, signal and noise transfer functions were derived for the CR-RC2 circuit with non-inverting amplifier. In particular, the equation for the internal noise of the shaper, which has been ignored in the current noise analysis, was derived. Through this, it was possible to analyze the effects of amplifier characteristics, resistance value, and signal gain for each stage on the overall noise in the radiation detector of the CSA–shaper structure. For comparison with the simulation, a circuit equivalent to the realistic radiation detector model was made and measurements under the same conditions as the simulation were made. As a result of the verification experiment, the measured values matched well with simulations under various conditions, and through this, the validity of this model was verified. Signal processing and noise analysis were mainly performed for PCB circuits using commercial components, but also included content for CMOS front-end detectors. This model consists only of analytic formulas for the time domain function and the transfer function, nonetheless it has been shown to give accurate results.

In elementary-particle physics, the energies of elementary particles or radiation events are measured or detected by means of a semiconductor detector readout system. A principle schematic of such a detection system is depicted in Fig. 5.1. An inverse biased photo sensitive diode (Si or Ge) detects charged particles or radiation events by generating electron-hole pairs within the detector material. The generated electrons drift in a high electrical field towards the positive-biased n+ contact of the detector and are finally collected. Since the collection time is very short, being in the order of several ns [5.1], [5.2], the detector output signal can be represented as a Dirac current impulse, the integral of which equals the total generated charge Q. The generated charge Q is integrated onto a small feedback capacitor C f . by means of a low noise charge sensitive amplifier (CSA) giving rise to a voltage step at the CSA output with an amplitude Q/C f . The wide use of the CSA at the front end stems from its low noise configuration and insensitivity of the gain to the detector capacitance variations. The step signal is fed to a main amplifier where pulse shaping is performed, primarily to optimize the S/N ratio of the readout system. Therefore, it is called a pulse shaper. In all cases, the resulting output signal is a rather narrow pulse suitable for further processing. Depending on the application, the pulse processing unit can simply be a Multi-Channel Analyzer (MCA) in radiation spectroscopy applications, a series of discriminators for event detections or sample-hold circuits in a multi-channel readout system to store the informations for serial read out. However, for resolution analyses, the detail of the circuits in the processing unit is of no concern and only the CSA and the pulse shaper will therefore be considered in this chapter.

Small cylindrical p-i-n semiconductor radiation detectors have been fabricated for use with internally administered radioisotope tracers and for internal dose measurements. The p-i-n semiconductor (1–4) radiation detector, because of its wide depletion region, has adequate sensitivity for either beta or gamma radiations. For this application, such detectors have been fashioned into cylinders having both diameter and height of 2 mm. Increased sensitivity may be achieved by increasing the height of the cylinder. The cylinders have been incorporated into polyethylene 4-foot catheters with an outside diameter of 3 mm.; these are sealed at the detector end and have standard microdot connectors at the other end. The connectors can be joined directly to BNC outlets through the use of adapters. Two types of catheters have been built. In one, only the p-i-n detector is incorporated in the catheter, while in the second, a microminiaturized emitter-follower and preamplifier are also incorporated. The present configuration of the electronics has a diameter of 4.1 mm., which can easily be reduced by a factor of two. The length of the emitter-follower is 5.3 mm. and that of the two-transistor preamplifier is 2.2 cm. The advantage gained through the use of the microminiaturized electronics is that a greater signal pulse height is achieved, thereby increasing the absolute sensitivity of the probe. The response of the detectors to radiation has been recorded both by counting individual pulses and by recording the change in dark current when operated with a back bias. The pulses recorded when exposed to a Co60 or Cs137 beam have a height of about ten times those due to noise in the case of the detector only. The increase in dark current produced when a back bias of 10 v is applied is 0.1 microampere for an approximate dose rate of 100 r/minute air. Through the use of a potentiometer circuit the dark current may be balanced out and the system may then be used for very low dose rates. Of course, pulse counting gives the ultimate in sensitivity, but, due to the situation of detector or electronics, one is limited in the range of high dose rates to about 1 r/minute. The magnitude of the back current is linear with dose rate in the range of 1 to 100 r/minute when a 100 kvp x-ray beam (h.v.1. = 1.5 mm. A1) is used.

A high-speed low-noise front-end ASIC prototype for ionization chambers of high-intensity beam monitoring

In this paper, we discuss the noise contribution of the current source transistors in the charge sensitive amplifier for application in the front-end semiconductor radiation detectors. We developed an analytical methodology that allow to determine the optimum geometry for the current source transistors, so that the current source transistor ends up contributing only a fraction of the input transistor noise in the charge sensitive amplifier. The proposed methodology ensures that the input transistor noise becomes a dominant factor in the amplifier, thus making the known input transistor noise optimization methodology easily applicable. The example charge sensitive amplifiers based on the dual PMOS cascode amplifier structure have been designed by adopting the proposed current source optimization methodology, and next have been simulated using the IBM CMOS 130nm technology. The proposed optimization methodology has been found in good agreement with simulation results using deep submicron CMOS technology.

In this paper, the design of a new low-power low-noise charge-sensitive amplifier (CSA) is presented. The proposed CSA is intended for capacitive sensor readout circuits such as interface circuits for solid-state detectors used in medical imaging and X-ray spectroscopy. A comprehensive noise analysis of readout systems that consist of a CSA followed by an RC-CR pulse shaper is presented. To facilitate predicting the noise behaviour of the system, the equivalent noise charge (ENC) equations are derived analytically. The readout circuit is designed and laid out in a 0.13-μm CMOS process. Post-layout simulations show that the conversion gain of the CSA with a 20 fF feedback capacitor is 37.5 mV/fC. The estimated ENC of the readout system is 38 ē-rms at a 1 μs peaking time with a detector capacitance of 0.5 pF and a leakage current of 50 pA. The integral nonlinearity of the CSA is less than 0.74% for 0.5–3 kē. The open-loop gain of the amplifier is ∼ 80 dB and the gain-bandwidth product is about 345 MHz. The CSA occupies 0.0021 mm2 and consumes 37.5 μW from a 1.2 V supply.