Article

A Mixed-Signal Spectroscopic-Grade and High-Functionality CMOS Readout Cell for Semiconductor X- Ray Pixel Detectors

Dept. of Electron. Eng. & Inf. Sci., Politec. di Milano, Como
IEEE Transactions on Nuclear Science (Impact Factor: 1.28). 11/2008; 55(5):2721 - 2726. DOI: 10.1109/TNS.2008.2003981
Source: IEEE Xplore

ABSTRACT

We present a mixed-signal CMOS front-end cell designed for semiconductor pixel detectors for X-gamma ray imaging and spectroscopy. The readout pixel cell (RPC) comprises an analog and a digital section to accomplish all the functionality of a spectroscopic-grade signal readout. The analog section includes a low noise charge preamplifier, a two stage shaper amplifier with digitally selectable shaping times from 1 mus to 10 mus, a baseline restorer, a high precision peak stretcher and an output amplifier. The digital section includes an amplitude discriminator with coarse and fine digital control of the threshold level, a peak discriminator, a current-mode trigger generator, a logic circuit to accomplish the pulse pile-up rejection and the RPC reset after the A/D conversion, the disable functions of the preamplifier and of the discriminators. The RPC has been designed and manufactured in 0.35 mum CMOS technology with a size of 300 mumtimes300 mum. The full functionality of the RPC has been successfully tested. At room temperature, the intrinsic equivalent noise charge is 15.7 electrons r.m.s. at 3.3 mus and the minimum noise slope is 22 electrons/pF at 8 mus, the linearity error is between -1.4% and +1.2% within 1.9 fC input signal dynamic. The RPC has separate voltage supplies (+3.3 V) and grounds for the analog and digital sections and the total power consumption is 495 muW.

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    • "• the maximum power consumption of the front-end electronics reading one detector half (SDD width of 120 mm) is ∼70 mW; • the maximum allowed system equivalent noise charge (ENC) is 19 e − r.m.s., i.e. an energy resolution of 200 eV FWHM at 6 keV for single channel events; • the front-end ASIC is based on the architecture of the Readout Cell presented in [9], where all stages but the preamplifier are considered already optimized. The ASIC will also contain an ADC consuming a given power (e.g. 1, 2 or 4 mW/chip) and is designed in the same CMOS 0.35 µm technology from Austriamicrosystems; – 7 – "
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    ABSTRACT: In this paper we present a spectrometer realized by bump-bonding a 300-¿m-pitch, 32 �? 32 pixel silicon X-ray detector chip to a 0.35-¿m CMOS, 3-cm2 read-out chip. The self-triggered, mixed analog-digital read-out chip, with 1024 channels, digitizes the X-ray photon energy with 10 bits of resolution, provides the coordinates of the triggered pixels and achieves 34 erms - of input referred noise, ±3.3 LSB of INL and ±0.2 LSB of DNL, while consuming 555 mW from a 3.3 V supply. Preliminary experimental results on the complete spectrometer, obtained both with electrical stimulation of the device and by irradiating the detector with X-rays, are reported.
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