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Description
Summary
A number of features make Micro-Pattern Gas Detectors (MPGD) attractive to be used in particle-physics experiments, astro-particle research and medical imaging. Among those are high spatial resolution, radiation hardness and inherent low material budget. The availability of highly integrated readout electronics allows for the design of gas-detector systems with channel densities comparable to that of modern silicon detectors.
Gossipo-3 is a small-size prototype of a future ASIC dedicated for readout of MPGD’s. Main specifications of such an IC will be compatible with requirements imposed upon ATLAS Pixel System for Upgraded Luminosities.
The prototype comprises a 32 by 32 active pixels readout array with a sensitive area of 3.1mm^2. The on-pixel part includes an analog-to-digital front-end circuit, a 4-bit threshold DAC and a high resolution Time-to-Digital Converter (TDC). The TDC-per-pixel architecture allows for the measurement of the drift time of individual primary electrons originated by MIP particles crossing the gas volume.
The main goal of this prototype is to optimize the design of the on-pixel circuits.
In order to be suitable for different applications (Trackers and TPC’s) the readout chip has to have different functionalities and modes of operation.
In TIME mode the arrival time of the hit signal will be measured in the range from 1.6ns to 100us as well as the size of the charge deposited on the pixel in the range from 400 electrons to 30 000 electrons.
We have chosen a hit signal-controlled TDC solution for digitization of the time information. In this scheme each pixel has an individual fast (Fosc≈600MHz) oscillator circuit connected to a fine time counter and a clock synchronous counter for coarse time measurements. The oscillator will be started every time the pixel is hit and will be stopped by the first leading edge of the clock signal (freq=40MHz). The clock synchronous counter gives a number of full clock periods between the Hit signal and the external Trigger signal [1].
In IMAGE mode the number of hits will be counted on each pixel in the range up to 24 bits.
Two triggering options will be available in the chip. These are external common Stop and internally generated Stop (fast OR).
In the Gossipo-3 prototype, the pixel array will be read-out serially. The output data of the pixel will be shifted out to the buffer of the adjacent pixel and thus on to the periphery. A final readout architecture will be worked out in the next prototypes.
[1] V.Gromov, R.Kluit, H. van der Graaf ”Development of a Front-end Pixel chip for Readout of Micro-Pattern Gas Detectors” Proceeding of Topical Workshop on Electronics for Particle Physics (TWEPP-08), pp.76-79, Naxos, Greece, September 2008.
