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Description
Summary
CALORIC, standing for CALORimetry Integrated Circuit, is a readout chip developed to fulfil the requirements of the silicon-tungsten electromagnetic calorimeter of the International Linear Collider (ILC). The compactness of this kind of detector and its large number of channels (up to several millions) impose a drastic limitation of the power consumption and an high level of integration.
A differential and synchronous architecture, based on a pure CMOS technology, is proposed. This readout channel is, first of all, composed of a low-noise Charge Sensitive Amplifier (CSA) which takes the fast input current pulse delivered by a silicon diode of the detector and delivers an output voltage proportional to the total charge contained in the input pulse. Next, a two-gain shaping, based on a Gated Integration (G.I.), is implemented to cover the 15 bits dynamic range required: an high-gain shaper processes signals from 4 fC up to 1 pC, and a low-gain shaper handles charges up to 10 pC. The G.I. performs also the analog memorization of the signal until it is digitized. Hence, the analog-to-digital conversion is carried out through a low-power full-custom 12-bit cyclic ADC. If the signal overloads the high-gain channel dynamic range, a comparator selects the low-gain channel to be digitized instead. Moreover, an auto-trigger channel has been implemented in order to select and store only events over the noise.
The timing sequence of the channel is managed by a digital IP. It controls the switches of the G.I., generates all needed clocks, drives the ADC and delivers the final result over 12 bits. The whole readout channel is power controlled, which permits to reduce the consumption according to the duty cycle of the beam collider.
The very-front-end channel has been evaluated using a 0.35 um CMOS technology. Measurements carried out on the prototype chip show a global non-linearity better than 0.2% for low energy particles (up to 0.4 pC), and limited to 2% for high energy particles (up to 6 pC). The Equivalent Noise Charge referred to the input of the channel is evaluated to 0.6 fC, which corresponds to a charge given by the MIP/6. With the timing sequence of the ILC, which presents a duty cycle of 1%, the power consumption of the complete channel is evaluated to 43 uW thanks to the power pulsing. The total area of the channel is 1.2 mm2 with an analog memory depth of 16.
