Speaker
Description
For LHC Run 4, ALICE will use stitched Monolithic Active Pixel Sensors (MAPS) to upgrade its Inner Tracking System (ITS3). The detector will require detector service electronics (DSE) to provide and monitor power supplies, forward clock and timing information, enable remote sensor configuration and monitoring, and convert copper 10 Gb/s serial data links to optical links. Installed within 30 cm of the detector barrel, the DSE is subject to stringent mechanical constraints and radiation exposure. This presentation will present the architecture, technological choices, and achieved performance of the prototype.
Summary (500 words)
Each half-layer of ITS3, from the inner to the outer layer, is built up from sensors consisting of 3, 4, or 5 identical segments (12 segments in total). Each of these requires 5 different power supplies:
• The main analog and digital voltages (GAVDD and GDVDD), with a typical value of 1.28V and an absolute maximum of 1.32V. The maximum currents are 540mA and 1780mA respectively.
• The service voltage (GSVDD), which must always be greater than GAVDD and GDVDD, (absolute maximum of 1.32V and current of 40mA).
• The transmitter supply voltage (TXVDD), set to 1.8V with an absolute maximum of 1.98V and a current of 455mA.
• The sensor reverse bias voltage (PSUB), at -1.2V, which is common to an entire half-layer
Each segment also requires a 160MHz reference clock and 2 bidirectional serial synchronous links of 5Mb/s for sensor configuration and monitoring. The sensor segment readout is performed via 8 serial links operating at 10Gb/s.
The DSE is composed of 3 different PCBs:
• The Detector Power Board (DPB), with one per half-barrel layer. It uses BPOL48 modules to convert the main 48V supply to 10V for the Service and Control Board (SCB), and radiation tolerant qualified op-amps to generate the PSUB voltage. The DPB is equipped with rescue communication links to each SCB it powers. This board features two lpGBT and VTRX+ pairs: one for monitoring the voltage and current provided by the DPB and for controlling and monitoring the PSUB value, and a second pair dedicated to the rescue function in case the main link fails.
• The SCB, one per segment, generates 4 positive power supplies using BPOL12. They are monitored and controlled by lpGBT and VTRX+. As the BPOL12 does not feature a remote sense functionality, and due to the long and asymmetric connections to both detector sides, an external voltage compensation circuit was implemented.
• The Segment Interface Board (SIB) is connected to the SCB via a 30cm long rigid flex PCB on one side and to a sensor segment via an FPC on the other side. It converts the segment's copper serial links to optical signals using 2 VTRX+ modules and conveys the slow control serial links and the reference clock.
The DSE provides the power supplies via ~30cm long cables to the detector’s A side and ~70cm long cables to the detector's C side, that are connected to the “sensor side” semi FPC of respectively about 25cm and 6cm.
Each segment consists of 144 tiles that can be individually activated. Thus, the system must handle significant load variations on the main power supplies (540mA on GAVDD, 1200mA on GVDD) and minimize the induced voltage drops to ensure safe operation.
Among the challenges addressed were limited space availability (8° cone, external diameter 285mm, thickness <33mm, length 377mm), the need to design a reliable, radiation-hardened power supply solution and the requirement to provide control and monitoring of the sensors. The performance in terms of noise and load regulation will be shown.