ALDO: A radiation-tolerant, low-noise, adjustable low drop-out linear regulator in 0.35 μm CMOS technology
Introduction
Starting from 2018, the LHCb RICH detector will undergo a substantial upgrade and the opto-electronic chain will be completely redesigned in order to operate at higher luminosity and rate [1], [2]. New photodetectors were selected and qualified in Milano Bicocca and the Hamamatsu R11265 and H12700 MaPMTs were chosen as the baseline photodetectors [3], [4]. The front-end electronics was also completely redesigned and a custom ASIC was developed for this specific purpose. The ASIC, named CLARO, has been already manufactured and thoroughly characterized [5], [6].
The CLARO preamplifier needs a stable and low noise power supply since its internal references are obtained from the supply voltage and also because the preamplifier is DC-coupled to the input.
The power supply scheme currently foresees the use of the CERN radiation-hard and low noise DC/DC regulator (FEASTMP) [7] directly connected to the front-end boards. However, in order to further improve the CLARO performance, a low drop-out linear regulator could be inserted between the DC/DC regulator and the front-end chips without changing much of the opto-electronic chain layout. This approach will be beneficial both for better noise filtering and also for achieving a more stable line regulation since a linear regulator can be installed much closer to the front-end ASIC.
Section snippets
Characteristics
ALDO is an adjustable low drop-out linear regulator prototype ASIC designed in AMS 0.35 μm CMOS technology. The simplified block diagram of the chip is shown in Fig. 1. The technology chosen is the same used for the CLARO chip which proved to be able to withstand up to 1 Mrad and 1013 neq cm−2.
ALDO can source up to 200 mA output current with an output voltage drop-out of 250 mV at full load. This will allow one ALDO to power a maximum of two front-end boards (16 CLARO chips or 128 channels) in the
Performance
A testboard was designed in order to evaluate the ALDO and DC/DC performance. This allowed us to test noise, temperature stability and will allow us to perform the irradiation campaign.
Noise and power supply rejection proved to be satisfying, according to both simulation results and real-world measurements: ALDO can suppress the DC/DC noise of 570 μV RMS (measured in a 10 Hz to 1 MHz bandwidth) down to less than 11.6 μV RMS. Test results are shown in Fig. 2 where the noise spectra in different
Conclusion
The first prototype of the ALDO chip was designed, manufactured and tested successfully. It demonstrated to meet the specifications requested for application in the LHCb RICH detector and this will allow us to proceed in the qualification process with an irradiation campaign to quantify its radiation hardness.
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