The architecture we are considering for a large scale detector is a tree-structured network of MCMs (Main Control Modules), SCMs (String Control Modules), LCMs (Local Control Modules) and DOMs (Digital Optical Modules) (see e.g. the LBNL-JPL group proposal ). The MCMs would be connected to the shore via electro-optical cables. Interconnections between control modules at the same level in the network hierarchy would ensure a path redundancy for data/control information.
A possible approach to digitize the signals at the optical module level is to have LCMs connected to several DOMs via bidirectional links. Each DOM produces a local trigger which is transmitted to the LCM. A higher level trigger produced in the LCM is sent back to the DOM's in order to enable digitization and data transmission.
The Digital Optical Module (DOM) that we are studying is inspired from , where it is proposed to develop a DOM based on a ASIC designed at LBL, the Analog Transient Waveform Recorder (ATWR).
We are developing a similar architecture, in a circuit called Analog Ring Sampler (ARS). The ARS ASIC has been constructed and is being tested. It consists of an array of 128 capacitor cells which samples and memorizes analog input signals. The sampling frequency is adjustable from 300 MHz to 1 GHz.
In order to reduce the amount of data to be transmitted, pulse shape discrimination (PSD) is performed in parallel to trigger building. The decision is made whether to provide only time and charge (SPE Mode) or to fully digitize pulse shapes departing from SPE (Waveform Mode).
The LCM is the next node in the digital network of the detector array. It is connected to about 10 DOMs on one hand, to the next digital node (e.g. String Control Module) on the other hand. It takes care of power distribution, slow control commands and data, trigger building and formatting and transmission of DOM data to the SCM.