Speaker
Description
Summary
Calorimeters which improve energy resolution by applying particle flow algorithms need high readout channel densities, at CALICE-AHCAL this is 60k per cubic-meter. Due to the high channel density the frontend electronics with the power hungry fast preamplifiers and multiplexers has to be integrated into the active volume of the sampling calorimeter. Avoidance of active cooling within the sensing volume is then required to maintain calorimeter homogeneity. Therefore very low power consumption for each channel is required. To reach the 40µW/channel consumption aimed at power cycling the frontend electronics of CALICE-AHCAL in step with the bunch delivery duty cycles, typically <0.5% foreseen in future linear e+e- collider designs, is required and reduces total power consumption by a factor 100. Switched current at the full scale detector then reach the order of kilo-Amperes and must be handled carefully to avoid electromagnetic interferences (EMI) with the calorimeter setup itself and with other sub-detectors.
The actors driving power cycling are the frontend ASIC’s near the SiPM-sensors within the active layers of the sampling calorimeter. They behave like switched current sinks. Measurements have demonstrated that the generated frequency spectrum contains frequencies from the bunch train cycle, 5Hz, up to a few 100MHz. The supporting electronics has to stabilize the voltage to a few 10mV. Simulations have been used to develop a concept and derive interference reducing measures. For high frequencies the current loops are closed locally using the multilayer structure of the PCB and capacitors nearby the switched current sinks. For medium frequencies fast voltage regulators and capacitor banks placed in the service area at the end of the active layer with a distance of 1-2m to the actor are used. RC-filters between the capacitor bank and the supplying cables to external power supplies will be used to minimize the EMI-disturbances to other sub-detectors in the low frequency range coupling through the infrastructure. For residual AC-components of the supply current it is important to keep the coupling between parts of the calorimeter and to other sub detectors low and a cabling scheme is proposed, which keeps the supply current and its return path close together, avoiding transformer like couplings. These measures are further supported by using individual floating power supplies. Each power-channel will supply only a few layers of the calorimeter to avoid large area current loops.
Using the simulate and derive design loop it has proven feasible to provide a voltage supply for the frontend ASIC’s with impedances of 1Ohm for a wide frequency range whilst keeping EMI-disturbances low by reducing the parasitic currents in the stainless steel structure of the calorimeter and the external cable trees to a few milli-Amperes/layer.
The talk describes the design chain from frontend PCB’s to external power supplies. Simulations supporting the concept will be presented as well as measurements on long detector units which will be available shortly.
