Speaker
Description
The High Granularity Calorimeter (HGCAL), presently being designed by the CMS collaboration to replace the CMS endcap calorimeters for the High Luminosity phase of LHC, will feature six million channels. The requirements for the front-end electronics are extremely challenging, including high dynamic range (0-10 pC), low noise (~2000e- to be able to calibrate on single MIP throughout the detector lifetime), high accuracy time information in order to mitigate the pileup effect (25 ps binning) and low power consumption (~15mW/channel), as well as the need to select and transmit trigger information with a high granularity. The front-end electronics will face a harsh radiation environment which will reach 200 Mrad at the end of life. It will work at a controlled temperature of minus 30 °C.
HGCROV-V2 is the second prototype of the front-end ASIC. It has 72 channels of the full analog chain: low noise, high gain preamplifier followed by single-to-differential 25ns shapers, 10-bit ADC 40 MHz SAR-ADC, which provides the charge measurement over the linear range of the preamplifier up to 100 fC. In the saturation range of the preamplifier, from 100 fC to 10 pC, a discriminator and TDC provide the charge information from TOT (Time Over Threshold) over 200 ns dynamic range and 50 ps binning. A fast discriminator and TDC provide timing information to 25 ps accuracy. The both charge and time measurements are kept in a DRAM memory waiting for a L1 accept. At the bunch crossing rate of 40 MHz, compressed charge data are sent out to participate to the L1 generation.
We will report the performances study with the evaluation boards, including signal-to-noise ratio, ADC and TDC performances, and the behavior after irradiation. The first prototype showed a strong digital coupling to the preamplifier input leading to a large coherent noise on charge and time measurements. In order to reduce this effect, the power supply rejection of the preamplifier was improved, the shaper and ADC architectures were changed, and especially we replace the wire bonding scheme by a bump bonding: the improvements on the performances will be showed as well.
