Configurable electronics with low noise and 14-bit dynamic range for photodiode-based photon detectors

Abstract

We describe the principles and measured performance of custom configurable 32-channel shaper/digitizer Front End Electronics (FEE) cards with 14-bit dynamic range for gain-adjustable photon detectors. The electronics has been designed for the PHOS calorimeter of ALICE with avalanche photodiode (APD) readout operated at -25 o C ambient temperature and a signal shaping time of 1 μs. The electronics has also been adopted by the EMCal detector of ALICE with the same APD readout, but operated at an ambient temperature of +20 o C and with a shaping time of 100ns. The CR-RC2 signal shapers on the FEE cards are implemented in discrete logic on a 10-layer board with two shaper sections for each input channel. The two shaper sections with gain ratio of 16:1 are digitized by 10-bit ADCs and provide an effective dynamic range of 14 bits. Gain adjustment for each individual APD is available through 32 bias voltage control registers of 10-bit range. The fixed gains and shaping times of the pole-zero compensated shapers are defined prior to FEE production by the values of a few R and C components. For trigger purposes, "fast OR" outputs with 12-bit dynamic range are available. FPGA based slave logic, combined with a USB processor supports a variety of remote control and monitoring features, including APD gain calibration. The measurements presented here for APDs at -25 o C ambient temperature and 1 μs shaping time achieve an average RMS noise level of 0.25 ADC counts or 290 electrons.The linearity over the dynamic range is better than 1%, as is the uniformity of shaping time and gain over 32 channels. Due to the excellent correspondence of the output pulse shape with offline fit, a differential timing resolution of less than 1.5 ns between channels has been achieved at ca. 2 GeV, i.e. at 1.5% of the dynamic range of PHOS.

Performance of prototypes for the ALICE electromagnetic calorimeter

“…A detailed description of the EMCal (PHOS) front end electronics (FEE) and their performance is given in Ref. [9]. The FEE has an effective 14-bit dynamic range over the interval 16 MeV to 250 GeV resulting in a Least Significant Bit on the low gain range of 250 MeV (10-bits) and on the high gain range of 16 MeV.…”

“…Here, τ = n · τ 0 with the shaper constant τ 0 and n=2 as the shaper is gaussian of second order (composed of a differentiator and two integrators [9]). The charge collected from the APD, and hence the energy deposited in the tower, is proportional to the value of the parameter A at the time value (t 0 + τ ) where the function peaks.…”

Energy Reconstruction Performance in the ATLAS Tile Calorimeter Operating at High Event Rate Conditions Using LHC Collision Data

“…Thus, H T p is computed again to improve the signal deconvolution process, calculating only the components that probably have information of interest and not only noise contribution. Before computing the (11), the method subtracts the pedestal value, which is usually calculated through a calibration run and store in a database.…”

“…In the electromagnetic calorimeter of the CMS experiment, the baseline method operates considering an unipolar pulse and compute the time when the pulse reach its maximum value [10]. In the ALICE experiment, the energy estimation process is made computing only the amplitude of the received pulse [11]. In the ATLAS electromagnetic calorimeter, both amplitude and temporal position of the digitized samples signal are computed [12].…”

The ATLAS muon Micromegas R&D project: towards large-size chambers for the s-LHC

“…The prototype chamber was then exposed to 120 GeV pions at the CERN H6 beam line during the summer of 2008. 32 strips of the prototype were connected to charge sensitive preamplifiers (CSP) with a voltage/charge conversion of 2 mV/fC, followed by electronics cards [10] with shapers of 200 ns peaking time and with a signal gain of 3.7 in the high gain channels and 0.23 in the corresponding low gain channels. The CSPs were efficiently spark protected via cross-coupled diodes and capacitive coupling.…”