Low-Noise Analog Electronic Devices for the PRISMA Spectrometer Focal Plane Detector

M. Romoli1, M. Di Pietro1, A. De Francesco1, A. Anastasio1, A. De Rosa1,2, P. Di Meo1, G. Inglima1,2, M. La Commara1,2, B. Martin1,2, V. Masone1, D. Pierroutsakou1, P. Parascandolo1, M. Sandoli1,2, M. Trotta1, A. M. Stefanini3, S. Beghini4, L.

Corradi3, E. Fioretto3, A. Gadea3, G. Montagnoli4, I. Pokrovskiy3, F. Scarlassara4, S. Szilner3

1 INFN, Sezione di Napoli, 2 Università "Federico II", Napoli, 3 INFN, LNL, Legnaro, 4 Università and INFN, Padova

INTRODUCTION

The Z-identification of the nuclei analyzed by the large acceptance PRISMA spectrometer is obtained using a standard ∆E-E technique, by means of the particle energy-loss inside a multi-anode ionization chamber (IC) system, that is part of the focal plane detector.

The energy resolution required has been obtained using low-noise analog devices specifically developed by the Electronics Service of the INFN – Sezione di Napoli.

The signals out-coming from the 40 anodes are treated with new low-cost charge preamplifiers, named CHAPLIN (CHArge Preamplifier Low-noise INFN Napoli), and then with new shaping and amplifying modules, named SPAM (SPectroscopy AMplifier).

CHAPLIN (PREAMPLIFIER)

The CHAPLIN circuit has been produced using hybrid technology on Alumina substrate (see fig.1) and its characteristics are reported in table 1. The CHAPLINs are mounted on shielded PCBs outside the PRISMA ionization chambers, but their low dissipation power also allows their utilization in high-vacuum setup, near the detectors, where the noise/signal ratio is strongly improved.

FIG. 1: Two CHAPLIN preamplifiers showing the component side and the back one (the one Euro Cent coin is shown for size comparison purpose).

The CHAPLIN presents interesting features which make it suitable to be used, with very satisfactory results, coupled to many different detector types (IC, Silicon SSD, PPAC cathode) with capacitance up to 2000 pF. It has already been used in different apparatuses (PRISMA, EXODET, SERPE, Saclay FF-Detector, RAMONA,…) and experiments were widely performed in various international Laboratories (LNL (Italy), LNS (Italy), CRC-LLN (Belgium), ANL (USA) and RIKEN (Japan)). A second version of the circuit has been also developed and produced, named CHAPLIN-2, with only a different conversion gain (5 mV/MeV) to allow the use of the preamplifier in experiments requiring a larger dynamical range.

Table 1. CHAPLIN Specifications

Input Capacitance 30 pF Risetime @ Csource=2 pF 22 ns Falltime @ Csource=2 pF 3.3 µs Sensitivity 30 mV/MeV Noise @ Csource=0 pF 300 e rms Feedback Capacitance 1 pF Feedback Resistance 10 MΩ Open Loop Gain 104 V/V Power dissipation 180 mW Max Energy Converted 200 MeV (output pos. signal) 270 MeV (output neg. signal) Output signal polarity Inverted Power supply +12 V, -12V

SPAM (SPECTROSCOPY AMPLIFIER)

The SPAM design has been developed including some useful improvements not presently available in commercial modules (for example, the possibilty to change the fast-timing output gain and polarity and an effective pole-zero cancellation system). Filters of the III order and low-noise integrated circuits have been used in order to reduce the noise/signal ratio.

The electronics for each single channel has been mounted on a separate PCB to allow a high modularity of the system and an easy portability on different future

electronic apparatuses. For the PRISMA experiments, the SPAM modules have been mounted on 16-channel NIM standard boards (see fig.2) and the main features of such devices are shown in table 2.

FIG. 2: A single SPAM module and a complete NIM 16-channel board.

Table 2. SPAM Specifications

Input: 16 ch. (50 Ohm or 1 kOhm) (LEMO conn.) Output: 16 ch. (max gain 1000x) (ECL conn.) X-Output: 16 ch. (max gain 10000x) (ECL conn.) Fast-Output: 16 ch. (ECL conn.) Output standard: differential or single ended Fine gain: 12-bit DAC (via SW) Coarse gain: 3-bit DAC (via SW) Shaping time: 0.5, 1.0, 2.0 and 4.0 µs (via SW) P-Z cancell.: 12-bit DAC full scale (via SW) Output pol.: positive or negative (via SW) Fast-Out pol.: positive or negative (via SW) Fast-Out gain: 1x or 5x (via SW) Offset: 12-bit DAC (2 x 8-chan. common) (via SW) Base-line restor.: automatic Power dissip.: 36 W

FIG. 3: The SPAM Manual Controller.

The digital control and the setup of the SPAM modules on the NIM boards is performed using the CAN (Controller Area Network) protocol v.2.0, originally developed for industrial purposes. A CAN network has been implemented by means of the MCP2510 and TLE6255G integrated circuits, supporting communication rates up to 1Mb/s and 33kb/s, respectively.

Through the SPI (Serial Pheriferal Interface) of the MCP2510 it is possible the communication between programmable units. For the SPAM boards and the SPAM Manual Controller, shown in fig.3, 8-bit PIC16F877 micro-controllers have been used. Moreover, also a Personal Computer has been used to setup and control the chain of SPAM boards. To perform such operations a LabView code and an appropriate interface between the parallel port of the PC and the SPI bus have been appositely developed. The main window of the SPAM control software and the interface circuit are shown in fig. 4.

FIG. 4: The PC-CAN interface circuit and the SPAM Control Software main window.