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Status of integrated preamplifiers for GERDA

Status of integrated preamplifiers for GERDA. F. Zocca, A. Pullia, S.Riboldi, C. Cattadori. GERDA meeting – MPI Heidelberg, Feb 20-22, 2006. Proposed circuit structure (from J. Gal*).

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Status of integrated preamplifiers for GERDA

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  1. Status of integrated preamplifiers for GERDA F. Zocca, A. Pullia, S.Riboldi, C. Cattadori GERDA meeting – MPI Heidelberg, Feb 20-22, 2006

  2. Proposed circuit structure (from J. Gal*) *J. Gal et al. “Realization of charge sensitive preamplifiers using current feedback operational amplifier”, Nucl. Instrum. And Meth., Vol. A366, pp. 145-147, 1995

  3. Tested preamp Test chip PREAMP 1 TEST struct MOSFETs PREAMP 1 pMOS + ext RF + ext bias Vmax = 550mV (50 Ohm) PREAMP 2 resistors PREAMP 2 pMOS + ext RF + int bias Vmax = 550mV (50 Ohm) MOSFETs PREAMP 3 TEST struct PREAMP 4 MOSFETs PREAMP 3 pMOS + reset pMOS + shaper MOSFETs PREAMP 4 pMOS + ext RF + ext bias Vmax = 2V (1 kOhm) HIGH VOLTAGE comp’s 3.3 mm CSP+OS simple CC=1.4pF CSP+OS simple CC=0.2pF CSP+OS simple CC=0.6pF CSP+OS simple CC=1pF CSP+OS simple CC=0pF CSP + OS simple CSP with new rail-to-rail output stage. Various comp cap’s CSP+OS cplx CC=1pF CSP+OS cplx CC=0pF CSP+OS cplx CC=2pF CSP+OS cplx CC=0.4pF CSP+OS cplx CC=1.4pF CSP + OS cplx CSP with new rail-to-rail output stage. Various comp cap’s OPAMP OPAMP OPAMP OPAMP 3.3 mm

  4. Test chip with wire bondings in 68LCC package Setup for cryogenic test

  5. Output stage & dynamic range The output stage must be able to drive a coax/twisted pair cable (or a 100 to 200  load) and must provide the largest negative voltage swing (hole signals) At T=300°K, with a negative power supply VEE = - 3V, the circuit can drive a 10m coaxial cable of 50  still providing a negative voltage swing of ~ 2.5V At T=77°K the negative swing reached is of ~ 2.4V CF = ~ 0.15 pF, Ctest = 1 pF Cdet = 15 pF Energy sensitivity (in Ge) at the preamp output = ~ 370 mV/MeV (~185 mV/MeV if 50  terminated) Inputdynamic range = ~6.5 MeV

  6. Rise time at T = 300 °K driving a 50 coaxial cable of different lengths ~ 13 ns with ~1m cable ~ 15 ns with ~10m cable

  7. Rise time at T = 77 °K driving a ~2m coaxial cable (50) 7.8 ns with no BW limit A fast rise time of ~ 8 ns to ~ 13 ns has been obtained but a little overshoot has still to be eliminated by a low-pass filter or by reducing the preamp bandwidth a little bit 13 ns with BW limit (equivalent to Anti-Aliasing filter)

  8. Decay time constant ~ 200 s both at room temperature and in liquid nitrogen T = 300 °K CF = ~ 0.15 pF RF = 1.2 G ~200s T = 77 °K ~200s

  9. Noise measurements Cdet = 15 pF At T =77 °K the substantial increase of the white series noise is mainly due to the decrease of the JFET tranconductance

  10. Tested preamp specs

  11. Future developments • Optimization of tested preamplifier • Tests with different values of Cdet and with values of CF ranging from 0.2 to 1 pF • Tests of more preamplifiers (with different values of compensation capacitance) • Design and test of a miniaturized setup • Tests with different cable types and lengths Activity schedule • March-June 2006: tests/optimization of existing chip. Design/realization of miniaturized PCB. Design of improved new chip. • June-September 2006: realization of new chip / tests of old chip (continued) • September-December 2006: tests of new chip

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