Gerda phase II FrontEnd resistorless BEGe or segmented

Gerda phase II Front-End: resistorless ? BEGe or segmented detectors « electrode cap of a few p. F Mounting of the front-end devices in the style used in ultra low noise X-ray spectrometers might be appropriate in order to exploit det low capacitance A few devices are mounted very close to the electrode, while the remaining part of the preamplifier is placed at some distance as connected with thin twisted-pair or coaxial cables Very FE to be placed very close to detector electrode FE devices include FET, CF, CTEST, RF. Chip resistors in the GW range have the poorest radio purity « a resistorless preampliflier could be best suited

Resistorless preamplifiers in literature Low-noise charge preamps with no feedback resistor are found in literature as developed for X-ray spectroscopy How does the feedback capacitance get discharged ? 1. FBF. This solution uses the gate-to-source forward biased FET junction to provide discharge current path (G. Bertuccio, P. Rehak, D. Xi, NIM A 326, pp. 71 -76, 1993) 2. BJT. This solution uses the transversal parasitic BJT of dual gate FET’s to provide discharge current path (P. Rehak, A. Fazzi, NIM A 439, pp. 391 -402, 2000) 3. MOSFETa. This solution uses a MOSFET in weak inversion in parallel to CF (P. O’Connor, G. Gramegna, P. Rehak, et al, IEEE Trans. Nucl. Sci, vol. 44, no. 3 pp. 318 -325, 1997) 4. MOSFETa + NL P/Z. This solution adds a non-linear Pole-Zero (P/Z) compensation to previous solution (G. Gramegna, P. O’Connor, P. Rehak, S. Hart, NIM A 390, pp. 241 -250, 1997) 5. MOSFETb. This solution uses a MOSFET to discharge CF through a negative feedback loop (B. Ludewigt, J. Jaklevic, I. Kipnis, et al, IEEE Trans. Nucl. Sci. , vol. 41, no. 4, 1994) 6. PULSED. This solution forces the preamplifier reset when its output crosses a preset threshold, or at fixed clocked times

Resistorless preamplifiers in literature • 1 and 2 are easy-to-implement as discrete-component circuits • 3, 4 and 5 are integrated circuits • 6 can be realized with discrete components or as an integrated circuit None of the shown circuits has been tested at cryogenic temperatures

Resistorless preamplifiers in literature Problem: g-ray spectroscopy requires much better linearity than X-ray spectroscopy. Can existing resistorless solutions be used ? Solution 4 shown in the list is the best candidate as it uses a technique to eliminate the nonlinearities of the reset device A study on existing/new solutions for resistorless charge preamplifiers suited for g-spectroscopy is needed and challenging

Resistorless preamplifiers in literature 2 ENC=13 el rms 1 ENC=19 el rms 3 5 4 ENC=40 el rms ENC=9 el rms ENC = 19 el rms Technical details can be found in the quoted papers