Cold amplifier @ Milano Bicocca 12 dic 2019 C. Brizzolari, P. - PowerPoint PPT Presentation

Cold amplifier @ Milano Bicocca 12 dic 2019 C. Brizzolari, P. Carniti, C. Cattadori, M. Citterio, A. Falcone, G. Franchi, N. Gallice, C. Gotti, A. Lucchini, M. Mellinato, G. Pessina, S. Riboldi, P. Sala, M. Tenti, F. Terranova, M. Torti

Original amplifier (TDR) THS4131 Work of G. Cancelo (FNAL) and others 2

THS4131 at roomT Original amplifier (TDR) 1.3 nV /√Hz at 100 kHz 3 nV /√Hz at 100 Hz Series (voltage) noise gives the dominant contribution • THS4131 at 77K: we measured 1.2 nV /√Hz, similar to room T • Low frequency noise 2x-3x larger w.r.t. room T • Power consumption: 3 mA at cold (+/-2.5 V -> 15 mW) • Limited dynamic range when driving 50 ohm lines • THS4131 measured at 77K 1.2 nV /√Hz at 100 kHz 10 nV /√Hz at 100 Hz 3

First tests at MiB Cold amplifier FBK array: 6x 4x4mm 2 SiPMs 4

Modified amp: schematic Q1: SiGe bipolar transistor (BFP640) for lower noise • U2: Fully differential opamp THS4531 for high open loop gain and differential outputs • (same family as the THS4131, see TDR) Flexibility in tuning gain-bandwidth product • Lower power consumption • Almost rail-to-rail outputs on 50 ohm load • For further details: arXiv:1911.06562 • 5

Dynamic performance Gain-bandwidth product ≈ 7 GHz • Flexibility to compensate the open loop gain by changing resistor values, • to maximize bandwidth depending on actual value of SiPM capacitance and closed loop gain Drives 12-meter 50-ohm lines (AC-terminated) with edges in the 20 ns range • Output dynamic range almost rail-to-rail • Total power consumption (Q1+U2+etc): 2.5 mW • 12 m output cables 26-27 ns differential rising edges ≈15 MHz closed loop bandwidth 6

Noise 0.37 nV /√Hz Dominant contribution from series white noise • Spectra at different operating currents of Q1 • At 77 K: • 0.4 nV /√Hz above 100 kHz (1 nV /√Hz at 10 kHz) 7

Signal to noise ratio (1) 1 tile , ≈1 cm 2 , ≈ 4.8 nF Screenshot unfiltered (BW ≈3 MHz, risetime ≈100 ns) S/N measured at 3V OV (gain 2.4x10 6 ) with one SiPM + added capacitance to simulate ganging • Yellow / red dots : measured for SiPMs with tau ≈ 800 ns / 100 ns , 300 kHz low pass filter • Yellow / red curves : calculated S/N from noise spectra and SiPM gain, 300 kHz low pass filter • → curves agree with measurement (dots) Green / blue : S/N with optimum (matched ) filter → • (For large capacitance the optimal S/N does not depend on tau) 8

Signal to noise ratio (2) 1 tile , ≈1 cm 2 , ≈ 4.8 nF Screenshot unfiltered (BW ≈3 MHz, risetime ≈100 ns) 48x 6x6 mm 2 ≈ 60 nF (assuming 35 pF/mm 2 ) At the values of capacitance corresponding to 48x 6x6 mm 2 : 48x 6x6 mm 2 ≈ 86 nF (assuming 50 pF/mm 2 ) S/N ≥ 4 with 300 kHz low pass, depending on tau • S/N ≥ 20 with optimum (matched) filter, independent of tau • 9

Signal to noise ratio (3) 48x 6x6 mm 2 x 53 pF/mm 2 ≈ 91 nF Same calculation, now with values expected from the next FBK batch of cryo SiPMs: • tau=400 ns, cap=53 pF/mm 2 , gain=2.4x10 6 (3 V overvoltage) Added the case of a low pass at 3 MHz (essentially unfiltered) • 10

Next steps Plans for the near future: Use a single power supply instead of dual +3 V / -1V [already tested with +3V, OK ] • Test H1164NL transformers for differential to single-ended conversion • (used in DAPHNE input stage) – in progress Fix the value of the supply voltage from the DAPHNE board (+3 V? +5 V?) • → 3 V preferred from our side, lower power consumption, same performance Input voltage of DAPHNE is 1 V maximum (AFE5808) • → set amplifier gain to have 2000 p.e. dynamic range in 1V (also depends on SiPM gain and overvoltage) Ensure compliance with grounding rules • 11