Discussion on the preamp and calibration circuit and layout G. Visser, IU 7/3/2014

Two-stage preamp Essentially same circuit previously discussed, prototyped Noninverting first stage (for flattest input impedance, lowest noise), inverting 2nd stage Transimpedance gain −3188 Ω Add the switched cal signal into 2nd stage input (which polarity?) +3.60 V 31 mA 14.3 W per boardstack

Two-stage preamp Power switching requirements… Have to be able to kill the preamp power dissipation No option to run without preamp – no point to that No need (IMHO) to selectively kill some channels power (discuss…) Don’t use the powerdown pins of the LMH6629, just kill the 3.6V power supply It serves no other loads (besides the preamps & cal circuitry) Slightly simplifies routing in preamp area One less way for spurious coupling / crosstalk to happen +3.6 V regulator circuit… 1 A load Drop ~1 V on linear regulator, ~1 W per carrier board Pass transistors or integrated regulator IC’s should be distributed over several locations directly adjacent to thermal tab areas of the board Besides the thermal advantage, that is the only way to fit it in the front section of the board

Calibration circuit requirements Bandwidth at least 500 MHz; to 1 GHz probably would be preferable  Justification: See the 508 MHz BPM signal cleanly Cal circuit shall not be a limiting factor in bandwidth of PMT signal path PMT signal shall not pass through a low-bandwidth mux like ADG3248 The general proposal is to sum a switched cal signal with the (always enabled!) PMT signal... Cal circuit shall not introduce crosstalk of PMT signals from one channel to another (more than 0.1%) Only at most one channel needs to get the calibration signal at a time Of course, no channels getting calibration signal is also a required mode Peak amplitude of calibration signal seen by IRSX should be supported up to 500 mV Switching times: 400 ns (??) global enable, 1 ms (??) channel select Calibration signal crosstalk (to unselected channels): 5% ok?? or 0.1% necessary??

Fanout on carrier board – tree option w/ 1:5 demux PE42452A-Z 4 x 4 mm2 all outputs disabled mode exists 5 ch @ −3 dB 5 ch @ −3 dB 1:5 1:5 1:5 1:5 3 ch @ −2 dB 3 ch @ −2 dB parking spot parking spot 1:5 1:5 3 ch @ −1 dB 3 ch @ −1 dB 1:5 1:5 from SCROD 5 ch @ −2 dB 5 ch @ −2 dB (the “parking spots” are desirable to tie down “long” lines passing near our sensitive circuitry)

Fanout on carrier board – tree option B w/ 1:5 demux PE42452A-Z 4 x 4 mm2 all outputs disabled mode exists 4 ch @ −3 dB 4 ch @ −3 dB 1:5 parking spot 1:5 n.c. n.c. 1:5 1:5 4 ch @ −2 dB 4 ch @ −2 dB 1:5 1:5 1:5 4 ch @ −2 dB 4 ch @ −2 dB n.c. n.c. 1:5 1:5 possibly could omit this buffer (but too many reflections?) there may be no room for this thing from SCROD 4 ch @ −3 dB 4 ch @ −3 dB

Fanout on carrier board – four busses option All channels receive nominally identical waveform, little skew There is of course a reflection made when the wave hits the junction of an enabled channel on the bus. If only one is enabled, the reflection is (nominally) absorbed at the source termination. This scheme depends on very light stub loading for disabled channels! At the block diagram level, this plan is the simplest. For high isolation, though, “SW” block contains several discrete components... However it’s not clear if we need that high isolation. 1.0 x 0.6 mm2 BAP51LX SW SW SW SW SW SW SW SW SW SW SW SW SW SW SW SW SW SW SW SW SW SW SW SW SW SW SW SW SW SW SW SW from SCROD additional switch/ isolation from external signals could be added here globally if required

500 μA bias (one or other diode)  300 mW per boardstack What is ? SW 1.0 x 0.6 mm2 BAP51LX 500 μA bias (one or other diode)  300 mW per boardstack

“and now something completey different...” 4 mils thick Indicates ~2000-3000 PSI peak, concentrated in about 0.25x0.4 inch2. Expect ~380 pounds per 6-32 screw torqued to 11 in-pounds (as these were). The sensor film looks like a useful diagnostic. Results make sense. Indicates we are not achieving good contact though! (And surface flatness/finish is part of the issue.)