MGPA status

Design progress since October: main efforts on process spread simulations -> look for robustness to manufacturing tolerances -> seek to improve by minor adjustments to design 4 gain channel version (equivalent gains to FPPA) -> ~ complete -> process spread can be tolerated but requires adjustments to diff O/P stage termination components to compensate for channel-to-channel pulse shape differences appearing as process moves -> arises because of different differential stage gains for different gain channels (see talk last time) -> may lead to production difficulties (e.g. termination components might need to be selected on test) possible improvements?

-> make use of FPPA spec review (“Memo on FPPA specifications”, C.Seez (August, 2002)) -> conclusions: 1. not possible to relax 60 pC full range signal 2. three gain ranges adequate for barrel 0 – 140 140 – 300 300 – 1250 GeV instead of 0 – 50 note: highest gain required 50 – 200 reduced by factor ~3 200 - 400 400 – 1500 3. three gain ranges also acceptable for endcap December, 2002 CMS Ecal 1

Possible improvements from going to 3 gains

using FPPA spec review conclusions can re-instate equal diff O/P gains, since highest gain can be reduced 4 – chan version 3 – chan version Overall gain 32 8 4 1 R G ~20 ~20 ~40 ~80 diff O/P gain 8 2 2 1 Overall gain ~10 ~5 ~1 R G ~20 ~40 ~200 diff O/P gain ~3 ~3 ~3 Gain range (barrel) [GeV] 0 - 125 125 - 250 250 - 1250 implications R = 200 W -> slightly increased noise for lowest gain range; 28,000 -> 34,000 electrons noise performance for other 2 ranges remains < 10,000 channel to channel pulse shape variation dependence on process spread now gone one less channel also helps with: power consumption layout: package minimum pin count reduced, can use more power pins December, 2002 CMS Ecal 2

process parameter variation pulse shape example (3 gain channel version)

s = -1.5

s = 0 high range: 0-6 pC (0.6 pC steps) mid range: 0-12 pC (1.2 pC steps) low range: 0-60 pC (6 pC steps) s = +1.5

small pulse shape variations s s = -1.5, 0, +1.5 (difficult to see here), but ~ no channel/channel differences moves process variables ( D L, VT) together so cumulative effect worse (in real situation D L and VT vary independently) other process simulations (fast/slow nmos/pmos and vice versa) also show good channel pulse shape matching December, 2002 CMS Ecal 3

Summary

4 – channel design ~ complete tolerant to process spread if diff O/P stage termination components “select-on-test” will complicate production testing possible improvements if move from 4 -> 3 gain channels FPPA spec review => physics performance safe removes channel/channel pulse shape variation with process spread overall improvements in design robustness (pin count, power) => reduced risk => well worth having from production perspective RAL (Marcus French) now looking at layout

Areas still needing attention

More process spread effects studies including supply voltage and temperature effects Transmission line effects between APD and MGPA some work begun here for endcap (50 – 75 cm coax) -> short duration ringing at charge amp O/P, but not much effect on overall pulse shape needs more work, particularly for barrel Power supply rejection – not looked at yet December, 2002 CMS Ecal 4