Chain of Modules using 1cm wide Cu Tape between hybrids SP- SP+ M0 M1 M2 M3 Initial test used External shunt control (subsequently reverted) Photo shows initial (inadequate) hookup wires which have been replaced by fatter ones. Power feed is choked to reject external noise, with 1nF + 10uF thereafter to provide local HF bypass. Link between modules is ~3mm wide Cu, no coils

H0H1H2H3H4H5H6H7 Colum n fC fC fC fC fC Chain of 5A (2144-3) H0H1H2H3H4H5H6H7 Colum n fC fC fC fC fC Chain of 9A (2182-3) – M2 using external shunt control DTN and ENC better on average, but not for every column

The Bigger Picture Caps here Choke on hookup wires (not to scale!) M2 now uses internal shunt control

H0H1H2H3H4H5H6H7 Colum n fC fC fC fC fC Chain of 9A (2186-3) – M2 using internal shunt control H0H1H2H3H4H5H6H7 Colum n fC fC fC fC fC Chain of 9A (2187-3) – M2 using internal shunt control, “column 3” shield ties added

Stavelet 0.50fC : M0 at 0.5fC : M1 at 0.5fC Sum(hits): simply sum the number of hits shown in each double trigger plot slices, each slice 100 events, each column 1280 channels

Stavelet 0.50fC : M2 at 0.5fC : M3 at 0.5fC Sum(hits): simply sum the number of hits shown in each double trigger plot

H0H1H2H3H4H5H6H7 Colum n fC 1fC fC fC fC Chain of 9A ( ) – M2 SP+ link with 12nH inductor H0H1H2H3H4H5H6H7 Colum n fC 1fC fC fC fC Chain of 9A ( ) – M2 SP- link with 12nH inductor

Interpretation CofM gives better DTN than CofH – No surprises External shunt regulation of M2 gave better DTN and ENC results than internal regulation – Due to inductance of wired links between boards? – Due to location of regulation at power entry? – Due to higher Vdd? Addition of “column 3” shield ties had no effect – No surprises Adding 12nH inductor to SP+ inter-hybrid link improves DTN verys slightly – Same inductor in SP- inter-hybrid link does nothing

Ideas: what next? Try a star point geometry – Remove the existing inter-module ties and instead bridge the current between modules using wires (or tape) soldered to the middle of the inter-hybrid copper tape links. – Should reduce HF currents on “odd” numbered hybrids (which have worse DTN). – If caps fitted at the star point, should also be better rejection of bus noise. – Does this make any sense? Reduce loop area of hookup Caps (10uF + 1nF) from each module to common HF return foil