1. Trip-t testing progress report discriminator fix
effects of long cables
- 19/12/05

2. linearity discontinuity
linearity discontinuity removed by setting IBT to zero -> disables T-pulse circuit
(advice from Paul Rubinov)
- 19/12/05

3. Trip-t schematic – front end
single channel
Q_IN
A OUTPUT
200fF
IBP
1.0 pF
3.0 pF
GAIN[3]
RESET Z
IFF
IBOPAMP
GAIN[2]
160fF
GAIN[1]
80fF
GAIN[0]
40fF + -
V_REF
IFFP2
x10
IB_T
IBCOMP
DISCRIM_OUT
V_TH
PLN_CLK
t OUTPUT
- 19/12/05

4. Effects of long cables Vbias
look at SiPM O/P directly on scope (Russian SiPM)
1 MW
thin coax or twisted pair
100nF
scope
50/100W
LED
SiPM
coax results (average pulse shape)
time offsets removed
raw data
20 cm / nsec
some reflection effects but not much effect on leading edge
- 19/12/05

5. Effects of long cables
twisted pair (different lengths of unshielded twist-and-flat)
raw data
time offsets removed
noticeable reflection effects on falling edge, but like coax not much on leading edge
- 19/12/05

6. Effects of long coax cables with TripT
use test channel – gives access to
signal just prior to pipeline (A output – see p.3)
Pipe Clock
coax results (with SiPM -averaged
pulse shapes)
lose amplitude as cable capacitance
increases (Tript designed for 35 pF)
non-ideal transmission line effects
more obvious for longer cables
note: not much reset time required
PreampReset
led pulse
Qin ~
1.5 pC
20 cm / nsec
- 19/12/05

7. Effects of long twisted pair cables with TripT
(different lengths of twist-and-flat)
instability develops for > 200 cm
pedestal effects (repetitive patterns after
reset removed) due to digital pickup
(lack of shielding)
probably OK up to ~ 100 cm
PipeClock
Preamp reset
led pulse
- 19/12/05

8. Conclusions linearity discontinuity
can be eliminated if disable T-Pulse circuit – good news
effects of long cables (preliminary study using TripT test channel)
coax
tranmission line effects (reflections) for longest lengths used
loss of signal amplitude as cable capacitance increases
twisted pair
up to ~ 100 cm may be OK
evidence of instability for > 200 cm
comments
miniature coax likely to be expensive – individual connectors on TFB (Trip-t Front-end Board)
but unshielded twisted pair gives vulnerability to pick-up (lots of digital signals on TFB)
is shielded TP an option? would be preferable even for short lengths, does it exist in suitable form?
can it be connectorized at reasonable cost? any suggestions welcome
effects on timing (discriminator timewalk) not yet studied (but scope pictures tend to suggest should not
be a problem)
personal opinion
try hard to keep SiPM-Tript distances as short as possible – danger of vulnerability to problems
(e.g. particularly interference with unshielded twisted pair) that may be curable in the lab, but which may
re-occur in the final system and be hard and/or costly to solve
- 19/12/05