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AIDA design review
Davide Braga
Steve Thomas
ASIC Design Group
31 July 2008
Overview
- x10 stage amplifier
- Peak Hold circuit
- Power supply stabilization
- Bias circuit – 8 bit DACs
- Offset (statistical analysis) and comparator threshold
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Single channel simulation
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Peak Hold
Shaper_out
•
nMOS & pMOS Peak Hold in parallel,
for both signal polarities
•
use of 5V transistors with low
leakage to allow read out in ~ms time
scale (~0.25V/s droop)
pMOS PH
Hold
Reset
Enable_pPH
nMOS PH
Hold
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Reset
Enable_nPH
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Peak Hold: linearity
pMOS PH
nMOS PH
Good integral non-linearity over wide voltage range for both architectures
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Peak Hold: minimum detectable signal
•
Minimum detectable signal
affected by input offset
•
pMOS PH:
nMOS PH:
~10mV
~4mV
Input offset
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Low Energy Channel
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Bias circuit: current
Biasing optimized to limit the current variation, but when preAmp output below ~200mV big
change in current. For better power supply stabilization may be appropriate to limit
ref_low to 200mV (→1.4V output swing)
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Bias circuit
References
Several internal reference
voltages need to be
selectable in order to adjust
the operating point of the
circuit for the best
performance
3
2.5
2.4
[V]
2
2
1.6
1.5
1.2
1
1
1
0.8
0.5
0
0.1
•
preAmp input reference
•
Shaper/PeakHold reference
•
Shaper bias
•
preAmp bias
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Bias circuit: 8bit DAC
nMOS (up to Vdd) and pMOS (down to gnd) DAC for voltage setting
Also comparator threshold must be selectable
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Offset (Monte Carlo results)
R
9R
preAmp
Shaper
X10 stage
•
Offset preamp:
σ~0.5mV
•
Offset shaper:
σ~2mV
•
Offset x10 stage:
σ~3mV
•
Offset comparator:
σ~30mV!
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comparator
(AC coupled to shaper, does not
propagate to comparator)
(~ 10 times offset previous stage!)
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Offset
Shaper input offset
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x10 stage in.offset
AIDA design review
Comparator in.offset
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Offset reduction
Some kind of offset
cancellation technique must
be implemented to achieve
required comparator
sensitivity
X10 stage
comparator
comparator threshold:
example of offset reduction technique
0.25%-10% FSR
→ after x10 stage 2.5%-100%
FSR≈1.5V → ≈37.5mV
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Conclusion
- complete channel analog/digital simulation to be
completed soon
- next submission dates: end of September, end of
October
- limitations to low threshold operation identified, to be
improved in a second iteration to avoid further delay
-September timescale still feasible if layout
straightforward
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