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AIDA ASIC
Davide Braga
Steve Thomas
ASIC Design Group
14 October 2010
Input comparator:
Now that the original diodes have been
replaced by diode-connected pass
transistors (not as fast or low
impedance) the active-link circuit must
take most of the input current.
To avoid the build up of a large input
voltage now that the passive link is
slower, the active link must respond
faster
Necessary to optimize the input
comparator
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Input comparator speed
~ -50%
-80%
Vin (d=100ns)
-with input diode-connected
transistors
-without
6.7ns
5.5ns
13ns
New comparator:
appreciably faster
across all corners
Vin (d=200ns)
no significant difference
between the two, the diodeconnected transistors don’t
conduce
3.3ns
old comparator
Vin (d=300ns)
NB: speed function of input voltage. In this simulation Vin=Vthreshold ±100mV, trise=tfall=10ns
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High ref, Qin=900pC (~18GeV) (1):
link charge
(d=100ns-200ns-300ns)
LEC charge
LEC charge LEC charge
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High ref, Qin=900pC (~18GeV) (2):
Q_input
Q_input
Q_input
Q_HEC
Q_HEC
link charge (detail)
(d=100ns-200ns-300ns)
Q_HEC
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High ref, Qin=900pC (~18GeV) (3):
The new comparator is
generally faster and loses less
charge for very fast inputs
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High ref, Qin=900pC (~18GeV) (4):
d=100ns
d=200ns
old comp
new comp
Significant improvement for slower
signals too.
(NB: old and new configurations in these
presentation have the same link, the only
difference is the input comparator)
d=300ns
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Low ref, Qin=900pC (~18GeV) (1):
Q_HEC_old
Q_HEC_old
Q_HEC_old
Q_HEC_new
Q_HEC_new
Q_HEC_new
Q_input
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Low ref, Qin=900pC (~18GeV) (2):
new
Vin
old
new
old
new
old
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Low ref, Qin=900pC (~18GeV) (3):
new
Vin
old
new
old
new
old
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Low ref, Qin=900pC (~18GeV) (3):
new
old
new
old
new
Current: fast (~ns) feature,
total current comparable
(NB: absolute value in this graph
due to ancillary circuits in the
schematic)
old
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Link leakage current:
Sample of the current
through the HEC/LEC link for
high-low input references,
different process corners.
The concern was that a
possible offset between the
amplifiers’ references could
cause significant current.
The current is <30 pA in the
worst case so it will be easily
handled by the feedback
compensation circuit
[fA]
[pA]
low_ref (0.4V),
comparator thresh=0.35V
T=
-10°C ÷ +50°C
Vdd=
3.0V ÷ 3.6V
Voffset_preAmps=±1.2mV
high_ref (1.6V),
comparator thresh=1.65V
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