aida asic davide braga steve thomas asic design group 14 october 2010
DESCRIPTION
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 Now that the original diodes have been replaced by diode-connected pass transistors (not as fast or low impedance) the active-link circuit must take most of the input current. - PowerPoint PPT PresentationTRANSCRIPT
AIDA ASICDavide Braga
Steve Thomas
ASIC Design Group
14 October 2010
14 October 2010 2
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Now that the original diodes have been replaced by diode-connected pass transistors (not as fast or low impedance) the active-link circuit must take most of the input current.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
14 October 2010 3
Input comparator speed
Vin (d=100ns)-with input diode-connected transistors-without
Vin (d=200ns)no significant difference between the two, the diode-connected transistors don’t conduce
Vin (d=300ns)
6.7ns 13ns
New comparator:appreciably fasteracross all corners
old comparator
NB: speed function of input voltage. In this simulation Vin=Vthreshold ±100mV, trise=tfall=10ns
5.5ns 3.3ns
-80%~ -50%
14 October 2010 4
High ref, Qin=900pC (~18GeV) (1):
link charge(d=100ns-200ns-300ns)
Q_i
nput
Q_H
EC
Q_input
Q_HEC
Q_input
Q_HEC
LEC charge
LEC charge LEC charge
14 October 2010 5
High ref, Qin=900pC (~18GeV) (2):
link charge (detail)(d=100ns-200ns-300ns)
Q_input
Q_HEC
Q_input
Q_HEC
Q_input
Q_HEC
14 October 2010 6
new c
omp
old c
omp new comp
old comp new comp
old comp
High ref, Qin=900pC (~18GeV) (3):
The new comparator is generally faster and loses less charge for very fast inputs
14 October 2010 7
old compnew comp
High ref, Qin=900pC (~18GeV) (4):
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=100ns
d=200ns
d=300ns
14 October 2010 8
Low ref, Qin=900pC (~18GeV) (1):
Q_input
Q_HEC_new
Q_HEC_old
Q_HEC_new
Q_HEC_old
Q_HEC_new
Q_HEC_old
14 October 2010 9
Low ref, Qin=900pC (~18GeV) (2):
new
old
new
old
new
old
Vin
14 October 2010 10
Low ref, Qin=900pC (~18GeV) (3):
new
old
new
old
new
old
Vin
14 October 2010 11
Low ref, Qin=900pC (~18GeV) (3):
new
old
new
old
new
old
Current: fast (~ns) feature,total current comparable(NB: absolute value in this graph due to ancillary circuits in the schematic)
14 October 2010 12
Link leakage current:
low_ref (0.4V),comparator thresh=0.35V
high_ref (1.6V),comparator thresh=1.65V
T= -10°C ÷ +50°CVdd= 3.0V ÷ 3.6VVoffset_preAmps= ±1.2mV
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
14 October 2010 13