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Now that the original diodes have been replaced by diode-connected pass transistors (not as fast or low impedance) the active-link circuit must take most of the input current.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