
AD9696/AD9698
–5–
REV. B
t
H
50%
50%
LATCH
ENABLE
DIFFERENTIAL
INPUT VOLTAGE
Q
TWO DIODES
ABOVE GROUND
LATCH
COMPARE
Q
t
PD
t
PD (E)
V
OS
– MINIMUM SETUP TIME (Typically 1.7ns)
– MINIMUM HOLD TIME (Typically 1.9ns)
– INPUT TO OUTPUT DELAY
– LATCH ENABLE TO OUTPUT DELAY
t
H
t
PD
t
S
t
PD (E)
– MINIMUM LATCH ENABLE PULSE WIDTH (Typically 2.5ns)
– INPUT OFFSET VOLTAGE
– OVERDRIVE VOLTAGE
V
OS
V
OD
t
PW (E)
V
OD
V
IN
t
PW (E)
t
S
AD9696/AD9698 Timing Diagram
DIE LAY OUT AND ME CHANICAL INFORMAT ION
Die Dimensions AD9696 . . . . . . . . . . . . . 59
×
71
×
15 (
±
2) mils
AD9698 . . . . . . . . . . . . 79
×
109
×
15 (
±
2) mils
Pad Dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
×
4 mils
Metalization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Aluminum
Backing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . None
Substrate Potential . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . –V
S
Passivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Nitride
T HE ORY OF OPE RAT ION
Refer to the block diagram of the AD9696/AD9698 compara-
tors. T he AD9696 and AD9698 T T L voltage comparator archi-
tecture consists of five basic stages: input, latch, gain, level shift
and output. Each stage is designed to provide optimal perfor-
mance and make it easy to use the comparators.
T he input stage operates with either a single +5-volt supply, or
with a +5-volt supply and a –5.2-volt supply. For optimum
power efficiency, the remaining stages operate with only a single
+5-volt supply. T he input stage is an input differential pair
without the customary emitter follower buffers. T his configura-
tion increases input bias currents but maximizes the input volt-
age range.
A latch stage allows the most recent output state to be retained
as long as the latch input is held high. In this way, the input to
the comparator can be changed without any change in the out-
put state. As soon as the latch enable input is switched to LOW,
the output changes to the new value dictated by the signal ap-
plied to the input stage.
T he gain stage assures that even with small values of input volt-
age, there will be sufficient levels applied to the following stages
to cause the output to switch T T L states as required. A level
shift stage between the gain stage and the T T L output stage
guarantees that appropriate voltage levels are applied from the
gain stage to the T T L output stage.
Only the output stage uses T T L logic levels; this minimum use
of T T L circuits maximizes speed and minimizes power con-
sumption. T he outputs are clamped with Schottky diodes to as-
sure that the rising and falling edges of the output signal are
closely matched.
T he AD9696 and AD9698 represent the state of the art in high
speed T T L voltage comparators. Great care has been taken to
optimize the propagation delay dispersion performance. T his as-
sures that the output delays will remain constant despite varying
levels of input overdrive. T his characteristic, along with closely
matched rising and falling outputs, provides extremely consis-
tent results at previously unattainable speeds.