AD8468

Rev. 0 | Page 8 of 12

Q OUTPUT

INPUT VOLTAGE

500mV OVERDRIVE

10mV OVERDRIVE

DISPERSION

Figure 10. Propagation Delay—Overdrive Dispersion

Q OUTPUT

INPUT VOLTAGE

10V/ns

1V/ns

DISPERSION

Figure 11. Propagation Delay—Slew Rate Dispersion

CROSSOVER BIAS POINT

Rail-to-rail inputs of this type, in both op amps and comparators,

have a dual front-end design. Certain devices are active near the

predetermined point in the common-mode range, a crossover

current reverses, and there are changes in measured offset

voltages and currents.

The AD8468 slightly elaborates on this scheme. Crossover

points can be found at approximately 0.8 V and 1.6 V.

MINIMUM INPUT SLEW RATE REQUIREMENT

With the rated load capacitance and normal good PC board

design practice, as discussed in the Optimizing Performance

section, these comparators should be stable at any input slew

rate with no hysteresis. Broadband noise from the input stage is

observed in place of the violent chattering seen with most other

high speed comparators. With additional capacitive loading or

poor bypassing, oscillation may be encountered. These oscilla-

tions are due to the high gain bandwidth of the comparator in

combination with feedback through parasitics in the package

and PC board. In many applications, chattering is not harmful.