ADCMP606_0610 AD [Analog Devices], ADCMP606_0610 Datasheet - Page 11

• Manufacturer Part Number: ADCMP606_0610
• Description: Rail-to-Rail, Very Fast, 2.5 V to 5.5 V, Single-Supply CML Comparators
• Manufacturer: AD [Analog Devices]

COMPARATOR PROPAGATION DELAY
DISPERSION
The ADCMP606/ADCMP607 comparators are designed to
reduce propagation delay dispersion over a wide input overdrive
range of 5 mV to V
variation in propagation delay that results from a change in the
degree of overdrive or slew rate (that is, how far or how fast the
input signal exceeds the switching threshold).
Propagation delay dispersion is a specification that becomes
important in high speed, time-critical applications, such as data
communication, automatic test and measurement, and instru-
mentation. It is also important in event-driven applications, such
as pulse spectroscopy, nuclear instrumentation, and medical
imaging. Dispersion is defined as the variation in propagation
delay as the input overdrive conditions are changed (Figure 15
and Figure 16).
The device dispersion is typically 2.3 ns as the overdrive varies
from 10 mV to 125 mV. This specification applies to both
positive and negative signals because each device has very closely
matched delays for positive-going and negative-going inputs as
well as very low output skews.
COMPARATOR HYSTERESIS
The addition of hysteresis to a comparator is often desirable in a
noisy environment, or when the differential input amplitudes
are relatively small or slow moving. Figure 17 shows the transfer
function for a comparator with hysteresis. As the input voltage
approaches the threshold (0.0 V, in this example) from below
the threshold region in a positive direction, the comparator
switches from low to high when the input crosses +V
INPUT VOLTAGE
INPUT VOLTAGE
Q/Q OUTPUT
Q/Q OUTPUT
Figure 15. Propagation Delay—Overdrive Dispersion
Figure 16. Propagation Delay—Slew Rate Dispersion
CCI
− 1 V. Propagation delay dispersion is the
10V/ns
1V/ns
500mV OVERDRIVE
10mV OVERDRIVE
DISPERSION
DISPERSION
V
V
N
N
± V
± V
OS
OS
H
/2, and the
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new switching threshold becomes −V
in the high state until the new threshold, −V
below the threshold region in a negative direction. In this manner,
noise or feedback output signals centered on 0.0 V input cannot
cause the comparator to switch states unless it exceeds the region
bounded by ±V
The customary technique for introducing hysteresis into a
comparator uses positive feedback from the output back to the
input. One limitation of this approach is that the amount of
hysteresis varies with the output logic levels, resulting in
hysteresis that is not symmetric about the threshold. The
external feedback network can also introduce significant
parasitics that reduce high speed performance and induce
oscillation in some cases.
This ADCMP607 comparator offers a programmable hysteresis
feature that can significantly improve accuracy and stability.
Connecting an external pull-down resistor or a current source
from the LE/HYS pin to GND, varies the amount of hysteresis
in a predictable, stable manner. Leaving the LE/HYS pin
disconnected or driving this pin high removes hysteresis. The
maximum hysteresis that can be applied using this pin is
approximately 160 mV. Figure 18 illustrates typical hysteresis
applied as a function of the external resistor value, and Figure 7
illustrates typical hysteresis as a function of the current.
400
350
300
250
200
150
100
50
0
50 100 150 200 250 300 350 400 450 500 550 600 650
Figure 17. Comparator Hysteresis Transfer Function
Figure 18. Hysteresis vs. R
H
/2.
–V
2
H
V
OUTPUT
CC
H
= 2.5V
V
YS
OL
ADCMP606/ADCMP607
0
RESISTOR (kΩ)
V
OH
HYS
H
/2. The comparator remains
Control Resistor
+V
2
H
INPUT
H
/2, is crossed from