AD8564 Analog Devices, Inc., AD8564 Datasheet - Page 10

• Manufacturer Part Number: AD8564
• Description: Quad 7 Ns Single Supply Comparator
• Manufacturer: Analog Devices, Inc.

AD8564
USING HYSTERESIS
Hysteresis can easily be added to a comparator through the
addition of positive feedback. Adding hysteresis to a comparator
offers an advantage in noisy environments where it is not desirable
for the output to toggle between states when the input signal is
near the switching threshold. Figure 17 shows a method for
configuring the AD8564 with hysteresis.
The input signal is connected directly to the inverting input of
the comparator. The output is fed back to the noninverting
input through R2 and R1. The ratio of R1 to R1 + R2 and the
output swing establishes the width of the hysteresis window,
with V
switching voltage. The output switches high when the input
REF
setting the center of the window or the average
Figure 17. Configuring the AD8564 with Hysteresis
V
REF
SIGNAL
R1
COMPARATOR
R2
C
F
Rev. B | Page 10 of 12
voltage is greater than V
the input voltage is less than V
where V
The C
the feedback network. This has the effect of increasing the
amount of hysteresis at high frequencies. This can be useful
when comparing a relatively slow signal in a high frequency
noise environment.
At frequencies greater than
window approaches V
At frequencies less than f
in Equation 1.
V
V
F
HI
LO
capacitor may also be added to introduce a pole into
+
=
=
is the positive supply voltage.
(
V
V
REF
+
−
⎛
⎜
⎜
⎝
1
1
−
−
V
R1
REF
HI
R1
HI
= V
+
P
)
, the threshold voltages remain as it is
R1
and does not switch low again until
R2
+
f
R1
P
+
– 1 V and V
⎞
⎟
⎟
⎠
LO
=
R2
, as given in Equation 2.
2
V
π
C
REF
1
F
R2
LO
, the hysteresis
= 0 V.
(1)
(2)