AD8564

Rev. B | Page 10 of 12

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.

COMPARATOR

SIGNAL

R1

R2

Figure 17. 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,

switching voltage. The output switches high when the input

(

)

REF

REF

HI

V

R2

R1

R1

V

V

V

+

−

−

=

+

1

(1)

⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

+

−

=

R2

R1

R1

V

V

REF

LO

1

(2)

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

R2

C

f

F

P

π

=

2

1

, the hysteresis

in Equation 1.