AD8611/AD8612

Data Sheet

Rev. B | Page 12 of 20

pole into the feedback network. This has the effect of increasing

the amount of hysteresis at high frequencies, which is useful

when comparing relatively slow signals in high frequency noise

Equation 1.

CLOCK TIMING RECOVERY

Comparators are often used in digital systems to recover clock

timing signals. High speed square waves transmitted over any

distance, even tens of centimeters, can become distorted due to

stray capacitance and inductance. Poor layout or improper

termination can also cause reflections on the transmission line,

further distorting the signal waveform. A high speed comparator

can recover the distorted waveform while maintaining a

minimum of delay.

100 mV peak-to-peak distorted clock signal into a 4 V peak-to-

peak square wave. The lower trace is the input to the AD8611,

and the upper trace is the QA or QB output from the comparator.

The AD8611 is powered from a 5 V single supply.

TIME (10ns/DIV)

2V/DIV

20mV/DIV

Figure 25. Using the AD8611 to Recover a Noisy Clock Signal

A 5 V, HIGH SPEED WINDOW COMPARATOR

A window comparator circuit detects when a signal is between

two fixed voltages. The AD8612 can create a high speed window

comparator, as shown in Figure 26. In this example, the

reference window voltages are set as:

4

3

4

2

1

2

R

R

R

V

R

R

R

V

LO

HI

+

=

+

=

The output of the A1 comparator goes high when the input

To ensure a minimum of switching delay, the use of high speed

transistors is recommended for Q1 and Q2. Using the AD8612

with 2N3960 transistors provides a total propagation delay from

Table 8. Window Comparator Output States

Input Voltage

≈ 200 mV

+5 V

≈ 200 mV

5V

5V

R1

R2

6

7

3

4

10

1

AD8612

1k

Ω

5V

R3

R4

9

8

11

5

12

14

AD8612

1k

Ω

Q1

5V

1k

Ω

500

Ω

Q2

500

Ω

NOTES

1. Q1, Q2 = 2N3960.

2. PINS 2 AND 13 ARE NO CONNECTS.

A1

A2

Figure 26. A High Speed Window Comparator