AD8611 datasheet(9/12 Pages) AD

9 / 12 page

AD8611/AD8612

–9–

REV. 0

A 5 V High-Speed Window Comparator

A window comparator circuit is used to detect when a signal is

between two fixed voltages. The AD8612 can be used to create

a high-speed window comparator, as shown in Figure 20. Here,

the reference window voltages are set as:

The output of the A1 comparator will go high when the input

signal exceeds VHI, and the output of A2 will go high only when

VIN drops below VLO. When the input voltage is between VHI and

VLO, both comparator outputs will be low, turning off both Q1 and

Q2, thus driving VOUT to a high state. If the input signal goes

outside of the reference voltage window, then VOUT will go low.

To ensure a minimum of switching delay, high-speed transistors

are recommended for Q1 and Q2. Using the AD8612 with

2N3960 transistors provides a total propagation delay from

VIN to VOUT of less than 10 ns.

Table III. Window Comparator Output States

VHI

VIN

AD612

VLO

AD612

VOUT

500

Q1, Q2 = 2N3960

500

PINS 2 AND 13 ARE NO CONNECTS

Figure 20. A High-Speed Window Comparator

VOUT

Input Voltage

= 200 mV

VIN < VLO

+ 5 V

VLO < VIN < VHI

= 200 mV

VIN > VHI

AD8611 Datasheet(PDF) 9 Page - Analog Devices