AD790SQ/883 查看數據表（PDF） - Analog Devices

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AD790SQ/883

Fast, Precision Comparator

Analog Devices 

AD790

– 5V

BIPOLAR

SIGNAL

INPUT

1k Ω

STANDARD

SCHOTTKY

DIODE

+ 5V

400Ω*

1

8

2

5

7

3

6

4

4.7V

0.3V

TTL

LEVEL

OUTPUT

GND

*A RESISTOR UP TO 10kΩ MAYBE USED TO

REDUCE THE SOURCE AND SINK CURRENT OF

THE DRIVER. HOWEVER, THIS WILL SLIGHTLY

LOWER THE MAXIMUM USABLE CLOCK RATE.

Figure 11. A Bipolar to CMOS TTL Line Receiver (N, Q

Package Pinout)

Bipolar to CMOS/TTL

It is sometimes desirable to translate a bipolar signal (e.g.,

± 5 V) coming from a communications cable or another section

of the system to CMOS/TTL logic levels; such an application is

referred to as a line receiver. Previously, the interface to the

bipolar signal required either a dual (± ) power supply or a refer-

ence voltage level about which the line receiver would switch.

The AD790 may be used in a simple circuit to provide a unique

capability: the ability to receive a bipolar signal while powered

from a single 5 V supply. Other comparators cannot perform

this task. Figure 11 shows a 1 kΩ resistor in series with the input

signal which is then clamped by a Schottky diode, holding the

input of the comparator at 0.4 V below ground. Although the

comparator is specified for a common mode range down to –VS,

(in this case ground) it is permissible to bring one of the inputs

a few hundred mV below ground. The comparator switches

around this level and produces a CMOS/TTL compatible swing.

The circuit will operate to switching frequencies of 20 MHz.

–8–

REV. D

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