AD790

REV.

–8–

2

3

1

4

6

7

5

8

TTL

LEVEL

OUTPUT

400 *

5V

+

GND

STANDARD

SCHOTTKY

DIODE

1k

A RESISTOR UP TO 10k

MAYBE USED TO

REDUCE THE SOURCE AND SINK CURRENT OF

THE DRIVER. HOWEVER, THIS WILL SLIGHTLY

LOWER THE MAXIMUM USABLE CLOCK RATE.

*

BIPOLAR

SIGNAL

INPUT

4.7V

0.3V

5V

–

Ω

Ω

Ω

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 k

Ω 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

(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.

E