AD790
Bipolar to CMOS/TTL
– 5V
BIPOLAR
SIGNAL
INPUT
1k
Ω
2
STANDARD
SCHOTTKY
DIODE
1
8
5
7
3
4
6
TTL
LEVEL
OUTPUT
+ 5V
4.7V
0.3V
400
Ω
*
GND
*A RESISTOR UP TO 10kΩ
Ω
MAYBE USED TO
REDUCE THE SOURCE AND SINK CURRENT OF
THE DRIVER. HOWEVER, THIS WILL SLIGHTLY
LOWER THE MAXIMUM USABLE CLOCK RATE.
Figure 19. A Bipolar to CMOS TTL Line Receiver (N, Q
Package Pinout)
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 bi-
polar 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 19 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 –V
S
,
(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.
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
8-Pin Plastic Mini-DIP (N-8) Package
8-Pin Cerdip (Q-8) Package
SOIC (SO-8) Package
PRINTED IN U.S.A.
–8–
REV. B
C1323–10–10/89
AD [ ANALOG DEVICES ]
