AD790
Bipolar to CMO S/TTL
+ 5V
–
5V
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/T T L 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.
T he 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 –VS,
(in this case ground) it is permissible to bring one of the inputs
a few hundred mV below ground. T he comparator switches
around this level and produces a CMOS/T T L compatible
swing. T he circuit will operate to switching frequencies of
20 MHz.
4.7V
0.3V
BIPOLAR
SIGNAL
INPUT
400Ω*
1
1k
Ω
8
2
3
TTL
LEVEL
OUTPUT
5
6
7
STANDARD
SCHOTTKY
DIODE
4
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 19. A Bipolar to CMOS TTL Line Receiver (N, Q
Package Pinout)
O UTLINE D IMENSIO NS
D imensions shown in inches and (mm).
8-P in P lastic Mini-D IP (N-8) P ackage
8-P in Cerdip (Q-8) P ackage
SO IC (SO -8) P ackage
–8–
REV. B
ADI [ ADI ]
