AD790 Analog Devices, Inc., AD790 Datasheet - Page 8

• Manufacturer Part Number: AD790
• Description: Fast, Precision Comparator
• Manufacturer: Analog Devices, Inc.

AD790
Figure 11. A Bipolar to CMOS TTL Line Receiver (N, Q
Package Pinout)
STANDARD
SCHOTTKY
*
A RESISTOR UP TO 10k
REDUCE THE SOURCE AND SINK CURRENT OF
THE DRIVER. HOWEVER, THIS WILL SLIGHTLY
LOWER THE MAXIMUM USABLE CLOCK RATE.
DIODE
1k
Ω
BIPOLAR
SIGNAL
INPUT
–
5V
Ω
2
3
MAYBE USED TO
1
4
8
GND
+
6
5V
5
400 *
7
Ω
TTL
LEVEL
OUTPUT
4.7V
0.3V
–8–
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 –V
(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.
REV. D
S
,