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AD790 4.7V

BIPOLAR SIGNAL INPUT

0.3V 400Ω * 1

1k Ω

8

2 STANDARD SCHOTTKY DIODE

5 7

TTL LEVEL OUTPUT

6

3 4

GND

• A RESISTOR UP TO 10kΩΩMAYBE 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 bipolar signal required either a dual (± ) power supply or a reference 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 –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.

C1323–10–10/89

Bipolar to CMOS/TTL + 5V

– 5V

OUTLINE DIMENSIONS Dimensions shown in inches and (mm).

8-Pin Plastic Mini-DIP (N-8) Package

8-Pin Cerdip (Q-8) Package

PRINTED IN U.S.A.

SOIC (SO-8) Package

–8–

REV. B