AD790,pdf datasheet (Fast, Precision Comparator)

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 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 –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.