There are
instances wherein the output of an operational
amplifier or a voltage comparator needs to be used for
driving the input of a CMOS or TTL gate. Since the voltage-current
characteristics and requirements of an op-amp or comparator differ from those of a CMOS
or TTL gate, it is good practice to use proper interfacial components
between them when connecting them to each other. Below are some
common techniques used in connecting an op amp or comparator to a CMOS
or TTL gate.
Figure 1.
Interfacing an Op Amp or Comparator to any CMOS gate using the same power supply
When the op
amp or comparator uses the same power supply as the CMOS gate that it is
driving, the simple interfacing technique shown in Figure 1 may be
employed. Here, a current-limiting resistor is just placed between the
op amp/comparator output
and the
CMOS gate input.
Figure 2.
Interfacing
an Op Amp or Comparator to any CMOS gate using
using different power
supplies
When the op
amp or comparator uses a power supply that's different from the supply
used by the CMOS gate that it is driving, the simple interfacing technique shown in Figure
2 may be employed. Here,
aside from a current-limiting resistor between the op amp output and the
CMOS gate input, input protection diodes are placed between the gate
input and the positive supply and between the gate input and ground.
Figure 3.
Interfacing
an Op Amp or Comparator to any TTL gate using the same power supply
When the op
amp or comparator uses the same 5-V power supply as the TTL gate that it
is driving, the simple interfacing technique shown in Figure 3 may be
employed. Here, a current-limiting resistor is just placed between the
op amp/comparator output
and the
TTL gate input. A shunt resistor is also placed across the gate input and
ground.
See Also:
Operational Amplifiers;
Logic Gates;
TTL
See
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