LT1720 Linear Technology, LT1720 Datasheet - Page 22

• Manufacturer Part Number: LT1720
• Description: 4ns/ 150MHz Dual Comparator with Independent Input/Output Supplies
• Manufacturer: Linear Technology

LT1720/LT1721
Coincidence Detector
High speed comparators are especially suited for interfac-
ing pulse-output transducers, such as particle detectors,
to logic circuitry. The matched delays of a monolithic dual
are well suited for those cases where the coincidence of
two pulses needs to be detected. The circuit of Figure 19
is a coincidence detector that uses an LT1720 and discrete
components as a fast AND gate.
The reference level is set to 1V, an arbitrary threshold. Only
when both input signals exceed this will a coincidence be
detected. The Schottky diodes from the comparator out-
puts to the base of the MRF-501 form the AND gate, while
the other two Schottkys provide for fast turn-off. A logic
22
APPLICATIONS
U
INFORMATION
U
W
COINCIDENCE COMPARATORS
51
51
5V
Figure 19. A 3ns Coincidence Detector
0.1 F
3.9k
1k
U
–
–
+
+
1/2 LT1720
1/2 LT1720
AND gate could instead be used, but would add consider-
ably more delay than the 300ps contributed by this dis-
crete stage.
This circuit can detect coincident pulses as narrow as 3ns.
For narrower pulses, the output will degrade gracefully,
responding, but with narrow pulses that don’t rise all the
way to “high” before starting to fall. The decision delay is
4.5ns with input signals 50mV or more above the refer-
ence level. This circuit creates a TTL compatible output but
it can typically drive CMOS as well.
For a more detailed description of the operation of this
circuit, see Application Note 75, pages 10 and 11.
4 1N5711
300ps AND GATE
5V
300
5V
MRF501
300
1720/21 F19
OUTPUT
GROUND
CASE LEAD