LT1720 Linear Technology, LT1720 Datasheet - Page 28

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

LT1720/LT1721
Pulse Stretcher
For detecting short pulses from a single sensor, a pulse
stretcher is often required. The circuit of Figure 20 acts as
a one-shot, stretching the width of an incoming pulse to a
consistent 100ns. Unlike a logic one-shot, this LT1720-
based circuit requires only 100pV-s of stimulus to trigger.
The circuit works as follows: Comparator C1 functions as
a threshold detector, whereas comparator C2 is config-
ured as a one-shot. The first comparator is prebiased with
a threshold of 8mV to overcome comparator and system
offsets and establish a low output in the absence of an
input signal. An input pulse sends the output of C1 high,
which in turn latches C2’s output high. The output of C2
is fed back to the input of the first comparator, causing
regeneration and latching both outputs high. Timing
28
TYPICAL
RELATED PARTS
PART NUMBER
LT1016
LT1116
LT1394
LT1671
LT1719
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
[phone] FAX: [phone] www.linear-tech.com
APPLICATION
DESCRIPTION
UltraFast Precision Comparator
12ns Single Supply Ground-Sensing Comparator
7ns, UltraFast, Single Supply Comparator
60ns, Low Power, Single Supply Comparator
4.5ns Single Supply 3V/5V Comparator
PULSE SOURCE
50
U
51
Figure 20. A 1ns Pulse Stretcher
6.8k
24
1N5711
15k
–
1/2 LT1720
+
C1
1/2 LT1720
5V
1k
R
2k
C2
capacitor C now begins charging through R and, at the
end of 100ns, C2 resets low. The output of C1 also goes
low, latching both outputs low. A new pulse at the input
of C1 can now restart the process. Timing capacitor C can
be increased without limit for longer output pulses.
This circuit has an ultimate sensitivity of better than 14mV
with 5ns to 10ns input pulses. It can even detect an
avalanche generated test pulse of just 1ns duration with
sensitivity better than 100mV.
better than the coincidence detector of Figure 14 because
the one-shot is configured to catch just 100mV of upward
movement from C1’s V
detector’s 3ns specification is based on a full, legitimate
logic high, without the help of a regenerative one-shot.
6
See Linear Technology Application Note 47, Appendix B. This circuit can detect the output of the
pulse generator described after 40dB attenuation.
–
+
0.01 F
2k
2k
Industry Standard 10ns Comparator
Single Comparator Similar to the LT1720/LT1721
COMMENTS
Single Supply Version of LT1016
6mA Single Supply Comparator
450 A Single Supply Comparator
C
100pF
1720/21 F20
OUTPUT
100ns
OL
, whereas the coincidence
LINEAR TECHNOLOGY CORPORATION 1998
6
17201f LT/TP 1099 4K • PRINTED IN USA
It can detect short events