LT1721IGN datasheet(28/28 Pages) LINER

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LT1720/LT1721

17201f LT/TP 1099 4K • PRINTED IN USA

©LINEAR TECHNOLOGY CORPORATION 1998

TYPICAL APPLICATION

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

(408)432-1900 q FAX:(408)434-0507 q www.linear-tech.com

PART NUMBER

DESCRIPTION

COMMENTS

LT1016

UltraFast Precision Comparator

Industry Standard 10ns Comparator

LT1116

12ns Single Supply Ground-Sensing Comparator

Single Supply Version of LT1016

LT1394

7ns, UltraFast, Single Supply Comparator

6mA Single Supply Comparator

LT1671

60ns, Low Power, Single Supply Comparator

450

µA Single Supply Comparator

LT1719

4.5ns Single Supply 3V/5V Comparator

Single Comparator Similar to the LT1720/LT1721

RELATED PARTS

Figure 20. A 1ns Pulse Stretcher

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

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.6 It can detect short events

better than the coincidence detector of Figure 14 because

the one-shot is conﬁgured to catch just 100mV of upward

movement from C1’s VOL, whereas the coincidence

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.

PULSE SOURCE

1/2 LT1720

Ω

6.8k

1N5711

Ω

15k

1720/21 F20

100pF

0.01

µF

OUTPUT

100ns

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