lt1671cs8-trpbf Linear Technology Corporation, lt1671cs8-trpbf Datasheet - Page 12

• Manufacturer Part Number: lt1671cs8-trpbf
• Description: 60ns, Low Power,single Supply, Ground-sensing Comparator
• Manufacturer: Linear Technology Corporation

PART NUMBER
LT1016
LT1116
LT1394
LT1720
UltraFast is a trademark of Linear Technology Corporation.
LT1671
4MHz Adaptive Trigger Circuit
Line and fiber-optic receivers often require an adaptive
trigger to compensate for variations in signal amplitude
and DC offsets. The circuit in Figure 9 triggers on 2mV to
175mV signal from 100Hz to 4MHz while operating from
a single 5V rail. A1, operating at a gain of 15, provides
wideband AC gain. The output of this stage biases a 2-way
peak detector (Q1 through Q4). The maximum peak is
stored in Q2’s emitter capacitor, while the minimum
excursion is retained in Q4’s emitter capacitor. The DC
value of the midpoint of A1’s output signal appears at the
junction of the 500pF capacitor and the 3M units. This
point always sits midway between the signal’s excursions,
regardless of absolute amplitude. This signal-adaptive
voltage is buffered by A2 to set the trigger voltage at the
10 F
RELATED PARTS
12
TYPICAL
5V
Q1, Q2, Q3, Q4 = CA3096 ARRAY: TIE SUBSTRATE (PIN 16) TO GROUND
+
2k
Figure 9. 4MHz Single Supply Adaptive Trigger. Output Comparator’s Threshold Varies Ratiometrically with
Input Amplitude, Maintaining Data Integrity over >85:1 Input Amplitude Range
= 1N4148
INPUT
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
[phone] FAX: [phone] www.linear-tech.com
750
0.1 F
APPLICATION
+
36
DESCRIPTION
UltraFast
12ns Single Supply Ground-Sensing Comparator
UltraFast Single Supply Comparator
UltraFast Dual Single Supply Comparator
100 F
+
–
LT1227
510
A1
5V
TM
Precision Comparator
0.1 F
U
Q3
Q1
13
15
3
2
2k
1
14
2k
12
5
10
11
6
4
5V
Q2
Q4
0.005 F
0.005 F
3M
3M
500pF
LT1671’s positive input. The LT1671’s negative input is
biased directly from A1’s output. The LT1671’s output, the
circuit’s output, is unaffected by > 85:1 signal amplitude
variations. Bandwidth limiting in A1 does not affect trig-
gering because the adaptive trigger threshold varies
ratiometrically to maintain circuit output.
Figure 10 shows operating waveforms at 4MHz. Trace A’s
input produces Trace B’s amplified output at A1. The
comparator’s output is Trace C.
+
–
470
LT1006
A2
5V
A = 10mV/DIV
B = 50mV/DIV
470
0.1 F
COMMENTS
Industry Standard 10ns Comparator
Single Supply Version of LT1016
7ns, 6mA Single Supply Comparator
Dual 4.5ns, 4mA Single Supply Comparator
C = 1mV/DIV
Figure 10. Adaptive Trigger
Responding to a 4MHz, 5mV Input.
Input Amplitude Variations from 2mV
to 175mV Are Accommodated
1671fs, sn1671 LT/TP 0499 4K • PRINTED IN USA
+
–
LT1671
LINEAR TECHNOLOGY CORPORATION 1998
50ns/DIV
TRIGGER
OUT
1671 F09
1671F10