LT1394CS8#TR Linear Technology, LT1394CS8#TR Datasheet - Page 14

• Manufacturer Part Number: LT1394CS8#TR
• Description: IC COMPARATOR 7NS LOW PWR 8SOIC
• Manufacturer: Linear Technology
• Series: UltraFast™r
• Type: General Purposer

Specifications of LT1394CS8#TR

• Number Of Elements: 1
• Output Type: CMOS, Complementary, TTL
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (0.154", 3.90mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

LT1394
APPLICATIONS
High Speed Adaptive Trigger Circuit
Line and fibre-optic receivers often require an adaptive
trigger to compensate for variations in signal amplitude
and DC offsets. The circuit in Figure 18 triggers on 2mV to
175mV signals from 100Hz to 45MHz 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 excur-
sion 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
always sits midway between the signal’s excursions,
egardless of absolute amplitude. This signal-adaptive volt-
age is buffered by A2 to set the trigger voltage at the
LT1394’s positive input. The LT1394’s negative input is
biased directly from A1’s output. The LT1394’s output, the
circuit’s output, is unaffected by >85:1 signal amplitude
variations. Bandwidth limiting in A1 does not affect trigger-
ing because the adaptive trigger threshold varies
ratiometrically to maintain circuit output.
14
10 F
5V
+
2k
INPUT
U
750
0.1 F
INFORMATION
U
Figure 18. 45MHz Single Supply Adaptive Trigger. Output Comparator’s
Threshold Varies Ratiometrically with Input Amplitude, Maintaining Data
Integrity over > 85:1 Input Amplitude Range
+
36
100 F
+
–
LT1227
A1
510
W
5V
0.1 F
units. This point
Q1
Q3
U
13
15
3
2
2k
0.005 F
14
1
2k
12
5
10
11
6
4
5V
Q2
Q4
0.005 F
3M
Figure 19 shows operating waveforms at 45MHz. Trace A’s
input produces Trace B’s amplified output at A1. The
comparator’s output is Trace C.
Split supply versions of this circuit can achieve band-
widths to 50MHz with wider input operating range.
500pF
3M
A = 0.1V/DIV
B = 0.1V/DIV
C = 5V/DIV
Figure 19. Adaptive Trigger Responding to a 40MHz,
5mV Input. Input Amplitude Variations from 2mV to
175mV Are Accommodated
+
–
470
LT1006
A2
5V
0.1 F
470
Q1, Q2, Q3, Q4 = CA3096 ARRAY:
TIE SUBSTRATE (PIN 16) TO GROUND
50ns/DIV
= 1N4148
+
–
LT1394
AN72 F64
TRIGGER
OUT
1394 F18