LT1116_15 Datasheet, PDF (7/8 Pages) Linear Technology – 12ns, Single Supply Ground-Sensing Comparator

LT1116
APPLICATIO S I FOR ATIO
High Speed Adaptive Trigger Circuit
Line receivers often require an adaptive trigger to
compensate for variations in signal amplitude and DC
offsets. The circuit in Figure 3 triggers on 2mV to 200mV
signals from 100Hz to 10MHz from a single 5V rail. The
trigger level is the average of the input signal’s positive and
negative peaks stored on 0.005µF capacitors. Pairs of
NPN and PNP transistors are used instead of diodes to
temperature compensate the peak detector.
To achieve single supply operation, the input signal must
be shifted into the pre-amplifier’s common mode range.
The input amplifier A1 adds a 1V level shift, while A2
provides a gain of 20 for high frequency signals.
Capacitors C1 and C2 insure that low frequency signals
see unity gain. Bandwidth limiting in A1 and A2 does not
affect triggering because the adaptive trigger threshold
varies ratiometrically to maintain circuit output.
5pF
1kΩ
CABLE _1kΩ
5V
V_IN
–
4R
A1
5V
200Ω
200Ω
LT1191
+
47µF
R
1000pF _100Ω
NPN = 2N3904
PNP = 2N3906
5V
3kΩ
1%
5V
+
A2
LT1192
–
0.005µF
0.005µF
500pF
5V
3MΩ
+
A3
3MΩ _LT1006
–
1kΩ
50Ω
3kΩ
1%
C1
100µF
C2
0.1µF
Figure 3. Fast Single Supply Adaptive Trigger
0.1µF
500Ω
5V
LT1116
Q
Q
TRIGGER
OUT
LT1116 • AI03
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
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