LMV7271_08 NSC [National Semiconductor], LMV7271_08 Datasheet - Page 14

• Manufacturer Part Number: LMV7271_08
• Description: Single & Dual, 1.8V Low Power Comparators with Rail-to-Rail Input
• Manufacturer: NSC [National Semiconductor]

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NEGATIVE PEAK DETECTOR
For the negative detector, the output transistor of the com-
parator acts as a low impedance current sink. Since there is
no pull-up resistor, the only discharge path will be the 1MΩ
resistor and any load impedance used. Decay time is
changed by varying the 1MΩ resistor.
SQUARE WAVE GENERATOR
A typical application for a comparator is as a square wave
oscillator. The circuit below generates a square wave whose
period is set by the RC time constant of the capacitor C
resistor R
signal propagation delay of the comparator, and by the ca-
pacitive loading at the output, which limits the output slew
rate.
4
. The maximum frequency is limited by the large
FIGURE 9. Negative Peak Detector
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1
and
14
To analyze the circuit, consider it when the output is high. That
implies that the inverted input (V
verting input (V
R
inverting input. The value of V
If R
At this point the comparator switches pulling down the output
to the negative rail. The value of V
If R
The capacitor C
V
parator switches again, bringing it back to the initial stage. The
time period is equal to twice the time it takes to discharge
C
the formula for the frequency is:
F = 1/(2·R
C
4,
1
from 2V
1
1
decreases till it is equal to V
and the voltage V
= R
= R
2
2
= R
= R
4
·C
CC
FIGURE 10. Squarewave Oscillator
1
/3 to V
3
3
·ln2)
A
then V
then V
1
). This causes the C
now discharges through R
CC
A1
A2
C
/3, which is given by R
increases till it is equal to the non-
= 2V
= V
CC
CC
A
/3
/3
at this point is
A2
C
) is lower than the non-in-
A
, at which point the com-
1
at this point is
to get charged through
4
, and the voltage
4
C
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1
.ln2. Hence
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