LMV331 Single / LMV393 Dual / LMV339 Quad
10008007
Solving these equations for t
1
and t
2
t
1
=R
4
C
1
ln2
t
2
=R
5
C
1
ln2
These terms will have a slight error due to the fact that V
max
is not exactly equal to 2/3 V
CC
but is actually reduced by the
diode drop to:
FIGURE 6. Crystal controlled Oscillator
PULSE GENERATOR WITH VARIABLE DUTY CYCLE
The pulse generator with variable duty cycle is just a minor
modification of the basic square wave generator. Providing a
separate charge and discharge path for capacitor C
1
gener-
ates a variable duty cycle. One path, through R
2
and D
2
will
charge the capacitor and set the pulse width (t
1
). The other
path, R
1
and D
1
will discharge the capacitor and set the time
between pulses (t
2
).
By varying resistor R
1
, the time between pulses of the gen-
erator can be changed without changing the pulse width.
Similarly, by varying R
2
, the pulse width will be altered without
affecting the time between pulses. Both controls will change
the frequency of the generator. The pulse width and time be-
tween pulses can be found from:
POSITIVE PEAK DETECTOR
Positive peak detector is basically the comparator operated
as a unit gain follower with a large holding capacitor from the
output to ground. Additional transistor is added to the output
to provide a low impedance current source. When the output
of the comparator goes high, current is passed through the
transistor to charge up the capacitor. The only discharge path
will be the 1 MΩ resistor shunting C1 and any load that is
connected to the output. The decay time can be altered simply
by changing the 1 MΩ resistor. The output should be used
through a high impedance follower to a avoid loading the out-
put of the peak detector.
10008009
FIGURE 7. Pulse Generator
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