ICL8038
With a dual supply voltage the external capacitor on Pin 10 can
V+
be shorted to ground to halt the ICL8038 oscillation. Figure 7
shows a FET switch, diode ANDed with an input strobe signal
to allow the output to always start on the same slope.
R
L
R
R
A
B
4
5
6
7
8
9
3
V+
R
ICL8038
11
R
R
B
15K
A
4
5
7
8
9
FM
2
10
12
C
81K
ICL8038
1N914
V- OR GND
2
FIGURE 5A. CONNECTIONS FOR FREQUENCY MODULATION
11
10
1N914
C
2N4392
-15V
STROBE
V+
100K
OFF
R
L
SWEEP
VOLTAGE
R
R
A
B
+15V (+10V)
-15V (-10V)
ON
4
5
6
9
3
FIGURE 7. STROBE TONE BURST GENERATOR
8
ICL8038
11
To obtain a 1000:1 Sweep Range on the ICL8038 the
voltage across external resistors R and R must decrease
A
B
to nearly zero. This requires that the highest voltage on
control Pin 8 exceed the voltage at the top of R and R by a
2
10
12
A
B
few hundred mV. The Circuit of Figure 8 achieves this by
using a diode to lower the effective supply voltage on the
ICL8038. The large resistor on pin 5 helps reduce duty cycle
variations with sweep.
C
81K
V- OR GND
FIGURE 5B. CONNECTIONS FOR FREQUENCY SWEEP
FIGURE 5.
The linearity of input sweep voltage versus output frequency
can be significantly improved by using an op amp as shown
in Figure 10.
Typical Applications
The sine wave output has a relatively high output impedance
(1kΩ Typ). The circuit of Figure 6 provides buffering, gain
and amplitude adjustment. A simple op amp follower could
also be used.
+10V
1N457
DUTY CYCLE
15K
0.1µF
1K
4.7K
V+
4.7K
R
R
B
A
AMPLITUDE
100K
5
4
6
9
3
2
4
5
6
7
8
2
+
741
-
10K
FREQ.
8
ICL8038
11
ICL8038
20K
10
12
4.7K
10
11
DISTORTION
100K
0.0047µF
20K
≈15M
C
-10V
V-
FIGURE 8. VARIABLE AUDIO OSCILLATOR, 20Hz TO 20kHzY
FIGURE 6. SINE WAVE OUTPUT BUFFER AMPLIFIERS
7
INTERSIL [ Intersil ]
