ICL8038
V +
2
DUTY
CYCLE
R
1
FREQUENCY
ADJUST
TRIANGLE
OUT
FM BIAS
V +
1
6
4
5
7
9
3
2
1
SINE WAVE
OUT
SQUARE
WAVE
OUT
ICL8038
11
VCO
IN
PHASE
DETECTOR
DEMODULATED
FM
SINE WAVE
ADJ.
INPUT
AMPLIFIER
8
10
12
R
2
TIMING
CAP.
SINE WAVE
ADJ.
LOW PASS
FILTER
V-/GND
FIGURE 9. WAVEFORM GENERATOR USED AS STABLE VCO IN A PHASE-LOCKED LOOP
HIGH FREQUENCY
SYMMETRY
10kΩ
100kΩ
500Ω
4.7kΩ
1N753A
4.7kΩ
(6.2V)
1MΩ
1kΩ
100kΩ
1,000pF
LOW FREQUENCY
SYMMETRY
4
5
6
9
+15V
SINE WAVE
OUTPUT
-
741
+
1kΩ
ICL8038
FUNCTION GENERATOR
+15V
8
3
-
-V
741
+
IN
P
4
+
2
10
11
12
50µF
15V
10kΩ
OFFSET
100kΩ
SINE WAVE
3,900pF
DISTORTION
-15V
FIGURE 10. LINEAR VOLTAGE CONTROLLED OSCILLATOR
Use in Phase Locked Loops
Its high frequency stability makes the ICL8038 an ideal Second, the DC output level of the amplifier must be made
building block for a phase locked loop as shown in Figure 10. compatible to the DC level required at the FM input of the
In this application the remaining functional blocks, the phase waveform generator (pin 8, 0.8V+). The simplest solution here
detector and the amplifier, can be formed by a number of is to provide a voltage divider to V+ (R , R as shown) if the
1
2
available ICs (e.g., MC4344, NE562, HA2800, HA2820).
amplifier has a lower output level, or to ground if its level is
higher. The divider can be made part of the low-pass filter.
In order to match these building blocks to each other, two
steps must be taken. First, two different supply voltages are This application not only provides for a free-running fre-
used and the square wave output is returned to the supply of quency with very low temperature drift, but is also has the
the phase detector. This assures that the VCO input voltage unique feature of producing a large reconstituted sinewave
will not exceed the capabilities of the phase detector. If a signal with a frequency identical to that at the input.
smaller VCO signal is required, a simple resistive voltage
For further information, see Harris Application Note AN013,
divider is connected between pin 9 of the waveform genera-
“Everything You Always Wanted to Know About the
tor and the VCO input of the phase detector.
ICL8038”.
8-160
HARRIS [ HARRIS CORPORATION ]
