icl8038 Intersil Corporation, icl8038 Datasheet - Page 8

• Manufacturer Part Number: icl8038
• Description: Precision Waveform Generator/voltage Controlled Oscillator
• Manufacturer: Intersil Corporation

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