ICL8038 Datasheet, PDF (8/10 Pages) Intersil Corporation – Precision Waveform Generator/Voltage Controlled Oscillator

V₁+
INPUT
ICL8038
VCO
IN
PHASE
DETECTOR
AMPLIFIER
R₁
FM BIAS
DUTY
CYCLE
FREQUENCY
ADJUST
74
5
SQUARE
WAVE
OUT
9
ICL8038
DEMODULATED
FM
R₂
LOW PASS
FILTER
8 ₁₀
11
TIMING
CAP.
V₂+
63
2
TRIANGLE
OUT
SINE WAVE
OUT
12 ¹
SINE WAVE
ADJ.
SINE WAVE
ADJ.
V-/GND
FIGURE 9. WAVEFORM GENERATOR USED AS STABLE VCO IN A PHASE-LOCKED LOOP
HIGH FREQUENCY
SYMMETRY
1,000pF
1N753A
(6.2V)
1kΩ
+15V
-
1kΩ
741
+
-V_IN
P₄
10kΩ
OFFSET
500Ω
4.7kΩ
4.7kΩ
10kΩ
1MΩ
4
5
69
100kΩ
ICL8038
8 _{FUNCTION GENERATOR} 3
10
11
3,900pF
12 ²
100kΩ
+
50µF
15V
SINE WAVE
DISTORTION
100kΩ
LOW FREQUENCY
SYMMETRY
+15V
-
741
+
SINE WAVE
OUTPUT
-15V
FIGURE 10. LINEAR VOLTAGE CONTROLLED OSCILLATOR
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.
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+ (R₁, R₂ as shown) if the
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”.
8