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AN1882 डेटा पत्रक PDF( Datasheet डाउनलोड )


डेटा पत्रक - NE568A as a Wideband FM Modulator - Philips

भाग संख्या AN1882
समारोह NE568A as a Wideband FM Modulator
मैन्युफैक्चरर्स Philips 
लोगो Philips लोगो 
पूर्व दर्शन
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<?=AN1882?> डेटा पत्रक पीडीएफ

AN1882 pdf
Philips Semiconductors
The NE568A as a wideband FM modulator
Application note
AN1882
0.1µF
4.7µF
100pF
VMOD
INPUT
RP
ENI
F PN
B BB
Y YY
P PP
1.8k
2.7k
+2.65V
2k
10µH
2.7k
+5V
freq. adj.
2k
16 1 7
18k
RFB
18
NE568A
0.1µF
30k
17
.01µF
20
1k
CL
19
.01µF
4
RL
1k
14 15 12 2
3 13 5
CO
CLPF
3.9k
2k
+6V
14
17
+
RFC
10
8
3
RFC
–6V
NE5539
MODULATOR
75OUTPUT
CL = 82pF
RL = 100
Figure 4. NE568A FM Modulation
SR01129
Calibration of the Frequency Deviation
The single-sided frequency deviation is a function of the amplitude
of the modulating signal and can be estimated by use of the graph in
Figure 5. Alternately, the exact modulation input amplitude required
for a given frequency deviation may be determined by use of the
standard Bessel function using the first carrier null method at the
assigned center frequency as described in the example below.
20
Next, a sine wave generator is set to FMOD and this signal fed into
the NE568A modulator. The modulator output signal is now
monitored with a spectrum analyzer as shown in the setup diagram
below (Figure 6). The input signal amplitude is increased from zero
amplitude upward until the 70MHz carrier spectral line begins to fall
(see Figure 7). As the amplitude is carefully increased, a definite
null will occur. Record the amplitude of the 2.9MHz generator at the
null. This is the required modulation input amplitude for operating at
a frequency deviation of 10% for any modulating frequency.
ATTEN 10dB
MKR -48.83dBm
16
RL 0dBm
10dBm/
70.00MHz
12
FPKp
8
4
Figure 6. Carrier Null Test
ATTEN 10dB
RL 0dBm
10dBm/
MKR -48.83dBm
70.00MHz
0
0
0.333
0.667
1
1.333
1.667
2
Vn
VOLTS (RMS)
SR01130
Figure 5. Modulator Frequency Deviation vs Input Volts (RMS)
Example: The first carrier null Bessel constant, B, is 2.4048. Using
this relationship and the modulation index equation as shown below,
the modulator can be accurately calibrated to the desired deviation.
For a center frequency of 70MHz and a desired modulator peak
frequency deviation of 10% (±7MHz), the proper modulating signal
frequency is first calculated by the relationship,
FMOD = FDEV/B
= 7 MHz/2.4048
= 2.9 MHz
START
22.50MHz
RBW 1.0MHz
VBW 1.0MHz
STOP 117.50MHz
SWP 50
SR01131
START
22.50MHz
RBW 1.0MHz
VBW 1.0MHz
STOP 117.50MHz
SWP 50SR01131
Figure 7. First Carrier Null Spectrum at 70MHz
1996 Jan 29
2

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