mc13176d ETC-unknow, mc13176d Datasheet - Page 11

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mc13176d

Manufacturer Part Number
mc13176d
Description
Fm/am Transmitter
Manufacturer
ETC-unknow
Datasheet

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Reference Crystal Oscillator (Pins 8 and 9)
number of mechanical modes. The lowest resonant
frequency mode is its fundamental while higher order modes
are called overtones. At each mechanical resonance, a
crystal behaves like a RLC series–tuned circuit having a
large inductor and a high Q. The inductor L s is series
resonance with a dynamic capacitor, C s determined by the
elasticity of the crystal lattice and a series resistance R s ,
which accounts for the power dissipated in heating the
crystal. This series RLC circuit is in parallel with a static
capacitance, C p which is created by the crystal block and by
the metal plates and leads that make contact with it.
resonant mode. It is assumed that other modes of resonance
are so far off frequency that their effects are negligible.
Series resonant frequency, f s is given by;
and parallel resonant frequency, f p is given by;
MOTOROLA RF/IF DEVICE DATA
Selection of Proper Crystal: A crystal can operate in a
Figure 24 is the equivalent circuit for a crystal in a single
f s = 1/2 (L s C s ) 1/2
f p = f s (1 + C s /C p ) 1/2
– 20
– 30
– 40
–10
(dBc)
(dBc)
Figure 22. Modulation Spectrum
Figure 20. Input Data Waveform
MC13175 MC13176
the frequency separation at resonance is given by;
Usually f p is less than 1% higher than f s , and a crystal exhibits
an extremely wide variation of the reactance with frequency
between f p and f s . A crystal oscillator circuit is very stable
with frequency. This high rate of change of impedance with
frequency stabilizes the oscillator, because any significant
change in oscillator frequency will cause a large phase shift
in the feedback loop keeping the oscillator on frequency.
f = f p –f s = f s [1 – (1 + C s /C p ) 1/2 ]
Figure 24. Crystal Equivalent Circuit
Figure 23. Unmodulated Carrier
Figure 21. Frequency Deviation
Cp
R 3
C 3
L 3
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