JPS6340928Y2 - - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a frequency shift modulator (FSK).

Conventionally, there has been a frequency modulator called a variable capacitance diode frequency modulator as shown in FIG. This is an emitter feedback type crystal oscillator consisting of a transistor 2, bias resistors 4, 6, 8, an oscillation capacitor 10, a feedback capacitor 12, a crystal resonator 14, etc., in which a capacitor 16 and a variable A capacitor 18 is connected to the capacitor 18, and an audio signal is supplied to the connection point between the capacitor 16 and the variable capacitor 18 via a resistor 20. In this frequency modulator, the variable capacitor 18 is
The oscillation frequency is changed by changing the value of , and a frequency modulated output is taken out from the output terminal 22, which has the advantage of being able to perform frequency modulation with a simple configuration. However, if a digital signal is supplied instead of an audio signal and used as an FSK modulator,
There was a problem that the frequency deviation became small.

The purpose of this invention is to provide an FSK modulator with a simple circuit configuration and a large frequency deviation using the emitter feedback crystal oscillator described above.

Therefore, in this invention, the crystal resonator of an emitter feedback crystal oscillator is connected to a reference potential point via an inductance connected in series and the collector-emitter conductive path of a transistor, and a binary digital signal is connected to the base of this transistor. This is a configuration that supplies

With this configuration, for example, when an H level digital signal is supplied to the base, the transistor becomes conductive, the crystal resonator and the inductance are connected in series to the reference potential point via the conductive resistance of the transistor, and the emitter feedback The oscillation frequency of a type crystal oscillator is lower than the fundamental oscillation frequency of the crystal oscillator, ₀ .
It becomes ₁ . In addition, when an L level digital signal is supplied to the base, the transistor becomes non-conductive, and the crystal resonator and inductance are connected to the reference potential point via the collector and emitter capacitance of the transistor, and the emitter feedback type The oscillation frequency of the crystal oscillator is the fundamental oscillation frequency of the crystal oscillator, ₀
The higher is ₂ . Therefore, the digital signal is H.
The oscillation frequency changes between ₁ and ₂ depending on whether it is low or low level, and can be used as an FSK modulator. As described above, according to this invention, a simple configuration can be achieved using an emitter feedback crystal oscillator.
FSK modulator can be realized.

This invention will be explained in detail below based on one embodiment shown in FIGS. 2 to 4. Incidentally, parts equivalent to those of the conventional one shown in FIG. 1 are given the same reference numerals, and explanation thereof will be omitted. In the conventional one, the capacitor 16 and the variable capacitor 18 were connected in series between the crystal resonator 14 and the reference potential point, whereas in this embodiment, the inductance 24 and the NPN
The collector-emitter conductive path of the transistor 26 is connected. A digital signal is supplied to the base of this transistor 26 via a resistor 28. In addition, 30 is a speed-up capacitor, which is connected in parallel with the resistor 28, and 32 is a modulation spurious prevention capacitor, which is connected to the transistor 2.
6 and a reference potential point.

In this FSK modulator, when an H level digital signal is supplied to the base of the transistor 26, since the transistor 26 is an NPN transistor, it becomes conductive, and as shown in FIG.
4 and the inductance 24 are the transistor 26
It is connected to a reference potential point via a conductive resistor 34 between the collector and emitter of. At this time, conductive resistance 3
Since 4 is very small, the oscillation frequency of the emitter feedback crystal oscillator becomes ₁ higher than the fundamental frequency of the crystal resonator 14 due to the influence of the inductance 24.

Similarly, when an L-level digital signal is supplied to the transistor 26, the transistor 26 becomes non-conductive, and the crystal resonator 14 and the inductance 24 are connected to the reference potential point via the collector-emitter capacitance 36 of the transistor 26. connected to. Therefore, this collector-emitter capacitance 36
Under the influence _of
2, which is lower than . In addition, the amount of frequency deviation ( ₁ −
₀ ) or ( ₀ - ₂ ) is determined by the value of the inductance 24 and the value of the collector-emitter capacitance 36, so in order to shift ₁ and ₂ equally in both positive and negative directions with respect to ₀ , the collector - It is necessary to measure the emitter-to-emitter capacitance 36 and determine the value of the inductance 24 accordingly.

In the above embodiment, the oscillation frequency is raised when the H level is high and the oscillation frequency is lowered when the L level is low.
The oscillation frequency may be increased when the level is high.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of a conventional frequency modulator, Fig. 2 is a circuit diagram of an embodiment of the FSK modulator according to this invention, and Fig. 3 is a circuit diagram of an H-level digital signal applied to the transistor 26 of the circuit of Fig. 2. Crystal oscillator, inductance and transistor 26 when supplied
FIG. 4 shows an equivalent circuit of the crystal resonator 14, inductance 24, and transistor 26 when an L-level digital signal is supplied to the transistor 26 of the circuit shown in FIG. 2...First transistor, 4...Emitter resistor,
6, 8... Bias resistor, 10... Oscillation capacitor, 12... Feedback capacitor, 14... Crystal resonator, 24... Inductance, 26... Second transistor.

Claims (1)

[Scope of utility model registration request] A collector-emitter conductive path and an emitter resistor of the first transistor are connected in series between the operating potential point and the reference potential point, and two bias resistors are connected between the operating potential point and the reference potential point. connect the devices in series, connect their mutual connection point to the base of the first transistor, connect an oscillation capacitor between the base and emitter of the first transistor, and connect the oscillation capacitor between the emitter of the first transistor and the above reference potential point. A feedback capacitor is connected to the base of the first transistor, a crystal resonator, an inductance, and a collector-emitter conduction path of the second transistor are connected between the base of the first transistor and the reference potential point, and a digital signal is connected to the base of the second transistor. FSK modulator that supplies the signal.