JP2002141746A - Crystal oscillation fsk modulation circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a crystal oscillation FSK modulation circuit that can realize high-speed FSK modulation. SOLUTION: The crystal oscillation FSK modulation circuit is provided with a crystal oscillation circuit, a small load circuit and a large load circuit that are selectively connected to the crystal oscillation circuit, a changeover means D1 that selects the small load circuit or the large load circuit depending on the level of an input pulse signal, and a resistor R6 connected in series or parallel with a capacitive reactance element C4 of the large load circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a crystal oscillation FSK modulation circuit, and more particularly, to a crystal oscillation FSK modulation circuit which switches a load capacitance according to a voltage level of an input pulse signal, thereby changing an oscillation frequency and outputting the same. About.

[0002]

2. Description of the Related Art A conventional crystal oscillation FSK (frequency shif) is used.
t keying) circuit is shown in FIG. This crystal oscillation FSK modulation circuit includes a transistor Q11 functioning as a modulation element.
And the bias resistors R11 and R11 of the transistor Q11.
12, R13, a capacitor C11 connected between the base and the emitter of the transistor Q11,
Capacitor C1 connected between the emitter of C.11 and ground.
2, a capacitor C13 connected between the emitter and the output terminal of the transistor Q11, resistors R14 and R15 for dividing the power supply voltage, a crystal oscillator X11 connected to the base of the transistor Q11, and a crystal oscillator X11. A diode D11 connected between the input terminals;
Capacitor C1 connected between the cathode of C.11 and ground.
4 and a capacitor C15 connected between the anode of the diode D11 and the ground. Here, for example, the capacitance of the capacitor C14 is set to about 4 pF,
Is about 1000 pF.

An input pulse signal is input to an input terminal of the crystal oscillation FSK modulation circuit. Input pulse signal is L
In this case, the diode D11 is turned off, and at this time, the crystal oscillator X11 and the transistor Q1 are turned off.
The oscillation circuit composed of 1 and the like oscillates at a frequency determined by the reactance of the capacitor C14, the capacitor C11, and the capacitor C12.

On the other hand, when the input pulse signal is at the H level, the diode D11 is turned on. At this time, the oscillation circuit composed of the crystal oscillator X11 and the transistor Q11 and the like includes capacitors C15, C11 and C12. It oscillates at a frequency determined by the reactance. That is, the crystal oscillation FSK modulation circuit is configured to output L or H
By changing the load capacity according to the level of
The oscillation frequency is changed, thereby realizing FSK modulation.

[0005]

In the above-described crystal oscillation FSK modulation circuit, as the modulation frequency increases, the frequency shift gradually becomes difficult to shift from one load capacitance to the oscillation of the other load capacitance, and the transmission waveform becomes higher. However, there is a problem that distortion occurs. Therefore, high-speed FSK modulation cannot be performed.
FSK modulation of about 00 bps was the limit.

The present invention has been made in view of the above-described problems, and has as its object to provide a crystal oscillation FSK modulation circuit capable of realizing higher-speed FSK modulation.

[0007]

In order to achieve the above object, a crystal oscillation FSK modulation circuit according to the present invention comprises a crystal oscillation circuit, a low load capacitance circuit selectively connected to the crystal oscillation circuit, and A high-load capacitance circuit, and switching means for switching between the low-load capacitance circuit and the high-load capacitance circuit according to the level of the input pulse signal, wherein the oscillation frequency is changed and output according to the level of the input pulse signal And
The high load capacitance circuit is characterized by including a resistor connected in series or parallel to the capacitive reactance element.

In a first embodiment of the present invention, the crystal oscillation circuit includes a transistor having a base terminal, a collector terminal, and an emitter terminal, and a first transistor connected between the emitter terminal and the base terminal of the transistor. A second capacitor connected between the emitter terminal of the transistor and the ground, and a crystal resonator connected to the base terminal of the transistor, wherein the switching means has an anode terminal connected to the input terminal. The low load capacitance circuit includes a third capacitor connected between the cathode terminal of the diode and ground, and the high load capacitance circuit is connected between the anode terminal of the diode and ground. A fourth capacitor,
The resistor is provided between an anode terminal of the diode and the fourth capacitor.

In a second embodiment of the present invention,
The crystal oscillation circuit includes a transistor having a base terminal, a collector terminal, and an emitter terminal; a first capacitor connected between the emitter terminal and the base terminal of the transistor; and a transistor connected between the emitter terminal of the transistor and ground. A second capacitor, and a crystal resonator connected to the base terminal of the transistor, wherein the switching means is a diode having an anode terminal connected to the input terminal, and the low load capacitance circuit is A third capacitor connected between the cathode terminal of the diode and the ground, the output impedance at the input terminal is used as the high-load capacitance circuit, and the resistor is connected between the anode terminal of the diode and the input terminal. It is located between them.

[0010] In a third embodiment of the present invention,
The crystal oscillation circuit includes a transistor having a base terminal, a collector terminal, and an emitter terminal; a first capacitor connected between the emitter terminal and the base terminal of the transistor; and a transistor connected between the emitter terminal of the transistor and ground. A second capacitor connected to a base terminal of the transistor, the switching means is a diode having a cathode terminal connected to an input terminal, and the low load capacitance circuit is A third capacitor connected between an anode terminal of the diode and the ground, the output impedance at the input terminal is used as the high load capacitance circuit, and the resistor is connected between the cathode terminal of the diode and the input terminal. It is located between them.

In a fourth embodiment of the present invention,
The crystal oscillation circuit includes a transistor having a base terminal, a collector terminal, and an emitter terminal; a first capacitor connected between the emitter terminal and the base terminal of the transistor; and a transistor connected between the emitter terminal of the transistor and ground. A second capacitor connected to the base terminal of the transistor, and the switching means includes a first connection terminal connected to the low load capacitance circuit, and a crystal resonator connected to the high load capacitance circuit. A second connection terminal connected to the switch, wherein the low load capacitance circuit includes a third capacitor connected between the first connection terminal of the changeover switch and the ground, and The circuit includes a fourth capacitor connected between a second connection terminal of the changeover switch and ground, and the resistor includes a second capacitor of the changeover switch. It is disposed between the connection terminal and the fourth capacitor.

In a fifth embodiment of the present invention,
The crystal oscillation circuit includes a transistor having a base terminal, a collector terminal, and an emitter terminal; a first capacitor connected between the emitter terminal and the base terminal of the transistor; and a transistor connected between the emitter terminal of the transistor and ground. A second capacitor connected to the base terminal of the transistor, and the switching means includes a first connection terminal connected to the low load capacitance circuit, and a crystal resonator connected to the high load capacitance circuit. A second connection terminal connected to the switch, wherein the low load capacitance circuit includes a third capacitor connected between the first connection terminal of the changeover switch and the ground, and The circuit includes a fourth capacitor connected between a second connection terminal of the changeover switch and ground, and the resistor includes a second capacitor of the changeover switch. Between the connection terminal and the ground, the fourth
Is arranged in parallel with the capacitor.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A quartz oscillation FS according to the present invention will be described below.
A K (frequency shift keying) modulation circuit will be described in detail with reference to the drawings.

FIG. 1 shows a crystal oscillation FSK to which the present invention is applied.
FIG. 3 is a diagram illustrating a first specific example of a modulation circuit. This crystal oscillation FSK modulation circuit includes a transistor Q1 functioning as a modulation element, and a bias resistor R1,
R2, R3, a capacitor C1 connected between the base and the emitter of the transistor Q1, a capacitor C2 connected between the emitter terminal of the transistor Q1 and the ground,
A capacitor C3 connected between the emitter of the transistor Q1 and the output terminal, and resistors R4 and R
5, a crystal unit X1 connected to the base of the transistor Q1, a diode D1 connected between the crystal unit X1 and the input terminal, a capacitor C4 connected between the cathode of the diode D1 and the ground, and a diode D1. And a capacitor C5 connected between the anode and the ground. In the first specific example, the diode D
A resistor R6 is connected between the cathode of No. 1 and the capacitor C4. In this specific example, the capacity of the capacitor C4 is set to about 4 pF, and the capacity of the capacitor C5 is set to about 100 pF.
0 pF.

An input pulse signal is input to an input terminal of the crystal oscillation FSK modulation circuit. Input pulse signal is L
Level, the diode D1 is turned off,
At this time, the oscillation circuit composed of the crystal unit X1, the transistor Q1, and the like includes a capacitor C4 and a capacitor C4.
1 and the capacitor C2 oscillate at a frequency determined by the reactance.

On the other hand, when the input pulse signal is at the H level, the diode D1 is turned on. At this time, the oscillating circuit including the crystal unit X1 and the transistor Q1 includes the capacitor C5, the capacitor C1, and the capacitor C1.
2 oscillates at a frequency determined by each reactance. That is, this crystal oscillation FSK modulation circuit changes the oscillation frequency by changing the load capacitance according to the level of L or H of the input pulse supplied to the input terminal, thereby realizing FSK modulation. I have.

Here, as a result of diligent studies by the present inventors, in the conventional crystal oscillation FSK modulation circuit, a change from the frequency under the oscillation condition with a large negative resistance to the frequency under the oscillation condition with a small negative resistance quickly occurs. 48 that will not be done
It has been found that this is the main cause of distortion in the transmission waveform at a transmission rate of 00 bps or more. Therefore, in the first specific example, as described above, the resistor R6 is provided between the anode terminal of the diode D1 and the capacitor C5,
As a result, a negative resistance difference between the two load capacitors is reduced, a stable frequency shift is realized, and a crystal oscillation FSK modulation circuit that can support high-speed FSK modulation is realized.

Specifically, in this crystal oscillation FSK modulation circuit, when the resistor R6 is not provided, that is, in the conventional configuration, the negative resistance value of the oscillation circuit when the input pulse is at the H level is 620Ω. And the negative resistance value of the oscillation circuit when the input pulse is at the L level is 390Ω. On the other hand, when the resistor R6 is provided as in this specific example, the negative resistance value of the oscillation circuit when the input pulse is at the H level is 430Ω, and the negative resistance value of the oscillation circuit when the input pulse is at the L level. Becomes 360Ω. In the conventional configuration, the frequency change of about ± 200 ppm at 4800 bps is reduced to about ± 100 to 120 at 9600 bps, but according to this specific example, the transmission rate is 960.
At 0 bps, a frequency change of about ± 180 can be obtained, and data transmission at a transmission rate of 9600 bps can be substantially realized.

FIG. 2 is a diagram showing a second specific example of the present invention. In FIG. 2, components common to FIG. 1 are denoted by common reference numerals, and description thereof will be omitted. In the second specific example, the output impedance of the input terminal is substituted for a high load capacitance circuit. Therefore, the high-capacity capacitor C5 in the first specific example is omitted, and the resistor R is connected between the input terminal and the anode terminal of the diode D1.
6 are connected.

FIG. 3 is a diagram showing a third specific example of the present invention. 3, components common to those in FIGS. 1 and 2 are denoted by common reference numerals, and description thereof is omitted.
The third specific example has substantially the same configuration as the second specific example. However, in the third specific example, the diode D1
Is reversed, that is, the diode D1 is connected to the input terminal side.
Are connected. The circuit shown in the third specific example is a circuit for inverting the logic of data with respect to the circuit shown in the second specific example.

FIG. 4 is a diagram showing a fourth specific example of the present invention. In FIG. 4, components common to FIGS. 1 to 3 are denoted by common reference numerals, and description thereof is omitted.
The crystal oscillation FSK modulation circuit shown in the fourth specific example includes a changeover switch S1 for switching a load capacitance. Specifically, the changeover switch S1 is connected to the capacitor C4
And a second connection terminal T2 connected to the ground via a resistor R6 and a capacitor C5 connected in series. In the crystal oscillation FSK modulation circuit shown in the fourth specific example, the load capacitance is switched by switching and connecting the movable terminal of the changeover switch S1 to the first connection terminal T1 and the second connection terminal T2.

FIG. 5 is a diagram showing a fifth specific example of the present invention. In FIG. 5, components common to those in FIGS. 1 to 4 are denoted by common reference numerals, and description thereof will be omitted.
The configuration of the fifth specific example is substantially the same as the configuration of the fourth specific example. However, in the fourth specific example, the capacitor C5
And the resistor R6 are connected in series. In the fifth specific example, the capacitor C5 and the resistor R6 are connected in parallel. Such a configuration is effective when it is necessary to reduce the negative resistance value of a load capacitance with strong oscillation.

[0023]

As described above, the crystal oscillation F according to the present invention is
The SK modulation circuit includes a crystal oscillation circuit, a low load capacitance circuit and a high load capacitance circuit selectively connected to the crystal oscillation circuit, and connects a resistor to the capacitive reactance element of the high load capacitance circuit. Therefore, the negative resistance difference between the low load capacity and the high load capacity can be reduced, and a stable frequency shift can be realized. Therefore, it is possible to realize a crystal oscillation FSK modulation circuit having a higher transmission rate than the conventional one and capable of supporting high-speed FSK modulation.

[Brief description of the drawings]

FIG. 1 is a diagram showing a first specific example of a crystal oscillation FSK circuit to which the present invention is applied.

FIG. 2 is a diagram showing a second specific example of the crystal oscillation FSK circuit to which the present invention is applied.

FIG. 3 is a diagram showing a third specific example of the crystal oscillation FSK circuit to which the present invention is applied.

FIG. 4 is a diagram showing a fourth specific example of the crystal oscillation FSK circuit to which the present invention is applied.

FIG. 5 is a diagram showing a fifth specific example of the crystal oscillation FSK circuit to which the present invention is applied.

FIG. 6 is a diagram showing a specific example of a conventional crystal oscillation FSK circuit.

[Explanation of symbols]

 Q1 Transistor C1 First capacitor C2 Second capacitor X1 Crystal resonator D1 Diode C4 Third capacitor C5 Fourth capacitor R6 Resistor

Claims (6)

[Claims] 1. A crystal oscillation circuit, a low load capacitance circuit and a high load capacitance circuit selectively connected to the crystal oscillation circuit, and the low load capacitance circuit and the high load capacitance circuit according to the level of an input pulse signal. And switching means for switching between
A crystal oscillation FSK modulation circuit that changes the oscillation frequency according to the level of an input pulse signal and outputs the oscillation frequency, comprising a resistor connected in series or parallel to the capacitive reactance element of the high load capacitance circuit. Crystal oscillation FSK modulation circuit. 2. A crystal oscillator circuit comprising: a transistor having a base terminal, a collector terminal, and an emitter terminal; a first capacitor connected between the emitter terminal and the base terminal of the transistor; A second capacitor connected between the ground and a crystal oscillator connected to a base terminal of the transistor, wherein the switching means is a diode having an anode terminal connected to the input terminal; The circuit includes a third terminal connected between the cathode terminal of the diode and ground.
Wherein the high load capacitance circuit includes a fourth capacitor connected between the anode terminal of the diode and ground, and the resistor is connected between the anode terminal of the diode and the fourth capacitor. 2. The crystal oscillation FSK modulation circuit according to claim 1, wherein 3. The crystal oscillation circuit includes a transistor having a base terminal, a collector terminal, and an emitter terminal, a first capacitor connected between the emitter terminal and the base terminal of the transistor, and an emitter terminal of the transistor. A second capacitor connected between the ground and a crystal oscillator connected to a base terminal of the transistor, wherein the switching means is a diode having an anode terminal connected to the input terminal; The circuit includes a third terminal connected between the cathode terminal of the diode and ground.
Wherein the high load capacitance circuit uses an output impedance at the input terminal, and the resistor is disposed between an anode terminal of the diode and the input terminal. The crystal oscillation FSK modulation circuit according to claim 1. 4. The crystal oscillation circuit includes a transistor having a base terminal, a collector terminal, and an emitter terminal, a first capacitor connected between the emitter terminal and the base terminal of the transistor, and an emitter terminal of the transistor. A second capacitor connected between the ground and a crystal oscillator connected to a base terminal of the transistor, wherein the switching means is a diode having a cathode terminal connected to an input terminal; The circuit includes a third terminal connected between the anode terminal of the diode and ground.
Wherein the high load capacitance circuit uses an output impedance at the input terminal, and the resistor is disposed between a cathode terminal of the diode and the input terminal. The crystal oscillation FSK modulation circuit according to claim 1. 5. The crystal oscillation circuit includes a transistor having a base terminal, a collector terminal, and an emitter terminal, a first capacitor connected between the emitter terminal and the base terminal of the transistor, and an emitter terminal of the transistor. A second capacitor connected between the ground, and a crystal resonator connected to a base terminal of the transistor, wherein the switching means includes a first connection terminal connected to the low load capacitance circuit; And a second connection terminal connected to the high load capacitance circuit, wherein the low load capacitance circuit includes a third capacitor connected between the first connection terminal of the changeover switch and ground. The high load capacitance circuit includes a fourth capacitor connected between a second connection terminal of the changeover switch and ground, and the resistor includes the changeover switch. Switch second connection terminal and the fourth connection terminal.
2. The crystal oscillation FSK modulation circuit according to claim 1, wherein said crystal oscillation FSK modulation circuit is disposed between said capacitor and said capacitor. 6. The crystal oscillation circuit includes a transistor having a base terminal, a collector terminal, and an emitter terminal, a first capacitor connected between the emitter terminal and the base terminal of the transistor, and an emitter terminal of the transistor. A second capacitor connected between the ground, and a crystal resonator connected to a base terminal of the transistor, wherein the switching means includes a first connection terminal connected to the low load capacitance circuit; And a second connection terminal connected to the high load capacitance circuit, wherein the low load capacitance circuit includes a third capacitor connected between the first connection terminal of the changeover switch and ground. The high load capacitance circuit includes a fourth capacitor connected between a second connection terminal of the changeover switch and ground, and the resistor includes the changeover switch. 2. The crystal oscillation FSK modulation circuit according to claim 1, wherein the crystal oscillation FSK modulation circuit is arranged between the second connection terminal of the switch and the ground in parallel with the fourth capacitor.