JP2002359521A - Frequency switching type crystal oscillator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a frequency switching type crystal oscillator capable of preventing fluctuations in the levels of oscillation frequency. SOLUTION: The oscillator comprises a first resonance circuit consisting of a first crystal vibrator, a first diode and a divided capacitor, a second resonance circuit consisting of a second crystal vibrator, a second diode and the divided capacitor, a transistor for oscillation whose base is connected to a connection point between the divided capacitor and the first and second diodes, first and third divided resistors for base bias connected between the first, second diodes and a power supply, and a second divided resistor for base bias connected between the connection point of the first, second diodes and the divided capacitor and a grounding potential.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a frequency-switching crystal oscillator (frequency-switching oscillator) as an industrial technical field, and more particularly to a high-frequency switching oscillator for preventing fluctuations in output level.

[0002]

2. Description of the Related Art A frequency switching oscillator is useful because an oscillation frequency can be selected as required. For example, application to a voltage controlled crystal oscillator in a high frequency band (for example, a 150 MHz band and a 600 MHz band) serving as an oscillation source for optical communication is being studied.

(Example of Prior Art) FIG. 3 is a circuit diagram of a frequency switching oscillator for explaining a conventional example of this kind. The frequency switching oscillator includes a plurality of, for example, two crystal oscillators 1 (ab) operating as inductor components, a split capacitor 2 (ab) forming a resonance circuit therewith, and an oscillation transistor for feedback-amplifying the resonance frequency of the resonance circuit. 3
The emitter of the oscillation transistor is grounded, for example, via the load resistor 4. The oscillation frequency generally depends on the resonance frequency of the resonance circuit, but is strictly determined by the series equivalent capacitance on the circuit side as viewed from the crystal unit 1 (ab).

Normally, the base of the oscillating transistor 3 is connected to the connection point between the crystal unit 1 (ab) and the dividing capacitor 2 (ab), the emitter is connected to the middle point of the dividing capacitor 2 (ab), and the collector is connected to the power supply Vcc. Connected to obtain an output Vo, for example, from the emitter. A bias voltage is supplied to the base of the transistor 3 by the divided bias resistor 5 (ab). Then, the crystal oscillator 1 (a
Switch b) to select the oscillation frequency. The electronic switch 7 is composed of a switching element made of a semiconductor, and ON and OF are selected by, for example, an external 1 or 0 signal.

In this case, as shown in FIG. 4, a voltage control type device in which a voltage variable capacitance element 6 is inserted between the crystal unit 1 (ab) of the resonance circuit and the ground and the oscillation frequency is varied by the control voltage Vc. I do. Reference numeral 8 in the drawing denotes a bypass capacitor between the power supply Vcc and the ground, reference numeral 9 denotes a high-frequency blocking resistor, and reference numeral 10 denotes a coupling capacitor.

[0006]

(Problems to be Solved by the Invention)
However, in the frequency switching oscillator having the above configuration, the crystal oscillator 1 (ab) is switched by the electronic switch 7. The electronic switch 7 has a temperature resistance characteristic in which a resistance value basically changes with temperature. Therefore, the high-frequency current in the oscillation closed loop including the resonance circuit and the feedback amplifier (oscillation transistor 3) changes with the temperature change, and there is a problem that the output level of the oscillation frequency changes with temperature.

Further, the crystal units 1 (ab) have different crystal impedances (CI). The bias voltage is common to each of the crystal units 1 (ab) and the resonance circuit formed therewith. Therefore, there has been a problem that the output level of each crystal oscillator also fluctuates.

(Object of the Invention) It is an object of the present invention to provide a frequency switching oscillator in which the fluctuation of the oscillation frequency level is prevented.

[0009]

According to the present invention, as described in the claims, a first resonance circuit including a first crystal resonator, a first diode, and a split capacitor; and a second crystal resonator. A second resonance circuit including a second diode and the split capacitor; an oscillation transistor having a base connected to a connection point between the split capacitor and the first and second diodes; And a first and a third divided resistor for a base bias, which are switched by an electronic switch, and a second for the base bias connected between a connection point between the first and second diodes and the divided capacitor and a ground potential. The basic solution is to use two-part resistors.

[0010]

In the present invention, since the bias resistor for setting the base bias voltage is switched by the electronic switch, there is no electronic switch in the oscillation closed loop including the first and second resonance circuits and the oscillation transistor. Therefore, the influence of the temperature characteristics of the electronic switch is reduced. Also, since the bias circuit is switched for each of the first and second resonance circuits, it can be set to a value corresponding to the CI of the first and second crystal units. Hereinafter, an embodiment of the present invention will be described.

[0011]

FIG. 1 is a circuit diagram of a frequency switching oscillator for explaining an embodiment of the present invention. The description of the same parts as those in the conventional example is simplified or omitted. The frequency switching oscillator is the first
, A second resonance circuit, an oscillation transistor 3, and first and second bias circuits. The first resonance circuit includes a first crystal resonator 1a, a first diode 11a and a split capacitor 2
(Ab). The second resonance circuit is the second crystal unit 1
b, second diode 11b and split capacitor 2 (ab)
Consists of

As described above, the oscillation transistor 3 has the emitter grounded via the load resistor 4 and the collector connected to the power supply. Then, the base is connected to a connection point between the split capacitor 2 (ab) shared by the first and second resonance circuits and the first and second diodes. Then, a bias voltage is supplied from the power supply Vcc by the first and second bias circuits.

The first bias circuit is a first bias circuit of the first resonance circuit.
A power-supply-side first divided resistor 12a provided between a connection point between the crystal unit 1a and the first diode 11a and the power supply Vcc.
, The first diode 11a and the split capacitor 2 (ab)
And the second divided resistor 5b on the ground side provided between the connection point of (1) and the ground.

The second bias circuit comprises a connection point between the second crystal unit 1b and the second diode 11b of the second resonance circuit and a power supply V.
cc, a third divided resistor 12b on the power supply side provided between
The aforementioned second ground-side second electrode provided between the connection point of the first diode 11a and the split capacitor 2 (ab) and the ground.
And a dividing resistor 5b. The first and third divided resistors 12 (ab) are arbitrarily switched by the electronic switch 7 and connected to the power supply Vcc.

In such a device, the first or second bias circuit, for example, the dividing resistor 12a is connected to the power supply Vcc by the electronic switch 7 to select the first bias circuit according to the required oscillation frequency. Then, the first crystal resonator 1a connected to the first bias circuit and the first diode 11a
And oscillates by operating the first resonance circuit including the split capacitor 2 (ab). In this case, the second diode 11
The current to the second resonance circuit (second crystal resonator 1b) is blocked by b, and only the first resonance circuit operates.

Alternatively, the dividing resistor 12b is connected to the power supply Vcc to select the second bias circuit, and the second crystal oscillator 1b,
The second resonance circuit including the second diode 11b and the split capacitor 2 (ab) is operated to oscillate. In this case, a first resonance circuit (first
The current to the crystal resonator 1a) is blocked, and only the second resonance circuit operates.

With such a configuration, when the first bias circuit is selected by, for example, the electronic switch 7, the first resonance circuit including the first crystal resonator 1a, the first diode 11a, and the division capacitor 2 (ab) is connected to the oscillation circuit. Transistor 3 forms a high-frequency oscillation closed loop. The electronic switch 7 does not exist in the high frequency oscillation closed loop. Therefore, even if the resistance value changes due to the temperature characteristics of the electronic switch 7, the influence on the high-frequency current is extremely small. Thus, a stable output can be obtained by preventing the output level from fluctuating. The same applies to the case where the second bias circuit is selected.

The first and second bias circuits share the ground-side second divisional resistor 5b, switch the power supply-side first and second divisional resistors 12 (ab), and provide the first and second resonance circuits. Connect independently to the circuit. Therefore, the bias voltage can be set independently for the first and second resonance circuits. That is, the bias voltage can be set according to the CI of the first and second crystal units 1 (ab). Thus, the same level of output can be obtained regardless of whether the first or second resonance circuit is selected.

[0019]

Others In the above embodiment, the description has been made only as a frequency switching oscillator. However, as shown in FIG. 2, the first and second crystal units 1 (ab) have the voltage variable capacitance element 9 and the high frequency May be connected to form a voltage control type. Although the first and second resonance circuits are switched, the switching may be performed by adding third to n-th resonance circuits (not shown).

[0020]

According to the present invention, the first and second resonance circuits are operated by switching the bias circuit for setting the base voltage of the oscillation transistor outside the oscillation closed loop. An oscillator can be provided.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a frequency switching oscillator illustrating an embodiment of the present invention.

FIG. 2 is a circuit diagram of a frequency switching oscillator illustrating another embodiment of the present invention.

FIG. 3 is a circuit diagram of a frequency switching oscillator explaining a conventional example.

FIG. 4 is a circuit diagram of a frequency switching oscillator explaining a conventional example.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Crystal oscillator, 2 division capacitor, 3 oscillation transistor, 4 load resistance, 5 and 12 division resistance, 6 voltage variable capacitance element, 7 electronic switch, 8 bypass capacitor, 9 high frequency blocking resistance, 10 coupling capacitor,
11 Diode.

Claims (1)

[Claims] A first resonance circuit including a first crystal resonator, a first diode, and a division capacitor; a second resonance circuit including a second crystal resonator, a second diode, and the division capacitor; An oscillation transistor having a base connected to a connection point between a capacitor and the first and second diodes, and first and third base biases connected between the first and second diodes and a power supply and switched by an electronic switch. A frequency switching oscillator comprising: a divided resistor; and a second divided resistor for base bias connected between a connection point between the first and second diodes and the divided capacitor and a ground potential.