JP2605188Y2 - Voltage controlled crystal oscillator - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage-controlled crystal oscillator that controls the control voltage of a variable capacitance diode to change the oscillation frequency of a crystal resonator.

[0002]

2. Description of the Related Art A conventional voltage controlled crystal oscillator has a circuit configuration as shown in FIG. In the drawing, X is a crystal oscillator, and one end of the crystal oscillator X has a variable capacitance diode Cv, a capacitor C2, and a trimmer capacitor CT.
Are connected in parallel, and at the other end of the crystal unit X,
The capacitor C1 is connected, and furthermore, an oscillating circuit section Y composed of a transistor, a resistor, a capacitor and the like is connected.

[0003] With such a circuit configuration, the crystal oscillator X
The capacitance components such as the variable capacitance diode Cv, the capacitor C2, and the trimmer capacitor CT at one end are combined and incorporated into a part of the equivalent CL circuit of the crystal unit X. Therefore, when a predetermined control voltage is supplied from the control terminal Vt, the capacitance of the variable capacitance diode Cv changes according to the control voltage, and the capacitance component of the CL circuit of the crystal unit X fluctuates. The oscillation frequency of the vibrator X fluctuates.

The capacitor C7 connected in series with the variable capacitance diode Cv is inserted to correct the non-linearity of the voltage characteristic of the variable capacitance diode Cv, and the resistor 5 is connected to the variable capacitance diode Cv. , The resistance value was usually 100 KΩ.

[0005]

Conventionally, the variable capacitance diode Cv used in the above-mentioned oscillation circuit has a specification of 5 V in many cases, and its characteristic has a voltage-capacity characteristic as shown by the line (a) in FIG. By connecting the capacitor C7 in series, the capacitor C7 is combined with the capacitance characteristic as shown by the line (b) to obtain a combined capacitance as shown by the line (c). The non-linearity characteristic of the diode Cv was reduced.

In this case, the control voltage supplied from the control terminal Vt is varied in the range of, for example, 1.0 to 4.0 V, centered at about 2.5 V, which is 1/2 of 5 V.

However, in recent years, in order to reduce the current consumption and the size of mounting devices (communication devices, etc.) using an oscillation circuit, it has been desired to use a variable capacitance diode Cv of a 3V specification, and a variable range of a control voltage is required. Is 1.5 V, for example, about 0.3 to 2.7 V.

That is, in the variable capacitance diode Cv, the voltage-capacitance characteristics become non-linear in a low voltage region, and the variable capacitance diode Cv must be used in this relatively low voltage region.

On the other hand, in the crystal unit X, the oscillation frequency characteristics vary depending on the cut-out angle from the crystal block, and a trimmer capacitor CT is used to compensate for the different frequency characteristics for each element. The control characteristics are
Since it depends on the ratio of the combined capacitance of the variable capacitance diode Cv and the capacitor C7 and the combined capacitance of the trimmer capacitor CT and the capacitor C2, the trimmer capacitor CT
In which the voltage control characteristic fluctuates due to the correction for each crystal unit. In particular, the variable capacitance diode of the 3V specification which operates in the low variable range of the control voltage of 0.7 to 2.7V In Cv, the fluctuation of the voltage control characteristic caused by the trimmer capacitor CT increases.

The present invention has been made in view of the above-described problems, and has as its object to change the trimmer capacitor so that the voltage control characteristics are not affected and the voltage control sensitivity of the variable capacitance diode is improved. An object of the present invention is to provide a controlled crystal oscillator.

[0011]

According to the present invention, a first combined capacitance component including a variable capacitance diode and a second combined capacitance component including a trimmer capacitor are connected in series to one end of a crystal unit. A voltage-controlled crystal oscillator in which a coupling capacitor and a combined capacitance component of an oscillation circuit are connected in series to the other end of the crystal unit, and the oscillation frequency is controlled by a first combined capacitance component including a variable capacitance diode. The first combined capacitance component is obtained by combining capacitance components of a variable capacitance diode, a capacitor connected in series to the variable capacitance diode, and a capacitor connected in parallel to the variable capacitance diode and the capacitor. The second combined capacitance component is a sum of capacitance components of a trimmer capacitor and a capacitor connected in parallel to the trimmer capacitor. It is a voltage controlled crystal oscillator, characterized by comprising a.

[0012]

According to the present invention, the capacitance of the variable capacitance diode Cv, the capacitor C7 connected in series to the variable capacitance diode Cv, and the capacitance C8 connected in parallel to the variable capacitance diode Cv and the capacitor C7 in FIG. Is combined with a first combined capacitance component, and a trimmer capacitor CT
The second combined capacitance component obtained by combining the capacitance of the capacitor C2 connected in parallel with the trimmer capacitor CT is connected in series to one end of the crystal unit.

A coupling capacitor C1 and an oscillation circuit Y are connected to the other end of the crystal unit, and the capacitance components are the capacitance component of the coupling capacitor C1 and the combined capacitance component of the oscillation circuit Y. They are connected in series.

That is, the reciprocal of the entire load capacitance CL is represented by a simple sum of the reciprocals of the respective capacitance components because the combined capacitance component and the capacitance component are connected in series. Thereby, the control of the oscillation frequency is achieved by adjusting these four capacitance components independently. Therefore, by adjusting the second combined capacitance component including the trimmer capacitor for correcting the frequency variation of each crystal unit, the frequency variation of the crystal unit in the initial state can be changed without affecting other combined capacitance components. Can be adjusted.

Further, when frequency control is performed by applying a predetermined control voltage, only the first combined capacitance component is controlled, and control can be performed without affecting other combined capacitance components. Therefore, the frequency variation between the transducers in the initial state is
The adjustment can be performed only by the second combined capacitance component, and the frequency control by the control voltage can be controlled only by the first combined capacitance component. As a result, the oscillation frequency can be controlled with high sensitivity by the control voltage without disturbing the adjusted condition in which the frequency fluctuation is corrected.

In particular, since the capacitance element is connected in series with the variable capacitance diode, the voltage of the variable capacitance diode
In the low-voltage region of control pressure reduction where the capacitance characteristic was a non-linear region, the characteristic was improved to be approximately linear, so that the non-linear characteristic of the variable capacitance diode was not promoted, and the control voltage was not increased. And an oscillation frequency are substantially proportional to each other, thereby obtaining a voltage-controlled crystal oscillator capable of obtaining an oscillation signal.

[0017]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing a voltage controlled type crystal oscillator according to the present invention.

FIG. 1 is a diagram showing a voltage controlled oscillation circuit used in the voltage controlled crystal oscillator of the present invention. In the figure, X is a quartz oscillator, Cv is a variable capacitance diode, CT
Is a trimmer capacitor, C1 to C8 are capacitors, and R1 to
R6 is a resistor, Q is an oscillation transistor, Vt is a control terminal, VCC is a power supply terminal, and O is an output terminal. In the figure, the dotted lines indicate the oscillation transistor Q and the resistor R1.
R4, and an oscillation circuit section Y composed of capacitors C3 to C6.

The crystal unit X is made of an AT-cut crystal piece, and one end of each of the crystal units X is connected to capacitors C7 and C8.
And a trimmer capacitor CT is connected via a variable capacitance diode Cv, and a capacitor C2 is connected via a capacitor C8 and in parallel with the trimmer capacitor CT.

That is, when the ground potential is viewed from one end of the crystal unit X, the capacitor C7, the variable capacitance diode Cv,
This means that the trimmer capacitors CT are connected in series.

The variable capacitance diode Cv is supplied with a control voltage from a control terminal Vt via a resistor R5 which is a reverse current limiting resistor. The capacitor C7 connected in series with the variable capacitance diode Cv is a capacitor inserted to correct nonlinearity in the low voltage region of the voltage characteristic of the variable capacitance diode Cv, as described with reference to FIG. is there.

In the above circuit diagram, one end of the crystal unit X is provided at one end with a combined capacitance circuit comprising a capacitor C7, a variable capacitance diode Cv and a capacitor C8 (the combined capacitance obtained by this combined capacitance circuit is a first combined capacitance component). And a first combined capacitance component Cp) and a trimmer capacitor Cp.
T and a capacitor C2 (a combined capacitor obtained by the combined capacitor circuit is a second combined capacitor component Cj
) Are connected in series. Further, on the other end side of the crystal unit X, a capacitor C1 (which is a coupling capacitor, the capacitance component of which is described as C1 for convenience) and a combined capacitance component (eg, capacitors C3 and C4) of the oscillation circuit Y are provided. This combined capacitance component is referred to as Ci).

Here, the first combined capacitance component Cp is Cp
= C8 + (CV * C7) / (Cv + C7), and the second combined capacitance component Cj is Cj = CT + C2. Note that C8, C7, and C2 are capacitors C8, C7,
The respective capacitance components of C2 are shown.

Accordingly, the load capacitance CL of the entire circuit is expressed by 1 / CL = 1 / Cp + 1 / Cj + 1 / C1 + 1 / Ci. After all, CL = 1 / (1 / Cp + 1 / Cj)
+ 1 / C1 + 1 / Ci).

In the above equation, the first combined capacitance component Cp which is the combined capacitance component including the variable capacitance diode Cv
Can be expressed as a single term in the equation with the capacitance component Cv of the variable capacitance diode Cv as the center. For this reason, when a control voltage is applied to control the oscillation frequency, it has no effect on the other combined capacitance, and has a large effect on the total load capacitance. it can.

In the conventional oscillation circuit shown in FIG. 4, since the variable capacitance diode Cv and the trimmer capacitor CT are connected in parallel, the combined capacitance of the variable capacitance diode Cv and the capacitance of the trimmer capacitor CT is all. Load capacity C
Since L is a single term when expressed by an equation, the capacitance of the trimmer capacitor CT has a large effect on the control voltage characteristics together with the variable capacitance of the variable capacitance diode Cv due to the actual control voltage.

On the other hand, as described above, the control terminal Vt
Since the oscillation frequency of the crystal resonator X due to the change in the capacitance of the variable capacitance diode Cv due to the control voltage from does not affect the trimmer capacitor CT that adjusts the different frequency characteristics of the crystal resonator in the initial state, Frequency control by this control voltage can be easily performed, and an output of a stable oscillation frequency can be derived from the output terminal O.

FIGS. 2 and 3 show circuit diagrams of another voltage-controlled crystal oscillator according to the present invention.

In the circuit shown in FIG. 2, the control voltage supplied to the variable capacitance diode Cv is divided by the resistors R5 and R7, and the voltage across the variable capacitance diode Cv is linearized by the voltage-capacity characteristic of the variable capacitance diode Cv. The control is in an excellent range.

In the circuit of FIG. 3, the load capacitance including the trimmer capacitor CT and the load capacitance including the variable capacitance diode Cv and the capacitor C7 are arranged opposite to those of FIG. On the side, a load capacitance including a trimmer capacitor CT is arranged.

With this configuration, the resistor R6 in FIG. 1 can be omitted.

[0032]

As described above, according to the present invention, the first combined capacitance component including the variable capacitance diode, the capacitors C7 and C8 for linearly compensating the voltage-capacity characteristics of the variable capacitance diode, and the trimmer A second combined capacitance component composed of a capacitor CT and a capacitor C2 is arranged in series at one end of the crystal unit. Further, the coupling capacitor C1 and the capacitors C3 and C4 of the oscillation circuit Y
Are combined in series with the other end of the crystal unit.

Therefore, when the capacitance of the trimmer capacitor is adjusted, only the second combined capacitance component is adjusted, and the first combined capacitance component including the variable capacitance diode Cv for controlling the frequency in the oscillation circuit is controlled. Influence can be reduced.

Further, since the first combined capacitance component including the variable capacitance diode is arranged in series with the crystal unit, the first combined capacitance component is directly affected without affecting other combined capacitances.
Since this affects the load capacitance CL of the entire circuit, the voltage control sensitivity of the capacitance change with respect to the control voltage supplied from the control terminal is improved.

Accordingly, a voltage controlled crystal oscillator is achieved in which the capacitance of the trimmer capacitor is not significantly affected by the voltage control characteristics and the voltage control sensitivity of the variable capacitance diode is improved.

[Brief description of the drawings]

FIG. 1 is a circuit diagram illustrating a circuit configuration of a voltage controlled crystal oscillator according to the present invention.

FIG. 2 is a circuit diagram illustrating another circuit configuration of the voltage controlled crystal oscillator of the present invention.

FIG. 3 is a circuit diagram illustrating another circuit configuration of the voltage controlled crystal oscillator of the present invention.

FIG. 4 is a circuit diagram illustrating a circuit configuration of a conventional voltage controlled oscillator.

FIG. 5 is a characteristic diagram showing a relationship between a control voltage, a capacitance of a variable capacitance diode, and a combined capacitance of a capacitor C7 in an oscillation circuit of a conventional voltage controlled oscillator.

[Description of numbering]

 X: Crystal oscillator Y: Oscillation circuit C1-C8: Capacitor R1-R7: Resistance Cv: Variable capacitance diode CT: Trimmer capacitor Vt ... Control terminals

Claims (1)

(57) [Scope of request for utility model registration] A variable capacitance diode is provided at one end of a crystal unit.
The first combined capacitance component including the capacitor and the trimmer capacitor
A second combined capacitance component is connected in series, and
Coupling capacitor on the other end of the vibrator, combined capacitance of oscillation circuit
Components are connected in series and the oscillation frequency is variable.
Controlled by a first combined capacitance component including a
A that the voltage controlled crystal oscillator, the first composite capacitance component of the variable capacitance diode, said
The capacitor connected in series with the variable capacitance diode
The variable capacitance diode and the capacitor are connected in parallel.
Made by synthesizing the capacitance component of the capacitor that is, the combined capacitance component of the second includes a trimmer capacitor,該To
Each capacitance with the capacitor connected in parallel with the lima capacitor
A voltage-controlled crystal characterized by combining components
Oscillator.