WO2005046046A1

WO2005046046A1 - Crystal oscillator

Info

Publication number: WO2005046046A1
Application number: PCT/JP2004/014964
Authority: WO
Inventors: Takehiro Yamamoto
Original assignee: Toyo Communication Equipment Co., Ltd.
Priority date: 2003-11-10
Filing date: 2004-10-08
Publication date: 2005-05-19
Also published as: JP2007019565A

Abstract

A crystal oscillator that exhibits an increased oscillator frequency variation amount in accordance with an externally supplied control voltage and that provides a frequency variation exhibiting an improved linearity. The crystal oscillator includes a frequency adjusting circuit configured by use of two MOS voltage variable capacitance elements. The back gate terminal of each MOS voltage variable capacitance element receives a control DC voltage via a respective one of level shift circuits. The voltage shift amount of one of the level shift circuits is established such that the corresponding MOS voltage variable capacitance element operates in a range where the C-V characteristic is linear in a range lower than the center voltage of the control DC voltage. The voltage shift amount of the other of the level shift circuits is established such that the corresponding MOS voltage variable capacitance element operates in a range where the C-V characteristic is linear in a range higher than the center voltage of the control DC voltage.

Description

Specification

Crystal oscillator

Technical field

The present invention relates to a crystal oscillator, and more particularly to a voltage-controlled crystal oscillator whose oscillation frequency changes based on a control DC voltage value supplied by an external force, and a voltage-controlled temperature-compensated crystal oscillator.

Background art

In recent years, a PLL (Phase Lock Loop) has been widely used as a signal source such as a local oscillator of a wireless communication device. In order to realize a high-precision PLL, it is common to use a crystal oscillator as the voltage controlled oscillator.

For example, Patent Document 1 discloses a voltage-controlled crystal oscillator configured using an inverter element. As is well known, the voltage controlled crystal oscillator utilizes a phenomenon in which the resonance frequency of the oscillator changes by changing the load capacitance of the resonance loop. In the above-mentioned publication, a voltage variable capacitance element is inserted into a resonance loop of a crystal oscillator using an inverter element, and the frequency output from the oscillator is controlled by a control DC voltage applied to the voltage variable capacitance element.

A variable capacitance diode is known as a general voltage variable capacitance element. However, since the variable capacitance diode is difficult to be integrated, it cannot be integrated with other components constituting the oscillation circuit, thereby hindering miniaturization and cost reduction.

On the other hand, there is a MOS voltage variable capacitance element as a voltage variable capacitance element, which is being applied to a crystal oscillator because of easy integration. (Patent Document 2)

[0003] Fig. 6 shows a voltage-controlled temperature-compensated crystal oscillator obtained by adding a temperature compensation circuit using a MOS-type voltage variable capacitance element and a frequency adjustment circuit using a MOS-type voltage variable capacitance element to a crystal oscillator using an inverter element. FIG. 3 is a circuit diagram illustrating an example of the embodiment.

In the figure, 1 is a crystal oscillator, R1 is a feedback resistor, 2 is an inverter element, 3 (in a broken line) is a temperature compensation circuit, and 4 (in a dashed line) is a frequency adjustment circuit.

Here, the frequency adjustment circuit 4 is composed of two MOS type voltage variable capacitance elements Dl and D2 and two Capacitor CI, C2 and resistors R2, R3.

The gate terminal of MOS voltage variable capacitance element D1 is connected to the input terminal of inverter element 2 via capacitor C1, and the gate terminal of MOS voltage variable capacitance element D2 is connected to the output terminal of inverter element 2 via capacitor C2. A knock gate terminal of each MOS-type voltage variable capacitance element is grounded. Then, an external control voltage is supplied to the connection point between the gate terminal of each MOS type voltage variable capacitor and the capacitor via the resistors R2 and R3.

[0004] Fig. 7 shows the relationship between the gate voltage and the capacitance (CV characteristic) of a MOS type voltage variable capacitance element, in which the capacitance value of the MOS type voltage variable capacitance element changes by changing the gate voltage. become. Since this MOS type voltage variable capacitance element forms a part of the load capacitance in the resonance loop of the oscillator, it is possible to obtain a frequency change according to the external control voltage based on the principle described above. .

Patent document 1: Japanese Patent Application Laid-Open No. 2002-026660

Patent Document 2: JP-A-11-088052

Disclosure of the invention

Problems to be solved by the invention

However, as is clear from FIG. 7, the area where the CV characteristic changes linearly is very small, and on both sides of this area, the change in capacitance with respect to the change in gate voltage gradually decreases, and the curve changes. When the gate voltage changes over time, the capacitance value does not change, but when it reaches the (saturated) region, it has a characteristic.

In other words, it is difficult to increase the variable frequency of the oscillator, and there are few areas with good linearity! There were drawbacks.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a crystal oscillator capable of increasing a frequency variable amount of an oscillator according to a control voltage supplied from the outside and obtaining a frequency change with good linearity.

Means for solving the problem

[0006] The present invention provides a frequency adjustment circuit including at least an inverter element, a crystal oscillator, and first and second MOS voltage variable capacitance elements, and the first and second MOS transistors. A first and a second level shift circuit for respectively shifting the level of the control DC voltage supplied to the back gate terminal of the type voltage variable capacitance element, wherein the gate of the first MOS type voltage variable capacitance element A terminal is connected to an input terminal side of the inverter element, and a gate terminal of the second MOS type voltage variable capacitance element is connected to an output terminal side of the inverter element, respectively. A DC bias voltage is applied to one of the gate terminals, and each back gate terminal of the first and second MOS voltage variable capacitance elements is grounded via a capacitor. And a control DC voltage is supplied via a second level shift circuit, and one of the first and second level shift circuits responds in an area lower than the center voltage of the control DC voltage. The first and second M The voltage shift amount is set so that the CV characteristic of the OS type voltage variable capacitance element operates in a linear region, and the other of the first and second level shift circuits is used to control the DC voltage of the control. The voltage shift amount is set so that the CV characteristics of the first and second MOS voltage variable capacitors corresponding to the region higher than the center voltage operate in a region where the CV characteristic is linear. Things.

The invention according to claim 2 is characterized by further comprising a temperature compensating circuit constituted by using a MOS type voltage variable capacitance element.

Further, the invention according to claim 3 is characterized in that the DC bias voltage is used as a reference voltage for both the temperature compensation circuit and the frequency adjustment circuit.

In the invention according to claim 4, the minimum value of the control DC voltage is V, and the maximum value is V.

min max

, The center voltage is V, and the capacitances of the first and second MOS type voltage variable capacitors are linear center.

The lower limit value of the gate voltage that changes periodically and V is the upper limit value.

GB1 GB2

Value is V Z2 and the DC bias voltage is V, the DC bias is applied.

DD ref

In one of the first and second level shift circuits for supplying a control DC voltage to the first and second MOS type voltage variable capacitance elements, the control DC voltage is V Outputs the voltage that changes from V / 2-V to V / 2-V when changing to V center max DD GB2 DD GB 1

Min center ref GB2 ref Bl so that the other level shift circuit outputs a voltage that changes from V -V to V -V when the control DC voltage changes from V to V. It is characterized by being set to.

The invention's effect

In the crystal oscillator according to the present invention, the control voltage supplied from the outside is separately supplied to each MOS type voltage variable capacitance element via the level shift circuit. The advantage is that the frequency variation of the oscillator according to the voltage is increased and a frequency change with good linearity is obtained.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will be described in detail with reference to examples.

FIG. 1 is a circuit diagram showing an embodiment of a crystal oscillator according to the present invention, and portions common to those in the circuit diagram shown in FIG.

A feature of the present invention, which is different from the conventional circuit shown in FIG. That is, the gate terminal of the MOS-type voltage variable capacitance element D1, which is the first MOS-type voltage variable capacitance element, is connected to the input terminal of the inverter element, and the MOS-type voltage variable capacitance element, which is the second MOS-type voltage variable capacitance element. The gate terminal of element D2 is arranged on the output end side of the inverter element via DC cut capacitor Cc, and the back gate terminals of MOS voltage variable capacitance elements D1 and D2 are grounded via capacitors Ca and Cb, respectively. The control voltage is supplied to the back gate terminals of the MOS voltage variable capacitance elements Dl and D2 via the level shift circuits 6 and 7, which are the first and second level shift circuits, respectively. It is.

At this time, a DC bias V is applied to the gate terminal of the MOS type voltage variable capacitance element D2. This DC bias V also functions as a reference voltage source for the temperature compensation circuit 3.

are doing.

If necessary, a gain adjuster 8 for adjusting the voltage value (oscillation width) of the control DC voltage may be inserted before the level shift circuits 6 and 7.

[0010] Here, the operation of the frequency adjustment circuit 5 will be described.

Fig. 2 is a diagram showing the CV characteristics of a MOS type voltage variable capacitance element. As shown in the figure, the lower limit of the gate voltage exhibiting a region with excellent linearity is defined as V, and the upper limit is defined as V.

GB1 GB2 Further, the minimum value and the maximum value of the control DC voltage are defined as V and the center voltage is defined as V and min max center, respectively.

Further, the threshold value of the inverter element 2 is defined as V Z2.

DD

FIG. 3 is a diagram showing a relationship between a control DC voltage supplied from an external force and voltages VC1 and VC2 supplied from the level shift circuits 6 and 7 to the MOS type voltage variable capacitance elements Dl and D2. FIG. 4 is a diagram showing a relationship between a control DC voltage supplied from the outside and a gate voltage of a MOS voltage variable capacitance element.

As shown in Fig. 3, in the level shift circuit that supplies the control voltage to the MOS type voltage variable capacitance element D1, as the control DC voltage changes from V to V, the center shift from (V-V) to the min center ref GB2

(V-V) is controlled by the MOS voltage variable capacitance element D2 to output a voltage that changes to ref GB1

The level shift circuit that supplies the control voltage is set to output a voltage that changes from (V / 2-V) to (V / 2-V) when the control DC voltage changes to the V force V at the center max.

DD GB2 DD GB1

I do.

By setting the level shift circuit in this way, as shown in Fig. 4, when the control DC voltage is V power V, the gate voltage of V power V is applied to the MOS type voltage variable capacitance element D1 by min center GB2 GB1

When the applied DC voltage is V force V, the MOS voltage variable capacitance element D2 center max

Is applied a gate voltage from V to V.

GB2 GB1

Therefore, as shown in FIG. 5, a linear relationship between the control voltage and the frequency variable amount can be obtained in a wider range than in the related art.

[0012] In short, the present invention provides that one of the level shift circuits operates one MOS type voltage variable capacitance element in an area where the CV characteristic is linear in an area lower than the center voltage of the control DC voltage, and the other operates such that The level shift circuit is characterized in that the voltage shift amount is set such that the other MOS type voltage variable capacitance element operates in a region where the CV characteristic is linear in a region higher than the center voltage of the control DC voltage. Is what you do.

Although the above-described embodiment includes the one including the temperature compensation circuit 3, the present invention may be applied to a voltage-controlled crystal oscillator in which the temperature compensation circuit is omitted.

Brief Description of Drawings

FIG. 1 is a circuit diagram showing an embodiment of a crystal oscillator according to the present invention. FIG. 2 is a view showing CV characteristics of a MOS type voltage variable capacitance element.

FIG. 3 is a diagram showing a relationship between a control DC voltage and a voltage supplied to a level shift circuit.

FIG. 4 is a diagram showing a relationship between a control DC voltage and a gate voltage of a MOS type voltage variable capacitor.

FIG. 5 is a diagram showing a relationship between a control voltage and a frequency variable amount.

FIG. 6 is a circuit diagram showing an embodiment of a conventional crystal oscillator.

FIG. 7 is a view showing CV characteristics of a MOS voltage variable capacitance element.

Explanation of symbols

1 Crystal oscillator, 2 Inverter element, 3 Temperature compensation circuit, 5 Frequency adjustment circuit, 6, 7 Level shift circuit, Dl, D2 MOS type voltage variable capacitance element, Ca, Cb capacitor

Claims

The scope of the claims

[1] A frequency adjustment circuit including at least an inverter element, a crystal oscillator, and first and second MOS-type voltage variable capacitance elements, and the first and second MOS-type voltage variable capacitance elements A first and a second level shift circuit for respectively shifting the level of the control DC voltage supplied to the back gate terminal of

A gate terminal of the first MOS type voltage variable capacitance element is connected to an input terminal side of the inverter element, and a gate terminal of the second MOS type voltage variable capacitance element is connected to an output terminal side of the inverter element. A DC bias voltage is applied to one of the gate terminals of the first and second MOS voltage variable capacitance elements,

Each back gate terminal of the first and second MOS type voltage variable capacitance elements is grounded via a capacitor, and a control DC voltage is supplied via the first and second level shift circuits, respectively.

One of the first and second level shift circuits is in a region where the CV characteristics of the first and second MOS type voltage variable capacitors corresponding to a region lower than the center voltage of the control DC voltage are linear. The amount of voltage shift is set to operate, and the other of the first and second level shift circuits corresponds to the first and second MOS types corresponding to a region higher than the center voltage of the control DC voltage. A crystal oscillator characterized in that a voltage shift amount is set so that the voltage variable capacitance element operates in a region where a CV characteristic is linear.

[2] The crystal oscillator according to claim 1, further comprising a temperature compensation circuit configured using a MOS type voltage variable capacitance element.

3. The crystal oscillator according to claim 2, wherein the DC bias voltage is used as a reference voltage for both the temperature compensation circuit and the frequency adjustment circuit.

[4] The minimum value of the control DC voltage is V, the maximum value is V, the center voltage is V, the min max center

The lower limit value of the gate voltage at which the capacitance of the first and second MOS type voltage variable capacitors changes linearly is V, the upper limit value is V, the threshold value of the inverter element is VZ2, and the DC voltage

GB1 GB2 DD When the bias voltage is V,

ref

One of the first and second level shift circuits for supplying a control DC voltage to the first and second MOS voltage variable capacitance elements to which the DC bias voltage has been applied In the shift circuit, when the control DC voltage changes from V to V,

center max DD GB2 is set to output a voltage that changes to V / 2-V, while the other level is set.

DD GB1

In the bell shift circuit, when the control DC voltage changes from V to V,

Claim ref GB1 characterized in that it is set to output a voltage that changes from mm center ref GB2 to V-v.

4. The crystal oscillator according to any one of 1 to 3.