JPH1197932A - Crystal oscillator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a crystal oscillator which can be improved in variation in oscillation frequency due to source voltage variation without increasing the circuit scale, lowering the use efficiency of the source voltage, and inducing an increase of phase noise. SOLUTION: A crystal oscillator consists of a crystal vibrator 17, a crystal oscillation circuit 21 composed of an inverter 19, a power source 11, and a frequency variation compensating circuit 15 and the capacity or reactance that the frequency compensating circuit 15 has is varied by varying the source voltage; and this variation is transmitted to the crystal oscillation circuit 21 to vary the oscillation frequency of the crystal oscillation circuit 21, so that this frequency variation cancels variation in the oscillation frequency of the crystal oscillation circuit 21 due to the source voltage variation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a crystal oscillator, and more particularly to a crystal oscillator having improved oscillation frequency stability against power supply voltage fluctuation.

[0002]

2. Description of the Related Art A crystal oscillator using a crystal oscillator has excellent frequency stability as compared with other oscillators. However, when used as a reference frequency oscillator of a wireless communication device, fluctuations in the oscillation frequency due to temperature change. In addition, fluctuations in the oscillation frequency due to fluctuations in the power supply voltage are important items that need to be improved. The fluctuation of the oscillation frequency due to the fluctuation of the power supply voltage is caused by the fact that the junction capacitance of the PN junction existing in the semiconductor integrated circuit and the gate input capacitance of the MOS transistor depend on the voltage when the oscillation circuit is constituted by a semiconductor integrated circuit using CMOS. It is mainly caused by change.

In order to improve the fluctuation of the oscillation frequency due to the fluctuation of the power supply voltage, it is a general measure to insert a regulator between the power supply and the oscillation circuit to absorb the fluctuation of the power supply voltage. .

[0004]

However, the insertion of the regulator causes an increase in the circuit scale, and the regulator needs a voltage difference between the input voltage and the output voltage of 0.3 V or more. However, there is a problem that the efficiency of use of the power supply voltage is reduced only, and further, phase noise harmful to the reference frequency oscillator of the wireless communication device is induced.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems, to increase the circuit scale, to reduce the power supply voltage utilization efficiency, and to increase the phase noise. Another object of the present invention is to provide a crystal oscillator capable of improving the fluctuation of the oscillation frequency due to the power supply voltage fluctuation.

[0006]

In order to achieve the above-mentioned object, a crystal oscillator according to the present invention comprises a crystal oscillator circuit comprising a crystal oscillator, an inverter provided on a semiconductor substrate, a power supply, And a fluctuation compensation circuit, wherein the power supply directly supplies power to the inverter of the oscillation circuit, and the fluctuation of the oscillation frequency caused by the voltage fluctuation of the power supply is compensated by the frequency fluctuation compensation circuit. .

[Operation] PN existing in a semiconductor integrated circuit
The junction is reverse biased by the power supply voltage in the operating state,
A depletion layer is formed. When the power supply voltage increases, the depletion layer of the reverse-biased PN junction expands, and the junction capacitance of the PN junction decreases. On the other hand, the gate input capacitance of the MOS transistor increases in proportion to the power supply voltage. When the former change is dominant, the oscillation frequency increases when the power supply voltage increases, but when the latter change is dominant, the oscillation frequency decreases when the power supply voltage increases. Since the superiority relationship between the former and the latter is determined by the size of various devices in the semiconductor integrated circuit and the value of the power supply voltage, the state of the fluctuation of the oscillation frequency caused by the fluctuation of the power supply voltage changes depending on these conditions.

A MOS capacitor having a structure in which an insulating film is sandwiched between a semiconductor substrate and a conductive electrode, or a circuit formed by connecting a capacitor and a variable resistance element capable of voltage control in series is capable of voltage control. Acts as reactance. The frequency fluctuation compensating circuit constituted by this voltage-controllable reactance can be connected to an oscillating circuit to control the oscillating frequency by a control voltage. If the control voltage of the frequency fluctuation compensation circuit is used as the power supply voltage to offset the fluctuation of the oscillation frequency, the fluctuation of the oscillation frequency due to the fluctuation of the power supply voltage can be reduced.

In a variable capacitance element in which an insulating film is sandwiched between a semiconductor substrate and a conductive electrode, when the semiconductor substrate, which is a component of the variable capacitance element, is formed of an N-type semiconductor substrate, the voltage applied to the conductive electrode increases. The capacitance value increases, and when a P-type semiconductor substrate is used, the opposite occurs, and the capacitance value decreases.

In the case of a reactance in which a capacitance element and a resistor are connected in series, the reactance increases when the resistance value of the connected resistor decreases, and the reactance decreases when the resistance value increases.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The preferred embodiments for implementing the crystal oscillator of the present invention will be described below with reference to the drawings. First, the crystal oscillator according to the first embodiment of the present invention will be described.

[First Embodiment] FIG. 1 is a block circuit diagram of a crystal oscillator according to a first embodiment of the present invention.
As shown in FIG. 1, in the crystal oscillator of the present invention, a crystal oscillation circuit 21, a power supply 11, a frequency fluctuation compensation circuit 1
And 5. The crystal oscillation circuit 21 includes the crystal oscillator 17
, An inverter 19, a feedback resistor 18 of the inverter 19, and a capacitive element 23.

FIG. 6 is a circuit diagram showing the configuration of the inverter. The same components as those in FIG. 1 are denoted by the same reference numerals. Next, the configuration of the inverter 19 shown in FIG. 1 will be described. The inverter 19 shown in FIG. 1 is configured by a CMOS connection of a P-channel MOS transistor 61 and an N-channel MOS transistor 63 provided on the same semiconductor substrate, as shown in FIG.

The power supply 11 is connected to a power supply input 12 of an inverter 19 of a crystal oscillation circuit 21 via a power supply output 13. The power supply 11 is connected via a power supply output 13 to a control voltage input 26 of the frequency fluctuation compensation circuit 15.
The reactance output 25 of the frequency fluctuation compensation circuit 15 is connected to the capacitance element 23 of the crystal oscillation circuit 21.

FIG. 2 is a circuit diagram showing a circuit configuration of the frequency fluctuation compensating circuit. The same components as those in FIG. 1 are denoted by the same reference numerals. Next, the configuration of the frequency fluctuation compensation circuit 15 shown in FIG. 1 will be described. As shown in FIG. 2, the frequency fluctuation compensating circuit 15 shown in FIG.
It is composed of 1.

The control voltage input 26 is connected to the variable capacitance element 31 via a resistor 33. Reactance output 25
Is connected to the variable capacitance element 31.

FIG. 7 is a structural diagram showing the structure of the variable capacitance element. Next, the configuration of the variable capacitance element 31 shown in FIG. 2 will be described. The variable capacitance element 31 shown in FIG. 2 includes a P-type semiconductor substrate 71, a conductive electrode 75, and an insulating film 73, as shown in FIG.

The conductive electrode 75 is made of a polycrystalline silicon film or a high melting point metal film, and the insulating film 73 is made of a silicon dioxide film obtained by oxidizing the semiconductor substrate 71. The semiconductor substrate 71 and the conductive electrode 75 sandwich the insulating film 73.

Next, the operation of the crystal oscillator according to the first embodiment of the present invention will be described with reference to FIGS. The power supply 11 outputs a power supply voltage to the control voltage input 26 of the frequency fluctuation compensation circuit 15 and the power supply input 12 of the inverter 19 of the crystal oscillation circuit 21 via the power supply output 13.

In the crystal oscillation circuit 21, when the power supply voltage output from the power supply 11 rises and the voltage input to the power supply input 12 of the inverter 19 rises, the inverter 19
Is increased in the gate input capacitance of the MOS transistor constituting the MOS transistor. On the other hand, the junction capacitance of the PN junction of the MOS transistor forming the inverter 19 decreases. When the increase in the gate input capacitance of the MOS transistor is more predominant than the decrease in the junction capacitance of the PN junction of the MOS transistor, the oscillation frequency of the crystal oscillation circuit 21 decreases as the power supply voltage increases.

In the frequency fluctuation compensation circuit 15, the control voltage input 26 applies the power supply voltage input from the power supply output 13 to the variable capacitance element 31.

In the variable capacitance element 31 formed of a P-type semiconductor substrate, the voltage output from the control voltage input 26 to the variable capacitance element 31 increases due to an increase in the power supply voltage output from the power supply 11, and the variable capacitance element 31 The capacitance of the capacitor 31 decreases and is transmitted to the crystal oscillation circuit 21 through the reactance output terminal 25, thereby reducing the equivalent capacitance of the capacitance element 23 and increasing the oscillation frequency of the crystal oscillation circuit 21. The capacitance value of the variable capacitance element 31 is adjusted so that the increase in the oscillation frequency is substantially equal to the decrease in the oscillation frequency of the crystal oscillation circuit 21 due to the increase in the power supply voltage. Offset and compensate for

[Second Embodiment] A crystal oscillator according to a second embodiment of the present invention will be described with reference to the drawings. Since the configuration of the crystal oscillator is the same as that shown in FIG. 1 used in the description of the first embodiment, the description is omitted. Since the configuration of the inverter is the same as that shown in FIG. 6 used in the description of the first embodiment, the description is omitted. The configuration of the frequency fluctuation compensating circuit is the same as that shown in FIG. 2 used in the description of the first embodiment, and thus the description is omitted. The structure of the variable capacitance element is
The only difference is that the semiconductor device is composed of an N-type semiconductor substrate 71. However, since it is the same as that shown in FIG. 7 used in the description of the first embodiment, the description is omitted.

Next, the operation of the crystal oscillator according to the second embodiment of the present invention will be described with reference to FIGS. The power supply 11 outputs a power supply voltage to the control voltage input 26 of the frequency fluctuation compensation circuit 15 and the power supply input 12 of the inverter 19 of the crystal oscillation circuit 21 via the power supply output 13.

In the crystal oscillation circuit 21, when the power supply voltage output from the power supply 11 rises and the voltage input to the power supply input 12 of the inverter 19 rises, the inverter 19
Is increased in the gate input capacitance of the MOS transistor constituting the MOS transistor. On the other hand, the junction capacitance of the PN junction of the MOS transistor forming the inverter 19 decreases.

If the decrease in the junction capacitance of the PN junction of the MOS transistor is more prevalent than the increase in the gate input capacitance of the MOS transistor, the oscillation frequency of the crystal oscillation circuit 21 increases as the power supply voltage increases. In the variable capacitance element 31 formed of an N-type semiconductor substrate, the voltage output from the control voltage input 26 to the variable capacitance element 31 increases due to an increase in the power supply voltage output from the power supply 11, and the capacitance of the variable capacitance element 31 increases. And the capacitance increase is caused by the reactance output terminal 2
5 to the crystal oscillation circuit 21,
Increase the equivalent capacitance and decrease the oscillation frequency.

The capacitance value of the variable capacitance element 31 is adjusted so that the decrease in the oscillation frequency and the increase in the oscillation frequency of the crystal oscillation circuit 21 due to the increase in the power supply voltage become substantially equal. Cancels and compensates for oscillation frequency fluctuations.

[Third Embodiment] A crystal oscillator according to a third embodiment of the present invention will be described with reference to the drawings. Since the configuration of the crystal oscillator is the same as that shown in FIG. 1 used in the description of the first embodiment, the description is omitted. Since the configuration of the inverter is the same as that shown in FIG. 6 used in the description of the first embodiment, the description is omitted. FIG. 3 is a circuit diagram showing a circuit configuration of the frequency variation compensating circuit, and the same components as those in FIG. 1 are denoted by the same reference numerals. Next, the configuration of the frequency fluctuation compensation circuit 15 shown in FIG. 1 will be described.

As shown in FIG. 3, the frequency fluctuation compensating circuit 15 shown in FIG. 1 includes resistors 39 and 41, an N-channel MOS transistor 43, an N-channel MOS transistor 37 as a voltage-controllable variable resistor, and a capacitor 35. It consists of.

The control voltage input 26 includes a resistor 39 and a resistor 41
And is connected to the gate 45 of the N-channel MOS transistor 43. Control voltage input 2
6 is connected to the drain 38 of the N-channel MOS transistor 43 and the gate 47 of the N-channel MOS transistor 37 via the resistor 40. Reactance output 25 is connected to capacitance element 35, which is connected to drain 36 of N-channel MOS transistor 37.

Next, the operation of the crystal oscillator according to the third embodiment of the present invention will be described with reference to FIGS. The power supply 11 outputs a power supply voltage to the control voltage input 26 of the frequency fluctuation compensation circuit 15 and the power supply input 12 of the inverter 19 of the crystal oscillation circuit 21 via the power supply output 13.

In the crystal oscillation circuit 21, when the power supply voltage output from the power supply 11 rises and the voltage input to the power supply input 12 of the inverter 19 rises, the inverter 19
Is increased in the gate input capacitance of the MOS transistor constituting the MOS transistor. On the other hand, the junction capacitance of the PN junction of the MOS transistor forming the inverter 19 decreases. If the increase in the gate input capacitance of the MOS transistor is more predominant than the decrease in the junction capacitance of the PN junction of the MOS transistor, the oscillation frequency of the crystal oscillation circuit 21 decreases as the power supply voltage increases.

In the frequency fluctuation compensating circuit 15, the control voltage input 26 divides the power supply voltage input from the power supply output 13 by a resistor 39 and a resistor 41 to form an N-channel MOS.
The voltage is applied to the gate 45 of the transistor 43. When the power supply voltage output from the power supply 11 rises, the control voltage input 26 is divided by a resistor 39 and a resistor 41 into N-channel MOS transistors.
The voltage applied to the gate 45 of the transistor 43 increases.

When the voltage of the gate 45 of the N-channel MOS transistor 43 increases, the resistance between the drain 38 and the source 34 of the N-channel MOS transistor 43 decreases, the current flowing through the resistor 40 increases, and the N-channel MOS transistor 43 increases.
The voltage of the gate 47 of the OS transistor 37 decreases.

When the voltage at the gate 47 of the N-channel MOS transistor 37 decreases, the resistance between the drain 36 and the source 42 of the N-channel MOS transistor 37 increases, the equivalent reactance of the quantity element 35 decreases, and the equivalent reactance decreases. Is transmitted to the crystal oscillation circuit 21 through the reactance output terminal 25, and reduces the equivalent reactance of the crystal oscillation circuit 21 and increases the oscillation frequency.

The capacitance value of the capacitive element 35 is adjusted so that the increase in the oscillation frequency and the decrease in the oscillation frequency of the crystal oscillation circuit 21 due to the increase in the power supply voltage become substantially equal to each other. Cancels and compensates for frequency variations.

[Fourth Embodiment] A crystal oscillator according to a fourth embodiment of the present invention will be described with reference to the drawings. Since the configuration of the crystal oscillator is the same as that shown in FIG. 1 used in the description of the first embodiment, the description is omitted. Since the configuration of the inverter is the same as that shown in FIG. 6 used in the description of the first embodiment, the description is omitted. FIG. 4 is a circuit diagram showing a circuit configuration of the frequency fluctuation compensation circuit, and the same components as those in FIG. 1 are denoted by the same reference numerals. Next, the configuration of the frequency fluctuation compensation circuit 15 shown in FIG. 1 will be described.

As shown in FIG. 4, the frequency fluctuation compensating circuit 15 shown in FIG. 1 includes resistors 39 and 41, an N-channel MOS transistor 37 as a voltage-controllable variable resistor, and a capacitor 35.

The control voltage input 26 includes a resistor 39 and a resistor 41
And is connected to the gate 47 of the N-channel MOS transistor 37. Reactance output 25 is connected to capacitance element 35, which is connected to drain 36 of N-channel MOS transistor 37.

Next, the operation of the crystal oscillator according to the fourth embodiment of the present invention will be described with reference to FIGS. The power supply 11 outputs a power supply voltage to the control voltage input 26 of the frequency fluctuation compensation circuit 15 and the power supply input 12 of the inverter 19 of the crystal oscillation circuit 21 via the power supply output 13.

In the crystal oscillation circuit 21, when the power supply voltage output from the power supply 11 rises and the voltage input to the power supply input 12 of the inverter 19 rises, the inverter 19
Is increased in the gate input capacitance of the MOS transistor constituting the MOS transistor. On the other hand, the junction capacitance of the PN junction of the MOS transistor forming the inverter 19 decreases.

If the decrease in the junction capacitance of the PN junction of the MOS transistor is more predominant than the increase in the gate input capacitance of the MOS transistor, the oscillation frequency of the crystal oscillation circuit 21 increases as the power supply voltage increases. In the frequency fluctuation compensating circuit 15, the control voltage input 26 divides the power supply voltage input from the power supply output 13 by a resistor 39 and a resistor 41,
Apply to

When the power supply voltage output from the power supply 11 rises, the control voltage input 26 is divided into a resistor 39 and a resistor 41 by resistance division, and the gate 4 of the N-channel MOS transistor 37 is divided.
The voltage applied to 7 rises.

When the voltage at the gate 47 of the N-channel MOS transistor 37 rises, the resistance between the drain 36 and the source 42 of the N-channel MOS transistor 37 decreases, the equivalent reactance of the capacitor 35 increases, and the equivalent The increase in reactance is caused by the reactance output terminal 25
Is transmitted to the crystal oscillation circuit 21 through the
1 increases the equivalent reactance and decreases the oscillation frequency. The capacitance value of the capacitive element 35 is adjusted so that the decrease in the oscillation frequency is substantially equal to the increase in the oscillation frequency of the crystal oscillation circuit 21 due to the increase in the power supply voltage. Offset and compensate.

[Fifth Embodiment] Next, a crystal oscillator according to a fifth embodiment of the present invention will be described with reference to the drawings.
Since the configuration of the crystal oscillator is the same as that shown in FIG. 1 used in the description of the first embodiment, the description is omitted. Since the configuration of the inverter is the same as that shown in FIG. 6 used in the description of the first embodiment, the description is omitted.

FIG. 5 is a circuit diagram showing a circuit configuration of the frequency fluctuation compensating circuit. The same components as those in FIG. 1 are denoted by the same reference numerals. Next, the configuration of the frequency fluctuation compensation circuit 15 shown in FIG. 1 will be described. As shown in FIG. 5, the frequency fluctuation compensation circuit 15 shown in FIG. 1 includes resistors 39 and 41, an N-channel MOS transistor 43, an N-channel MOS transistor 37 as a voltage-controllable variable resistor, a capacitor 35, and a selection switch. It is composed of the element 45.

The control voltage input 26 includes a resistor 39 and a resistor 41
And the gate 45 of the N-channel MOS transistor 43 and the terminal 4 of the selection switch element 45
8 is connected. The control voltage input 26 is connected to the drain 38 of the N-channel MOS transistor 43 via the resistor 40.
And the terminal 46 of the selection switch element 45.

The terminal 49 of the selection switch element 45 is
It is connected to the gate 47 of the S transistor 37. Reactance output 25 is connected to capacitance element 35, which is connected to drain 3 of N-channel MOS transistor 37.
6 is connected.

Next, the operation of the crystal oscillator according to the fifth embodiment of the present invention will be described with reference to FIGS. The power supply 11 outputs a power supply voltage to the control voltage input 26 of the frequency fluctuation compensation circuit 15 and the power supply input 12 of the inverter 19 of the crystal oscillation circuit 21 via the power supply output 13.

In the crystal oscillation circuit 21, when the power supply voltage output from the power supply 11 rises and the voltage input to the power supply input 12 of the inverter 19 rises, the inverter 19
Is increased in the gate input capacitance of the MOS transistor constituting the MOS transistor. On the other hand, the junction capacitance of the PN junction of the MOS transistor forming the inverter 19 decreases.

If the increase in the gate input capacitance of the MOS transistor is more predominant than the decrease in the junction capacitance of the PN junction of the MOS transistor, the oscillation frequency of the crystal oscillation circuit 21 decreases as the power supply voltage increases. The terminal 49 and the terminal 4 of the selection switch element 45 are
6 is turned on. The subsequent operation of the frequency fluctuation compensation circuit is exactly the same as the operation described in the third embodiment, and a description thereof will be omitted.

Next, the increase in the gate input capacitance of the MOS transistor is dominant as compared with the decrease in the junction capacitance of the PN junction of the MOS transistor, and the frequency when the oscillation frequency of the crystal oscillation circuit 21 decreases as the power supply voltage increases. The operation of the fluctuation compensation circuit will be described.

In the frequency fluctuation compensating circuit 15, the terminals 49 and 48 of the selection switch element 45 are made conductive. The subsequent operation of the frequency fluctuation compensating circuit is exactly the same as the operation described in the fourth embodiment, and a description thereof will be omitted.

As described above, in the fifth embodiment, the operation of the frequency fluctuation compensating circuit is changed by switching the common state of the selection switch element 45 to increase the frequency accompanying the power supply voltage fluctuation of the crystal oscillation circuit 21 or The feature is that it can respond to any fluctuation direction of the decrease.

[0055]

As described above, according to the present invention, the fluctuation of the oscillation frequency due to the fluctuation of the power supply voltage can be suppressed without introducing a regulator. The fluctuation characteristics of the oscillation frequency can be improved without lowering the voltage use efficiency and without sacrificing the phase noise characteristics.

[Brief description of the drawings]

FIG. 1 is a block circuit diagram showing an oscillator according to an embodiment of the present invention.

FIG. 2 is a circuit diagram illustrating a frequency fluctuation compensation circuit according to an embodiment of the present invention.

FIG. 3 is a circuit diagram illustrating a frequency fluctuation compensation circuit according to an embodiment of the present invention.

FIG. 4 is a circuit diagram showing a frequency fluctuation compensation circuit according to the embodiment of the present invention.

FIG. 5 is a circuit diagram showing a frequency fluctuation compensation circuit according to the embodiment of the present invention.

FIG. 6 is a circuit diagram showing an inverter of the crystal oscillation circuit of the oscillator according to the embodiment of the present invention.

FIG. 7 is a sectional view showing a variable capacitance element according to the embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 11 power supply 15 frequency fluctuation compensation circuit 17 crystal oscillator 19 inverter 21 crystal oscillation circuit

Claims (5)

[Claims] 1. A power supply comprising: a crystal oscillation circuit including a crystal resonator; an inverter provided on a semiconductor substrate;
Frequency fluctuation compensation circuit, and the power supply directly supplies power to the inverter of the oscillation circuit,
Oscillation frequency fluctuation caused by power supply voltage fluctuation,
A crystal oscillator characterized in that it is compensated by a frequency fluctuation compensation circuit. 2. The frequency variation compensating circuit according to claim 1, further comprising a selection switch element, wherein said selection switch element enables an arbitrary combination of a voltage increasing direction and a frequency increasing direction. Characterized crystal oscillator. 3. The frequency fluctuation compensating circuit according to claim 1 or 2, wherein the frequency fluctuation compensating circuit comprises a variable capacitance element provided on the semiconductor substrate, wherein the variable capacitance element has a structure in which a semiconductor substrate and a conductive electrode sandwich an insulating film. A crystal oscillator characterized by the following. 4. The crystal oscillator according to claim 1, wherein the frequency fluctuation compensating circuit comprises a capacitor and a voltage-controllable variable resistor connected in series. 5. The crystal oscillator according to claim 4, wherein the variable resistance element capable of voltage control comprises a MOS transistor.