JP4155447B2 - Oscillator circuit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a voltage controlled oscillator whose oscillation frequency changes in accordance with a change in control voltage.
[0002]
[Prior art]
Conventionally, a voltage-controlled oscillator is known as one whose oscillation frequency changes in response to a control voltage. One of the applications of this oscillation frequency variable technology is a voltage controlled oscillator using a crystal resonator (or crystal oscillator), which has recently been incorporated into a miniaturized mobile product that can be carried by a person.
[0003]
On the other hand, the basic frequency variable method of the voltage controlled oscillator is that a piezoelectric vibrator and a feedback resistor connected between the inverter and the input / output of the inverter, and an input / output terminal of the inverter are connected to a capacitor via MOS transistors, A control voltage is input to the gate of the MOS transistor, the control voltage is changed to change the apparent capacitance value, and the frequency is varied.
[0004]
[Patent Document 1]
Japanese Patent Laid-Open No. 11-220329
[Problems to be solved by the invention]
As the voltage-controlled oscillator is downsized as in the above-described use environment, the sensitivity at low frequencies becomes dull and it is difficult to ensure a variable frequency range. In addition, as voltage control oscillators are rapidly becoming smaller and lower power consumption as a recent need, the adjustment range of the control voltage is becoming narrower, and it is now impossible to secure a variable frequency range as described above. is there.
[0006]
[Means for Solving the Problems]
In order to solve the above problems, the present invention provides an inverter, a feedback resistor connected in parallel to the inverter, a capacitor connected between the input / output of the inverter and the ground, and the input / output terminal of the inverter. In the piezoelectric oscillator constituted by the piezoelectric vibrator formed , a circuit having an on-resistance of the MOS transistor and a time constant by the capacitor by connecting a MOS transistor between the input / output terminal of the inverter and the capacitor And the oscillation frequency is varied by a control voltage that simultaneously changes the gate of the MOS transistor and the current flowing through the inverter .
[0007]
In short, by changing the control voltage, the apparent capacitance value change and the current value flowing in inverse with the control voltage are changed simultaneously, thereby changing the transconductance value of the inverter and changing the oscillation frequency.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the accompanying drawings. In each figure, the same numerals indicate the same objects. FIG. 1 shows an oscillation circuit configuration of an embodiment of the present invention. An inverter 1, a feedback resistor 3 connected in parallel to the inverter 1, a capacitor 4 connected between the input and output of the inverter 1 and the ground, and a piezoelectric vibrator 2 connected between the input and output terminals of the inverter 1 a piezoelectric oscillator including in, the I ₂ flows that by I _1, which is controlled by a control voltage Vc to the inverter 1 to drive the piezoelectric vibrator 2 is a current mirror circuit, a feedback resistor and an inverter 1 and the piezoelectric vibrator 3 And the piezoelectric oscillation circuit comprised by the capacitor | condenser 4 oscillates with a predetermined frequency.
[0009]
In the circuit of FIG. 1, the principle of the present invention has been explained. The characteristic diagram of FIG. 2 is a control voltage viewed from the input terminal of the inverter 1. The on-resistance of the MOS transistor 11 and the capacitor 21, and the on-resistance of the MOS transistor 12. Each of the capacitor 22 and the capacitor 22 has a CR circuit, and the discharge capacity per unit time varies depending on the MOS transistor on-resistance. By looking at this as an apparent capacity, it changes depending on the apparent variable capacity seen from the input / output terminal of the inverter 1.
[0010]
With these operations, when the control voltage Vc changes, the on-resistance value of the MOS transistor changes and the apparent capacitance value changes. At the same time, the oscillation frequency is changed by changing the transconductance of the inverter 1 by the control voltage Vc.
In this embodiment, a quartz crystal vibrator is used as the piezoelectric vibrator, and it goes without saying that the same effect can be obtained even with other piezoelectric materials.
[0011]
【The invention's effect】
As is apparent from the above description of the embodiments, the present invention simultaneously changes the transconductance value of the inverter by changing the apparent voltage change and the current value flowing through the inverter with the same control voltage. And change the oscillation frequency. As a result, an allowable frequency variable width can be ensured even in a low frequency band with low sensitivity. Further, even if the control voltage width is narrow, a large frequency variable width can be obtained.
[Brief description of the drawings]
FIG. 1 is a circuit diagram of an embodiment of the present invention.
FIG. 2 is a characteristic diagram showing the principle and results of the present invention.
[Explanation of symbols]
1 Inverter 2 Piezoelectric vibrator 3 Feedback resistors 21 and 12 Capacitor

Claims (1)

Piezoelectric oscillator comprising an inverter, a feedback resistor connected in parallel to the inverter, a capacitor connected between the input / output and the ground of the inverter, and a piezoelectric vibrator connected between the input / output terminals of the inverter In this case, a MOS transistor is connected between the input / output terminal of the inverter and the capacitor, thereby forming a circuit having an on-resistance of the MOS transistor and a time constant by the capacitor. The gate of the MOS transistor and the inverter An oscillation circuit characterized in that the oscillation frequency is varied by a control voltage that simultaneously changes the current flowing through the capacitor .

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