JPH08148937A - Voltage controlled piezoelectric oscillator - Google Patents

Abstract

PURPOSE: To miniaturize an IC chip in the case of an IC processing by utilizing a Miller effect and obtaining the effect equivalent to large capacitance by small capacitance in a voltage controlled piezoelectric oscillator using a Colpitts type oscillation circuit using a transistor. CONSTITUTION: The Colpitts circuit of the transistor is used. One end of a piezoelectric vibrator X is connected to the base of the transistor Q1 of an oscillation part and the other end is connected to the gate of an MOSFET (FET1). A control voltage VC is applied through a resistor RG to the gate of the FET1 and the amplification degree of the FET1 is changed by the control voltage VC. Then, the capacitance is connected serially to the piezoelectric vibrator X and it has the same effect as the case of connecting the capacitance appearently larger than the capacitance of a capacitor C1 by the Miller effect. Thus, at the time of using the piezoelectric vibrator X of the fundamental waves of 4kHz for instance and using 10pF in the capacitor C1, the frequency change amount of equal to or more than 300×10<-6> is secured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage controlled piezoelectric oscillator suitable for downsizing an IC chip.

[0002]

2. Description of the Related Art FIG. 5 shows a circuit diagram of a general voltage-controlled piezoelectric oscillator of the prior art. The cathode side of the variable capacitance diode D1 is connected to the ground and the anode side is connected to the terminal of the piezoelectric vibrator X on the ground side of the piezoelectric vibrator of a general Colpitts oscillator circuit, and the frequency is controlled via a resistor at this connection point. Supply the voltage. When the voltage of the voltage control terminal VC is changed, the capacitance changes in accordance with the change of the voltage applied to the variable capacitance diode D1, and the frequency of the voltage controlled piezoelectric oscillator changes.

[0003]

In the prior art, in order to expand the frequency variable range of the voltage controlled piezoelectric oscillator, the variable width of the capacitance of the variable capacitance diode D1 must be increased. When the oscillation circuit of the voltage-controlled piezoelectric oscillator using the large-capacity variable capacitance diode D1 is integrated into an IC,
The variable-capacitance diode D1 having a large capacitance requires a large area in the IC chip, which causes a problem that the IC chip becomes large.

[0004]

[Means for Solving the Problems] By obtaining a large capacity effect with a small capacity by utilizing the mirror effect, an IC chip can be downsized and the problem has been solved.

[0005]

Background In recent years, as electronic devices have been downsized, oscillators have been downsized. Therefore, the oscillation circuit is an IC
The number of cases that are becoming more common is increasing. Further, if the frequency variable width of the voltage controlled piezoelectric oscillator is to be increased, it is necessary to increase the capacitance of the variable capacitance diode D1, which requires a large IC chip area. this is,
Go against the direction of miniaturization. Therefore, the capacitance Cin of the capacitor C1 placed between the input and the output of the amplifier having the amplification degree A as viewed from the input side of the circuit is Cin = (1 + A) · C1. That is, the mirror effect is adopted which brings about a large capacity effect with a small capacity. Although the Miller effect itself is not new, the present invention not only aims to reduce the size of the IC chip by utilizing the Miller effect, but also controls the amplification degree of the amplifier used for the Miller effect by voltage control to reduce the capacitance. It's changing a lot.

[0006]

FIG. 3 is a circuit diagram of an embodiment (using the mirror effect) of the present invention. In this example, MOSFET (FET
1), the capacitance Cin between the input terminals Y and Y ′ is Cin = (1+) due to the amplification degree A of the circuit and the capacitor C1.
A) · C1 and the amplification degree A can be changed by controlling the gate voltage Vin of the FET1. Therefore, Cin can be changed by controlling the gate voltage of the FET1.

(Embodiment 1) FIG. 1 shows an embodiment of the present invention. In this embodiment, a Colpitts circuit of transistors is used. One end of the piezoelectric vibrator X is connected to the base of the transistor Q1 of the oscillation unit, and the other end is connected to the MOSFET (FE
It is connected to the gate of T1). The control voltage VC is applied to the gate of the FET1 via the resistor RG. The amplification degree of the FET1 is changed at the control voltage VC. Capacitance is connected in series with the piezoelectric vibrator X, but it is the same as having an apparently larger capacity than the capacitor C1 due to the mirror effect. 10pF to the capacitor C1 as shown in
It was possible to secure a frequency change amount of 300 × 10 ⁻⁶ or more when using a. Further, by taking the characteristics of the FET 1 into consideration, a larger frequency change can be made.

(Embodiment 2) FIG. 2 shows an example using a CMOS circuit oscillator. The frequency is changed by connecting the FET1 to the CMOSQ2 input section and changing the gate voltage. A crystal oscillator, a ceramic oscillator, or the like is used as the piezoelectric oscillator used in the voltage-controlled piezoelectric oscillator.

[0009]

According to the present invention, when the oscillation circuit of the voltage controlled piezoelectric oscillator is integrated into an IC, a large-capacity variable capacitance diode is not used. Therefore, there is an effect that the chip size can be reduced, and the size can be reduced. Moreover, the cost has been reduced.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a voltage-controlled piezoelectric oscillator including transistors according to an embodiment of the present invention.

FIG. 2 is a circuit diagram of a voltage-controlled piezoelectric oscillator based on CMOS showing an embodiment of the present invention.

FIG. 3 is a circuit diagram of a Miller effect showing an embodiment of the present invention.

FIG. 4 is a graph showing a frequency change with respect to a control voltage in the example of the present invention.

FIG. 5 is a circuit diagram showing a conventional technique.

[Explanation of symbols]

 Q1 transistor Q2 CMOSIC X piezoelectric vibrator FET1 MOSFET C1 capacitor Rf feedback resistance RG resistance D1 variable capacitance diode

Claims (2)

[Claims] 1. A voltage controlled piezoelectric oscillator using a Colpitts type oscillation circuit using a transistor, wherein the other terminal of the piezoelectric vibrator connected to the base of the transistor is connected to the gate of the MOSFET.
Connect a capacitor between the gate and drain of the
A voltage-controlled piezoelectric oscillator characterized in that a control voltage is applied to the gate of an FET. 2. A voltage-controlled piezoelectric oscillator using an oscillation circuit in which a feedback resistor and a piezoelectric vibrator are connected in parallel between the input and output of a CMOSIC inverter, wherein a MOSFET gate is connected to an input terminal of the CMOSIC inverter via a capacitor. Connect a capacitor between the gate and drain of the MOSFET,
A voltage controlled piezoelectric oscillator characterized in that a control voltage is applied to the gate of ET.