JP2003032039A - Piezoelectric oscillation circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piezoelectric oscillation circuit that is excellent in a start characteristic and also excellent in a phase noise characteristic and a frequency stability. SOLUTION: The piezoelectric oscillation circuit has an amplifier circuit and a piezoelectric vibrator used for a frequency control element, an output of a ring oscillator is supplied to a required point in an oscillation loop of the piezoelectric oscillation circuit, and the ring oscillator is operated for only a required time after application of power, then no deterioration in the noise characteristic in a steady oscillation state is caused.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric oscillator circuit, and more particularly to a small piezoelectric oscillator circuit having excellent starting characteristics.

[0002]

2. Description of the Related Art In a mobile phone, a crystal oscillator used as a reference oscillation source is intermittently operated to reduce power consumption so that it can be used continuously for a long time. In order for the crystal oscillator to operate normally immediately after being turned on, it is desired that the start-up time required from turning on the power to oscillate a desired output signal is short, and is disclosed in Japanese Patent Application No. 8-51017. Such a structure has been put to practical use.

FIG. 4 is a circuit diagram of an example of the crystal oscillator having the improved starting characteristic described in the above publication. The crystal oscillator 100 shown in the figure is a typical Colpitts type crystal oscillator.
It is arranged to connect the other end of the crystal unit 103 connected to the base of 01 through the capacitor 102 to the power supply line Vcc, and at this time, the power supply line Vcc is grounded through the capacitor 104 having a relatively large value. As a result, the power supply line Vcc is part of the oscillation loop.

That is, in order for the oscillation circuit to continue the oscillation operation, as is well known, it is necessary to construct an oscillation loop circuit in which both ends of the crystal oscillator are loop-connected in an alternating current manner. A circuit in which a division capacitor 105 connected in series to one end of the oscillator 103 and the other end of the crystal oscillator 103 are AC-connected to the power supply line Vcc and the capacitor 104 via the ground is configured as an oscillation loop circuit. is doing. With such a configuration, in the crystal oscillator 100, the oscillation operation is continued, and a voltage having a voltage level equivalent to the power supply voltage is applied to the crystal resonator 103 immediately after the power supply voltage is applied. Therefore, the crystal unit 103
Since a large vibration is applied to, the starting time until the oscillation signal reaches the required level is short.

[0005]

However, in the crystal oscillator having the above-described structure, since the power supply line Vcc is used as a part of the oscillation loop, the noise contained in the power supply voltage and the power supply line Vcc are mediated. Since the noise mixed in as a result is directly applied to the crystal unit 103,
Due to the influence, the phase noise characteristic may be deteriorated. Furthermore, there is a problem in that the frequency may fluctuate by affecting the oscillation loop due to fluctuations in other circuit elements (reactance components) connected to the power supply terminal.

That is, the crystal oscillator 10 having the above structure
0 is a capacitance 1 interposed between the power supply line Vcc and the ground
Although 04 also serves as a bypass capacitor, it is generally impossible to completely remove noise mixed in from innumerable parts of the power supply voltage and the power supply line Vcc, even if a plurality of bypass capacitors are provided. is there. Therefore, this noise signal is output together with the oscillation signal after being amplified by the amplifier circuit provided in the oscillation circuit, which deteriorates the phase noise characteristic of the crystal oscillator 100.

When the output signal of such a crystal oscillator is used for digital processing, if a noise signal mixed in the output signal is at a high level, a bit error will occur during data processing. There are cases. Further, since the power supply line Vcc is included in the oscillation loop, the so-called load capacitance component is a component on the side where the crystal oscillator 100 is mounted in addition to the capacitance due to the electronic components and the wiring pattern that constitute the crystal oscillator 100. Since the bypass capacitor connected to the power supply line Vcc and the stray capacitance are included, when adjusting the output frequency of the crystal oscillator 100, it is necessary to set a state in which these values are assumed in advance.

However, in such an adjusting method, the value of the bypass capacitor used in the device in which the crystal oscillator is mounted is often different from device to device, so that the crystal oscillator is adjusted so as to correspond to each device. Although it is necessary to change the conditions, it is impossible to unify the values for stray capacitances, as is well known. Therefore, the condition when performing the above frequency adjustment is not always the condition when using an oscillator. Not necessarily the same. Therefore, even if the oscillation frequency of each crystal oscillator is adjusted so as to finally output the specified frequency before mounting on the device, the value of the stray capacitance at this time and the floating on the side of the device on which the crystal oscillator 100 is mounted are adjusted. In many cases, the capacitance value does not match, and the load capacitance varies with the difference in the stray capacitance value. As a result, the output frequency of the crystal oscillator 100 incorporated in the device and the required output. There is a gap with the frequency.

An object of the present invention is to provide a crystal oscillator having excellent starting characteristics, phase noise characteristics, and frequency stability by solving the above problems of the piezoelectric oscillation circuit.

[0010]

In order to solve the above problems, the invention according to claim 1 of the present invention has an amplifier circuit and a piezoelectric vibrator used as a frequency control element, and the oscillation of the piezoelectric oscillation circuit. The output of the ring oscillator is supplied to a required portion in the loop, and the ring oscillator is configured to operate only for a required time after the power is turned on.

According to a second aspect of the present invention, a piezoelectric oscillator circuit including an amplifier circuit and a piezoelectric vibrator, a ring oscillator, a circuit for controlling the operation of the ring oscillator, and an output of the ring oscillator of the piezoelectric oscillator circuit. It is characterized in that the ring oscillator is operated only for a short time immediately after the power is turned on, by including means for supplying the required portion.

The invention according to claim 3 is characterized in that, in addition to the invention according to claim 1 or claim 2, the oscillation frequencies of the piezoelectric oscillation circuit and the ring oscillator are substantially the same or in an integral multiple relationship. To do.

According to a fourth aspect of the present invention, there is provided an amplifying circuit and a piezoelectric vibrator used as a frequency control element, and the output of the CR oscillating circuit is supplied to a required portion in an oscillation loop of the piezoelectric oscillating circuit. The oscillating circuit is characterized in that the oscillating circuit is configured to operate only for a required time after the power is turned on.

According to a fifth aspect of the present invention, there is provided a piezoelectric oscillation circuit including an amplification circuit and a piezoelectric vibrator, a CR oscillation circuit, a circuit for controlling the operation of the CR oscillation circuit, and an output of the CR oscillation circuit. And a means for supplying the required portion of the piezoelectric oscillation circuit, wherein the CR oscillation circuit operates only for a short time immediately after the power is turned on.

The invention according to claim 6 is characterized in that, in addition to the invention according to claim 4 or claim 5, the oscillation frequencies of the piezoelectric oscillation circuit and the CR oscillation circuit are substantially the same or in an integral multiple relationship. And

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below based on the illustrated embodiments. FIG. 1 is a circuit diagram showing an embodiment of a crystal oscillator according to the present invention. The crystal oscillator 1 shown in the figure includes a crystal oscillator circuit 2 and a ring oscillator 3.
And a control circuit 4 for controlling the operation of the ring oscillator 3. The crystal oscillating circuit 2 is, for example, a general Colpitts type crystal oscillating circuit, and a series circuit including a capacitor 6 and a capacitor 7 forming a part of load capacitance is inserted and connected between the base of the oscillating transistor 5 and the ground. Then
The midpoint of connection of the series circuit is connected to the emitter of the transistor 5, the resistor 8 is inserted and connected between the emitter of the transistor and the ground, and the resistor 9 and the resistor 10 are connected so as to appropriately supply the base bias of the transistor 5. A resistor 11 is connected between the collector of the transistor 5 and the power supply voltage Vcc line.

Further, the crystal oscillator 12 is connected to the base of the transistor 5, and the capacitor 13 forming a part of the load capacitance is inserted and connected between the other end of the crystal oscillator 12 and the ground. The oscillator output OUT is connected to the emitter of the transistor 5 via the capacitor 14. The ring oscillator 3 is, for example, five CMOS inverters 15 to 19 connected in a ring shape.
Of the crystal oscillator 12 and one end of the crystal unit 12 are connected via a DC-cutting capacitor 20.
The power supply terminal of is connected to the power supply voltage Vcc line through the control circuit 4 as described later.

The control circuit 4 inserts and connects a capacitor 22 between the base of the transistor 21 used as a switch element and the power supply voltage Vcc line, grounds the base of the transistor 21 through a resistor 23, and collects the collector of the transistor 21. Is connected to the power supply terminals of the inverters 15 to 19 via the resistor 24. The operation of the crystal oscillator 1 having such a configuration will be described below. Since the crystal oscillator circuit 2 is a general Colpitts type as described above, its operation will be omitted.

First, the operating principle of the ring oscillator 3 will be described. Since a delay time τ is generally generated between the input and output of the inverter circuit, the ring oscillator 3
In the case of, the input of the first-stage inverter circuit 15 is theoretical H
Then, the theoretical L is output from the output of the fifth-stage inverter circuit with a delay of 5τ, and the signal of this theoretical L is fed back to the input of the first-stage inverter circuit 15. At this time, when the desired oscillation frequency of the ring oscillator 3 is f, if the delay time τ is set so that the delay time 5τ = 1 / 2f, the theoretical L signal is input to the ring oscillator 15 of the first stage. The signal of theoretical H is output from the inverter 19 at the final stage after a delay of 5τ. And as above, the inverter circuits alternate
The ring oscillator 3 can output the oscillation frequency f by repeatedly outputting the theoretical signals of L and H.

The ring oscillator 3 operates in this manner when the control circuit 3 operates and the power supply voltage Vcc line and the ring oscillator 3 become conductive. That is, the control circuit 3 immediately after the power supply voltage Vcc is applied,
A charge current is generated in the transistor, and a part of this charge current is supplied as the base current of the transistor 21, so that the transistor 21 is turned on and the power supply voltage Vcc line and the ring oscillator 3 are brought into conduction, whereby the ring oscillator 3 Oscillates. At this time, the ring oscillator 3
Has a smaller Q value than the crystal oscillator circuit 2 and thus has an inferior excitation frequency accuracy, but on the other hand, it has excellent starting characteristics. Therefore, the ring oscillator 3 is earlier than the crystal oscillator circuit 2. Output oscillation signal.

When the ring oscillator 3 oscillates, its output signal current is supplied to the crystal oscillator 12 via the capacitor 20, which causes the crystal oscillator 12 to have a timing substantially equal to the activation start timing of the ring oscillator 3. As a result, the crystal oscillator 1 can be started at high speed because the time required for the output signal to reach a desired level is shortened. When the required time has passed since the power supply voltage Vcc was applied, the capacitor 22 is sufficiently charged and the previous charge current does not occur. Therefore, the transistor 21 that has made the power supply voltage Vcc line and the control circuit 3 conductive. The base oscillator is not supplied with the base current and is turned off. Accordingly, the oscillating operation of the ring oscillator 3 whose power is cut off is stopped.

Therefore, after a lapse of a required time from the application of the power supply voltage Vcc, the crystal oscillator 1 is in a steady oscillation state in which only the Colpitts type crystal oscillation circuit 2 operates, and no extra current consumption is required. Power supply voltage Vc
Since the c line and the oscillation loop are non-conducting, no noise signal is supplied from the ring oscillator 3 and the crystal oscillator 1
Does not deteriorate the noise characteristics of. Further, according to such a configuration, when the circuit elements other than the crystal oscillator 12 are integrated into an IC, an inductance element (coil) that causes an increase in the size of the IC chip is not included, so that the crystal oscillation circuit 1 can be downsized. It is valid.

FIG. 2 is a circuit diagram showing another embodiment of the crystal oscillator according to the present invention. Crystal oscillator 1-2 shown in FIG.
Is characterized by CR oscillator circuit 2 instead of ring oscillator 3.
It is in the place equipped with 5. The CR oscillation circuit 25 has three stages of inverter circuits 15 to 17 connected in series, and the output end of the inverter circuit 16 and the input end of the inverter circuit 15 have a capacitance of 2
6, the output terminal of the inverter circuit 17 and the input terminal of the inverter circuit 15 are connected via the resistor 27,
The power supply terminals of the inverter circuits 15 to 17 are connected to the emitter of the transistor 21 via the resistor 24, and the output terminal of the inverter circuit 17 is connected to one end of the crystal unit 12 via the capacitor 20. And capacitance 26 and resistance 27
Since the differential circuit is constituted by and, the differential waveform signal shown in FIG. 3 is generated at the input end of the inverter circuit 15.

The CR oscillating circuit 25, when the differential waveform signal is equal to or higher than the threshold voltage VTH of the inverter circuit,
Since a theoretical L output signal is generated at the output end of the inverter circuit 15, the theoretical L output signal is generated at the output end of the inverter circuit 17.
When the differential waveform signal is less than or equal to the threshold voltage VTH, a theoretical H output signal is generated at the output end of the inverter circuit 15, so that the theoretical H signal is output from the output end of the inverter circuit 17. Output signal of
Since a differential waveform signal is generated again at the input terminal of the inverter circuit 15 based on the output signal of the inverter circuit 17, these operations can be repeated to cause self-oscillation. In this case, the oscillation frequency f of the CR oscillation circuit 25 is generally f≈1 / (2.2 × C26 × R27) as the capacitance value C26 of the capacitor 26 and the resistance value R27 of the resistor 27, and the capacitance 26 and the resistor 27 are
It is possible to set by the value of.

The crystal oscillator 1-configured in this way
Even if it is 2, the control circuit 4 only needs the CR oscillation circuit 2 for the required time.
5, the CR oscillator circuit 25 has a smaller Q value than the crystal oscillator circuit.
As in the case of, in the steady oscillation state, it is possible to start at high speed without deteriorating the noise characteristics and further increasing the current consumption, and further, since the inductance element is not used, the size can be reduced. It is also suitable for Further, although the present invention has been described by using the crystal oscillator as the piezoelectric oscillator, the present invention is not limited to this and may be applied to an oscillator using any piezoelectric oscillator.

[0025]

As described above, the piezoelectric oscillation circuit according to the present invention has the amplification circuit and the piezoelectric vibrator used as the frequency control element, and the ring oscillator of the ring oscillator is provided at a required portion in the oscillation loop of the piezoelectric oscillation circuit. Since the output is supplied and the ring oscillator is configured to operate only for the required time after the power is turned on, the noise characteristic is not deteriorated in the steady oscillation state.

[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 circuit diagram showing another embodiment of the crystal oscillator according to the present invention. .

FIG. 3 shows a differential waveform of a CR oscillator circuit.

FIG. 4 is a circuit diagram of a conventional crystal oscillator.

[Explanation of symbols]

1, 1-2 crystal oscillator, 2 crystal oscillator circuit, 3 ring oscillator, 4 control circuit, 5, 21 transistor, 6,
7, 13, 14, 20, 22, 26 capacity, 8, 9, 1
0, 11, 23, 24, 27 resistors, 12 crystal oscillators, 1
5, 16, 17, 18, 19 Inverter circuit, 25CR
Oscillation circuit, 100 crystal oscillator, 101 transistor, 1
02, 104, 105 capacity, 103 crystal unit,

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 5J043 AA05 AA12 AA26 LL01 LL04                       LL06                 5J079 AA04 BA22 BA39 EA05 FA02                       FA14 FA21 FB00 FB03 FB23                       GA02 KA05

Claims (6)

[Claims] 1. An amplifier circuit and a piezoelectric vibrator used as a frequency control element, wherein the output of a ring oscillator is supplied to a required portion in an oscillation loop of the piezoelectric oscillator circuit, and the ring oscillator has a required time after power is turned on. A piezoelectric oscillation circuit characterized by being configured to operate only. 2. A piezoelectric oscillator circuit including an amplifier circuit and a piezoelectric vibrator, a ring oscillator, a circuit for controlling the operation of the ring oscillator, and means for supplying the output of the ring oscillator to a required portion of the piezoelectric oscillator circuit. And a ring oscillator that is configured to operate only for a short time immediately after power is turned on. 3. The piezoelectric oscillation circuit according to claim 1, wherein the oscillation frequencies of the piezoelectric oscillation circuit and the ring oscillator are substantially the same or have an integral multiple relationship. 4. An amplifier circuit and a piezoelectric vibrator used as a frequency control element, wherein the output of the CR oscillation circuit is supplied to a required portion in an oscillation loop of the piezoelectric oscillation circuit, and the CR oscillation circuit is powered on. A piezoelectric oscillation circuit characterized by being configured to operate only for a required time. 5. A piezoelectric oscillation circuit including an amplifier circuit and a piezoelectric vibrator, a CR oscillation circuit, a circuit for controlling the operation of the CR oscillation circuit, and an output of the CR oscillation circuit for a required portion of the piezoelectric oscillation circuit. And a means for supplying the power to the CR oscillation circuit, and the CR oscillation circuit operates only for a short time immediately after the power is turned on. 6. The piezoelectric oscillation circuit according to claim 4, wherein the oscillation frequencies of the piezoelectric oscillation circuit and the CR oscillation circuit are substantially the same or have an integral multiple relationship.