JPH066135A - Crystal oscillator - Google Patents

Abstract

PURPOSE:To realize a 3rd overtone crystal oscillator with less current consumption. CONSTITUTION:An output of a 1st inverter 11 connects with a gate of a 2nd inverter 13, and an output of the 2nd inverter 13 connects with a gate of a 3rd inverter 15. Then an output of the 3rd inverter 15 and a gate of the 1st inverter 11 are connected by a feedback resistor 3 to form an inverting amplifier, which is used for the oscillation circuit to obtain the crystal oscillator.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a crystal oscillator structure using an inverting amplifier.

[0002]

2. Description of the Related Art The demand for faster operation of computers and electronic devices for image processing has been increasing year by year. These electronic devices have a reference signal source with a stable oscillation frequency inside the system, and the timing of the operation of each circuit is controlled by the signal from this reference signal source.
Therefore, in order to speed up the operation of these electronic devices, it is necessary to increase the oscillation frequency of the reference signal source.

A crystal oscillator is most often used as a reference signal source in electronic equipment. Usually, a crystal oscillator called an AT plate is used to form the oscillator.

The crystal resonator of the AT plate is characterized in that the thinner the thickness, the higher the oscillation frequency, but at the same time, the thinner the thickness, the more difficult it is for industrial mass production. There is. In the current industrial technology, the AT plate crystal oscillator having an oscillation frequency of about 30 MHz is the limit in mass production.

However, the oscillation frequency of the reference signal source required by recent electronic equipment is 50 MHz or 100 MHz.
Since the frequency is as high as MHz, the crystal oscillator of AT plate using the fundamental wave cannot support it. Therefore, instead of using the fundamental wave of the crystal oscillator of the AT plate, a crystal oscillator that oscillates at a frequency three times the fundamental wave has attracted attention. Such a crystal oscillator is called a third-order overtone crystal oscillator.

The third-order overtone type crystal oscillator needs some means to suppress oscillation at the fundamental wave and oscillate at a frequency three times as high as the fundamental wave. By reducing the feedback resistance of the oscillation circuit, The possibility of oscillation in the overtone mode has been reported, for example, at the following academic conference.

National Institute of Electronics, Information and Communication Engineers 70th Anniversary National Convention 507 "CMOS Overtone Crystal Oscillator" Masahiro Toki Shinichi Hattori 1987

The structure of a conventional third-order overtone crystal oscillator will be described below with reference to the drawings. FIG. 3 is a circuit diagram showing an oscillation circuit portion in a third-order overtone type crystal oscillator having a conventional configuration using an oscillation inverter, a feedback resistor, a crystal oscillator, and a capacitor. For crystal oscillators,
An output buffer and the like are included in addition to the oscillator circuit, but detailed description thereof will be omitted.

As shown in FIG. 3, an oscillating inverter 1, a feedback resistor 3 and a crystal oscillator 5 are connected in parallel, and a capacitor 7 and a capacitor 9 are provided between their connection points and a power source.
Are connected respectively.

According to the above-mentioned document, when the value of the feedback resistor 3 is set to a certain limit or less, the fundamental wave cannot oscillate,
It will oscillate in overtone mode. The resistance value of the limit is determined by the frequency of the fundamental wave of the crystal resonator 1 used, and the higher the frequency of the fundamental wave, the smaller the resistance value of the limit at which the fundamental wave cannot oscillate. For example, in the case of a crystal oscillator having a fundamental wave frequency of about 10 MHz, the value of the feedback resistor 3 at which the oscillation of the fundamental wave is disabled is about 30 kΩ.

Therefore, in the conventional third-order overtone type crystal oscillator shown in FIG. 3, when the oscillation frequency of 36 MHz is obtained, the fundamental wave of the crystal oscillator 1 is set to 12 MH.
z and the resistance value of the feedback resistor 3 is set to 30 kΩ or less to realize oscillation in the third-order overtone mode.

[0012]

However, the crystal oscillator of the ordinary AT plate has a strong tendency to oscillate at the frequency of the fundamental wave, and if the value of the feedback resistor 3 is reduced as described above, the third order Oscillation in overtone mode is difficult. Therefore, the driving force of the oscillating inverter 1 is increased to improve the oscillation startability, or a special crystal oscillator that is easier to oscillate in the third overtone mode than in the fundamental wave is used.

Even when such a special crystal oscillator is used, it is still difficult to oscillate as compared with the case of oscillating the crystal oscillator of the ordinary AT plate at the frequency of the fundamental wave, and the oscillation inverter is still present. The oscillation startability is increased by increasing the driving force of 1.

Increasing the driving power of the oscillation inverter means, for example, in the case of an oscillation inverter formed of MOS transistors, the channel length of the MOS transistors is shortened or the channel width is widened. All of these increase the through current of the oscillation inverter and increase the current consumption of the oscillation circuit.

That is, in the conventional third-order overtone type crystal oscillator, there is no choice but to use an oscillating inverter having a large driving force in order to enhance the oscillation starting property, which causes a problem that the current consumption increases.

An object of the present invention is to solve the above problems and to provide a third-order overtone type crystal oscillator which consumes less current than the conventional one.

[0017]

In order to achieve the above object, the structure of the crystal oscillator according to the present invention is such that the output of the first inverter is connected to the gate of the second inverter, and the output of the second inverter is connected. Connected to the gate of the third inverter,
The inverting amplifier is formed by connecting the output of the third inverter and the gate of the first inverter via a feedback resistor having a resistance value of 30 kΩ or less, and the inverting amplifier is used in an oscillation circuit. I am trying.

[0018]

As a method of increasing the oscillation startability of the oscillator circuit, there is a method of increasing the amplification factor in the inverting amplification period in addition to increasing the driving force of the oscillation inverter described above. In the present invention, the role of the oscillation inverter of the conventional third-order overtone type crystal oscillator is realized by the serial three-stage configuration of three inverters.

The serial three-stage configuration of these three inverters is
Since the amplification factor is extremely high due to the synergistic effect of the amplification action of each inverter, oscillation in the third overtone mode is possible without increasing the driving force of each inverter so much. That is, the oscillator circuit can be configured with an inverter having a relatively small through current, and the current consumption of the oscillator circuit can be reduced.

Further, in the present invention, the waveform shaping effect of each inverter greatly contributes to the reduction of the current consumption of the oscillation circuit. The current consumption of the inverter is the sum of the through current and the charging / discharging current. Of these, the through current is a useless current that does not contribute to oscillation, so it is desirable to reduce it as much as possible.

Since the through current of the inverter becomes maximum when the input voltage to the gate is near the inversion voltage, when a waveform such as a sine wave that slowly traverses around the inversion voltage is input to the gate. Has a large through current, and when a waveform such as a rectangular wave that instantaneously crosses the inversion voltage is input to the gate, the through current is small.

In the configuration of the present invention, the waveform input to the gate of the first inverter is a sine wave, but the output of the first inverter, that is, the input of the second inverter, is generated by the waveform shaping effect of the first inverter. Becomes closer to a rectangular wave, and due to the waveform shaping effect of the second inverter,
The input of the third inverter is closer to a square wave. Therefore, the through current of the second inverter and the third inverter is very small.

[0023]

An embodiment of the present invention will be described in detail below with reference to the drawings. FIG. 1 is an embodiment showing an oscillation circuit portion of a crystal oscillator in the configuration of the present invention. In FIG. 1, the same elements as those of FIG. 3 showing the conventional configuration are denoted by the same reference numerals and the description thereof is omitted. Further, detailed description of parts other than the oscillation circuit such as the output buffer will be omitted.

As shown in FIG. 1, the first inverter 11
Is connected to the gate of the second inverter 13, and the output of the second inverter 13 is input to the gate of the third inverter 15. Furthermore, between the output of the third inverter 15 and the gate of the first inverter 11, 30 kΩ
The following feedback resistor 3 is connected to form an inverting amplifier.

A crystal oscillator 5 is connected in parallel with the feedback resistor 3, and a capacitor 7 is provided between these connection points and the power supply.
The point that the oscillation circuit is configured by connecting the capacitor 9 and the capacitor 9 is similar to the conventional crystal oscillator.

The current consumption of the entire oscillation circuit of the embodiment shown in FIG. 1 is the sum of the through current and charge / discharge current of each of the three inverters. Of these, due to the reduction of the through current,
It will be described below that the reduction of current consumption, which is the object of the present invention, has been achieved.

First, the charge / discharge current will be described. Since the first inverter 11 is only driving the gate of the second inverter 13, and the second inverter 13 is only driving the gate of the third inverter 15, the first inverter 11 is The charging / discharging current of the inverter 11 and the second inverter 13 is very small. The charge / discharge current of the third inverter 15 is an indispensable current for driving a load such as a crystal oscillator, and has the same magnitude as that of the conventional example.

Therefore, in the embodiment shown in FIG. 1, the charge / discharge current is slightly increased by the charge / discharge current of the first inverter 11 and the second inverter 13 as compared with the conventional example.

Next, the through current will be described. The signal input to the gate of the first inverter 11 is not only amplified by the first inverter 11 but also the second inverter 1
3 is also amplified, and is further amplified by the third inverter 15.

Therefore, the inverting amplifier having the configuration shown in FIG. 1 has an extremely high amplification factor, and the first inverter 11 and the second inverter 11
Even if the driving power of the inverter 13 and the third inverter 15 is small, the oscillation in the third overtone mode is possible.

As described above, since an inverter having a small driving force has a small through current, each inverter having the configuration of FIG. 1 can have a smaller through current as compared with the oscillation inverter in the conventional example.

The signal waveform input to the gate of the first inverter 11 is a sine wave because it is restricted by the crystal unit 5, but the second inverter 13 is affected by the waveform shaping effect of the first inverter 11. The input waveform of the gate of the third inverter 15 becomes close to a rectangular wave, and the waveform shaping effect of the second inverter 13 makes the input waveform of the gate of the third inverter 15 substantially rectangular.

Therefore, as described above, the shoot-through current between the second inverter 13 and the third inverter 15 is very small, and the shoot-through current of the entire oscillation circuit is substantially equal to the shoot-through current of the first inverter 11.

As is clear from the above description, in the oscillation circuit shown in FIG. 1, the reduction of the through current is achieved as compared with the conventional example, which compensates for the slight increase in the charging / discharging current. The overall consumption of the oscillator circuit is reduced.

By the way, as described above, due to the waveform shaping effect of the first inverter 11, a signal close to a rectangular wave is input to the gates of the second inverter 13 and the third inverter 15.

Therefore, at least the second inverter 13
And the third inverter 15 with complementary field effect (CMO
If they are formed by S) transistors, current flows in these inverters only when the operation is inverted, and further reduction of current consumption can be achieved. This is the second aspect of the present invention.
Is a feature of.

Next, the third and fourth features of the present invention will be described with reference to another embodiment of the present invention. FIG. 2 is an embodiment showing the oscillation circuit portion of the crystal oscillator in the configuration of the present invention, in which all three inverters in FIG. 1 are formed by CMOS transistors. In FIG. 2, the first
1 showing the embodiment of FIG. Further, detailed description of parts other than the oscillation circuit such as the output buffer will be omitted.

As shown in FIG. 2, the first P channel MO
The S-transistor 17 and the first N-channel MOS transistor 19 form a first inverter 11 and a second P-channel MOS transistor.
Channel MOS transistor 21 and second N channel M
The OS transistor 23 forms the second inverter 13, and the third P-channel MOS transistor 25 and the third N-channel MOS transistor 27 form the third inverter 15.

Here, the size of each MOS transistor is made different. As will be described later, this is configured so that the channel length or the channel width is different. Other configurations are the same as those in FIG.

As described in the description of the embodiment of FIG. 1, only the third inverter 15 drives the load such as the crystal unit 5. The second inverter 13 is only driving the gate of the third inverter 15, and the first inverter 11 is the second inverter 13 only.
It is only driving the gate of.

It is known that when such a structure is formed by a CMOS inverter, the driving force of the inverter in the preceding stage is usually ¼ or less of the driving force of the inverter in the succeeding stage.

Therefore, the driving power of the second inverter 13 can be reduced to ¼ or less of the driving power of the third inverter 15, and the driving power of the first inverter 11 can be driven by the second inverter 13. It can be less than 1/4 of the force.

That is, in the present invention, the driving force of the first inverter 11 can be made extremely small.

As described above, since an inverter having a small driving force has a small through current, the fact that the driving force of the first inverter 11 can be made very small means that the through current of the first inverter 11 is very small. It means that it can be made smaller.

Further, as described above, in the crystal oscillator according to the present invention, the through current of the entire oscillation circuit is substantially equal to the through current of the first inverter 11.

Therefore, the driving force of the second inverter 13 is made smaller than that of the third inverter 15, and
By making the driving force of the first inverter 11 smaller than that of the inverter 13, the through current of the entire oscillation circuit can be made extremely small, and the consumption current can be greatly reduced.

Reducing the driving power of the inverter means narrowing the channel width or lengthening the channel length in the inverter composed of MOS transistors.

This is shown in FIG. 2 in which the size of each MOS transistor is different.
More specifically, the configuration of FIG. 2 is as follows.

That is, in FIG. 2, the channel lengths of the first P-channel MOS transistor 17, the second P-channel MOS transistor 21, and the third P-channel MOS transistor 25 are made equal, and the first N-channel MOS transistor is also made. 19, the second N-channel MOS transistor 23, and the third N-channel MOS transistor 27 have the same channel length, and the second P-channel MOS transistor 21 has a channel width equal to that of the third P-channel MOS transistor 25. Narrower than the channel width of the first P-channel MOS transistor 17 and the channel width of the first P-channel MOS transistor 17
Narrower than the channel width of the second N-channel MO
The channel width of the S transistor 23 is made narrower than that of the third N-channel MOS transistor 27, and the channel width of the first N-channel MOS transistor 19 is made smaller than that of the second N-channel MOS transistor 23. By making it narrower, the driving force of the second inverter 13 is made smaller than that of the third inverter 15,
Furthermore, the first inverter 1 is better than the second inverter 13.
The driving force of 1 is reduced. This is the third feature of the present invention.

Alternatively, in FIG. 2, the channel widths of the first P-channel MOS transistor 17, the second P-channel MOS transistor 21, and the third P-channel MOS transistor 25 are made equal, and the first N-channel MOS transistor is also made. 19, the second N-channel MOS transistor 23, and the third N-channel MOS transistor 27 have the same channel width, and the second P-channel MOS transistor 21 has a channel length equal to that of the third P-channel MOS transistor 25. The channel length of the first P-channel MOS transistor 17 is smaller than that of the second P-channel MOS transistor 21.
Narrower than the channel length of the second N-channel MO
The channel length of the S transistor 23 is made narrower than that of the third N-channel MOS transistor 27, and the channel length of the first N-channel MOS transistor 19 is made smaller than that of the second N-channel MOS transistor 23. By making it narrower, the driving force of the second inverter 13 is made smaller than that of the third inverter 15,
Furthermore, the first inverter 1 is better than the second inverter 13.
The driving force of 1 is reduced. This is the fourth feature of the present invention.

[0051]

As is apparent from the above description, an inverting amplifier is formed by a series three-stage configuration of an inverter and a feedback resistance of 30 kΩ or less, and a crystal oscillation circuit is formed by using this inverting amplifier. Through current can be reduced. In particular, the through current is significantly reduced by configuring the inverter with a CMOS, further reducing the driving force of the second inverter than that of the third inverter, and making the driving force of the first inverter smaller than that of the second inverter. Can be made. This makes it possible to provide a third-order overtone type crystal oscillator with low current consumption, and the effect is very large.

[Brief description of drawings]

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

FIG. 2 is a circuit diagram showing a crystal oscillator circuit according to an embodiment of the present invention.

FIG. 3 is a circuit diagram showing a crystal oscillation circuit in a conventional example.

[Explanation of symbols]

 1 Oscillation Inverter 5 Crystal Oscillator 11 First Inverter 13 Second Inverter 15 Third Inverter 17 First P-Channel MOS Transistor 19 First N-Channel MOS Transistor 21 Second P-Channel MOS Transistor 23 Second N-channel MOS transistor 25 Third P-channel MOS transistor 27 Third N-channel MOS transistor

Claims (4)

[Claims] 1. The output of the first inverter is connected to the gate of the second inverter, and the output of the second inverter is connected to the third inverter.
And an output of the third inverter and a gate of the first inverter are connected via a feedback resistor to form an inverting amplifier, and the inverting amplifier is used in an oscillation circuit. A crystal oscillator that does. 2. The crystal oscillator according to claim 1, wherein at least the second inverter and the third inverter are formed by complementary field effect transistors. 3. A first inverter is constituted by the first P-channel MOS transistor and the first N-channel MOS transistor, and a second inverter is constituted by the second P-channel MOS transistor and the second N-channel MOS transistor.
The third inverter is configured by the third P-channel MOS transistor and the third N-channel MOS transistor, and the first P-channel MOS transistor, the second P-channel MOS transistor, and the third P-channel MOS transistor are configured. The channel lengths of the P-channel MOS transistor and the first N-channel MOS transistor, the second N-channel MOS transistor, and the third N-channel MO are equalized.
The channel length of the S-transistor is made equal, the channel width of the second P-channel MOS transistor is made narrower than the channel width of the third P-channel MOS transistor,
The channel width of the first P-channel MOS transistor is
The channel width of the second N-channel MOS transistor is narrower than that of the second P-channel MOS transistor, and the channel width of the second N-channel MOS transistor is narrower than that of the third N-channel MOS transistor. The crystal oscillator according to claim 1, wherein the channel width is narrower than the channel width of the second N-channel MOS transistor. 4. A first inverter is constituted by the first P-channel MOS transistor and the first N-channel MOS transistor, and a second inverter is constituted by the second P-channel MOS transistor and the second N-channel MOS transistor.
The third inverter is configured by the third P-channel MOS transistor and the third N-channel MOS transistor, and the first P-channel MOS transistor, the second P-channel MOS transistor, and the third P-channel MOS transistor are configured. The channel widths of the P-channel MOS transistor and the first N-channel MOS transistor, the second N-channel MOS transistor, and the third N-channel MO are made equal.
The channel width of the S transistor is made equal, and the channel length of the second P channel MOS transistor is made longer than the channel length of the third P channel MOS transistor.
The channel length of the first P-channel MOS transistor is
The channel length of the second N-channel MOS transistor is made longer than that of the second P-channel MOS transistor, and the channel length of the second N-channel MOS transistor is made longer than that of the third N-channel MOS transistor. The crystal oscillator according to claim 1, wherein the channel length is made longer than the channel length of the second N-channel MOS transistor.