JPH06120734A - High frequency oscillation circuit for crystal oscillator - Google Patents

Abstract

PURPOSE:To obtain a crystal oscillator in which a high frequency beyond about 25MHz can be obtained at a low cost, in an oscillation circuit using a crystal vibrator. CONSTITUTION:This circuit is equipped with a crystal vibrator 1 having a certain basic wave frequency, basic wave oscillation circuit 2 having a sufficiently large negative resistance value to the basic wave frequency, and rectangular wave generating circuit 3 which converts the output of the basic wave oscillation circuit 2 into a rectangular wave. Then, a BPF 4 takes out arbitrary frequency components from the basic wave included in the rectangular wave and higher harmonics having the odd number-fold frequency. And also, the circuit is equipped with an amplifier circuit 5 which amplifies the output of the BPF 4 into a prescribed amplitude.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oscillator circuit using a crystal oscillator. The crystal oscillator is
A thin crystal crystal is cut out at a certain angle and sandwiched between metal electrodes. It vibrates regularly at a certain frequency that resonates with the dimensions of the vibrator.

From a crystal oscillator having this crystal oscillator,
To obtain a high frequency of about 30 to 100 MHz,
It is necessary to make the built-in crystal unit quite thin. However, there are technical and cost problems, and the product is 25M.
It is difficult to supply a large amount of products having a frequency exceeding about Hz at a low price.

[0003]

2. Description of the Related Art A crystal oscillator has a characteristic of oscillating at a fundamental wave and an odd multiple thereof. Specifically, if the fundamental wave is 10 MHz, 10 MHz, 30 MHz, 50 MHz, 70M
It oscillates at Hz. Utilizing this characteristic, in general, an oscillator in a frequency band of 25 MHz or more widely uses a method of extracting a frequency that is an odd multiple of the fundamental wave.

In order to obtain a high frequency exceeding about 25 MHz, an oscillation circuit having the largest oscillation margin for harmonics, mostly third-order harmonics, is used to extract three times the frequency of the fundamental wave. For example, if the fundamental wave is 10 MHz and a third harmonic is used, a high frequency of 30 MHz can be extracted.

FIG. 4 is a diagram showing a configuration of a conventional oscillator that oscillates a third harmonic to extract a high frequency. In the figure, a tertiary wave oscillator circuit 12 selectively extracts and outputs a tertiary wave generated by the crystal oscillator 11, and an amplifier circuit 13 amplifies and outputs an oscillation output of the tertiary wave oscillator circuit 12. It is a thing.

[0006]

Crystal oscillators are widely used as high-precision, low-priced oscillation sources in industrial and consumer equipment. However, as the speed of electronic equipment increases, the oscillation frequency of crystal oscillators increases. As it goes up, various problems are becoming apparent. The problem will be described below by taking the third harmonic as an example.

It is extremely difficult to provide a circuit system that can oscillate only a third-order wave at a low cost with an oscillation margin of an oscillation circuit. In the end, a circuit system that can oscillate a non-third-order wave, that is, a fundamental wave, a fifth-order wave, etc. I have to take it. Therefore, there is a problem that there is always a risk of oscillation at a frequency other than the third wave.

FIG. 5A is a diagram for explaining the oscillation margin of the third-order wave oscillator circuit. In the figure, the vertical axis of the graph shows the negative resistance value, and the frequency with the larger negative resistance value is the frequency at which oscillation is easier. The horizontal axis of the graph shows the frequency, where'f 'is the fundamental wave and' 3 '.
f'denotes a third-order harmonic wave, and '5f' indicates a fifth-order harmonic wave.

In FIG. 5 (a), the third-order wave oscillation circuit having the oscillation margin indicated by the letter "a" shows a very large negative resistance value at "3f". Although it oscillates, it exhibits a relatively large negative resistance value at other frequencies, so that it easily oscillates even with a fundamental wave or a fifth-order wave.

On the other hand, in FIG. 5A, the third-order wave oscillation circuit having the oscillation margin indicated by the letter b has a small negative resistance value as a whole, and has a small oscillation margin also in the third-order wave. This third-order wave oscillation circuit does not oscillate with the fundamental wave, but may oscillate with the fifth-order wave. As described above, an ideal circuit having a characteristic of oscillating only with a third-order wave cannot be easily manufactured.

Similarly, at which frequency, for example, the fundamental wave, the third-order wave, or the fifth-order wave, the crystal oscillator is most likely to oscillate is determined by the CI value (CI: critical impedance) of each frequency. To be done.

However, in order to lower the CI value of only the third-order wave and make it easier to oscillate, it is necessary to determine the optimum shape of the vibrator. However, there is a factor that the technical difficulty is very high, and the development cost, the period, and the manufacturing cost required for this are serious problems.

Furthermore, when the third harmonic is used, the oscillator becomes extremely vulnerable to minute defects of the vibrator, foreign matter on the front and back surfaces, and the like. FIG. 5B is a diagram for explaining the fluctuation amount of the CI value due to a vibrator defect, adhesion of a foreign substance, or the like.

As shown in the figure, the fluctuation amount of the CI value in the fundamental wave is small, but the fluctuation amount of the CI value in the higher harmonic wave such as the third wave is large. In other words, the harmonic oscillator circuit
This change in the CI value causes various adverse effects.

Therefore, in the harmonic oscillation circuit, due to the progress of the defective portion, the reliability is remarkably lowered, and a problem frequently occurs in the market. Further, a large change in the CI value also greatly affects the product yield.

For this reason, in the oscillator manufacturing process, it is indispensable to take cleanliness measures similar to those in the semiconductor manufacturing process, and each vendor makes a large investment in ensuring quality. However, despite the large investment, the quality of the market is deteriorated due to the high frequency.

The present invention has been made in view of the above-mentioned conventional problems, and in the case of fundamental wave oscillation, stable oscillator operation and an inexpensive oscillation circuit can be easily realized. Focusing on the fundamental wave oscillation instead of the harmonic oscillation,
It is an object of the present invention to provide a means for realizing an oscillator capable of obtaining a high frequency exceeding about 5 MHz.

[0018]

According to the invention, the above mentioned objects are achieved by means of the patent claims.

That is, the present invention is an oscillating circuit using a crystal oscillator, wherein a crystal oscillator having a certain fundamental wave frequency and a sufficiently large negative resistance with respect to the fundamental wave frequency of the crystal oscillator. A fundamental wave oscillation circuit with a value, a rectangular wave generation circuit that converts the output of this fundamental wave oscillation circuit into a rectangular wave, and a fundamental wave included in the rectangular wave and a harmonic with an odd multiple Is a high-frequency oscillator circuit for a crystal oscillator, which comprises a bandpass filter for extracting the frequency component of 1) and an amplifier circuit for amplifying the output of the bandpass filter to a predetermined amplitude.

FIG. 1 is a diagram for explaining the principle of the present invention. In the figure, the crystal resonator 1 vibrates regularly at a frequency of a fundamental wave and an odd multiple thereof. Fundamental wave oscillator 2
Is to extract a fundamental wave, and the rectangular wave generation circuit 3 converts a sine wave into a rectangular wave. Bandpass filter 4
Is an odd harmonic included in the rectangular wave, and extracts only an arbitrary harmonic, and the amplifier circuit 5 amplifies it.
It is formatted and output.

[0021]

2 (a) is a diagram for explaining the output of the fundamental wave oscillation circuit, and FIG. 2 (b) is a diagram for explaining the output of the rectangular wave generation circuit.
(C) of the bandpass filter, and FIG.
FIG. 4 is a diagram illustrating each output of the amplifier circuit.

As shown in FIGS. 2A to 2D, the output of the fundamental wave oscillating circuit is a sine-waveform fundamental wave, and the output of the rectangular wave generating circuit converts the fundamental wave by an amplifying, slicing circuit or the like. The output of the bandpass filter is
A specific harmonic component included in the rectangular wave is extracted, and the output of the amplifier circuit is obtained by amplifying and shaping the waveform of the harmonic component.

[0023]

EXAMPLE The present invention focuses on the fact that if a fundamental wave is used, it is possible to oscillate very stably. Using a fundamental wave oscillation instead of a harmonic oscillation, the cost is low and the reliability is high. Realize a crystal oscillator.

In the present invention, the output taken out by the fundamental wave oscillation is converted into a rectangular wave, and any frequency component in the rectangular wave is taken out and used, thereby avoiding the use of harmonic oscillation of the oscillator, which is problematic, and stabilizing the oscillation. To get the output. The circuit can be composed of a crystal oscillator, a fundamental wave oscillation circuit, a bandpass filter, and an amplification circuit.

Crystal oscillator The only characteristic required for a crystal oscillator is that the CI value of the fundamental wave is sufficiently smaller than the absolute value of the negative resistance value of the next stage, and other CI values do not matter. . Therefore, it is extremely easy to design and manufacture the vibrator.

Oscillation Circuit The oscillation circuit may take any circuit system. However, the negative resistance value has a sufficient margin with respect to the CI value of the preceding-stage vibrator, and has a structure in which the negative resistance value becomes positive with respect to harmonics.

FIG. 3A is a diagram for explaining the oscillation margin of the fundamental wave oscillation circuit that can be used in the present invention. This fundamental wave oscillation circuit exhibits a high negative resistance value at the fundamental wave and a positive resistance value at the higher harmonic waves of the third order and higher. Therefore, it has an ideal characteristic of oscillating only the fundamental wave.

Rectangular Wave Generation Circuit This circuit converts the oscillation output (sine wave) generated in the previous stage into a rectangular wave. This can be easily realized by saturating the output waveform with an amplifier circuit having a large gain.

FIG. 3B is a diagram showing frequency components included in the rectangular wave. As shown in the figure, the fundamental wave component is contained in a very large amount, but the third-order wave component and the fifth-order wave component are also included to some extent. A high frequency can be obtained by extracting the third-order wave and fifth-order wave components.

Bandpass Filter A rectangular wave contains odd-order harmonic components as described above, and an arbitrary frequency therein is extracted using a bandpass filter. The circuit system may be arbitrary.

Amplification circuit Amplifies the harmonic component extracted by the bandpass filter to a predetermined amplitude. 25M easily from the output of this amplifier circuit
A high frequency exceeding Hz can be obtained.

A conventional oscillator, that is, a resonator is can-sealed, a band-pass filter or the like is added to the resonator, or special screening is performed to achieve high reliability. It can be said that the oscillator circuit according to the present invention is more advantageous than the oscillator in terms of price and reliability.

However, it is more expensive than an oscillator of the type in which a vibrator is used for third-order oscillation, and it may be disadvantageous in downsizing depending on the shape of parts constituting the bandpass filter.

[0034]

As described above, according to the present invention,
Since the crystal oscillator itself is used for fundamental wave oscillation, an extremely stable oscillation output can be obtained. Therefore, a high-frequency oscillator with extremely high reliability can be realized at a low price. Moreover, since it is possible to easily take out harmonics such as fifth and seventh orders that are difficult to handle with a vibrator, it is very advantageous for making super-high frequencies higher than the fifth order.

[Brief description of drawings]

FIG. 1 is a diagram illustrating the principle of the present invention.

FIG. 2 is a diagram illustrating each output of a fundamental wave oscillation circuit, a rectangular wave generation circuit, a bandpass filter, and an amplification circuit.

FIG. 3 is a diagram for explaining an example of the present invention.

FIG. 4 is a diagram showing a configuration of a conventional oscillator that oscillates a third harmonic to extract a high frequency.

FIG. 5 is a diagram for explaining a problem of the conventional technique.

[Explanation of symbols]

 1, 11 Crystal oscillator 2 Fundamental wave oscillation circuit 3 Rectangular wave generation circuit 4 Band pass filter 5, 13 Amplification circuit 12 Third wave oscillation circuit

Claims (1)

[Claims] 1. An oscillation circuit using a crystal oscillator, comprising: a crystal oscillator (1) having a certain fundamental frequency; and a sufficiently large negative frequency with respect to the fundamental frequency of the crystal oscillator (1). Fundamental wave oscillating circuit (2) having a resistance value, a rectangular wave generating circuit (3) for converting the output of the fundamental wave oscillating circuit (2) into a rectangular wave, and the fundamental wave included in the rectangular wave and its odd multiples. A band pass filter (4) for extracting an arbitrary frequency component from the harmonics having the frequency of, and an amplifier circuit (5) for amplifying the output of the band pass filter (4) to a predetermined amplitude. High-frequency oscillator circuit for crystal oscillators.