JPH0520005Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a crystal oscillation circuit that oscillates a rectangular wave using a crystal resonator and a C-MOS inverter.

Since the natural frequency of a crystal resonator has very little variation due to temperature, it is possible to construct an oscillation circuit with high frequency stability, and it is used as a standard pulse generator for clock signals, etc.

[Conventional technology]

FIG. 2 shows a circuit diagram of a conventional crystal oscillator circuit that is composed of a crystal resonator and a C-MOS inverter (hereinafter all C-MOS inverters will be simply referred to as inverters) and generates a rectangular wave. In FIG. 2, a crystal resonator 1 and an inverter 2 are connected in parallel, and the inverter 2 and a resistor 3 connected in parallel to the inverter 2 form an amplifier. Further, the input end and output end of this inverter 2 are grounded via capacitors 4 and 5, respectively. Furthermore, an inverter 6 for waveform shaping is connected to the output end of the inverter 2.

In such an oscillation circuit, when DC voltage V _O is applied to inverter 2, crystal oscillator 1 and inverter 2
Electric power is exchanged between the crystal resonator 1 and the crystal resonator 1, which oscillates at a voltage _VB as shown in FIG. 3 in accordance with its natural frequency. However, this output waveform is far from a rectangular wave. Therefore, when the output of this crystal oscillation circuit is further shaped through an inverter 6, it is converted into a substantially rectangular wave voltage V _C as shown in FIG. 3, although the voltage phase differs by approximately 180 degrees.

[Problem that the invention attempts to solve]

It is desirable that the output of a standard pulse generator used for clock signals of electronic equipment has a stable frequency at a predetermined value, and that the waveform is a rectangular wave with steep rises and falls. In the conventional oscillation circuit shown in Fig. 2, the voltage V _B in the first stage is far from a rectangular wave as shown in Fig. 3, and although the voltage V _C has been slightly improved, the end of the rise and fall still remains. The drawback was that the waveform was loose. In order to further shape this, as shown in FIG. 4, the circuit shown in FIG. 2 may be used as is, and a waveform shaping inverter 7 may be connected in series with the inverter 6. In this way, the output voltage V _D of the inverter 7 may oscillate as a rectangular wave with steep rises and falls depending on the circuit constants as shown in _FIG . This oscillation circuit has the disadvantage that it often stops oscillating because it is negatively fed back to the input side of inverter 2 via the capacitance C _S1 between the output end and the input end of inverter 2, so this needs to be adjusted. However, there are problems such as limiting the characteristics of each member and paying attention to the wiring.

An object of the present invention is to provide a crystal oscillation circuit that can easily and reliably oscillate and can generate a rectangular wave with steep rises and falls.

[Means for solving problems]

In order to solve the above-mentioned problems, the present invention provides a crystal oscillator circuit in which a crystal resonator and a first inverter are connected in parallel, and a second inverter is connected in series to the output terminal of the crystal oscillation circuit. An input resistor is connected to the input terminal of the inverter, and a third inverter is connected in series to the output terminal of the second inverter.

[Effect]

This oscillation circuit creates an unbalanced DC bias voltage by connecting an input resistor between the input end and the power supply or between the input end and the ground, ensuring that minute vibrations when the power is turned on do not become balanced. oscillates to Therefore, even if two stages of inverters on the output side are connected in series, oscillation does not stop and a correct rectangular wave can be obtained.

[Example of idea]

FIG. 1 shows an embodiment of the present invention. Here the second
Components that are the same as those in FIGS. 2 and 4 are given the same reference numerals as in FIGS. 2 and 4. In Fig. 1, the crystal oscillation circuit is composed of a crystal resonator 1, an inverter 2, a resistor 3, both capacitors 4 and 5, an inverter 6, etc., as in the conventional circuit, and an inverter is connected in series to the output terminal of the inverter 6. 7 is connected. Furthermore, an input resistor 8 is connected between the input end of the inverter 2 and ground. This input resistance 8 is the inverter 2
It may be connected as shown by the broken line between the input end of the power supply and the power supply.

In such a circuit, resistor 3 is Rf, input resistor 8
Ri, the bias voltage at the input terminal of inverter 2 is
If V _A is the voltage at the output end of inverter 2, and V _B is the voltage at the output end of inverter 2,
When the input terminal of this inverter 2 is grounded with an input resistor 8, the voltage V _B is V _B = (1 + Rf / Ri) × V _A , and the input resistor 8 is connected between the input terminal of the inverter 2 and the power supply.
The voltage V _B when connected is V _B = (1-Rf/Ri) ×
V _A , the bias voltage V _A becomes unbalanced between the input end and the output end, and due to the stray capacitance C _S1 between the output end of the inverter 7 and the input end of the oscillation circuit, the output of the inverter 7 becomes the input end of the oscillation circuit. Even if negative feedback is given to the circuit, it will not reach an equilibrium state, so this circuit will definitely oscillate. Moreover, since two stages of waveform shaping are performed by both inverters 6 and 7, the output voltage V _D at the output terminal of the inverter 7 rises as shown in FIG. 3, and a rectangular wave with a steep fall is obtained.

[Effect of idea]

According to the present invention, the input terminal of the oscillation circuit is grounded by an input resistor, or this input resistor is connected between the input terminal and the power supply, so that the bias voltage becomes unbalanced between the input terminal and the output terminal, and due to stray capacitance. Even if the output from the output end is negatively fed back to the input end, it will not be in a balanced state, so even if the waveform is shaped by two inverters, it will reliably oscillate and a rectangular wave with steep rises and falls can be obtained.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing an embodiment of the crystal oscillation circuit according to the present invention, Figs. 2 and 4 are circuit diagrams showing conventional examples of the crystal oscillation circuit, and Fig. 3 shows the state of each part of the crystal oscillation circuit. FIG. 1...Crystal resonator, 2, 6, 7...Inverter, 8...Input resistance.

Claims (1)

[Scope of utility model registration request] In a crystal oscillator circuit in which a crystal resonator and a first C-MOS inverter are connected in parallel, and a second C-MOS inverter is connected in series to the output terminal thereof, the input terminal of the first C-MOS inverter is A crystal oscillation circuit characterized in that an input resistor is connected to the oscillator, and a third C-MOS inverter is connected in series to the output terminal of the second C-MOS inverter.