JPH03285403A - Piezoelectric oscillation circuit - Google Patents

Abstract

PURPOSE:To secure stable oscillation without increasing a current at the time of activation without self excited oscillation with satisfactory activation as well by connecting a high-pass filter, which is composed of a resistor and a capacitor, serially to a piezoelectric oscillator and suppressing a resistance value less than 50kOMEGA. CONSTITUTION:An inverter is a logic circuit composed of the NAND or OR circuit of a C-MOS or the like. A resistor RB is connected between the input and output terminals of the inverter. For such a resistor PB, the high resistance of 500KOMEGA-lMOMEGA is used. At the input/output terminal of the inverter, the piezoelectric oscillator, first capacitor CS and second capacitor CD are serially connected. For the first capacitor CS, the capacitor of 5-50pF is used and for the resistor RD, resistance less than 50kOMEGA is used. Then, the high-pass filter is composed of the first capacitor CS, second capacitor CD and resistor RD. The second capacitor CD also has function to black direct current. For this capacitor CD, the capacitor of 5-50pF is used.

Description

DETAILED DESCRIPTION OF THE INVENTION OBJECTS OF THE INVENTION [Field of Industrial Application] The present invention relates to a piezoelectric oscillation circuit that is suitable for mounting on an IC and that facilitates high-frequency oscillation.

[Prior Art J] Piezoelectric oscillators, especially oscillators using crystal oscillators, have been widely used in the past, and are widely used for local oscillators in communication devices, computer clocks, and the like. High frequencies are often used, and overtone oscillation is also used.

FIG. 5 shows a conventional piezoelectric oscillation circuit, in which a crystal resonator is connected to the input/output terminals of an inverter, and a feedback resistor R1 is similarly connected to the input/output terminals of the inverter IC. A circuit is used in which capacitors ci and c2 for excavation are connected between the input terminal and output terminal of the inverter and ground, respectively. In this basic circuit, the feedback resistor R1 is set to 5 to IO.
It is widely known that overtone oscillation is easily caused by setting the feedback resistance to KΩ, but if the feedback resistance is made small, a large amount of current flows at the time of start-up, and the start of oscillation is delayed. It also has the disadvantage of being prone to self-sustained oscillation.

[Problems to be solved by the invention] In a piezoelectric oscillation circuit using an inverter, when oscillating at a high frequency, there is an increase in current at startup, especially during overtone oscillation, startup is slow, and self-oscillation is easy to occur. It is necessary to eliminate such shortcomings.

For this purpose, the feedback resistance must be large, approximately 500 Ω.
~IMΩ is preferred.

[Object of the present invention] The present invention aims to eliminate the above-mentioned drawbacks when generating high-frequency oscillation with a piezoelectric oscillation circuit using an inverter, and to provide a piezoelectric oscillation circuit that improves startup and does not self-oscillate.

<Structure of the present invention> [Means for solving the problems] Therefore, in the present invention, a piezoelectric vibrator is integrated between the input and output terminals of an inverter, and a high-pass filter consisting of a resistor and a capacitor is connected in series with the piezoelectric vibrator. Uses a piezoelectric oscillation circuit. When such a circuit is used, a high resistance can be used as the feedback resistor.

[Function] The circuit according to the present invention constitutes a high-pass filter made of CR by a resistor inserted between the first capacitor and the second capacitor connected in series with the piezoelectric vibrator and the ground. The second capacitor also functions to cut off direct current.

[Embodiment] FIG. 1 is a circuit diagram showing an embodiment of the present invention. The inverter 1 is a logic circuit such as a NAND or OR circuit such as C-MOS. A resistor 2 is connected between the input and output terminals of the input terminal. This resistor 2 is 500Ω to IMΩ
A high resistance is used.

A piezoelectric vibrator, a first capacitor C8, and a second capacitor CD are connected in series to the input/output terminals of the inverter. A resistor RD is connected to ground between the first capacitor C8 and the second capacitor CD.

An oscillation capacitor CG of 5 to 50 pF is connected between the input terminal of the inverter 1 and the ground.

The first capacitor C8 uses a capacitor of 5 to 50 pF. In addition, the resistor RD uses a resistor of 50 Ω or less, and the first capacitor C8 and the second capacitor CD
A high-pass filter is constituted by the resistor RD and the resistor RD.

The second capacitor CD also functions to cut off direct current.

This capacitor CD uses a capacitor of 5 to 50 pF.

Figure 2 is a graph showing the frequency-negative resistance characteristics of the piezoelectric oscillator circuit of the present invention, where the vertical axis is the negative resistance, and the lower it goes, the deeper the negative resistance becomes, indicating a state where oscillation is easier. . In this graph, the first capacitor C8 and the second capacitor CD
is kept constant and is varied using the resistance RD as a parameter. It can be seen that as the resistance RD increases, the frequency range in which the negative resistance exhibits negative resistance increases down to low frequencies, and the negative resistance value increases. As a result, the resistance RD can be selected according to the required frequency, and a value of 50Ω or less is practical. For example, if you need the third-order overtone frequency F, you can choose a resistor RD that has a sufficiently small negative resistance near 3/F or that does not show negative resistance but acts as a resistance. .

Furthermore, if you increase the capacitor C8 and resistor RD as shown in the circuit shown in Figure 3, and connect the capacitor C81, resistor RD1, and if necessary, capacitor C52 and resistor RD2 as shown in the diagram, the negative resistance characteristic will become steeper. This makes it possible to cut oscillations on the low frequency side.

FIG. 4 is a circuit diagram showing another embodiment, in which a high-pass filter is connected to the input terminal side of the inverter IC.

Even in this case, it is effective in high frequency oscillation, especially in overtone oscillation.

According to the present invention, since the feedback resistance can be large, there is no fear of self-sustained oscillation, and the rise time can also be made faster. Furthermore, since it is composed of a resistor and a low-capacitance capacitor, it can be mounted on an IC chip, and there is no need to add inductance when using a conventional high-pass filter, making it ideal for mounting on an IC.

In addition to crystal, the piezoelectric material may be lithium tantalate, piezoelectric ceramic, or the like.

Effects of the Present Invention In conventional inverter oscillation circuits, the feedback resistance was small and startup was slow and self-oscillation was likely to occur during high-frequency oscillation, especially overtone oscillation, but the present invention eliminates self-oscillation. In addition, the start-up is good, and stable oscillation can be ensured without any increase in current during start-up. Furthermore, since it is a resistor and a low capacitance capacitor, it can be mounted on an IC, contributing to miniaturization of the oscillator.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an embodiment of the present invention, Fig. 2 shows frequency and negative resistance characteristics when using the circuit of the present invention, and Figs. 3 and 4 show other embodiments. Circuit diagram FIG. 5 is a conventional oscillation circuit diagram. 1...Inverter, C8...First capacitor, CD...Second capacitor, RD...Resistor, R... ...Feedback resistance

Claims (1)

[Claims] In a piezoelectric oscillation circuit that connects a piezoelectric vibrator between the input and output terminals of an inverter to oscillate, a high-pass filter consisting of a resistor and a capacitor is connected in series with the piezoelectric vibrator, and the resistance value is 50KΩ or less. piezoelectric oscillation circuit.