JP3318148B2 - Crystal oscillation circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a crystal oscillation circuit using a CMOS inverter.

[0002]

2. Description of the Related Art As shown in FIG. 4, a prior art is a crystal oscillation circuit in which a crystal oscillator X and a resistor R0 are connected between an input and an output of a CMOS inverter, and the crystal oscillator X and a resistor R1 are connected in series. As a result, the excitation level was suppressed.

[0003]

In the prior art, a resistor R1 of a crystal oscillation circuit and a crystal resonator X are connected in series. Since the equivalent series resistance RX of the crystal unit differs depending on the crystal unit and is distributed in a certain range, the effect of reducing the excitation level of the crystal unit X largely depends on the value of the equivalent series resistance RX of the crystal unit. Problem.

[0004]

In order to keep the effect of reducing the excitation level of the crystal unit constant, a resistor R2 is connected between a point where a resistor is connected in series with the crystal unit X and ground, and an oscillation circuit is connected. The problem was solved by dividing the excitation level of R1 and R2 and exciting the crystal resonator with the output.

[0005]

When the excitation level of the crystal unit is 1 when the resistance R1 is 0 in FIG. 1, the ratio of the excitation level reduced by inserting the resistance R1 is RX / (RX
+ R1).

As an example of substituting specific numerical values using the above formula, when the resistance R1 is considered to be 90Ω, the equivalent series resistance RX of the crystal unit is 1/10 at 10Ω, and the equivalent value of the crystal unit is 1/10. When the series resistance RX is 30Ω, it becomes 1/4, and the excitation level applied to the crystal unit is greatly affected by the equivalent series resistance RX of the crystal unit. However, FIG.
As shown in (1), by setting the excitation level from the oscillation circuit to the ratio of the resistor R1 to the resistor R2 to 9: 1, R1 / (R1 + R
2) That is, the quartz resonator is excited by dividing it by 1/10 with a resistor, and the excitation level can be reduced to about 1/10 without substantially affecting the equivalent series resistance RX of the quartz resonator. Note that the capacitor C3 is for blocking a direct current in order to avoid fluctuations in the bias of the oscillation circuit due to the resistor R2.

[0007]

Embodiments of the present invention will be described below with reference to the accompanying drawings. In each drawing, the same reference numeral indicates the same object. In the conventional crystal oscillation circuit shown in FIG. 4, when the resistor R1 which is a circuit for reducing the excitation level and the crystal resonator X are connected in series, the value of the resistor R1 is constant and the equivalent series resistance RX of the crystal resonator changes. Is that the excitation level directly changes according to the amount of change in the equivalent series resistance RX of the crystal resonator. For example, when the input oscillation level is 1, when the resistance R1 is 100Ω and the equivalent series resistance RX of the crystal unit is 10Ω, the excitation level applied to the crystal unit becomes 9%, but the equivalent series resistance RX of the crystal unit is 9%. When the resistance is 20Ω, the excitation level applied to the crystal resonator is greatly increased to 17%.

FIG. 1 is a circuit diagram showing an embodiment of the present invention. As shown in FIG. 1, between a connection point where a resistor R1 is connected in series with the crystal unit X, which is the same circuit unit, and a ground,
One end of the resistor R2 is connected, and the other terminal of the resistor R2 is connected to ground via a capacitor C3. Resistance R1 and resistance R2
As described in the section of the operation, the ratio of reducing = R1
/ (R1 + R2). FIG. 1 shows an example in which the excitation level of the crystal unit is reduced to an L type by an attenuation circuit. FIG. 2 shows an embodiment in which the excitation level is reduced by replacing the attenuation circuit of FIG. 1 with an L-type to a T-type. FIG. 3 shows FIG.
This is an embodiment in which the excitation level is reduced by replacing the T-type damping circuit with the π-type.

[0009]

According to the present invention, the excitation level of the crystal unit can be stably reduced by the damping circuit without being affected by the equivalent series resistance of the crystal unit.
As a result, abnormal oscillation including high-order oscillation of the crystal unit was prevented, and discontinuity of temperature characteristics was prevented from occurring due to coupling with other modes of vibration, significantly improving the quality of the crystal oscillation circuit. did.

[0010]

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of an L-type attenuation circuit according to the present invention.

FIG. 2 is a circuit diagram showing an embodiment of a T-type attenuation circuit according to the present invention.

FIG. 3 is a circuit diagram showing an embodiment using a π-type attenuation circuit according to the present invention.

FIG. 4 is a circuit diagram showing a conventional technique.

[Explanation of symbols]

R0, R1, R2, R3 Resistance X Quartz crystal unit C1, C2, C3, C4 Capacitor IC1, IC2 CMOS inverter

Claims (1)

(57) [Claims] 1. A crystal oscillation circuit in which a resistor and a quartz oscillator are connected between the input and output of a CMOS inverter, and a resistor is connected in series with the quartz oscillator, and a ground between the quartz oscillator and the resistor is grounded. A crystal oscillation circuit, wherein a capacitor and a resistor are connected in series. [0001]