JP2015070311A - Oscillation circuit and crystal oscillator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To oscillate at a desired frequency, while suppressing the drive level.SOLUTION: An oscillation circuit 1 includes a crystal oscillator X, a first resistor Rx connected in series with the crystal oscillator X, an inductor Lx connected in series with the crystal oscillator X and first resistor Rx, a first capacitor C1 provided between one end of a series circuit SC including the crystal oscillator X, first resistor Rx and inductor Lx and the ground, a second capacitor C2 provided between the other end of the series circuit SC and the ground, and an amplifier circuit A provided in parallel with the series circuit SC.

Description

  The present invention relates to an oscillation circuit and a crystal oscillator.

Conventionally, an oscillation circuit using a crystal resonator is known (for example, see Patent Document 1). FIG. 7 is an electric circuit diagram of the conventional oscillation circuit 100.
The oscillation circuit 100 includes a crystal resonator 101, a first capacitor 102, a second capacitor 103, an amplifier circuit 104, a feedback resistor 105, a limiting resistor 106, and an output terminal 107.

  A first capacitor 102 is connected between the first terminal of the crystal unit 101 and the ground, and a second capacitor 103 is connected between the second terminal of the crystal unit 101 and the ground. The crystal resonator 101, the amplifier circuit 104, and the feedback resistor 105 are connected in parallel. The limiting resistor 106 is provided between the crystal unit 101 and the amplifier circuit 104.

Japanese Utility Model Publication No. 6-54308

  Incidentally, in the oscillation circuit 100, in order to prevent destruction of the crystal resonator 101 due to vibration, a resistor is connected in series with the crystal resonator 101 to suppress the drive level. However, even if a resistor is connected in series to the crystal unit 101, the drive level may not be sufficiently suppressed.

  In this case, it may be possible to further suppress the drive level by reducing the load capacitances of the first capacitor 102 and the second capacitor 103. However, if the capacitances of the first capacitor 102 and the second capacitor 103 are reduced, the oscillation frequency There is a problem that becomes high.

  Therefore, the present invention has been made in view of these points, and an object thereof is to provide an oscillation circuit that can oscillate at a desired oscillation frequency while suppressing a drive level, and a crystal oscillator including the oscillation circuit. And

  An oscillation circuit according to a first aspect of the present invention includes a crystal resonator, a first resistor connected in series with the crystal resonator, an inductor connected in series with the crystal resonator and the first resistor, A first capacitor provided between one end of a series circuit including a crystal resonator, the first resistor, and the inductor and the ground; a second capacitor provided between the other end of the series circuit and the ground; And an amplifier circuit provided in parallel with the series circuit. The oscillation circuit may further include a second resistor provided between the amplifier circuit and the series circuit.

  The amplifier circuit, the first resistor, the first capacitor, and the second capacitor are provided in a single semiconductor integrated circuit, and the crystal resonator and the inductor are provided outside the semiconductor integrated circuit. It may be done. The semiconductor integrated circuit may include an adjustment unit that adjusts capacitances of the first capacitor and the second capacitor.

  In addition, the oscillation circuit may further include a connection unit that detachably connects the crystal resonator.

  A crystal oscillator according to a second aspect of the present invention includes the above oscillation circuit, a substrate on which the oscillation circuit is provided, and a housing that houses the substrate.

  According to the present invention, it is possible to oscillate at a desired oscillation frequency while suppressing the drive level.

FIG. 3 is an electric circuit diagram of the oscillation circuit according to the first embodiment. It is a figure which shows the value of each element in the oscillation circuit which concerns on 1st Embodiment, and the measurement result of the frequency deviation of a negative resistance, a drive level, and a frequency. It is an electric circuit diagram of a conventional oscillation circuit. It is a figure which shows the value of each element in the conventional oscillation circuit, and the measurement result of the frequency deviation of a negative resistance, a drive level, and a frequency. It is a figure which shows the structure of the oscillation circuit which concerns on 2nd Embodiment. It is a figure which shows the structure of the oscillation circuit which concerns on 3rd Embodiment. It is an electric circuit diagram of a conventional oscillation circuit.

<First Embodiment>
FIG. 1 is an electric circuit diagram of the oscillation circuit 1 according to the first embodiment.
The oscillation circuit 1 includes a crystal resonator X, a first resistor Rx, an inductor Lx, a first capacitor C1, a second capacitor C2, a third capacitor C3, a fourth capacitor C4, an amplifier circuit A, A second resistor Rd, a third resistor Rf, and an output terminal T are provided. The crystal resonator X is, for example, a crystal resonator (AT cut crystal resonator) using an AT cut crystal piece.

  The first resistor Rx is connected in series with the crystal unit X. The first resistor Rx can suppress the amount of change in the oscillation frequency when the value of the equivalent resistance of the crystal unit X varies and the oscillation frequency of the oscillation circuit 1 changes. For example, when the equivalent resistance of the crystal unit X changes in the range of 50Ω to 100Ω with changes in the ambient temperature, the change rate of the equivalent resistance is 100%. On the other hand, when the first resistance Rx of 100Ω is provided in series with the crystal unit X, the resistance value of the first resistor Rx and the equivalent resistance of the crystal unit X ranges from 150Ω to 200Ω. Therefore, the change rate of the resistance value is 33%. As described above, the change rate of the oscillation value can be suppressed by reducing the change rate of the resistance value.

  Further, the first resistor Rx can suppress the amount of current flowing through the crystal resonator X. Therefore, the drive level can be suppressed by providing the first resistor Rx in series with the crystal unit X.

  The inductor Lx is connected in series with the crystal unit X and the first resistor Rx. Since the oscillation circuit 1 includes the inductor Lx, the resonance frequency of the oscillation circuit 1 is lower than that in the case where the inductor Lx is not included.

The crystal resonator X, the inductor Lx, and the first resistor Rx constitute a series circuit SC.
The first capacitor C1 is connected between one end of the series circuit SC and the ground.
The second capacitor C2 is connected between the other end of the series circuit SC and the ground.
Based on the capacitance of the first capacitor C1 and the second capacitor C2, the oscillation frequency and drive level of the oscillation circuit 1 are determined.

  The third capacitor C3 and the fourth capacitor C4 are connected in series. The third capacitor C3 is connected between the other end of the series circuit SC and the fourth capacitor C4. The fourth capacitor C4 is connected between the third capacitor C3 and the ground. The fourth capacitor C4 is a trimmer capacitor and is mainly used for adjusting the oscillation frequency.

The amplifier circuit A is an inverter, for example, and is connected in parallel with the series circuit 14. The amplifier circuit A amplifies the oscillation signal oscillated in the oscillation circuit 1 and outputs the amplified signal to the output terminal T.
The second resistor Rd is provided between the amplifier circuit A and the series circuit SC, and is used to adjust the drive level. The second resistor Rd prevents an excessive current from flowing into the crystal unit X and destroying the crystal unit X.
The third resistor Rf is connected in parallel with the amplifier circuit A, and feeds back the current output from the amplifier circuit A to maintain oscillation.

[Adjustment procedure]
Subsequently, an adjustment procedure of the oscillation circuit 1 will be described.
First, the value of the first resistor Rx is adjusted so that the drive level is within a predetermined target range. Subsequently, when the drive level is not sufficiently suppressed by adjusting the first resistance Rx, the impedance of the oscillation circuit 1 is increased by reducing the capacitance of the first capacitor C1 and the second capacitor C2, and the drive level Is further suppressed.

  However, by reducing the capacitance of the first capacitor C1 and the second capacitor C2, the oscillation frequency shifts higher. When the oscillation frequency is higher than the target oscillation frequency, the oscillation frequency is shifted low by increasing the inductance of the inductor Lx. Thereby, it is possible to oscillate at a desired oscillation frequency while suppressing the drive level of the oscillation circuit 1.

[Measurement results]
Subsequently, an actual measurement result when the negative resistance and the drive level characteristic are adjusted in the oscillation circuit 1 according to the present embodiment is shown. FIG. 2 is a diagram illustrating the values of each element in the oscillation circuit 1 according to the present embodiment and the measurement results of the negative resistance (−R), the drive level (DL), and the frequency deviation (dF / F).

  Here, the target value of the negative resistance is set to 100Ω or more, and the target value of the drive level is set to 100 μW or less. In order to suppress the drive level, Rd was set to 1500Ω and Rx was set to 470Ω. Further, the capacities of the first capacitor C1 and the third capacitor are made lower than those of the conventional oscillation circuit. For the fourth capacitor C4, the maximum value was 10 pF, and adjustment was performed between 3.5 pF and 10 pF. In order to sufficiently reduce the frequency deviation when the capacitances of the first capacitor C1 and the third capacitor are low, the inductance of Lx is set to 2.2 μH.

  As a result of the measurement, the frequency deviation was 0 ppm, the negative resistance was 340Ω, and the drive level was 70.0 μW, and the negative resistance and the drive level were able to be within the target range while oscillating at a desired oscillation frequency.

[Comparative example]
Next, an actual measurement result when the negative resistance and the drive level characteristic are adjusted in the conventional oscillation circuit 200 is shown. FIG. 3 is an electric circuit diagram of the conventional oscillation circuit 200. As shown in FIG. 3, the conventional oscillation circuit 200 is a circuit obtained by removing the inductor Lx from the oscillation circuit 1 of the present embodiment. FIG. 4 is a diagram showing the values of each element in the conventional oscillation circuit 2 and the measurement results of the negative resistance, the drive level, and the frequency deviation.

As shown in FIG. 4, in the measurement of the conventional oscillation circuit 200, the value of each element in the oscillation circuit 200 was changed and the measurement was performed for four patterns.
As a result of the measurement, the frequency deviation of each pattern exceeded at least 30 ppm, and it was not possible to oscillate at the desired oscillation frequency. In addition, both the negative resistance and the drive level could not be simultaneously within the target range.

[Effect of this embodiment]
As described above, according to the present embodiment, the oscillation circuit 1 includes the crystal resonator X, the first resistor Rx connected in series with the crystal resonator X, and the inductor connected in series with the crystal resonator X and the first resistor Rx. Lx, a first capacitor C1 provided between one end of the series circuit SC including the crystal resonator X, the first resistor Rx, and the inductor Lx and the ground, and provided between the other end of the series circuit SC and the ground. The second capacitor C2 and the amplifier circuit A provided in parallel with the series circuit SC.

  By doing in this way, the oscillation circuit 1 can suppress the drive level and the frequency change accompanying the change of the equivalent resistance of the crystal resonator X by adjusting the first resistance Rx. Then, after the drive level is suppressed by the first resistor Rx, the oscillation circuit 1 reduces the capacitance of the first capacitor C1 and the second capacitor C2 and further shifts the oscillation frequency to further suppress the drive level. The oscillation frequency can be shifted low by adjusting the inductance of the inductor Lx. Therefore, the oscillation circuit 1 can oscillate at a desired oscillation frequency while suppressing the drive level.

<Second Embodiment>
FIG. 5 is a diagram illustrating a configuration of the oscillation circuit 2 according to the second embodiment. Unlike the oscillation circuit 1 according to the first embodiment, the oscillation circuit 2 is the same in other respects in that a part of the circuit is provided in the semiconductor integrated circuit 20. Specifically, as shown in FIG. 5, the amplifier circuit A, the first resistor Rx, the second resistor Rd, the third resistor Rf, the first capacitor C1, and the second capacitor C2 are combined into a single semiconductor integrated circuit 20. Is provided. Further, the crystal resonator X and the inductor Lx are provided outside the semiconductor integrated circuit 20.

  In the semiconductor integrated circuit 20, the first capacitor C1 and the second capacitor C2 are configured by a capacitor array or a varicap diode. In addition, the semiconductor integrated circuit 20 includes an adjustment unit 21 that adjusts the capacitance of at least one of the first capacitor C1 and the second capacitor C2.

  For example, when the first capacitor C1 and the second capacitor C2 are each composed of a capacitor array having a plurality of capacitors, the adjustment unit 21 includes a selector that selects some of the plurality of capacitors. The adjustment unit 21 adjusts the capacitance by switching at least one of the selectors of the first capacitor C1 and the second capacitor C2 in accordance with a control signal input from the outside of the semiconductor integrated circuit 20.

  When the first capacitor C1 and the second capacitor C2 are configured by varicap diodes, the adjustment unit 21 applies a voltage according to a control signal input from the outside of the semiconductor integrated circuit 20 to the varicap diodes. To adjust the capacity.

  As described above, the oscillation circuit 2 is reduced in size by incorporating the amplifier circuit A, the first resistor Rx, the second resistor Rd, the third resistor Rf, the first capacitor C1, and the second capacitor C2 in the semiconductor integrated circuit 20. Is possible. Also, by incorporating the first capacitor C1 and the second capacitor C2 in the semiconductor integrated circuit 20, a capacitor array or a varicap diode can be used as the first capacitor C1 and the second capacitor C2. As a result, the adjustment unit 21 can finely adjust the capacitances of the first capacitor C1 and the second capacitor C2 by an external control signal. Therefore, according to the oscillation circuit 2, the oscillation frequency is adjusted without changing the circuit configuration. be able to.

  In the present embodiment, the example in which the adjustment unit 21 adjusts the capacitance of the capacitor has been described. However, the adjustment unit 21 adjusts any one of the first resistor Rx, the second resistor Rd, and the third resistor Rf. Also good.

<Third Embodiment>
FIG. 6 is a diagram illustrating a configuration of the oscillation circuit 3 according to the third embodiment. Unlike the oscillation circuit 1 according to the first embodiment, the oscillation circuit 3 is the same in other respects in that the oscillation circuit 3 includes a connection unit 30 that detachably connects the crystal resonator X. The connection unit 30 is provided at a connection point between both ends of the crystal unit X and elements other than the crystal unit X in the oscillation circuit 3.

  The connection unit 30 is, for example, a socket that connects both ends of the crystal unit X to other elements. The amplifier circuit A, the first resistor Rx, the second resistor Rd, the third resistor Rf, the first capacitor C1, the second capacitor C2, the third capacitor C3, the fourth capacitor C4, and the connection unit 30 included in the oscillation circuit 3 are, for example, It is fixed to the printed circuit board by soldering. By inserting the crystal unit X into the connection unit 30, the crystal unit functions as the oscillation circuit 3.

  Since the oscillation circuit 3 includes the connection unit 30, the user of the oscillation circuit 3 can easily change the electrical characteristics including the frequency of the oscillation signal by exchanging the crystal unit X.

  In the oscillation circuit 3, as in the oscillation circuit 2 according to the second embodiment, the oscillation circuit 3 includes an amplifier circuit A, a first resistor Rx, a second resistor Rd, a third resistor Rf, a first capacitor C1, and a second capacitor. The capacitor C2 and the adjustment unit 21 may be built in the semiconductor integrated circuit 20. In this way, when the crystal unit X is replaced, it can be easily adjusted to a desired frequency by an external control signal.

<Fourth Embodiment>
A crystal oscillator according to the fourth embodiment includes a printed circuit board on which the oscillation circuit 1, the oscillation circuit 2, or the oscillation circuit 3 according to the above-described embodiment is mounted, and a housing that houses the printed circuit board. The casing has a ground terminal connected to the ground of the oscillation circuit, a power supply terminal for inputting power supplied to the amplification circuit A of the oscillation circuit, and an oscillation signal output from the oscillation circuit Is output.

  As mentioned above, although this invention was demonstrated using embodiment, the technical scope of this invention is not limited to the range as described in the said embodiment. It will be apparent to those skilled in the art that various modifications or improvements can be added to the above embodiment. It is apparent from the scope of the claims that the embodiments added with such changes or improvements can be included in the technical scope of the present invention.

  For example, in the above-described embodiment, the example in which the inductor Lx, the crystal unit X, and the first resistor Rx are connected in series in this order has been described, but the connection order of these elements is arbitrary. For example, the crystal unit X, the inductor Lx, and the first resistor Rx may be connected in this order.

DESCRIPTION OF SYMBOLS 1 ... Oscillation circuit, 2 ... Oscillation circuit, 3 ... Oscillation circuit, 20 ... Semiconductor integrated circuit, 21 ... Adjustment part, 30 ... Connection part, A ... Amplification circuit, C1 ... 1st capacitor, C2 ... 2nd capacitor, C3 ... 3rd capacitor, C4 ... 4th capacitor, Lx ... Inductor, Rx ... 1st resistance, Rd ... 2nd resistance, Rf ... 3rd resistance, T ... Output terminal, X ... Crystal oscillator, 100 ... Conventional oscillation circuit, 101 ... Crystal oscillator, 102 ... 1st Capacitor 103 ... Second capacitor 104 ... Amplifier circuit 105 ... Feedback resistor 106 ... Limit resistor 107 ... Output terminal 200 ... Oscillator circuit

Claims (6)

A crystal unit,
A first resistor connected in series with the crystal resonator;
An inductor connected in series with the crystal resonator and the first resistor;
A first capacitor provided between one end of a series circuit including the crystal resonator, the first resistor, and the inductor and a ground;
A second capacitor provided between the other end of the series circuit and the ground;
An amplifier circuit provided in parallel with the series circuit;
An oscillation circuit comprising: A second resistor provided between the amplifier circuit and the series circuit;
The oscillation circuit according to claim 1. The amplifier circuit, the first resistor, the first capacitor, and the second capacitor are provided in a single semiconductor integrated circuit;
The crystal resonator and the inductor are provided outside the semiconductor integrated circuit,
The oscillation circuit according to claim 1 or 2. The semiconductor integrated circuit includes an adjustment unit that adjusts capacitances of the first capacitor and the second capacitor.
The oscillation circuit according to claim 3. It further comprises a connection part for detachably connecting the crystal unit,
The oscillation circuit according to any one of claims 1 to 4. The oscillation circuit according to any one of claims 1 to 5,
A substrate provided with the oscillation circuit;
A housing for housing the substrate;
A crystal oscillator comprising:

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