JP5098979B2 - Piezoelectric oscillator - Google Patents

Description

  The present invention relates to a Pierce type piezoelectric oscillator.

  Piezoelectric oscillators have advantages such as frequency stability, small size, light weight, and low price, and are used in many fields of communication equipment and electronic equipment. Among them, temperature compensated piezoelectric oscillators that compensate for the frequency temperature characteristics of piezoelectric vibrators ( TCXO) is widely used for mobile phones and the like. The piezoelectric oscillator includes a Pierce type piezoelectric oscillator and a Colpitts type piezoelectric oscillator. The Pierce-type piezoelectric oscillator can be operated with a low power supply voltage and is suitable for circuit integration. However, the frequency that can be output with a low current is only 10 to 30 MHz, and there is a problem that a high frequency cannot be output. .

  FIG. 9 is a circuit diagram showing a conventional Pierce BC type piezoelectric oscillator 8 having a self-bias circuit. As shown in FIG. 9, the Pierce BC type piezoelectric oscillator 8 includes an oscillation circuit 108 and a buffer circuit BUF. The oscillation circuit 108 includes an oscillation transistor Q1, a base terminal and a collector of the oscillation transistor Q1. The piezoelectric vibrator 10 and the feedback resistor R0 are connected between the terminals, and the capacitive elements C1 and C2 are respectively connected between both ends of the piezoelectric vibrator 10 and the ground potential line GND. The buffer circuit BUF is connected to the collector terminal of the oscillation transistor Q1 that is the output of the oscillation circuit. A current source 20 is connected to the collector terminal of the oscillation transistor Q1.

  In order to increase the output frequency of the oscillation circuit 108, it is necessary to sufficiently increase the negative resistance value of the oscillation circuit 108 at a desired oscillation frequency. The negative resistance value (−Rn) of the oscillation circuit 108 is −Rn = gm / (ωC1C2), where gm is the mutual conductance value of the oscillation transistor Q1. Therefore, in order to increase the negative resistance value, it is necessary to decrease the capacitance values of the capacitive elements C1 and C2 or increase the mutual conductance value gm.

  However, when the capacitance values of the capacitive elements C1 and C2 are reduced, the load capacitance of the oscillation circuit 108 is also reduced, and the frequency sensitivity is increased more than necessary. For this reason, the influence of the external load capacitance due to the buffer circuit BUF connected to the output of the oscillation circuit 108 (the collector terminal of the oscillation transistor Q1) becomes large, causing power supply fluctuations and deterioration over time. Further, when the capacitance values of the capacitive elements C1 and C2 are reduced, the circuit loss of the oscillation circuit 108 is increased, the circuit Q value is reduced, and the C / N ratio (Carrier to Noise Ratio) is deteriorated.

  In order to solve this problem, for example, Patent Document 1 describes a Pierce type crystal oscillation circuit including a level shift circuit between an output of an oscillation circuit and an external load in order to reduce the influence of an external load capacitance. Has been. However, such a Pierce type crystal oscillation circuit has a problem that it is not suitable for integration because the circuit scale is increased by the level shift circuit and the current consumption is increased.

  Further, in the method of increasing the mutual conductance value gm of the oscillation transistor Q1 in order to increase the negative resistance value, it is necessary to increase the collector current Ic, and the current consumption of the oscillation circuit 108 increases.

  In order to solve this problem, for example, Patent Document 2 describes a method in which a feedback circuit (emitter follower circuit) is provided between a collector and an emitter of an oscillation transistor in a Colpitts type oscillation circuit. By adding the feedback circuit, the negative resistance characteristic of the oscillation circuit is improved, and a sufficiently high negative resistance value can be obtained at a high frequency.

  However, when such a feedback circuit is applied to a Pierce type oscillation circuit, a current for operating the feedback circuit is required, resulting in an increase in current consumption. Further, the coupling capacity of the feedback circuit (C4 and C5 in FIG. 8 of Patent Document 2) has a very large value and is not suitable for integration. Further, by adding a feedback circuit, a sufficient negative resistance can be obtained, but the frequency region is several hundred MHz (see FIG. 2 of Patent Document 2), and several tens of MHz used for a quartz AT vibrator or the like. Far beyond the realm of

  As another method for increasing the negative resistance, for example, Patent Document 3 describes a method of Darlington connection of an oscillation transistor in a Colpitts type crystal oscillation circuit. By connecting the oscillation transistor to the Darlington connection, the current amplification factor Hfe of the oscillation transistor can be increased and the mutual conductance value gm can be increased, so that the negative resistance can be increased.

Japanese Patent Laid-Open No. 2002-16439 (FIG. 1) Japanese Patent Laying-Open No. 2005-86378 (FIG. 8) JP 2002-237725 A (FIG. 1)

  However, the negative resistance is increased by connecting the oscillation transistor to the Darlington connection, but the oscillation frequency is lowered. FIG. 9 shows a simulation result in a Colpitts-type crystal oscillation circuit. 10A shows a conventional Colpitts crystal oscillation circuit, FIG. 10B shows a Colpitts crystal oscillation circuit in which an oscillation transistor is connected by Darlington, and FIG. 10C shows respective negative resistance values. It is a graph which shows.

  This method also produces the same result when the oscillation transistor is Darlington connected by a Pierce type oscillation circuit. This is because the current amplification factor Hfe of the oscillation transistor increases by connecting the oscillation transistor to the Darlington connection, but the mirror capacitance between the collector and the emitter of the oscillation transistor also increases, and the negative resistance deteriorates at high frequencies. Conceivable.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms or application examples.

[Application Example 1]
A piezoelectric vibrator; a first capacitive element connected between one terminal of the piezoelectric vibrator and a ground potential line; and a second capacitive terminal connected between the other terminal of the piezoelectric vibrator and the ground potential line. The second capacitor element and the collector terminal are connected to one terminal of the piezoelectric vibrator, the base terminal is connected to the other terminal of the piezoelectric vibrator, and the emitter terminal is connected to the ground potential line. And the base terminal is connected to the collector terminal of the oscillation transistor via a first resistor, the collector terminal is connected to the collector terminal of the oscillation transistor via a second resistor, and the emitter terminal is An oscillation assisting transistor connected to the base terminal of the oscillation transistor.

  According to this configuration, the oscillation auxiliary transistor and the oscillation transistor can increase the amplification factor without increasing the circuit current and obtain a negative resistance larger than that of the conventional configuration, so that oscillation can be performed at a high frequency. Furthermore, since only the oscillation auxiliary transistor and the first resistor are increased from the conventional circuit configuration, high integration and low current consumption can be realized.

[Application Example 2]
The piezoelectric oscillator according to the above, further comprising a third capacitive element connected between one terminal of the piezoelectric vibrator and a collector terminal of the oscillation transistor.

  According to this configuration, the third capacitive element can move the valley of the negative resistance to the higher frequency side, so that it is possible to oscillate at a higher frequency and further assist in oscillation than the conventional circuit configuration. Since only the number of transistors and the first resistor are increased, high integration and low current consumption can be realized.

[Application Example 3]
The piezoelectric oscillator according to the above, further comprising a fourth capacitive element connected between the other terminal of the piezoelectric vibrator and a base terminal of the oscillation transistor.

  According to this configuration, since the negative resistance can be further increased by the fourth capacitive element, it is possible to oscillate at a high frequency, and further, the oscillation assisting transistor and the first capacitance can be increased compared to the conventional circuit configuration. Since only the resistance increases, high integration and low current consumption can be realized.

[Application Example 4]
In the piezoelectric oscillator described above, a third capacitive element connected between one terminal of the piezoelectric vibrator and a collector terminal of the oscillation transistor, the other terminal of the piezoelectric vibrator, and the oscillation And a fourth capacitive element connected between the base terminal of the transistor.

  According to this configuration, the third capacitor element and the fourth capacitor element allow the negative resistance valley to move to the higher frequency side and oscillate at a higher frequency, and moreover than the conventional circuit configuration. Since only the oscillation auxiliary transistor, the first resistor, and the third and fourth capacitive elements are increased, high integration and low current consumption can be realized.

  Hereinafter, embodiments of a piezoelectric oscillator will be described with reference to the drawings.

(First embodiment)
<Configuration of piezoelectric oscillator>
First, the configuration of the piezoelectric oscillator according to the first embodiment will be described with reference to FIG. FIG. 1 is a circuit diagram showing the configuration of the piezoelectric oscillator according to the first embodiment.

  As shown in FIG. 1, the piezoelectric oscillator 1 includes an oscillation circuit 101 and a buffer circuit BUF.

  The oscillation circuit 101 includes an oscillation transistor Q1 having an emitter terminal connected to the ground potential line GND, a piezoelectric vibrator 10 connected between a base terminal and a collector terminal of the oscillation transistor Q1, and the piezoelectric vibrator 10 The first capacitor element C1 and the second capacitor element C2 connected between the both ends and the ground potential line GND, and the base terminal are connected to the collector terminal of the oscillation transistor Q1 via the first resistor Rb. The oscillation auxiliary transistor Q2 whose collector terminal is connected to the collector terminal of the oscillation transistor Q1 via the second resistor Rc, and whose emitter terminal is connected to the base terminal of the oscillation transistor Q1, and the collector of the oscillation transistor Q1 And a current source 20 connected between the terminal and the power supply potential line VDD. The buffer circuit BUF is connected to the collector terminal of the oscillation transistor Q1 that is the output of the oscillation circuit 101.

  The difference between the conventional oscillation circuit 108 and the oscillation circuit 101 shown in FIG. 9 is that the feedback resistor R0 is replaced with an oscillation assisting transistor Q2, a first resistor Rb, and a second resistor Rc.

  Since the oscillation assisting transistor Q2 supports the improvement of the amplification efficiency by the oscillation transistor Q1, a larger negative resistance than the conventional one can be obtained by the amplification effect of the oscillation assisting transistor Q2 and the oscillation transistor Q1. Start-up characteristics can be obtained.

  Since the current flowing through the oscillation auxiliary transistor Q2, the first resistor Rb, and the second resistor Rc is equal to the base current of the oscillation transistor Q1, it is compared with the case where only the feedback resistor R0 of the conventional oscillation circuit 108 is configured. However, there is no increase in current.

  Even when the current amplification factor Hfe of the oscillation transistor Q1 decreases and the negative resistance decreases, the base current increases due to the decrease in the current amplification factor Hfe, and the current flowing through the oscillation auxiliary transistor Q2 increases conversely. The oscillation assisting transistor Q2 can greatly support the improvement of the amplification efficiency by the oscillation transistor Q1. That is, by appropriately selecting the oscillation frequency, it is possible to suppress the deterioration of the negative resistance due to the decrease in the current amplification factor Hfe.

  The operation of the piezoelectric oscillator according to the first embodiment will be described with reference to FIG. FIG. 2 is a graph showing the operation of the piezoelectric oscillator according to the first embodiment.

  As shown in FIG. 2, the peak of the negative resistance of the output OUT8 of the conventional piezoelectric oscillator 8 was about 10 MHz. The peak of the negative resistance of the output OUT of the piezoelectric oscillator 1 of the present embodiment is about 24 MHz, and it can be seen that an output at a high frequency is possible compared to the conventional case.

  According to the present embodiment described above, the following effects can be obtained.

  In this embodiment, since the amplification factor is increased by the oscillation assisting transistor Q2 and the oscillation transistor Q1, a larger negative resistance can be obtained at a higher frequency than in the conventional configuration, so that oscillation can be performed at a higher frequency. Furthermore, since only the oscillation auxiliary transistor Q2 and the first resistor Rb are increased from the conventional circuit configuration, high integration and low current consumption can be realized.

  While the embodiments of the piezoelectric oscillator have been described above, the present invention is not limited to these embodiments, and can be implemented in various forms without departing from the scope of the invention. Hereinafter, a modification will be described.

  (Modification 1) Modification 1 of the piezoelectric oscillator will be described. FIG. 3 is a circuit diagram illustrating a configuration of the piezoelectric oscillator according to the first modification. As shown in FIG. 3, the piezoelectric oscillator 3 is different from the piezoelectric oscillator 1 of the first embodiment in that the collector terminal of the oscillation transistor Q1 and one terminal of the piezoelectric vibrator 10 (on the first capacitive element C1 side). It further includes a third capacitive element C3 connected therebetween. FIG. 4 is a graph showing the operation of the piezoelectric oscillator according to the first modification. According to this configuration, the phase of the signal fed back from the collector of the oscillation transistor Q1 to the capacitive element C1 and the piezoelectric vibrator 10 is changed by the third capacitive element C3, and the negative resistance peak position has a high frequency. It becomes possible to oscillate at a higher frequency.

  (Modification 2) Modification 2 of the piezoelectric oscillator will be described. FIG. 5 is a circuit diagram showing a configuration of a piezoelectric oscillator according to the second modification. As shown in FIG. 5, the piezoelectric oscillator 4 is different from the piezoelectric oscillator 1 of the first embodiment in that the base terminal of the oscillation transistor Q1 and the other terminal of the piezoelectric vibrator 10 (second capacitor element C2 side). It further includes a fourth capacitive element C4 connected therebetween. According to this configuration, since the negative resistance can be further increased at a high frequency by the fourth capacitive element C4, it is possible to oscillate at a high frequency as in the first modification.

  (Modification 3) Modification 3 of the piezoelectric oscillator will be described. FIG. 6 is a circuit diagram illustrating a configuration of a piezoelectric oscillator according to the third modification. As shown in FIG. 6, the piezoelectric oscillator 5 is different from the piezoelectric oscillator 1 of the first embodiment in that the collector terminal of the oscillation transistor Q1 and one terminal of the piezoelectric vibrator 10 (on the first capacitor element C1 side). A third capacitive element C3 connected between the base terminal of the oscillation transistor Q1 and the other terminal (second capacitive element C2 side) of the piezoelectric vibrator 10 with respect to the piezoelectric oscillator 1; And a fourth capacitive element C4. According to this configuration, since the negative resistance can be further increased at a higher frequency by the third capacitive element C3 and the fourth capacitive element C4, it is possible to oscillate at a higher frequency as in the first modification. .

  (Modification 4) Modification 4 of the piezoelectric oscillator will be described. FIG. 7 is a circuit diagram showing a configuration of the piezoelectric oscillator according to the fourth modification. As shown in FIG. 7, in the piezoelectric oscillator 6, a variable capacitor VC1 is connected instead of the first capacitor C1 constituting the piezoelectric oscillator 5 of Modification 3, and a variable capacitor is replaced instead of the second capacitor C2. The element VC2 is connected, the control voltage Vc is applied to the variable capacitance element VC1 via the resistor R1, and the control voltage Vc is applied to the variable capacitance element VC2 via the resistor R2. According to this configuration, the frequency output from the control voltage Vc can be controlled. In this example, the capacitive elements C3 and C4 increase the negative resistance value and function as a DC cut capacitor for the DC voltage applied to the variable capacitive elements VC1 and VC2.

  (Modification 5) Modification 5 of the piezoelectric oscillator will be described. FIG. 8 is a circuit diagram showing a configuration of a piezoelectric oscillator according to the fifth modification. As shown in FIG. 8, the piezoelectric oscillator 7 further includes a resistor Re connected between the emitter terminal of the oscillation assisting transistor Q2 and the base terminal of the oscillation transistor Q1 with respect to the piezoelectric oscillator 1 of the first embodiment. Consists of including. The configuration including the resistor Re can be similarly applied to the piezoelectric oscillators 3, 4, 5, and 6.

1 is a circuit diagram showing a configuration of a piezoelectric oscillator according to a first embodiment. The graph which shows operation | movement of the piezoelectric oscillator which concerns on 1st Embodiment. The circuit diagram which shows the structure of the piezoelectric oscillator which concerns on the modification 1. FIG. 6 is a graph showing the operation of a piezoelectric oscillator according to Modification Example 1. FIG. 6 is a circuit diagram showing a configuration of a piezoelectric oscillator according to Modification 2. FIG. 10 is a circuit diagram showing a configuration of a piezoelectric oscillator according to Modification 3. FIG. 10 is a circuit diagram showing a configuration of a piezoelectric oscillator according to Modification 4. FIG. 10 is a circuit diagram showing a configuration of a piezoelectric oscillator according to Modification 5. The circuit diagram which shows the structure of the conventional piezoelectric oscillator. (A) A conventional Colpitts-type crystal oscillation circuit, (B) a Colpitts-type crystal oscillation circuit in which oscillation transistors are connected by Darlington, and (C) graphs showing respective output frequencies.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Piezoelectric oscillator, 3 ... Piezo oscillator, 4 ... Piezo oscillator, 5 ... Piezo oscillator, 7 ... Piezo oscillator, 10 ... Piezo vibrator, 20 ... Current source, 101 ... Oscillator circuit, 108 ... Oscillator circuit .

Claims (4)

A piezoelectric vibrator;
A first capacitive element connected between one terminal of the piezoelectric vibrator and a ground potential line;
A second capacitive element connected between the other terminal of the piezoelectric vibrator and the ground potential line;
An oscillation transistor having a collector terminal connected to one terminal of the piezoelectric vibrator, a base terminal connected to the other terminal of the piezoelectric vibrator, and an emitter terminal connected to the ground potential line;
A base terminal is connected to the collector terminal of the oscillation transistor via a first resistor, a collector terminal is connected to the collector terminal of the oscillation transistor via a second resistor, and an emitter terminal is connected to the oscillation transistor. An oscillation assisting transistor connected to the base terminal;
A piezoelectric oscillator comprising: The piezoelectric oscillator according to claim 1,
A third capacitive element connected between one terminal of the piezoelectric vibrator and a collector terminal of the oscillation transistor;
A piezoelectric oscillator characterized by that. The piezoelectric oscillator according to claim 1,
A fourth capacitive element connected between the other terminal of the piezoelectric vibrator and a base terminal of the oscillation transistor;
A piezoelectric oscillator characterized by that. The piezoelectric oscillator according to claim 1,
A third capacitive element connected between one terminal of the piezoelectric vibrator and a collector terminal of the oscillation transistor;
A fourth capacitive element connected between the other terminal of the piezoelectric vibrator and a base terminal of the oscillation transistor;
Further including
A piezoelectric oscillator characterized by that.

Images