Oscillator

Abstract

To provide an oscillator with improved negative resistance at high frequencies.SOLUTION: An oscillator 10 includes a crystal resonator 20, an oscillation inverter 22 that amplifies a signal output from the crystal resonator, and a common-drain amplifier circuit 28 connected in series with the oscillation inverter. The oscillation inverter includes an inverter 23 whose output is connected to the input of the common-drain amplifier circuit, and a feedback resistor 24 for the inverter. One end of the crystal resonator is connected to the input of the inverter, and the other end of the crystal resonator is connected to the output of the common-drain amplifier circuit.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to oscillators. [Background technology]

[0002] BACKGROUND ART There is known an oscillator that includes a vibrator and an oscillation inverter that amplifies a signal output from the vibrator (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 1-300605 Summary of the Invention [Problem to be solved by the invention]

[0004] In conventional oscillators, the negative resistance tends to decrease as the frequency increases. When the negative resistance decreases, problems occur, such as the oscillator becoming less likely to oscillate. Therefore, there is a demand for oscillators with improved negative resistance at high frequencies.

[0005] The present disclosure aims to provide an oscillator with improved negative resistance at high frequencies. [Means for solving the problem]

[0006] In order to achieve the above object, an oscillator according to a first aspect of the present disclosure includes a vibrator, an oscillation inverter that amplifies a signal output from the vibrator, and a drain-grounded amplifier circuit connected in series with the oscillation inverter.

[0007] In a second aspect of the oscillator, in the oscillator of the first aspect, the oscillation inverter includes an inverter whose output is connected to the input of the drain-grounded amplifier circuit and a feedback resistor of the inverter, and one end of the vibrator is connected to the input of the inverter and the other end of the vibrator is connected to the output of the drain-grounded amplifier circuit.

[0008] In the oscillator of a third aspect, in the oscillator of the second aspect, the inverter is a CMOS inverter.

[0009] The oscillator of a fourth aspect is the oscillator of the first aspect, further comprising a coupling element connected between the oscillation inverter and the common-drain amplifier circuit. [Effects of the Invention]

[0010] According to the present disclosure, it is possible to provide an oscillator with improved negative resistance at high frequencies. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a circuit diagram illustrating an example of a configuration of an oscillator according to an embodiment. [Figure 2] 1 is a circuit diagram showing an example of a configuration of an oscillation inverter and a common-drain amplifier circuit according to an embodiment; [Figure 3] FIG. 10 is a circuit diagram illustrating another example of the configuration of the oscillator according to the embodiment. [Figure 4] 10A and 10B are diagrams for explaining the relationship between negative resistance and frequency of the oscillator according to the embodiment. [Figure 5] FIG. 1 is a circuit diagram showing an example of the configuration of a conventional oscillator. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. Note that the following embodiments do not limit the technology of the present disclosure.

[0013] The configuration of the oscillator of this embodiment will be described. Fig. 1 shows a circuit diagram illustrating an example of the configuration of an oscillator 10 according to the present embodiment. The oscillator 10 shown in Fig. 1 is an SPXO (Simple Packaged Crystal Oscillator) that uses a crystal resonator 20 as an example of the resonator according to the present disclosure. As shown in Fig. 1, the oscillator 10 according to the present embodiment includes the crystal resonator 20, an oscillation inverter 22, a coupling element 26, a common-drain amplifier circuit 28, a load capacitance element 30, and a load capacitance element 32.

[0014] One end of the crystal unit 20 (the end on the left side in FIG. 1) is connected to ground via a load capacitance element 30. The other end of the crystal unit 20 (the end on the right side in FIG. 1) is connected to ground via a load capacitance element 32.

[0015] The oscillation inverter 22 amplifies the signal output from the crystal resonator 20. As shown in Figures 1 and 2, the oscillation inverter 22 of this embodiment includes an inverter 23 and a feedback resistor 24. In this embodiment, as shown in Figure 2, a CMOS (Complementary Metal Oxide Semiconductor) inverter having a PMOS transistor 40 and an NMOS transistor 42 is used as the inverter 23.

[0016] The oscillation inverter 22 is connected to one end of the crystal resonator 20. Specifically, the input of the inverter 23 and one end of the feedback resistor 24 (on the left side in FIG. 2) are connected to one end of the crystal resonator 20.

[0017] The common-drain amplifier circuit 28 is connected in series with the oscillation inverter 22 via a coupling element 26. The coupling element 26 is a capacitor that cuts the DC component of the signal output from the oscillation inverter 22 by capacitively coupling the oscillation inverter 22 in the preceding stage with the common-drain amplifier circuit 28 in the succeeding stage. The output of the oscillation inverter 22 is connected to one terminal (the terminal on the right side in FIG. 1) of the coupling element 26. The input of the common-drain amplifier circuit 28 is connected to the other terminal (the terminal on the left side in FIG. 1) of the coupling element 26.

[0018] The drain-grounded amplifier circuit 28 is a so-called source follower, and as shown in FIG. 2, includes a resistor 50, a resistor 52, an NMOS transistor 54, and an NMOS transistor 56 and an NMOS transistor 58 that form a current mirror.

[0019] The NMOS transistor 54 of the drain-grounded amplifier circuit 28 has a drain terminal connected to the power supply, a gate terminal connected to the feedback resistor 24 via the coupling element 26, and a source terminal connected to the other end of the crystal resonator 20. The NMOS transistor 54 outputs a signal from the source terminal according to the voltage applied to the gate terminal.

[0020] In this way, the drain-grounded amplifier circuit 28 has the characteristics of high input impedance and low output impedance, and functions as a buffer because it outputs a signal from the source terminal of the NMOS transistor 54. By functioning as a buffer, the drain-grounded amplifier circuit 28 can pass more current in response to changes in the magnitude of the load resistance.

[0021] The gm (mutual conductance) corresponding to the amplification factor of the drain-grounded amplifier circuit 28 increases as the current flow increases.

[0022] Therefore, it is possible to increase gm obtained by the oscillation inverter 22 and the drain-grounded amplifier circuit 28. Increasing gm makes it possible to increase the negative resistance of the oscillator 10. In particular, it is possible to increase the negative resistance at high frequencies.

[0023] The size of the drain-grounded amplifier circuit 28, specifically, the gm and the like obtained by the drain-grounded amplifier circuit 28, may be adjusted according to the desired negative resistance in the frequency band in which the oscillator 10 is used and the size of the oscillation inverter 22 (the gm and the like obtained by the oscillation inverter 22).

[0024] As described above, the oscillator 10 shown in Fig. 1 is an SPXO, but it may be another type of oscillator. For example, it may be a TCXO (Temperature Compensated Crystal Oscillator), a VCXO (Voltage Controlled Crystal Oscillator), or an OCXO (Oven Controlled Crystal Oscillator). Fig. 3 shows a circuit diagram illustrating an example of the configuration when the oscillator 10 is a VCXO.

[0025] 3, oscillator 10, which is a VCXO, includes crystal unit 20, oscillation inverter 22, coupling element 26, drain-grounded amplifier circuit 28, capacitance element 31 that cuts DC components, capacitance element 33 that cuts DC components, variable capacitance element 60, variable capacitance element 62, bias resistor 64, and bias resistor 66. Oscillation inverter 22 includes inverter 23 and feedback resistor 24.

[0026] One end of the crystal unit 20 (the end on the left side in FIG. 3) is connected to ground via a capacitance element 31 and a variable capacitance element 60. The other end of the crystal unit 20 (the end on the right side in FIG. 3) is connected to ground via a capacitance element 33 and a variable capacitance element 62. An externally applied control voltage VC is applied to the variable capacitance elements 60 and 62 via bias resistors 64 and 66. The capacitance values ​​of the variable capacitance elements 60 and 62 are changed by the control voltage VC, thereby changing the oscillation frequency of the oscillator 10.

[0027] 3, the oscillation inverter 22 and the grounded-drain amplifier circuit 28 are also connected in series via a coupling element 26. The output of the inverter 23 of the oscillation inverter 22 and one end of the feedback resistor 24 (on the left side in FIG. 2) are connected to one end of the crystal unit 20, and the output of the grounded-drain amplifier circuit 28 is connected to the other end of the crystal unit 20. The oscillation inverter 22 and the grounded-drain amplifier circuit 28 can be configured similarly to the oscillation inverter 22 and the grounded-drain amplifier circuit 28 shown in FIG. 2.

[0028] Therefore, as described above, even in the oscillator 10, which is a VCXO shown in Fig. 3, it is possible to increase gm obtained by the oscillation inverter 22 and the drain-grounded amplifier circuit 28. Increasing gm makes it possible to increase the negative resistance of the oscillator 10. In particular, it is possible to increase the negative resistance at high frequencies.

[0029] Fig. 4 shows an example of the change in negative resistance with respect to frequency, as a comparison with the conventional oscillator 100 shown in Fig. 5. In Fig. 4, the change in negative resistance with respect to frequency in the oscillator 10 of this embodiment is shown by a solid line, and the change in negative resistance with respect to frequency in the conventional oscillator 100 is shown by a dotted line. Note that "large negative resistance" means that the absolute value of the resistance value is large. For example, the negative resistance is larger at -150Ω than at -100Ω.

[0030] 5 includes a crystal unit 120, an oscillation inverter 122, a capacitance element 131 that cuts off DC components, a capacitance element 133 that cuts off DC components, a variable capacitance element 160, a variable capacitance element 162, a bias resistor 164, and a bias resistor 166. The oscillation inverter 122 also includes an inverter 123 and a feedback resistor 124. That is, the conventional oscillator 100 does not include a common-drain amplifier circuit 28. The oscillator 100 has a load capacitance equivalent to that of the oscillator 10 of this embodiment.

[0031] 4, in the conventional oscillator 100, the negative resistance decreases as the frequency increases. On the other hand, in the oscillator 10 of this embodiment, the decrease in negative resistance at high frequencies is suppressed compared to the conventional oscillator 10. In this way, the oscillator 10 of this embodiment can improve the negative resistance at high frequencies.

[0032] As described above, the oscillator 10 of each of the above embodiments includes a crystal resonator 20, an oscillation inverter 22 that amplifies a signal output from the crystal resonator 20, and a drain-grounded amplifier circuit 28 connected in series with the oscillation inverter 22.

[0033] In the oscillator 10 of each of the above-described embodiments, by including the drain-grounded amplifier circuit 28 connected in series with the oscillation inverter 22, gm can be increased, and therefore the negative resistance at high frequencies can be increased.

[0034] Therefore, the negative resistance at high frequencies can be improved. Since the negative resistance at high frequencies can be improved in this way, the oscillator 10 can widen the frequency band in which a desired negative resistance can be obtained.

[0035] Generally, in an oscillator, the negative resistance can be increased by reducing the load capacitance (CL), but reducing the load capacitance causes a problem of worsening phase noise. In contrast, in the oscillator 10 of each of the above embodiments, the negative resistance can be increased without reducing the load capacitance, thereby suppressing the deterioration of phase noise.

[0036] Furthermore, if an attempt is made to obtain a gm equivalent to that obtained by the oscillation inverter 22 using only the oscillation inverter 22, the size of the MOS transistors constituting the oscillation inverter 22 would become relatively large, resulting in an increase in chip area. By using a common-drain amplifier circuit 28 as in the oscillator 10, the increase in chip area can be suppressed.

[0037] Furthermore, in the oscillator 10 of each of the above-described embodiments, the drain-grounded amplifier circuit 28 is configured using a CMOS transistor, which makes it possible to suppress an increase in current consumption and an increase in chip area compared to when a bipolar transistor is used.

[0038] In the oscillator 10 of each of the above embodiments, the resonator is the quartz crystal resonator 20, but the resonator may be something other than the quartz crystal resonator 20. For example, it may be a ceramic resonator, a silicon resonator, or the like.

[0039] Furthermore, the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention. [Explanation of symbols]

[0040] 10 Oscillators 20 crystal oscillator 22 Oscillation inverter 23 Inverter 24 Feedback resistor 26 Coupling element 28 Common-Drain Amplifier Circuit

Claims

1. A vibrator and an oscillation inverter that amplifies a signal output from the oscillator; a drain-grounded amplifier circuit connected in series with the oscillation inverter; An oscillator comprising:

2. The oscillation inverter is an inverter having an output connected to an input of the drain-grounded amplifier circuit; and a feedback resistor of the inverter; One end of the vibrator is connected to the input of the inverter, and the other end of the vibrator is connected to the output of the drain-grounded amplifier circuit.

2. The oscillator of claim 1.

3. The inverter is a CMOS inverter.

3. The oscillator according to claim 2.

4. The oscillator further includes a coupling element connected between the oscillation inverter and the drain-grounded amplifier circuit.

2. The oscillator of claim 1.

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