Oscillator circuit and electronic device

Abstract

To provide an oscillation circuit capable of satisfying both of high-speed starting and low current consumption.SOLUTION: An oscillation circuit (1) includes a pierce circuit (2) and a Colpitts circuit (3) sharing input parts of an oscillator (X1) and amplifiers (A1, A2). Switches (SW1, SW2) connected between output parts of amplifiers (A1, A2) of each of the pierce circuit (2) and the Colpitts circuit (3) and the ground are controlled to output an oscillation signal of the pierce circuit (2) at oscillation starting and to control an oscillation signal of the Colpitts circuit (3) at steady oscillation.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an oscillator circuit using a resonator. [Background technology]

[0002] In recent years, there has been a demand for longer battery life in small cordless electronic devices with wireless circuits, such as mobile phones and Internet-Of-Things (IoT) devices in which all things are connected to the Internet. As a result, reducing the power consumption of the electronic circuits and electronic components used in these devices has become an important technological issue.

[0003] Conventionally, inverter-based Pierce circuits using quartz crystal resonators as shown in Figure 10A have been widely used in oscillator circuits for small IoT communication devices, and have been used for many decades due to their simple circuit configuration. However, they have technical issues in that they require a long oscillation startup time because the voltage component required for oscillation cannot be large, and they consume a lot of power to constantly pass current. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Masaya Miyahara, Yukiya Endo, Kenichi Okada, and Akira Matsuzawa, “A 64μs Start-Up 26 / 40 MHz Crystal Oscillator with Negative Resistance Boosting Technique Using Reconfigurable Multi-Stage Amplifier”, Proc. IEEE Symp. VLSI Circuits, 2018 [Non-Patent Document 2] Zule Xu, Noritoshi Kimura, Kenichi Okada, and Masaya Miyahara, “Ultralow-Power Class-C Complementary Colpitts Crystal Oscillator”, IEEE Journal of Solid-State Circuits, Letters, VOL. 3, 2020 Summary of the Invention [Problem to be solved by the invention]

[0005] In Non-Patent Document 1, in order to overcome the problem of the slow oscillation startup time in the Pierce circuit, a circuit shown in Fig. 10B is proposed in which a boost circuit is added to speed up the oscillation startup time. Meanwhile, Non-Patent Document 2 proposes a circuit shown in Fig. 11B, which is different from the Pierce circuit but is modeled after the source-follower-based Colpitts circuit shown in Fig. 11A and can reduce the steady-state current during oscillation.

[0006] If it were possible to combine the advantages of the above two circuits, that is, the fast oscillation startup time of the circuit in Fig. 10B and the reduction of the steady-state current during oscillation of Fig. 11B, it would be possible to achieve even lower power consumption than the Pierce circuit. However, since the base circuit formats are different, it is difficult to incorporate one circuit into the other.

[0007] The present invention has been made in order to solve the above-mentioned problems, and has an object to provide an oscillation circuit that is capable of achieving both fast startup and low current consumption. [Means for solving the problem]

[0008] The oscillator circuit of the present invention comprises a Pierce circuit and a Colpitts circuit which share the input of an amplifier with an oscillator, and a switch connected between the output of the amplifier of each of the Pierce circuit and the Colpitts circuit and ground, the switch being controlled to output an oscillation signal of the Pierce circuit at the start of oscillation, and to output an oscillation signal of the Colpitts circuit during steady-state oscillation.

[0009] The oscillation circuit of the present invention is an oscillation circuit composed of a Pierce circuit and a Colpitts circuit, in which a first amplifier (A1) of the Pierce circuit and a second amplifier (A2) of the Colpitts circuit share an input section, and includes a first oscillation capacitance (C1) and a first switch (SW1) connected in parallel with the first oscillation capacitance (C1) between the output section of the first amplifier (A1) and ground, and a second oscillation capacitance (C2) and a second switch (SW2) connected in parallel with the second oscillation capacitance (C2) between the output section of the second amplifier (A2) and ground. The amplifier is provided with a second switch (SW2), a vibrator (X1) between the input and output of the first amplifier (A1), and a third oscillation capacitance (C3) between the input and output of the second amplifier (A2). The amplifier is configured to perform oscillation operations in a first mode at the start of oscillation in which the first switch (SW1) and the second switch (SW2) are in an open state and a closed state, respectively, and in a second mode during steady-state oscillation in which the first switch (SW1) and the second switch (SW2) are in a closed state and an open state, respectively.

[0010] In one configuration example of the oscillator circuit of the present invention, the vibrator is a Langasite type piezoelectric single crystal vibrator.

[0011] In addition, in one configuration example of the oscillation circuit of the present invention, when the oscillation amplitude at the start of oscillation of the Pierce circuit reaches 70% to 95% of the final convergence amplitude, the first mode is switched to the second mode.

[0012] In addition, in one configuration example of the oscillator circuit of the present invention, switching from the first mode to the second mode is performed based on a control signal from an oscillation detection circuit that compares the oscillation amplitude of the Pierce circuit with a predetermined reference value.

[0013] In addition, in one configuration example of the oscillator circuit of the present invention, the first amplifier has a configuration in which a plurality of amplifier circuits are cascaded, a first-stage amplifier circuit of the plurality of amplifier circuits has a capacitive feedforward path, and the second amplifier is a source follower in which an NMOS transistor and a PMOS transistor are cascaded.

[0014] Moreover, an electronic device according to the present invention includes the above-mentioned oscillator circuit. Effect of the Invention

[0015] According to the present invention, it is possible to provide an oscillation circuit that can achieve both fast startup and low current consumption. [Brief description of the drawings]

[0016] [Figure 1] FIG. 1 is a diagram showing an example of the configuration of an oscillator circuit according to an embodiment of the present invention. [Figure 2A] FIG. 2A is a diagram for explaining the state of the switches at the start of oscillation of the oscillator circuit according to the embodiment of the present invention. [Figure 2B] FIG. 2B is a diagram for explaining the state of the switches during steady oscillation of the oscillator circuit according to the embodiment of the present invention. [Diagram 3] FIG. 3 shows a typical equivalent circuit of an oscillator that uses a piezoelectric vibrator. [Figure 4] FIG. 4 shows an example of representative values ​​of the equivalent circuit constants of a vibrator. [Diagram 5] FIG. 5 is a diagram showing an example of an oscillation amplitude startup characteristic according to an embodiment of the present invention. [Figure 6] FIG. 6 is a diagram showing an example of an oscillation frequency startup characteristic according to an embodiment of the present invention. [Figure 7]FIG. 7 is a diagram showing the phase noise characteristic of the oscillator circuit according to the embodiment of the present invention. [Figure 8] FIG. 8 is a diagram showing oscillation characteristics when a Pierce circuit and a Colpitts circuit are switched by a switch according to the embodiment of the present invention. [Figure 9] FIG. 9 is a diagram showing an outline of an oscillation detection circuit connected to an oscillation circuit according to an embodiment of the present invention. [Figure 10A] FIG. 10A shows an example of the configuration of a Pierce circuit. [Figure 10B] FIG. 10B is an example of a Pierce circuit with a boost circuit. [Figure 11A] FIG. 11A shows an example of the configuration of a Colpitts circuit. [Figure 11B] FIG. 11B is a specific example of a source-follower type Colpitts circuit. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] The Pierce circuit shown in FIG. 10B is inverter-based. On the other hand, the Colpitts circuit shown in FIG. 11B is source-follower-based. The Pierce circuit has the advantage that the current is large and the oscillation startup time is relatively fast. On the other hand, the source-follower-based Colpitts circuit has the advantage that the current consumption is relatively low in a steady oscillation state. In the oscillator circuit according to the embodiment of the present invention, both of the above-mentioned circuit formats are mixed and the circuit that outputs the oscillation signal is switched between oscillation startup and steady oscillation, thereby achieving both fast startup and low current consumption.

[0018] FIG. 1 is a diagram showing a configuration example of an oscillator circuit according to an embodiment of the present invention. The oscillator circuit 1 according to this embodiment is an oscillator circuit composed of a Pierce circuit 2, a Colpitts circuit 3, and a switch connected to the output part of each circuit. The Pierce circuit 2 and the Colpitts circuit 3 are configured to share a vibrator and to share the input part of each amplifier. The output part of each amplifier of the Pierce circuit 2 and the Colpitts circuit 3 is provided with two switches connected to ground. These two switches are controlled to output the oscillation signal of the Pierce circuit 2 at the start of oscillation and to output the oscillation signal of the Colpitts circuit 3 during steady oscillation.

[0019] More specifically, the input parts of the amplifiers (first amplifier A1, second amplifier A2) of the Pierce circuit 2 and the Colpitts circuit 3 are shared, and oscillation capacitances (first oscillation capacitance C1, second oscillation capacitance C2) are provided between the output parts of the first amplifier A1 and the second amplifier A2 and ground, and switches (first switch SW1, second switch SW2) connected in parallel to the oscillation capacitances (C1, C2), and a vibrator X1 is provided between the input / output of the first amplifier A1, and an oscillation capacitance C3 (third oscillation capacitance) is provided between the input / output of the second amplifier A2.

[0020] 2A and 2B are diagrams for explaining the switch states at the time of oscillation startup and steady oscillation of the oscillation circuit. Two operation modes are applied, where SW1 and SW2 are open and closed at oscillation startup, and SW1 and SW2 are closed and open at steady oscillation, respectively, and the oscillation operation is performed as the Pierce circuit 2 at oscillation startup, and as the Colpitts circuit 3 at steady oscillation. By configuring the operation mode to switch between oscillation startup and steady oscillation, it is possible to realize an oscillation circuit that achieves both fast startup and low current consumption.

[0021] Here, as the Pierce circuit, a circuit having a boost circuit in which a plurality of amplifier circuits are connected in cascade to enhance the oscillation startup capability as shown in FIG. 10B may be applied, and as the Colpitts circuit, a circuit that further reduces the current consumption in a steady oscillation state as shown in FIG. 11B may be applied.

[0022] In FIG. 10B, the amplifier A1 of the Pierce circuit has a configuration in which three amplifier circuits (gm1 to gm3) are cascade-connected, and the first and second amplifier circuits (gm1, gm2) are boost circuits. The first amplifier circuit gm1 further has a capacitive feed-forward path using a capacitance Cf. In FIG. 11B, the amplifier A2 of the Colpitts circuit is a source-follower type Colpitts circuit in which an NMOS transistor T1 and a PMOS transistor T2 are cascade-connected. The number of amplifier circuit stages of the amplifier A1 of the Pierce circuit is not limited to three stages as illustrated in FIG. 10B.

[0023] Generally, a quartz crystal unit (Quartz) is often used for the oscillator X1. However, the oscillator CTGS (Ca3TaGa3Si2O 14 ) may be applied. Figure 3 shows a typical equivalent circuit of an oscillator using a piezoelectric vibrator. The right diagram in Figure 3 is a simplified equivalent circuit diagram of the left diagram. The left side of the dotted line in the figure shows the equivalent circuit of the vibrator, and the right side shows the equivalent circuit of the oscillation circuit. In order to oscillate, a negative resistance R on the oscillation circuit side that cancels the series equivalent resistance Rx on the vibrator side is required. N It is necessary to generate a negative resistance R N By increasing the value of , the oscillation startup time can be shortened.

[0024] Figure 4 shows the representative values ​​of the equivalent circuit constants of the vibrator. The amplifier A1 of the Pierce circuit is configured with three cascaded amplifier circuits and is equipped with a capacitive feedforward path, which results in a large negative resistance R with low power consumption. N Furthermore, by using the Langasite-based resonator CTGS as the resonator of the oscillation circuit 1, the series equivalent inductance Lm is approximately one order of magnitude smaller than that of a quartz crystal resonator, so that the oscillation startup time can be shortened by one order of magnitude.

[0025] 5 and 6 are examples of oscillation amplitude startup characteristics and oscillation frequency startup characteristics according to an embodiment of the present invention. These characteristics are obtained when, in the configuration example of FIG. 1, a circuit having a boost circuit shown in FIG. 10B is applied to the Pierce circuit, a source follower in which an NMOS transistor and a PMOS transistor are cascaded as shown in FIG. 11B is applied to the source follower type Colpitts circuit, and a Langasite-based resonator CTGS is applied to the resonator X1.

[0026] To show the features of each circuit, the graphs in Figures 5 and 6 show only the characteristics of the Pierce circuit, which has a fast oscillation startup, and only the characteristics of the source-follower Colpitts circuit, which has a small steady-state current during oscillation. The values ​​in Figure 5 are the time it takes for the oscillation amplitude in the Pierce circuit to reach a specified steady-state value, and the values ​​in Figure 6 are the time it takes for the oscillation frequency in each circuit to stabilize at a specified value, and the value of the stable oscillation frequency.

[0027] As shown in Figures 5 and 6, the oscillation startup time is about 10 μsec for both amplitude and frequency, which is about 1 / 50 of the general startup time when using a quartz crystal oscillator. In addition, by using the source-follower type Colpitts circuit in Figure 11B, the steady-state current during oscillation can be reduced compared to a conventional Colpitts circuit. For example, in Non-Patent Document 2, the steady-state current during oscillation can be reduced to about 1 / 5 compared to a conventional Colpitts circuit.

[0028] In addition, by applying the source follower type Colpitts circuit of FIG. 11B instead of the Pierce circuit during steady oscillation, the phase noise characteristic of the oscillator circuit related to the code error rate of the communication device can be improved. FIG. 7 is a diagram showing the phase noise characteristic of the oscillator circuit according to the embodiment of the present invention. As shown in FIG. 7, the phase noise, which is an important oscillator circuit performance for communication devices, is improved by about 9 dB in the range of offset frequency to the fundamental frequency of the oscillator circuit up to 100 Hz, compared to the conventional Pierce oscillator circuit. In this way, by using the oscillator circuit of this embodiment, the phase noise characteristic during steady oscillation can be improved compared to the conventional Pierce oscillator circuit.

[0029] Regarding the timing of transition from the Pierce circuit for oscillation startup to the Colpitts circuit for steady-state oscillation, i.e., the switching timing of the switches (SW1, SW2), in order to make the transition of the oscillation frequency smooth, it is necessary to make use of the fast oscillation startup speed, which is a feature of the Pierce circuit, and stabilize the amplitude at the time of oscillation startup to a certain extent. For example, the optimal timing for switching the switch is when the amplitude reaches 70% to 95% of the final convergence amplitude.

[0030] 8 is a diagram showing the oscillation characteristics when a switch is used to switch between the Pierce circuit and the Colpitts circuit in the oscillation circuit 1. At the point when the amplitude at the start of oscillation of the Pierce circuit reaches 70% to 95% of the final convergence amplitude, a stable natural frequency vibration is generated in the oscillator X1 of the Pierce circuit, so that even in the Colpitts circuit, which starts slowly by itself, the oscillation state is maintained by sharing the oscillator X1 with the Pierce circuit, which has a stable natural frequency vibration, and the transition of the oscillation frequency is performed smoothly.

[0031] A switching condition for smoother transition of the oscillation frequency is that the equivalent capacitance seen from the vibrator X1 side is the same before and after switching. In reality, a step in the oscillation amplitude occurs at the time of switching because the type of the oscillator circuit 1 changes, but this does not cause a problem in practical use as long as the amplitude is above a certain level on the load side to which the oscillator circuit 1 of the present invention is connected. On the other hand, there is a problem that the frequency fluctuation at the time of switching is output directly to the load side. Therefore, in order to reduce the frequency fluctuation at the time of switching, it is important that the equivalent capacitance seen from the vibrator X1 is the same before and after switching.

[0032] The trigger signal for switching the switches (SW1, SW2) may be output from a circuit that monitors the oscillation amplitude of the Pierce circuit. For example, as shown in Fig. 9, an oscillation detection circuit 4 is provided in the subsequent stage of the oscillation circuit 1, and this oscillation detection circuit 4 is configured to output a control signal when the oscillation amplitude of the oscillation signal Vxo1 of the Pierce circuit becomes equal to or greater than a predetermined reference value, and the control signal output from the oscillation detection circuit 4 can be used as a trigger signal for switching the switches (SW1, SW2).

[0033] The oscillation detection circuit 4 is configured to switch from a first mode in which the oscillation signal Vxo1 of the Pierce circuit is output to a second mode in which the oscillation signal Vxo2 of the Colpitts circuit is output by switching the switches (SW1, SW2) according to the oscillation amplitude of the oscillation signal Vxo1 of the Pierce circuit. The switching condition in which the oscillation amplitude of the Pierce circuit is 70% to 95% of the final convergence amplitude is one example, and the oscillation detection circuit 4 can appropriately determine the switching condition according to various conditions in the electronic device to which it is applied. For example, the switching condition can also be determined in consideration of the equivalent capacitance before and after switching as seen from the vibrator as described above.

[0034] As described above, according to the present embodiment, it is possible to realize an oscillator circuit that achieves both fast startup and low current consumption. By applying the oscillator circuit of the present embodiment to electronic devices such as mobile phones and IoT devices, it is possible to contribute to reducing the power consumption of the electronic devices. [Industrial Applicability]

[0035] The present invention can be applied to an oscillator circuit used in a small electronic device. [Explanation of symbols]

[0036] 1...oscillator circuit, 2...Pierce circuit, 3...Colpitts circuit, 4...oscillator detection circuit, A1, A2...amplifiers, C1, C2, C3...oscillator capacitance, SW1, SW2...switches, X1...oscillator.

Claims

1. An oscillator circuit comprising a Pierce circuit and a Colpitts circuit, the first amplifier (A1) of the Pierce circuit and the second amplifier (A2) of the Colpitts circuit share an input section; a first oscillation capacitance (C1) and a first switch (SW1) connected in parallel with the first oscillation capacitance (C1) between an output part of the first amplifier (A1) and ground; a second oscillation capacitance (C2) and a second switch (SW2) connected in parallel with the second oscillation capacitance (C2) between an output of the second amplifier (A2) and ground; a transducer (X1) between the input section and the output section of the first amplifier (A1); a third oscillation capacitance (C3) between the input and the output of the second amplifier (A2); The oscillator is configured to perform an oscillation operation in a first mode at the start of oscillation in which the first switch (SW1) and the second switch (SW2) are in an open state and a closed state, respectively, and in a second mode during steady oscillation in which the first switch (SW1) and the second switch (SW2) are in a closed state and an open state, respectively. Oscillator circuit.

2. 2. The oscillator circuit according to claim 1, The vibrator is a vibrator using a Langasite type piezoelectric single crystal. An oscillator circuit comprising:

3. 3. The oscillator circuit according to claim 1, When the oscillation amplitude at the start of oscillation of the Pierce circuit reaches 70% to 95% of the final convergence amplitude, the first mode is switched to the second mode. An oscillator circuit comprising:

4. 4. The oscillator circuit according to claim 3, The switching from the first mode to the second mode is performed based on a control signal from an oscillation detection circuit which compares the oscillation amplitude of the Pierce circuit with a predetermined reference value. An oscillator circuit comprising:

5. 5. The oscillator circuit according to claim 1, The first amplifier has a configuration in which a plurality of amplifier circuits are connected in series, and a first stage amplifier circuit of the plurality of amplifier circuits has a capacitive feedforward path, The second amplifier is a source follower in which an NMOS transistor and a PMOS transistor are cascaded. An oscillator circuit comprising:

6. Equipped with an oscillator circuit according to any one of claims 1 to 5 An electronic device characterized by:

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