JP2022131314A - Oscillation circuit and electronic apparatus - Google Patents

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

The present invention relates to an oscillator circuit using a vibrator.

In recent years, mobile phones and IoT (Internet-Of-Things) devices, in which all kinds of things are connected to the Internet, have been required to extend the battery life of small electronic devices with cordless wireless circuits. It is an important technical issue to reduce the power consumption of the electronic circuits and electronic components used in such devices.

Inverter-based Pierce circuits using crystal oscillators, such as the one shown in FIG. It's been in use for decades. However, since a large voltage component for oscillation cannot be taken, there are technical problems such as a slow oscillation start-up time and a large power consumption for steady current flow.

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 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

Non-Patent Document 1 proposes a circuit shown in FIG. 10B in which a boost circuit is added to speed up the oscillation start-up time in order to overcome the problem that the oscillation start-up time is slow in the Pierce circuit. On the other hand, Non-Patent Document 2 proposes a circuit shown in FIG. 11B that is different from the Pierce circuit but is based on the source-follower-based Colpitts circuit shown in FIG. 11A and that can reduce the steady-state current during oscillation. .

If the advantages of the above two circuits, that is, the fast oscillation start-up time of the circuit of FIG. 10B and the reduction of the steady-state current during oscillation of FIG. However, there is a problem that it is difficult to incorporate one circuit into the other circuit because the base circuit formats are different.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an oscillator circuit capable of achieving both high-speed start-up and low current consumption.

An oscillation circuit of the present invention comprises a Pierce circuit and a Colpitts circuit that share an input part of an oscillator and an amplifier, and a switch connected between the output part of each amplifier of the Pierce circuit and the Colpitts circuit and ground, The switch is controlled so as to output the oscillation signal of the Pierce circuit during oscillation startup, and to output the oscillation signal of the Colpitts circuit during steady oscillation.

An oscillator circuit of the present invention comprises a Pierce circuit and a Colpitts circuit, wherein the first amplifier (A1) of the Pierce circuit and the second amplifier (A2) of the Colpitts circuit are input parts and a first switch (SW1) connected in parallel with the first oscillation capacitor (C1) and the first oscillation capacitor (C1) between the output of the first amplifier (A1) and ground. and a second switch (SW2) connected in parallel with the second oscillation capacitor (C2) and the second oscillation capacitor (C2) between the output of the second amplifier (A2) and ground a vibrator (X1) between the input and output of the first amplifier (A1); and a third oscillation capacitor (X1) between the input and output of the second amplifier (A2) C3), a first mode during oscillation startup in which the first switch (SW1) and the second switch (SW2) are in an open state and a closed state, respectively; 2 switches (SW2) are closed and opened, respectively.

In one configuration example of the oscillation circuit of the present invention, the vibrator is a langasite piezoelectric single crystal vibrator.

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

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

Further, in one configuration example of the oscillation circuit of the present invention, the first amplifier has a configuration in which a plurality of amplifier circuits are connected in cascade, and the first stage amplifier circuit of the plurality of amplifier circuits is a capacitive feedforward path. and the second amplifier is a source follower in which an NMOS transistor and a PMOS transistor are cascaded.

Further, an electronic device of the present invention includes the oscillation circuit described above.

According to the present invention, it is possible to provide an oscillation circuit capable of achieving both high-speed startup and low current consumption.

FIG. 1 is a diagram showing a configuration example of an oscillator circuit according to an embodiment of the present invention. FIG. 2A is a diagram for explaining the states of the switches when the oscillator circuit according to the embodiment of the present invention starts oscillating. FIG. 2B is a diagram for explaining the states of the switches during steady oscillation of the oscillation circuit according to the embodiment of the present invention. FIG. 3 is a general equivalent circuit of an oscillator using a piezoelectric vibrator. FIG. 4 shows an example of representative values of the equivalent circuit constants of the vibrator. FIG. 5 is a diagram showing an example of oscillation amplitude starting characteristics according to the embodiment of the present invention. FIG. 6 is a diagram showing an example of oscillation frequency start-up characteristics according to the embodiment of the present invention. FIG. 7 is a diagram showing phase noise characteristics of the oscillator circuit according to the embodiment of the present invention. FIG. 8 is a diagram showing oscillation characteristics when switching between the Pierce circuit and the Colpitts circuit according to the embodiment of the present invention. FIG. 9 is a diagram showing an outline of an oscillation detection circuit connected to the oscillation circuit according to the embodiment of the invention. FIG. 10A is a configuration example of a Pierce circuit. FIG. 10B is a specific example of a Pierce circuit with a boost circuit. FIG. 11A is a configuration example of a Colpitts circuit. FIG. 11B is a specific example of a source follower Colpitts circuit.

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 start-up time is relatively short. On the other hand, the source-follower-based Colpitts circuit has the advantage of relatively low current consumption in steady state oscillation. In the oscillator circuit according to the embodiment of the present invention, both of the circuit types described above are combined, and by switching the circuit that outputs the oscillation signal during oscillation startup and steady oscillation, both high-speed startup and low current consumption are achieved. do.

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 the present embodiment is an oscillator circuit composed of a Pierce circuit 2, a Colpitts circuit 3, and switches connected to the output portions of each circuit. The Pierce circuit 2 and the Colpitts circuit 3 are configured to share an oscillator and share the input of each amplifier. The outputs of the amplifiers of the Pierce circuit 2 and the Colpitts circuit 3 are each provided with two switches connected to ground. These two switches are controlled so as 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 at the time of steady oscillation.

More specifically, the input section of each amplifier (first amplifier A1, second amplifier A2) of the Pierce circuit 2 and the Colpitts circuit 3 is shared, and the output sections of the first amplifier A1 and the second amplifier A2 are shared. and ground, the oscillation capacitors (first oscillation capacitor C1, second oscillation capacitor C2) and the switches (first switch SW1, second switch SW2) connected in parallel with the oscillation capacitors (C1, C2) , an oscillator X1 is provided between the input and output of the first amplifier A1, and an oscillation capacitor C3 (third oscillation capacitor) is provided between the input and output of the second amplifier A2.

2A and 2B are diagrams for explaining the states of the switches when the oscillation circuit starts to oscillate and when it oscillates steadily. Applying two operation modes in which SW1 and SW2 are in an open state and a closed state when oscillation is started, and SW1 and SW2 are in a closed state and an open state when steady oscillation is applied, and causes the Pierce circuit 2 to perform an oscillation operation when oscillation is started, The Colpitts circuit 3 is caused to oscillate during steady-state oscillation. By adopting a configuration in which the operation mode is switched between oscillation start-up and steady-state oscillation, it is possible to realize an oscillation circuit that achieves both high-speed start-up and low current consumption.

Here, as the Pierce circuit, a circuit having a boost circuit in which a plurality of amplifier circuits for increasing the oscillation starting capability are cascaded as shown in FIG. 10B is applied, and as the Colpitts circuit, as shown in FIG. A circuit that further reduces current consumption in a steady oscillation state may be applied.

In FIG. 10B, the amplifier A1 of the Pierce circuit has a configuration in which three stages of amplifier circuits (gm1 to gm3) are cascaded, and the first and second stage amplifier circuits (gm1, gm2) are boost circuits. . The first-stage amplifier circuit gm1 further includes a capacitance feedforward path with a capacitance Cf. In FIG. 11B, the amplifier A2 of the Colpitts circuit is a source-follower Colpitts circuit in which an NMOS transistor T1 and a PMOS transistor T2 are cascaded. The number of stages of the amplifier circuit of the amplifier A1 of the Pierce circuit is not limited to three stages illustrated in FIG. 10B.

_In general, a crystal oscillator _{( Quartz} ) is often used for the oscillator _X1 . may apply. FIG. 3 is a general equivalent circuit of an oscillator using a piezoelectric vibrator. The right diagram of FIG. 3 is an equivalent circuit diagram in which the left diagram is simplified. 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, it is necessary to generate a negative resistance RN on the oscillation circuit side that cancels out the series equivalent resistance _Rx on the _vibrator side. can be shortened.

FIG. 4 shows representative values of the equivalent circuit constants of the vibrator. A larger negative resistance _RN can be obtained with less power consumption by configuring the amplifier A1 of the Pierce circuit in three cascaded stages and providing a capacitive feedforward path. Furthermore, by applying the Langasite oscillator CTGS as the oscillator of the oscillation circuit 1, the series equivalent inductance Lm is about one order smaller than that of the crystal oscillator, so that the oscillation start-up time can be shortened by one order of magnitude.

5 and 6 are examples of oscillation amplitude start-up characteristics and oscillation frequency start-up characteristics according to the embodiment of the present invention. In the configuration example of FIG. 1, a circuit having a boost circuit shown in FIG. 10B is applied to the Pierce circuit, and a source follower in which an NMOS transistor and a PMOS transistor are cascaded shown in FIG. This is the characteristic when the Langasite oscillator CTGS is applied to .

In order to show the features of each circuit, the graphs in FIGS. 5 and 6 show the characteristics of only the Pierce circuit, which starts oscillation quickly, and the characteristics of the source follower-type Colpitts circuit, which has a small steady-state current during oscillation, respectively. The numerical values in FIG. 5 are the time required for the oscillation amplitude in the Pierce circuit to reach a predetermined steady-state value, and the numerical values in FIG. is the value of the oscillation frequency when

As shown in FIGS. 5 and 6, the oscillation start-up time is about 10 μsec for both amplitude and frequency, which is about 1/50 of the general start-up time using a crystal oscillator. Also, by using the source-follower Colpitts circuit of FIG. 11B, the steady-state current during oscillation can be reduced as compared with the conventional Colpitts circuit. For example, in Non-Patent Document 2, the steady-state current during oscillation can be suppressed to about one-fifth of that in the conventional Colpitts circuit.

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

Regarding the timing of transition from the Pierce circuit for starting oscillation to the Colpitts circuit for steady oscillation, that is, the switching timing of the switches (SW1, SW2), in order to smooth the transition of the oscillation frequency, the amplitude at the start of oscillation of the Pierce circuit is stabilized to some extent, and it is necessary to take advantage of the speed of oscillation start-up, which is a feature of the Pierce circuit. For example, the timing of reaching 70% to 95% of the final convergence amplitude is the optimum switch switching timing.

FIG. 8 is a diagram showing the oscillation characteristics when switching between the Pierce circuit and the Colpitts circuit in the oscillation circuit 1. In FIG. At the time when the oscillation startup amplitude of the Pierce circuit reaches 70% to 95% of the final convergence amplitude, a stable natural frequency oscillation is generated in the oscillator X1 of the Pierce circuit, so the Colpitts circuit alone is slow to start. In this case, by sharing the Pierce circuit and the vibrator X1, which oscillates at a stable natural frequency, the oscillating state is maintained as it is, and the oscillating frequency shifts smoothly.

One of the switching conditions 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. Actually, in the oscillation amplitude at the time of switching, since the form of the oscillation circuit 1 is changed, a difference in amplitude occurs. If there is, there will be no problem in actual use. On the other hand, there is a problem that the frequency fluctuation at the time of switching is directly output 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.

A 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 after the oscillation circuit 1. In this oscillation detection circuit 4, when the oscillation amplitude of the oscillation signal Vxo1 of the Pierce circuit exceeds a predetermined reference value, a control signal is generated. The control signal output from the oscillation detection circuit 4 can be used as a trigger signal for switching the switches (SW1, SW2).

The oscillation detection circuit 4 switches the switches (SW1, SW2) in accordance with the oscillation amplitude of the oscillation signal Vxo1 of the Pierce circuit, thereby switching the oscillation signal Vxo1 of the Colpitts circuit from the first mode of outputting the oscillation signal Vxo1 of the Pierce circuit. It is configured to switch to a second mode for outputting the oscillation signal Vxo2. The switching condition that the oscillation amplitude of the Pierce circuit is 70% to 95% of the final convergence amplitude is an example, and in the oscillation detection circuit 4, the switching condition can be appropriately determined according to various conditions of the electronic equipment etc. to which it is applied. can. For example, the switching conditions can be determined in consideration of the above-described equivalent capacitances before and after switching as seen from the vibrator.

As described above, according to the present embodiment, it is possible to realize an oscillation circuit that achieves both high-speed start-up and low current consumption. By applying the oscillation circuit of this embodiment to electronic devices such as mobile phones and IoT devices, for example, it is possible to contribute to low power consumption of electronic devices.

INDUSTRIAL APPLICABILITY The present invention can be applied to oscillator circuits used in small electronic devices.

1 Oscillation circuit 2 Pierce circuit 3 Colpitts circuit 4 Oscillation detection circuit A1, A2 Amplifier C1, C2, C3 Oscillation capacitor SW1, SW2 Switch X1 Vibrator.

Claims (7)

Equipped with a Pierce circuit and a Colpitts circuit that share the input part of the oscillator and the amplifier,
a switch connected between the output of each amplifier of the Pierce circuit and the Colpitts circuit and ground;
The switch is controlled to output the oscillation signal of the Pierce circuit during oscillation startup, and to output the oscillation signal of the Colpitts circuit during steady oscillation. An oscillation 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;
A first oscillation capacitor (C1) and a first switch (SW1) connected in parallel with the first oscillation capacitor (C1) are provided between the output of the first amplifier (A1) and ground,
A second switch (SW2) connected in parallel with a second oscillation capacitor (C2) and the second oscillation capacitor (C2) is provided between the output of the second amplifier (A2) and ground,
An oscillator (X1) is provided between the input section and the output section of the first amplifier (A1),
A third oscillation capacitor (C3) is provided between the input section and the output section of the second amplifier (A2),
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; An oscillation circuit configured to perform an oscillation operation in a second mode during steady oscillation in which SW2) is closed and opened, respectively. 3. The oscillator circuit according to claim 2,
An oscillation circuit, wherein the vibrator is a vibrator using a langasite-type piezoelectric single crystal. 4. In the oscillator circuit according to claim 2 or 3,
wherein switching from the first mode to the second mode is performed when the oscillation amplitude at the start of oscillation of the Pierce circuit reaches 70% to 95% of the final convergence amplitude. . 5. The oscillator circuit according to claim 4,
The 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. oscillator circuit. The oscillator circuit according to any one of claims 2 to 5,
The first amplifier has a configuration in which a plurality of amplifier circuits are cascaded, and a first-stage amplifier circuit of the plurality of amplifier circuits has a capacitive feedforward path,
The oscillator circuit, wherein the second amplifier is a source follower in which an NMOS transistor and a PMOS transistor are cascaded. An electronic device comprising the oscillation circuit according to any one of claims 1 to 6.

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