Oscillation circuit and electronic appliance

Abstract

To provide an oscillation circuit that facilitates high-speed start and high-frequency oscillation.SOLUTION: An oscillation circuit (1) according to the present invention includes a Colpitts oscillation circuit including an amplification circuit (A1) connected between a connection point between an oscillator (X1) and a first capacitor (CF) and a connection point between the first capacitor (CF) and a second capacitor (CO). The amplification circuit (A1) is a source follower in which an NMOS transistor and a PMOS transistor are cascade-connected. A differential amplification circuit (A2) that is inserted into an oscillation loop of the Colpitts oscillation circuit at least when the oscillation is started, and that includes a first input terminal and a second input terminal is provided. A feedback path (3) configured so that a part of the output of the Colpitts oscillation circuit is fed back to the second input terminal of the differential amplification circuit (A2) is also provided.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 mobile phones and Internet-of-Things (IoT) devices, in which all kinds of things are connected to the Internet, and reducing the power consumption of the electronic circuits and electronic components used in these devices has become an important technological challenge.

[0003] Conventionally, inverter-based Pierce circuits using a resonator as shown in Figure 9 have been widely used as reference oscillator circuits for use in small IoT communication devices, and are composed of an active element section built into an IC, fixed capacitors Ca1 and Ca2, and a resonator X1. This inverter-based Pierce circuit has a simple circuit configuration and is easy to use, but on the other hand, it has the issue of large power consumption due to the constant flow of current.

[0004] As a solution to the above problem, a source-follower-based Colpitts oscillator circuit in which MOS transistors are configured in a complementary manner was proposed in Patent Document 1. The configuration shown in Patent Document 1 has succeeded in reducing the current consumption in a steady state (oscillation state) by one order of magnitude compared to a conventional Pierce circuit. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 6967248 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the source-follower-based Colpitts circuit has the problem that the oscillation startup time is slower than that of a conventional Pierce circuit. In addition, when the oscillation frequency is high, a large negative resistance cannot be obtained, so the oscillation conditions are not satisfied and oscillation does not occur.

[0007] The present invention has been made to solve the above problems, and an object of the present invention is to provide an oscillation circuit that facilitates high-speed startup and high-frequency oscillation. [Means for solving the problem]

[0008] The oscillation circuit of the present invention comprises a Colpitts oscillation circuit including an amplifier circuit (A1) connected between a connection point between an oscillator (X1) and a first capacitance (CF) and a connection point between the first capacitance (CF) and a second capacitance (CO), the amplifier circuit (A1) being a source follower in which an NMOS transistor and a PMOS transistor are cascaded, and which is inserted into an oscillation loop of the Colpitts oscillation circuit at least at the start of oscillation, and which includes a differential amplifier circuit (A2) having a first input terminal and a second input terminal, and a feedback path configured such that a portion of the output of the Colpitts oscillation circuit is fed back to the second input terminal of the differential amplifier circuit (A2).

[0009] In addition, in one configuration example of the oscillator circuit of the present invention, the feedback path has a feedback amount adjustment function.

[0010] Moreover, in one configuration example of the oscillator circuit of the present invention, the first input terminal of the differential amplifier circuit (A2) is connected to a connection point between the vibrator (X1) and the first capacitance (CF), and the output terminal of the differential amplifier circuit (A2) is connected to an input terminal of the amplifier circuit (A1).

[0011] In addition, in one configuration example of the oscillation circuit of the present invention, at the time of oscillation startup, a first mode oscillation operation is performed in which the differential amplifier circuit (A2) is operated, and during steady-state oscillation, a second mode oscillation operation is performed in which the operation of the differential amplifier circuit (A2) is stopped.

[0012] In one embodiment of the present invention, the oscillator circuit further comprises a detection circuit for detecting an oscillation amplitude of the oscillator circuit, The detection circuit is configured to switch from the first mode to the second mode when the oscillation amplitude at oscillation startup reaches 70% to 95% of a final convergence amplitude.

[0013] Moreover, an electronic device according to the present invention includes the above-mentioned oscillator circuit. Effect of the Invention

[0014] According to the present invention, it is possible to provide an oscillation circuit that facilitates high-speed startup and high-frequency oscillation. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a diagram showing an example of the configuration of an oscillator circuit according to a first embodiment of the present invention. [Diagram 2] FIG. 2 is a diagram showing a configuration example of an equivalent circuit of a vibrator and an oscillation circuit. [Diagram 3] FIG. 3 is a diagram showing frequency characteristics of the negative resistance of a Colpitts oscillator circuit. [Figure 4] FIG. 4 is a diagram showing frequency characteristics of the negative resistance according to the first embodiment of the present invention. [Diagram 5] FIG. 5 is a diagram showing frequency characteristics of the negative resistance according to the first embodiment of the present invention. [Figure 6] FIG. 6 is a diagram showing an example of the configuration of a feedback adjustment circuit in the oscillator circuit of the present invention. [Figure 7] FIG. 7 is a diagram showing an example of the configuration of an oscillator circuit according to the second embodiment of the present invention. [Figure 8] FIG. 8 is a diagram showing an example of an oscillation amplitude startup characteristic according to the second embodiment of the present invention. [Figure 9] FIG. 9 is a diagram showing another configuration example of the oscillator circuit according to the second embodiment of the present invention. [Figure 10] FIG. 10 is a diagram showing an example of the configuration of a switch in the oscillator circuit of the present invention. [Figure 11] FIG. 11 shows an example of the configuration of an oscillator circuit using a conventional Pierce circuit. [Figure 12] FIG. 12 shows an example of the configuration of a conventional oscillator circuit that switches between a Pierce circuit and a Colpitts circuit. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] <First embodiment> 1 is a diagram showing a configuration example of an oscillation circuit according to a first embodiment of the present invention. The oscillation circuit according to this embodiment includes a Colpitts oscillation circuit including an amplifier circuit (A1) connected between a connection point between a resonator (X1) and a first capacitance (CF) and a connection point between the first capacitance (CF) and a second capacitance (CO), a differential amplifier circuit (A2) having a first input terminal and a second input terminal, and a feedback path 3 configured such that a part of the output of the Colpitts oscillation circuit is fed back to the second input terminal of the differential amplifier circuit (A2).

[0017] The amplifier circuit (A1) in the configuration example of Figure 1 is a complementary source follower. For example, the amplifier circuit (A1) can be configured as a source follower in which an NMOS transistor and a PMOS transistor are cascade-connected. A feedback amount adjustment circuit 2 is installed in the feedback path 3, and is configured to adjust the amount of feedback.

[0018] In the configuration example of Fig. 1, the differential amplifier circuit (A2) is inserted in the front stage of the amplifier circuit (A1) in the oscillation loop of the Colpitts oscillation circuit, but the position where the differential amplifier circuit (A2) is inserted is not limited to the configuration of Fig. 1. It is sufficient that the differential amplifier circuit (A2) maintains the phase condition maintained by the Colpitts oscillation circuit. For example, the differential amplifier circuit (A2) may be inserted in the rear stage of the amplifier circuit (A1), or in the front stage or rear stage of the oscillation capacitance (CF) in the oscillation loop.

[0019] Figure 2(a) shows the equivalent circuit of a vibrator. The equivalent circuit of the vibrator (X1) consists of the equivalent series resistance (Rm), equivalent series capacitance (Cm), equivalent series inductance (Lm), and equivalent parallel capacitance (Cp). Figure 2(b) shows a typical equivalent circuit of an oscillator circuit using a piezoelectric vibrator. The left side of the dotted line in Figure 2(b) shows the equivalent circuit of the vibrator, and the right side shows the equivalent circuit of the oscillator circuit. Rx is the equivalent series resistance under load on the vibrator side, the load capacitance (CL) is the equivalent series capacitance (Rn) on the oscillator circuit side as seen from the vibrator side, and is the negative resistance of the oscillator circuit.

[0020] In order to oscillate, it is necessary to generate a negative resistance (Rn) on the oscillator circuit side that cancels out the series equivalent resistance (Rx) on the vibrator side, and by making the value of the negative resistance (Rn) larger, the oscillation startup time can be shortened.

[0021] In this embodiment, a differential amplifier circuit (A2) is inserted in series into the oscillation loop of the Colpitts oscillation circuit. One of the input terminals of the differential amplifier circuit (A2) is directly connected to the oscillation loop, and a part of the output of the Colpitts oscillation circuit is fed back to the other of the second input terminals of the differential amplifier circuit (A2).

[0022] In one path of the input terminal, the differential amplifier circuit (A2) needs to maintain the phase condition maintained by the original oscillation loop, so the input / output phase difference of the differential amplifier circuit (A2) is zero. In the other path of the input terminal, by adjusting the amount of feedback, it is possible to add a phase rotation according to the amount of feedback to the differential amplifier circuit (A2). As a result, it is possible to change the frequency characteristic of the negative resistance.

[0023] Figures 3 to 5 are graphs showing the frequency characteristics of negative resistance when the equivalent capacitance (CL) on the circuit side seen from the resonator (X1) is changed. The smaller the equivalent capacitance (CL), the easier it is to obtain a large negative resistance on the high frequency side. Therefore, if you want to facilitate high frequency oscillation, you can increase the amount of feedback under conditions where the load capacitance is reduced. When the amount of feedback is small (K = 11 / 16), the frequency characteristics are as shown in Figure 4, and when the amount of feedback is large (K = 14 / 16), the frequency characteristics are as shown in Figure 5; the smaller the amount of feedback, the more geared towards low frequencies.

[0024] Comparing the negative resistance when the differential amplifier circuit (A2) is turned off and only the Colpitts oscillator circuit is used (Fig. 3) with the negative resistance when the differential amplifier circuit is turned on (Figs. 4 and 5), it was possible to obtain a negative resistance approximately 10 times higher at 50 MHz. Furthermore, a negative resistance of 200 Ω was obtained at 100 MHz, making it possible to oscillate with the Colpitts oscillator circuit even at that frequency.

[0025] By applying the present invention, it is possible to increase the negative resistance of the oscillator circuit or change the frequency characteristics of the negative resistance, thereby realizing an oscillator circuit that allows for greater design freedom for fast startup and high-frequency oscillation.

[0026] In addition, in the conventional oscillator circuit of FIG. 11, the frequency characteristics of the negative resistance can be changed by changing the oscillation capacitance. However, according to this embodiment, it is possible to realize an oscillator circuit with a high degree of design freedom while facilitating fast startup and high frequency oscillation compared to the conventional configuration.

[0027] Fig. 6 is a diagram showing an example of the configuration of a feedback adjustment circuit in an oscillator circuit of the present invention. In Fig. 6(a), a feedback signal is input from a terminal (VINN) of a differential amplifier circuit. The differential amplifier circuit has a differential pair of transistors (a transistor pair with VINN and VINP as input terminals) configured in parallel, for example, with 16 of each, and when reducing the amount of feedback, the number of operating transistors on the VINN side is reduced from 16. Specifically, the number of operating transistors can be reduced and the amount of feedback adjusted by switching the transistor gate from the signal side to the GND side with a switch or the like to turn off the transistor.

[0028] In Fig. 6(a), the number of operating transistors is controlled to adjust the amount of feedback, but in Fig. 6(b), the amount of feedback is controlled by a resistor voltage divider placed in front of the transistor without controlling the number of operating transistors. The amount of feedback can also be controlled by replacing the resistor with a capacitor using the same voltage division concept.

[0029] <Second embodiment> 1 of the first embodiment, the differential amplifier circuit (A2) operates not only during oscillation startup but also during steady oscillation, which is useful when the amplifier circuit (A1) alone does not have enough negative resistance to maintain steady oscillation. On the other hand, there is a problem that the oscillation noise characteristics deteriorate and current consumption increases when the differential amplifier circuit (A2) continues to operate even during steady oscillation.

[0030] Fig. 7 is a diagram showing a configuration example of an oscillator circuit according to a second embodiment of the present invention. The feature of this embodiment is that the oscillator circuit of Fig. 1 of the first embodiment is configured such that the differential amplifier circuit is operated only at the time of oscillation startup and the operation of the differential amplifier circuit is stopped during steady oscillation.

[0031] In the configuration example of FIG. 7, the oscillator is configured to switch between a first mode of oscillation operation in which the differential amplifier circuit (A2) is operated at oscillation startup and a second mode of oscillation operation in which the operation of the differential amplifier circuit (A2) is stopped during steady oscillation.

[0032] Conventionally, an oscillation circuit has been proposed that switches between two oscillation circuits during oscillation startup and steady oscillation, as shown in FIG. 12 (see, for example, JP 2022-131314 A). The oscillation circuit in FIG. 12 is configured to operate the Colpitts oscillation circuit during steady oscillation and to use an inverter-based Pierce circuit only during oscillation startup. The Colpitts circuit has a problem that the oscillation startup time is slower than that of the Pierce circuit, and by using the Pierce circuit during oscillation startup, both high-speed startup and low power consumption are achieved.

[0033] The problem with the configuration in Figure 12 is that discontinuities in the output voltage amplitude and oscillation frequency are likely to occur when switching the oscillation circuit. The cause of discontinuities in the output voltage amplitude is that the inverter-based Pierce oscillation circuit that oscillates at startup is likely to saturate at a low oscillation amplitude.

[0034] The cause of the discontinuity in the oscillation frequency is that only one of the three oscillation capacitors in the oscillation circuit in Figure 12 is used in common during oscillation startup and steady oscillation. It is not impossible to adjust this discontinuity in the oscillation frequency, but it requires a lot of man-hours, which makes it difficult to produce a low-cost product.

[0035] In the second embodiment, the circuit that operates at the start of oscillation of the oscillation circuit is changed from an inverter-based Pierce circuit to a differential amplifier circuit (A2) with feedback control. By using the differential amplifier circuit (A2) at the start of oscillation, it is possible to eliminate discontinuities that occur in the output voltage amplitude and oscillation frequency, which were problems in the oscillation circuit of FIG.

[0036] 7, the circuit switches between a first mode oscillation operation in which the differential amplifier circuit (A2) is operated at the time of oscillation startup and a second mode oscillation operation in which the differential amplifier circuit (A2) is stopped at the time of steady oscillation. To this end, the circuit is provided with a switch (SW1) for bypassing the differential amplifier circuit (A2) and connecting the input and output of the differential amplifier circuit (A2) at the time of steady oscillation, and an ON / OFF input terminal for operating the differential amplifier circuit (A2) at the time of oscillation startup and stopping the differential amplifier circuit (A2) at the time of steady oscillation.

[0037] In the configuration of Fig. 12, only one of the three oscillation capacitances is used in common during oscillation startup and steady oscillation, so discontinuity in the oscillation frequency was likely to occur before and after switching. On the other hand, the oscillation circuit used in this embodiment is a single source-follower-based Colpitts oscillation circuit both during oscillation startup and steady oscillation, and is configured to operate the differential amplifier circuit (A2) inserted in the oscillation loop only during oscillation startup. With this configuration, the oscillation capacitance used before and after switching does not change, so it is possible to reduce discontinuity in the oscillation frequency before and after switching.

[0038] Fig. 8 is a diagram showing an example of the oscillation amplitude start-up characteristic according to the embodiment of the present invention. As shown in the upper part of Fig. 8, the inverter-based Pierce oscillation circuit used at the start-up of the oscillation circuit of Fig. 12 is prone to saturation at a stage where the oscillation amplitude is small, so that the oscillation growth has an amplitude step from start-up to steady oscillation.

[0039] In this embodiment, by using a differential amplifier circuit (A2) at the start of oscillation, as shown in the lower part of FIG. 8, it is possible to eliminate the discontinuity in output voltage amplitude that is a problem in the oscillation circuit of FIG.

[0040] Regarding the timing of transition from oscillation startup to the Colpitts circuit during steady oscillation, that is, the timing of switching the switch (SW1) and turning off the differential amplifier (A2), in order to smooth the transition of the oscillation frequency, it is necessary to switch the switch at a stage where the oscillation amplitude at the oscillation startup has stabilized to a certain extent. For example, the optimal timing for switching the switch is when it has reached 70% to 95% of the final convergence amplitude.

[0041] The trigger signal for switching the switch (SW1) may be output from a circuit that monitors the oscillation amplitude of the oscillation circuit 1. For example, as shown in Fig. 9, an oscillation amplitude detection circuit 4 is provided downstream of the oscillation circuit 1, and this oscillation amplitude detection circuit 4 is configured to output a control signal when the oscillation amplitude of the oscillation signal Vo of the Colpitts circuit becomes equal to or exceeds a predetermined reference value. This allows the control signal output from the oscillation amplitude detection circuit 4 to be used as a trigger signal for switching the switch (SW1) and turning the differential amplifier (A2) ON / OFF.

[0042] The oscillation amplitude detection circuit 4 is configured to switch from a first mode in which the differential amplifier circuit (A2) is operated to a second mode in which the differential amplifier circuit is turned OFF by turning on / off the switch (SW1) and the differential amplifier circuit (A2) based on the oscillation amplitude of the oscillation signal Vo of the oscillation circuit. The switching condition in which the oscillation amplitude of the oscillation circuit is 70% to 95% of the final convergence amplitude is one example, and the oscillation amplitude detection circuit 4 can appropriately determine the switching condition according to various conditions in the electronic device to which it is applied.

[0043] The configuration of the switch that switches from the first mode in which the differential amplifier circuit (A2) is operated to the second mode in which the differential amplifier circuit is turned OFF is not limited to those exemplified in FIGS.

[0044] Fig. 10 is a diagram showing an example of the configuration of a switch in an oscillator circuit of the present invention. In the example of the configuration in Fig. 10, SW1 is a switch that switches the signal input to amplifier circuit A1, which is a complementary source follower. When the control signal is "High", SW1 connects the output terminal of the differential amplifier circuit (A2) to the input terminal of the amplifier circuit (A1). Conversely, when the control signal is "Low", SW1 connects one of the input terminals of the differential amplifier circuit (A2) to the input terminal of the amplifier circuit A1.

[0045] SW2 in Figure 10 is a switch that controls the ON / OFF of the differential amplifier (A2). The output of SW2 is connected to the current source control terminal of the differential amplifier circuit (A2). When the control signal is "High", SW2 selects a bias (VBN) sufficient to operate the differential amplifier circuit (A2). Conversely, when the control signal is "Low", SW2 selects a bias (VSS) that turns the differential amplifier circuit (A2) OFF.

[0046] The oscillator circuit used in this embodiment is only a source follower-based Colpitts oscillator circuit both at the time of oscillation startup and during steady-state oscillation. The source follower-based Colpitts oscillator circuit has the advantage that it can be used with low current consumption and low noise.

[0047] In this embodiment, in order to utilize the characteristics of the source follower-based Colpitts oscillator circuit, the differential amplifier circuit is operated at the time of oscillation startup to increase the negative resistance, thereby shortening the oscillation startup time and enabling high frequency oscillation. On the other hand, during steady oscillation, the differential amplifier circuit is stopped and the value of the negative resistance is set to a relatively low value that can maintain steady oscillation, thereby making it possible to configure the current consumption to be relatively low.

[0048] At oscillation startup, current consumption increases compared to steady-state oscillation due to the amount of operation of the differential amplifier circuit, but due to the effect of shortening the startup time, power consumption can be reduced in the same way as in the oscillation circuit of FIG.

[0049] As described above, according to the present embodiment, it is possible to realize an oscillator circuit that facilitates high-speed startup and high-frequency oscillation. 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]

[0050] The present invention can be applied to an oscillator circuit used in a small electronic device. [Explanation of symbols]

[0051] 1...oscillator circuit, 2...feedback adjustment circuit, 3...feedback path, A1...amplifier circuit, A2...differential amplifier circuit, X1...resonator, CF,CO...oscillator capacitance.

Claims

1. a Colpitts oscillation circuit including an amplifier circuit (A1) connected between a connection point between an oscillator (X1) and a first capacitance (CF) and a connection point between the first capacitance (CF) and a second capacitance (CO); The amplifier circuit (A1) is a source follower in which an NMOS transistor and a PMOS transistor are cascaded, a differential amplifier circuit (A2) that is inserted in an oscillation loop of the Colpitts oscillation circuit at least during oscillation startup and has a first input terminal and a second input terminal; a feedback path configured so that a portion of the output of the Colpitts oscillator circuit is fed back to the second input terminal of the differential amplifier circuit (A2); Oscillator circuit.

2. The feedback path has a feedback amount adjustment function.

2. The oscillator circuit according to claim 1 .

3. the first input terminal of the differential amplifier circuit (A2) is connected to a connection point between the vibrator (X1) and the first capacitance (CF); The output terminal of the differential amplifier circuit (A2) is connected to the input terminal of the amplifier circuit (A1).

2. The oscillator circuit according to claim 1 .

4. A first mode oscillation operation is performed in which the differential amplifier circuit (A2) is operated at the time of oscillation startup, and a second mode oscillation operation is performed in which the operation of the differential amplifier circuit (A2) is stopped at the time of steady oscillation.

2. The oscillator circuit according to claim 1 .

5. a detection circuit for detecting an oscillation amplitude of the oscillation circuit; The detection circuit is configured to switch from the first mode to the second mode when the oscillation amplitude at the time of oscillation startup reaches 70% to 95% of the final convergence amplitude.

5. The oscillator circuit according to claim 4,

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

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