Crystal oscillator and crystal oscillator startup method

Abstract

The present invention relates to a crystal oscillator and a startup operation method of a crystal oscillator, the crystal oscillator comprising: a crystal resonator comprising a first terminal and a second terminal, an electronic oscillator circuit connected to the crystal resonator, a first capacitor comprising a first terminal and a second terminal, the second terminal being connected to the first terminal of the crystal resonator, a second capacitor comprising a first terminal and a second terminal, the second terminal being connected to the second terminal of the crystal resonator, characterized in that the crystal oscillator further comprises a switch comprising a first terminal, a second terminal and a third terminal, wherein the conductivity between the first terminal and the second terminal of the switch is controlled by the voltage at the third terminal, the first terminal of the switch is connected to the first terminal of the first capacitor, and the second terminal of the switch is connected to the first terminal of the second capacitor.

Description

Technical Field

[0001] The present invention relates to a crystal oscillator and a portable electronic device comprising the crystal oscillator. In another aspect, the present invention relates to a method for starting up a crystal oscillator. Background Art

[0002] Crystal oscillators are well known in the art. A crystal oscillator is an electronic oscillator circuit that uses the mechanical resonance of a vibrating crystal of piezoelectric material to generate an electrical signal with a precise frequency. This frequency is commonly used, for example, to keep track of time in quartz-controlled wristwatches, to provide a stable clock signal for digital integrated circuits, and / or to stabilize the frequency of radio transmitters and receivers.

[0003] Conventional crystal oscillators of the so-called Pierce or Colpitts design typically feature two capacitors, which are typically excited by a controller to provide relatively fast oscillator startup. To quickly start the crystal oscillator, the crystal is typically electrically excited at its terminals. The crystal terminals are typically charged by a first capacitor and a second capacitor, respectively. To achieve this, the excitation circuit provides for charging and unloading of the two capacitors, which are in turn connected to ground. With this conventional oscillator architecture, the frequent charging and unloading of the grounded capacitors results in significant power consumption.

[0004] It is therefore an object of the present invention to provide an improved crystal oscillator which provides a considerably faster start-up sequence and consumes less electrical power than hitherto known solutions. This is particularly important for mobile applications where the crystal oscillator is driven by a battery which provides a limited source of electrical energy. Summary of the Invention

[0005] The above needs are solved by a crystal oscillator, a portable electronic device and a method for starting up a crystal oscillator according to the features of the independent claims. Further features of the invention are the subject of the dependent claims.

[0006] In one aspect, a crystal oscillator is provided. The crystal oscillator includes a crystal resonator, which includes a first terminal and a second terminal. The crystal oscillator also includes an electronic oscillator circuit connected to the crystal resonator. The crystal oscillator also includes a first capacitor and a second capacitor. The first capacitor includes a first terminal and a second terminal. The second terminal of the first capacitor is connected to the first terminal of the crystal resonator. The second capacitor also includes a first terminal and a second terminal. Similarly, in this case, the second terminal is connected to the second terminal of the crystal resonator.

[0007] The crystal oscillator also includes a switch. The switch includes a first terminal, a second terminal, and a third terminal. The third terminal allows the conductivity between the first and second terminals of the switch to be controlled and / or modified. In other words, the conductivity between the first and second terminals of the switch can be controlled by the voltage at the third terminal. The first terminal of the switch is connected to the first terminal of the first capacitor, and the second terminal of the switch is connected to the first terminal of the second capacitor.

[0008] The switch allows the crystal resonator to be excited during the startup phase of the crystal oscillator by frequently charging and discharging the first and second capacitors. Once oscillation begins, the switch allows and provides for lowering the oscillator's impedance. Typically, the switch allows the crystal oscillator to be switched from startup mode to drive mode. In drive mode, the conductivity between the first and second terminals of the switch is relatively low.

[0009] In effect, the switch is open, providing for periodic charging and discharging of the first and second capacitors. When switching to drive mode, the conductivity between the first and second terminals of the switch increases. This effectively decouples the first and second conductors from the controller or startup controller, significantly reducing power consumption. When switching to drive mode, the first and second capacitors no longer need to be loaded and unloaded. Instead, the capacitors now operate and behave like so-called coupled capacitors.

[0010] According to another embodiment, an electronic oscillator circuit includes an input terminal and an output terminal. The input terminal of the electronic oscillator circuit is connected to a first terminal of a crystal resonator. The output terminal of the electronic oscillator circuit is connected to a second terminal of the crystal resonator. In practice, the crystal resonator is connected in parallel to the input and output terminals of the electronic oscillator circuit. Furthermore, a first capacitor is connected in series with the first terminal of the crystal resonator. A second capacitor is connected in series with the second terminal of the crystal resonator. Thus, the first capacitor is connected in series with the input terminal of the electronic oscillator circuit, while the second capacitor is connected in series with the output terminal of the electronic oscillator circuit.

[0011] The switch is typically connected between the first terminal of the first capacitor and the first terminal of the second capacitor. This allows for modification of the conductivity between the first terminals of the first and second capacitors during and / or for the crystal oscillator's startup process. When in startup mode, the switch is typically open, and no connection is made between the first terminal of the first capacitor and the first terminal of the second capacitor. When the crystal oscillator is switched to drive mode, the first terminal of the first capacitor and the first terminal of the second capacitor can be effectively connected, thereby reducing impedance to ground and effectively decoupling the first and second capacitors from an input source, such as provided by a startup controller.

[0012] Therefore, in another example of a crystal oscillator, the operation of the crystal oscillator can be switched from a startup mode to a drive mode. In the startup mode, the conductivity between the first terminal and the second terminal of the switch is lower than the conductivity between the first terminal and the second terminal of the switch in the drive mode. Typically, the switch is implemented as a MOS transistor, which includes a drain, a source, and a gate. The drain and the source are connected to the first terminal of the first capacitor and the first terminal of the second capacitor, respectively. The voltage at the gate can usually be controlled by a startup controller. In this way, the startup controller is operable and can switch the transistor, and thus the switch, between the startup mode and the drive mode.

[0013] According to another example, the crystal oscillator includes a first buffer amplifier and a second buffer amplifier. The output terminal of the first buffer amplifier is connected to the first terminal of the first capacitor. The output terminal of the second buffer amplifier is connected to the first terminal of the second capacitor.

[0014] The first and second buffer amplifiers provide the electrical impedance transformation of the startup controller to the first and second capacitors, and thereby to the electronic oscillator circuit. In this way, and in accordance with Thévenin's law, the impedance effectively presented at the crystal resonator (typically implemented as a quartz crystal) can remain relatively constant over time. Consequently, the impedance seen by the crystal resonator can effectively remain constant and / or unchanged during both the startup mode and the drive mode. This is particularly beneficial for the operation of the electronic oscillator circuit and the generation of the clock signal provided by the electronic oscillator circuit, particularly when the crystal oscillator is switched from the startup mode to the drive mode.

[0015] According to another example, a crystal oscillator includes a startup controller including a phase output and a startup control output. Typically, the startup controller is configured to initiate and control a startup process of the crystal oscillator. The phase output of the startup controller is typically connected or connectable to the crystal resonator and / or the first and second capacitors, thereby providing a resonator excitation or phase input for the electronic oscillator circuit.

[0016] The startup control output is active and operable to control the operating mode of the crystal oscillator. Thus, the startup control output is configured to provide a corresponding control signal to the switch to switch between a startup mode and a drive mode of the crystal oscillator.

[0017] According to another example, a startup control output of the startup controller is connected to the third terminal of the switch. The startup control output is particularly operable to change the configuration of the switch and thereby the operating mode of the oscillator circuit. In this way, the startup controller can directly control the operating mode of the crystal oscillator.

[0018] According to another example, a phase signal provided at a phase output of the startup controller can be coupled to a first terminal of a first capacitor as a first phase signal. The phase signal provided at the phase output can also be coupled to a first terminal of a second capacitor as a second phase signal. Typically, there is a phase shift between the first and second phase signals. The first and second phase signals can be in anti-phase or complementary to each other. The first and second phase signals are oscillating signals that can be used to regularly or frequently charge and discharge the first and second capacitors, at least during the startup mode.

[0019] Typically, in another example, the second phase signal at the first terminal of the second capacitor is inversely phased and / or phase-shifted from the first phase signal at or provided to the first terminal of the first capacitor. To provide first and second phase signals that correspond to each other but are phase-shifted or inversely phased, one of the first terminals of the first and second capacitors is directly connected to the phase output of the startup controller, while the other of the first terminals of the first and second capacitors is connected to the phase output of the startup controller via an inverter.

[0020] Typically, the first and second phase signals are derived and / or obtained from a common source, ie from the phase output of the startup controller. In this way, a well-defined phase shift between the first and second phase signals can be obtained and maintained.

[0021] According to another example, a crystal oscillator includes a first logic gate and a second logic gate. The first and second logic gates each include a first input terminal and a second input terminal. The first input terminals of the first and second logic gates are connected to a phase output of a startup controller. The second input terminals of the first and second logic gates are connected to a startup control output of the startup controller.

[0022] In some examples, at least one of the first and second logic gates is implemented as a logic AND gate. In some examples, both the first and second logic gates are implemented as logic AND gates. Here, one of the first input terminals of the first and second logic gates can be directly connected to the phase output of the startup controller, wherein the other of the first input terminals of the first and second logic gates can be connected to the phase output of the startup controller via an inverter.

[0023] In other examples, one of the first and second logic gates is implemented as a logic AND gate, and the other of the first and second logic gates is implemented as a logic NAND gate.

[0024] When both logic gates are implemented as logic AND gates, the outputs of the respective first and second gates can be effectively set to 0 by respective control signals provided by the enable control output of the enable controller. Typically, the outputs of the first and second logic gates are connected to inputs of first and second buffer amplifiers, respectively, and / or to first terminals of first and second capacitors, respectively.

[0025] By setting the enable control signal provided at the enable control output to a logic zero, the phase inputs to the first and second capacitors may be effectively shut off by the enable controller.

[0026] According to another example, one of the first input terminals of the first and second logic gates is coupled to the phase output of an inverter. Assuming the phase output of the startup controller provides a periodic oscillating signal, the output of the first logic gate can effectively be inverted or 180° phase-shifted from the output of the second logic gate. This can provide the required phase shift between the first and second phase signals used to charge or discharge the first and second capacitors and / or drive the first and second buffer amplifiers.

[0027] According to another example, the second input terminals of the first and second logic gates are connected to the third terminal of the switch via an inverter. This allows for concurrent operation of the first and second logic gates during the switching behavior of the switch. In practice, by using an inverter between the third terminal of the switch and the second input terminals of the first and second logic gates, the switch can be effectively turned on, thereby switching the crystal oscillator to a drive mode. Simultaneously or concurrently with the turning on of the switch, the first and second logic gates can be effectively turned off, and the first and second phase signals used to charge the first and second capacitors will no longer be generated. This effectively saves power.

[0028] According to another example, the output terminal of the first logic gate is connected to the input terminal of the first buffer amplifier, and the output terminal of the second logic gate is connected to the input terminal of the second buffer amplifier. In this way, the first and second logic gates are operable to drive the respective first and second buffer amplifiers. In practice, the first logic gate, the first buffer amplifier, and the first capacitor are arranged in series. Correspondingly, the second logic gate, the second buffer amplifier, and the second capacitor are also arranged in series.

[0029] According to another aspect, a portable electronic device is provided. The portable electronic device can be implemented as a wearable electronic device configured to be worn by a user. The portable electronic device includes a housing, a power source, and a crystal oscillator, as described above, disposed within the housing. The crystal oscillator is driven or powered by the power source. The power source can include a battery. The battery can be a rechargeable battery. The portable or wearable electronic device can be implemented as a watch, wristwatch, or smartwatch. The crystal oscillator provides a clock signal and an output terminal thereof, which provides a well-defined clock for driving electronic circuits of the portable electronic device.

[0030] According to another example, a portable electronic device includes a display and a movement mechanism. The movement mechanism is operably connected to the display. The movement mechanism includes a crystal oscillator. The movement mechanism can be implemented mechanically and / or electronically. When implemented mechanically, the movement mechanism includes at least the crystal oscillator described above, which provides a well-defined clock signal for driving the mechanically implemented movement mechanism.

[0031] According to another aspect, the present invention also relates to a method for starting up a crystal oscillator. The method includes providing a crystal oscillator as described above and operating the crystal oscillator in a start-up mode. During the start-up mode, first and second phase signals are supplied to first and second capacitors of the crystal oscillator. Typically, when oscillation begins, a switch of the crystal oscillator is operated, thereby switching the crystal oscillator from the start-up mode to the drive mode. When or by switching the crystal oscillator to the drive mode, the first and second phase signals are no longer supplied to the first and second capacitors, thereby minimizing the power consumption of the crystal oscillator. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] An example of a crystal oscillator is described in more detail below with reference to the accompanying drawings, in which:

[0033] Figure 1 : A block diagram schematically illustrating an example of a crystal oscillator,

[0034] Figure 2 : schematically illustrates an example of a portable electronic device equipped with a crystal oscillator, and

[0035] Figure 3 : A flow chart showing the startup operation method of a crystal oscillator. DETAILED DESCRIPTION

[0036] exist Figure 1 , a block diagram of one embodiment of a crystal oscillator 10 is described in more detail. The crystal oscillator 10 includes a crystal resonator 12. The crystal resonator 12 typically comprises a quartz crystal. The crystal oscillator 10 also includes an electronic oscillator circuit 14 electrically connected to the crystal resonator 12. The crystal resonator 12 and the electronic oscillator circuit 14 are connected in parallel. The electronic oscillator circuit 14 includes an output terminal 50 through which a well-defined and frequency-stable clock signal synchronized with the resonant frequency of the crystal resonator 12 can be provided.

[0037] The crystal oscillator 10 further includes a first capacitor 21 and a second capacitor 22. The first capacitor 21 and the second capacitor 22 are connected to respective input terminals 47 and output terminals 49 of the electronic oscillator circuit 14. Specifically, the first capacitor 21 includes a second terminal 25 electrically connected to the first input terminal 47 of the electronic oscillator circuit 14. The second capacitor 22 includes a second terminal 26 electrically connected to the second output terminal 49 of the electronic oscillator circuit.

[0038] The crystal resonator 12 includes a first terminal 27. The first terminal 27 is electrically connected to the second terminal 25 and the first input terminal 47. The second terminal 29 of the crystal resonator 12 is electrically connected to the second terminal 26 of the second capacitor 22 and to the second output terminal 49 of the electronic oscillator circuit 14.

[0039] Crystal oscillator 10 also includes a switch 30. Switch 30 can be implemented as a MOS transistor. Switch 30 includes a first terminal 31, a second terminal 32, and at least one third terminal 33. First terminal 31 and second terminal 32 are implemented by the source and drain of a transistor. Third terminal 33 is implemented by the gate of the transistor or switch 30. First terminal 31 of switch 30 is connected to first terminal 23 of first capacitor 21. Second terminal 32 of switch 30 is connected to first terminal 24 of second capacitor 22.

[0040] The first capacitor 21 and the second capacitor 22 are operable to input a drive frequency to the crystal resonator 12 and / or the electronic oscillator circuit 14. The capacitors 21, 22 are typically driven by a phase signal provided by the phase output 17 of the startup controller 16. The startup controller 16 is used to provide phase-shifted drive signals to the first capacitor 21 and the second capacitor 22 at least during a startup phase of a startup procedure of the crystal oscillator 10.

[0041] Specifically, the switch 30 is configured to switch the crystal oscillator 10 between a startup mode and a drive mode. In the startup mode, the first capacitor 21 and the second capacitor 22 are frequently charged and discharged by the startup controller 16. In the drive mode, the first capacitor 21 and the second capacitor 22 are effectively decoupled from the startup controller 16.

[0042] In the startup mode, the switch 30 is open and, therefore, the conductivity between the first terminal 31 and the second terminal 32 of the switch 30 is relatively low. Switching of the switch 30 results in an increase in the conductivity between the first terminal 31 and the second terminal 32. This reduces the impedance seen by the electronic oscillator circuit 14 and significantly reduces the power consumption of the crystal oscillator during the startup phase.

[0043] Startup controller 16 includes a phase output 17 and a start control output 18. Phase output 17 provides an oscillating phase signal having a frequency that is typically within the frequency range of crystal resonator 12. Startup control output 18 provides a start control signal. The start control signal can be a logic 1 or a logic 0. If the start control signal provided at start control output 18 is high or equal to a logic 1, crystal oscillator 10 is in a start mode. If the signal at start control output 18 is zero or low, crystal oscillator 10 is in a drive mode.

[0044] like Figure 1 As shown, the third terminal 33 of the switch 30 is connected to the start control output 18 via an inverter 62. Thus, when the start control signal at the start control output 18 is high, the switch 30 is effectively off. Vice versa, when the start control signal at the start control output 18 is low or zero, the switch 30 is on.

[0045] Crystal oscillator 10 also includes a first logic gate 51 and a second logic gate 52. Both first logic gate 51 and second logic gate 52 are implemented as logical AND gates. First logic gate 51 includes a first input terminal 53 connected to phase output 17 of startup controller 16. Second input terminal 55 is connected to startup control output 18 of startup controller 16. Similarly, second logic gate 52 includes a first input terminal 54 and a second input terminal 56. Second input terminal 56 is connected to startup control output 18 of startup controller 16. First input terminal 54 is connected to phase output 17 of startup controller 16 via another inverter 60.

[0046] Thus, the input signals provided at the first input terminal 53 of the first logic gate 51 and the first input terminal 54 of the second logic gate 52 are mutually inverted or 180° phase-shifted by means of the inverter 60. Thus, corresponding phase-shifted or inverted signals can be provided at the output terminal 57 of the first logic gate 51 and the output terminal 58 of the second logic gate 52, respectively.

[0047] An output terminal 57 of the first logic gate 51 is connected to an input terminal 43 of the first buffer amplifier 41. A corresponding output 45 of the first buffer amplifier 41 is connected to the first terminal 31 of the switch 30 and the first terminal 23 of the first capacitor 21. Similarly, a second buffer amplifier 42 is provided. An input terminal 44 of the second buffer amplifier 42 is connected to an output 58 of the second logic gate 52. An output terminal 46 of the second buffer amplifier 42 is connected to the second terminal 32 of the switch 30 and the first terminal 24 of the second capacitor 22.

[0048] The buffer amplifiers 41 , 42 are input impedances seen by the crystal resonator 12 that can be kept substantially constant for each mode of operation of the crystal oscillator. In this way, a fairly constant and stable frequency output can be provided at the output terminal 50 of the electronic oscillator circuit 14 .

[0049] The implementation of two logic AND gates 51 and 52 and the coupling of the second input terminals 55 and 56 of the logic gates 51 and 52 to the start control output 18, together with the anti-phase coupling of the third terminal 33 of the switch 30 to the start control output 18, provide a concurrent switching behavior. Since the switch 30 is effectively off, when the start control signal provided at the start control output is high, the first logic gate 51 and the second logic gate 52 provide phase-shifted first and second phase signals, which can be used to drive the first and second buffer amplifiers 41 and 42, respectively, and charge and discharge the first and second capacitors 21 and 22.

[0050] When the enable control output 18 switches to logic 0, the switch 30 is effectively turned on and the phase inputs provided by the arrangement of first and second logic gates 51 , 52 and first and second buffer amplifiers 41 , 42 are simultaneously effectively turned off.

[0051] exist Figure 2 , an example of a portable electronic device 100 implemented as a wristwatch is shown. The portable electronic device 100 includes a housing 101 and a wristband 103. The electronic device 100 is also provided with a hand movement mechanism 105 connected or coupled to a display 102. Figure 2 As shown only briefly in FIG, the electronic device is further provided with a power supply 104, for example a battery, and a crystal oscillator 10 as described above. The crystal oscillator 10 provides a well-defined, frequency-stable and thus quite accurate clock signal.

[0052] Finally, in Figure 3 The flowchart of the method for starting the crystal oscillator is shown schematically in FIG. Figure 1 The crystal oscillator 10 is described. In a first step 200, the crystal oscillator 10 is operated in a startup mode. Here, a first phase signal and a second phase signal are supplied to the first capacitor 21 and the second capacitor 22 of the crystal oscillator 10. Thereafter, when the electronic oscillator circuit 14 begins to oscillate, the crystal oscillator 10 is switched to a drive mode by using the switch 30 of the crystal oscillator.

[0053] When the electronic oscillator circuit 14 starts oscillating, the switching of the crystal oscillator from the start-up mode to the drive mode is controlled by the start-up controller 16. For this purpose, a feedback (not shown) from the electronic oscillator circuit 14 to the start-up controller 16 may be provided.

[0054] Reference Signs List

[0055] 10. Crystal Oscillator

[0056] 12 Crystal Resonator

[0057] 14 Electronic Oscillator Circuit

[0058] 16 Start the controller

[0059] 17 Phase Output

[0060] 18 Start control output

[0061] 21 Capacitor

[0062] 22 capacitors

[0063] 23 terminals

[0064] 24 terminals

[0065] 25 terminals

[0066] 26 terminals

[0067] 27 terminals

[0068] 29 terminals

[0069] 30 switches

[0070] 31 terminal

[0071] 32 terminals

[0072] 33 terminals

[0073] 41 Buffer Amplifier

[0074] 42 Buffer Amplifier

[0075] 43 Input terminals

[0076] 44 Input terminals

[0077] 45 output terminals

[0078] 46 output terminals

[0079] 47 terminals

[0080] 49 terminals

[0081] 50 Output terminals

[0082] 51 logic gates

[0083] 52 logic gates

[0084] 53 Input terminals

[0085] 54 Input terminals

[0086] 55 Input terminal

[0087] 56 Input terminals

[0088] 57 Output terminal

[0089] 58 output terminals

[0090] 60 Inverter

[0091] 62 Inverter

[0092] 100 electronic devices

[0093] 101 housing

[0094] 102 Display

[0095] 103 wristband

[0096] 104 Power Supply

[0097] 105 needle movement mechanism

Claims

1. A crystal oscillator (10), comprising: - a crystal resonator (12), said crystal resonator (12) comprising a first terminal (27) and a second terminal (29), an electronic oscillator circuit (14) connected to the crystal resonator (12), the crystal resonator (12) and the electronic oscillator circuit (14) being connected in parallel, the electronic oscillator circuit (14) comprising an output terminal (50) through which a well-defined and frequency-stable clock signal is provided that is synchronized with the resonant frequency of the crystal resonator (12), a first capacitor (21), comprising a first terminal (23) and a second terminal (25), the second terminal (25) of the first capacitor (21) being connected to the first terminal (27) of the crystal resonator (12), a second capacitor (22), the second capacitor (22) comprising a first terminal (24) and a second terminal (26), the second terminal (26) of the second capacitor (22) being connected to the second terminal (29) of the crystal resonator (12), wherein the crystal oscillator (10) further comprises: a switch (30) comprising a first terminal (31), a second terminal (32) and a third terminal (33), wherein conductivity between the first terminal (31) of the switch (30) and the second terminal (32) of the switch (30) is controlled by a voltage at the third terminal (33) of the switch (30), wherein the first terminal (31) of the switch (30) is connected to the first terminal (23) of the first capacitor (21), the second terminal (32) of the switch (30) is connected to the first terminal (24) of the second capacitor (22), and The crystal oscillator (10) comprises a first buffer amplifier (41) and a second buffer amplifier (42), wherein an output terminal (45) of the first buffer amplifier (41) is connected to the first terminal (23) of the first capacitor (21), and an output terminal (46) of the second buffer amplifier (42) is connected to the first terminal (24) of the second capacitor (22).

2. The crystal oscillator (10) according to claim 1, wherein The electronic oscillator circuit (14) comprises a first input terminal (47) and a second output terminal (49), wherein the first input terminal (47) of the electronic oscillator circuit (14) is connected to the first terminal (27) of the crystal resonator (12), and the second output terminal (49) of the electronic oscillator circuit (14) is connected to the second terminal (29) of the crystal resonator (12).

3. The crystal oscillator (10) according to claim 1 or 2, wherein: The operation of the crystal oscillator (10) is switchable from a start-up mode to a drive mode, wherein when in the start-up mode, the conductivity between the first terminal (31) of the switch (30) and the second terminal (32) of the switch (30) is lower than the conductivity between the first terminal (31) of the switch (30) and the second terminal (32) of the switch (30) in the drive mode.

4. The crystal oscillator (10) of claim 1 or 2, further comprising a startup controller (16), the startup controller (16) comprising a phase output (17) and a startup control output (18).

5. The crystal oscillator (10) according to claim 4, wherein: The startup control output (18) is connected to the third terminal (33) of the switch (30).

6. The crystal oscillator according to claim 4, wherein: The phase signal provided at the phase output (17) is capable of being coupled as a first phase signal to the first terminal (23) of the first capacitor (21), and the phase signal provided at the phase output (17) is also coupled as a second phase signal to the first terminal (24) of the second capacitor (22), the first phase signal and the second phase signal having a phase shift.

7. The crystal oscillator (10) according to claim 6, further comprising a first logic gate (51) and a second logic gate (52), wherein the first logic gate (51) and the second logic gate (52) each comprise a first input terminal (53, 54) and a second input terminal (55, 56), wherein The first input terminals (53, 54) of the first logic gate (51) and the second logic gate (52) are connected to the phase output (17) of the startup controller (16), and the second input terminals (55, 56) of the first logic gate (51) and the second logic gate (52) are connected to the startup control output (18) of the startup controller (16).

8. The crystal oscillator (10) according to claim 7, wherein: One of the first input terminals (53, 54) of the first logic gate (51) and the second logic gate (52) is coupled to the phase output (17) via an inverter (60).

9. The crystal oscillator (10) according to claim 7, wherein: The second input terminals (55, 56) of the first logic gate (51) and the second logic gate (52) are connected to the third terminal (33) of the switch (30) via an inverter (62).

10. The crystal oscillator (10) according to any one of claims 7 to 9, wherein: The output terminal (57) of the first logic gate (51) is connected to the input terminal (43) of the first buffer amplifier (41), and the output terminal (58) of the second logic gate (52) is connected to the input terminal (44) of the second buffer amplifier (42).

11. A portable electronic device (100) comprising a housing (101), a power supply (104) and a crystal oscillator (10) according to any one of the preceding claims arranged inside the housing (101), wherein: The crystal oscillator (10) is driven by the power supply (104).

12. The portable electronic device (100) according to claim 11, further comprising a display (102) and a hand movement mechanism (105) operatively connected to the display (102), wherein: The hand-moving mechanism (105) includes the crystal oscillator (10).

13. A method for starting a crystal oscillator (10), the method comprising the following steps: - providing a crystal oscillator (10) according to any one of the preceding claims 1 to 11, - operating the crystal oscillator (10) in a startup mode, thereby providing a first phase signal and a second phase signal to a first capacitor (21) and a second capacitor (22) of the crystal oscillator (10), and - switching the switch (30) of the crystal oscillator (10) so that the crystal oscillator (10) switches from the start-up mode to the drive mode.

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