Method of starting a crystal oscillator with external clock injection, crystal oscillator and monitoring circuit

Abstract

The application provides a method for starting a crystal oscillator (XO) by means of external clock injection, an XO and a monitoring circuit. The XO comprises an XO core circuit, an external oscillator and an injection switch, wherein the quality factor of the external oscillator is lower than that of the XO core circuit. The method comprises: generating an injection signal by using the external oscillator; and turning on the injection switch to inject the energy of the injection signal into the XO core circuit, so as to generate an amplitude modulation signal according to the combination of the injection signal and an inherent oscillation signal from the XO core circuit; and controlling the external oscillator to selectively change the injection frequency of the injection signal according to the amplitude modulation signal. By using the technical solution of the application, the overall starting time of the XO can be reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the fast start-up of a crystal oscillator (XO) and more particularly, to a method of starting an XO by means of external clock injection, an associated XO and a monitoring circuit. BACKGROUND

[0002] For future communication applications (e.g., duty-cycled wireless / wired systems), when there is no data to send or receive, a crystal oscillator (XO) within a communication device can enter a sleep mode (e.g., disable the oscillation of the XO) to save power; when there is data to send or receive, the XO can enter a wake-up mode to start oscillation, and then enter a listen mode with stable oscillation, so that the communication device can normally send or receive data.

[0003] For example, the time period corresponding to the listen mode can be 1 millisecond (ms), and the time period corresponding to the wake-up mode (which can be referred to as the start-up time T START ) can be 5 ms, where the wake-up mode consumes power (e.g., 42.7% of the total power). Therefore, the start-up time of the XO can become a bottleneck for reducing the average power. Designers can try to reduce the start-up time by controlling the negative resistance within the XO, but this can bring additional power consumption. Therefore, a novel method of starting an XO and related architecture are needed to solve the problems of the related art. SUMMARY

[0004] It is an object of the present application to provide a method of starting a crystal oscillator (XO) by means of external clock injection, an associated XO and a monitoring circuit, to speed up the start-up of the XO without greatly increasing the additional energy consumption.

[0005] At least one embodiment of the present invention provides a method of starting an XO with the aid of an external clock injection. The method can include generating an injection signal with an external oscillator external to an XO core circuit of the XO, wherein the XO includes the XO core circuit, the external oscillator external to the XO core circuit, and at least one injection switch. The at least one injection switch is coupled between an injection node of the XO and an output of the XO core circuit, the external oscillator is coupled to the injection node, and a quality factor of the external oscillator is lower than a quality factor of the XO core circuit; turning on the at least one injection switch to inject energy of the injection signal into the XO core circuit to increase energy of an inherent oscillation signal of the XO core circuit during a start-up of the XO, wherein a modulated signal is generated at the injection node from a combination of the injection signal and the inherent oscillation signal; and controlling the external oscillator to selectively vary an injection frequency of the injection signal in accordance with the modulated signal. More particularly, the at least one injection switch is turned on when the external oscillator selectively varies the injection frequency of the injection signal.

[0006] At least one embodiment of the present invention provides an XO. The XO can include an XO core circuit, an external oscillator, at least one injection switch, and a frequency controller, wherein the external oscillator is coupled to an injection node of the XO, the at least one injection switch is coupled between the injection node of the XO and an output of the XO core circuit, and the frequency controller is coupled to the external oscillator. The XO core circuit can be configured to generate an inherent oscillation signal within the XO core circuit. The external oscillator can be configured to generate an injection signal within the external oscillator, wherein a quality factor of the external oscillator is lower than a quality factor of the XO core circuit. For example, when the at least one injection switch is turned on, energy of the injection signal is injected into the XO core circuit to increase energy of the inherent oscillation signal during a start-up of the XO, and a modulated signal is generated at the injection node from a combination of the injection signal and the inherent oscillation signal. The frequency controller can be configured to receive the modulated signal and control the external oscillator to selectively vary an injection frequency of the injection signal in accordance with the modulated signal. More particularly, the at least one injection switch is turned on when the external oscillator selectively varies the injection frequency of the injection signal.

[0007] At least one embodiment of the present invention provides a monitoring circuit for generating a successive comparison result of a demodulation voltage sequence carrying information of a relative phase between an injection signal of an XO and an inherent oscillation signal of the XO. The monitoring circuit can include an amplifier, a capacitor and a loop switch. The amplifier can be configured to receive the demodulation voltage sequence through a first input of the amplifier, wherein the demodulation voltage sequence includes a first voltage and a second voltage following the first voltage. The capacitor is coupled to a second input of the amplifier and can be configured to sequentially store the demodulation voltage sequence. The loop switch is coupled between the second input and an output of the amplifier and is configured to control a configuration of the amplifier. For example, when the loop switch is turned on, the amplifier is configured as a unity gain buffer to transmit the first voltage from the first input of the amplifier to the capacitor. When the loop switch is turned off, the amplifier is configured as a comparator for comparing the second voltage on the first input of the amplifier with the first voltage stored on the capacitor and generating a comparison result of the successive comparison result, wherein the comparison result carries information of the relative phase between the injection signal and the inherent oscillation signal of the XO for controlling an injection frequency of the injection signal.

[0008] The start-up method and related XO provided by embodiments of the present invention can inject energy into the XO core circuit by using an external oscillator to accelerate the start-up process of the XO. Advantageously, the injection switch coupled between the external oscillator and the XO core circuit can be turned on directly during the start-up process, thereby optimizing the efficiency of clock injection. In some embodiments, when adjusting the injection frequency (locked to the inherent frequency of the XO core circuit), the injection switch can be always turned on, turned on for at least a period of time, or turned on and turned off alternately to optimize or improve the efficiency of clock injection. Compared with the prior art, the overall start-up time of the XO can be greatly reduced. Therefore, the present invention can optimize the overall performance of the XO without causing any side effects, or optimize the overall performance of the XO in a way that is unlikely to cause side effects.

[0009] These and other objects of the present invention will no doubt become apparent to those of ordinary skill in the art after reading the following detailed description of the preferred embodiments, illustrated in the various drawing figures. BRIEF DESCRIPTION OF DRAWINGS

[0010] Figure 1 is a schematic diagram illustrating the concept of starting a crystal oscillator (XO) by means of external clock injection according to an embodiment of the present invention.

[0011] Figure 2 is a schematic diagram illustrating an XO according to an embodiment of the present invention.

[0012] Figure 3 is a start-up by means of external clock injection according to an embodiment of the application Figure 2 is a flow chart of the method of the XO shown in

[0013] Figure 4 is a schematic diagram showing a waveform pattern of some signals with varying relative phase according to an embodiment of the application.

[0014] Figure 5 shows the relationship between the growth rate of the intrinsic oscillation signal and the relative phase according to an embodiment of the application.

[0015] Figure 6 is a schematic diagram showing a detailed implementation of the generation of a series of demodulation voltages by a demodulation circuit according to an embodiment of the application.

[0016] Figure 7 shows some details of the relationship between the relative phase and the distortion according to an embodiment of the application.

[0017] Figure 8 shows some details of the relationship between the relative phase and the demodulation voltage according to an embodiment of the application.

[0018] Figure 9 shows some details of the relationship between the relative phase and the distortion according to an embodiment of the application.

[0019] Figure 10 shows some details of the relationship between the relative phase and the demodulation voltage according to an embodiment of the application.

[0020] Figure 11 is a schematic diagram showing a detailed implementation of the XO according to an embodiment of the application Figure 2 shown in

[0021] Figure 12 shows the operation of the monitoring circuit in the preset phase, Figure 11 shown in

[0022] Figure 13 shows the operation of the monitoring circuit in the evaluation phase, Figure 11 shown in

[0023] Figure 14 is a schematic diagram showing a detailed implementation of the XO shown in Figure 2

[0024] Figure 15 is a schematic diagram showing a detailed implementation of the XO according to another embodiment of the application Figure 2 shown in​

[0025] Figure 16 is according to an embodiment of the application Figure 15 a timing diagram of some signals within the illustrated embodiment.

[0026] Figure 17 is a schematic diagram illustrating a detailed implementation of the XO shown in Figure 2

[0027] Figure 18 illustrates some details related to controlling the injection frequency according to an embodiment of the application.

[0028] Figure 19 illustrates some details related to controlling the injection frequency according to another embodiment of the application. DETAILED DESCRIPTION

[0029] Certain terminology is used in the following description and claims to refer to particular components. As one skilled in the art will appreciate, electronic companies can refer to a component by different names. This document does not intend to distinguish between components that differ in name but not in function. In the following description and claims, the terms "include" and "comprise" are used in an open-ended fashion, and thus should be interpreted to mean "including, but not limited to...". Also, the term "couple" is intended to mean either an indirect or direct electrical connection. Thus, if one device is coupled to another device, that connection can be through a direct electrical connection, or through an indirect electrical connection via other devices and connections.

[0030] Figure 1 is a schematic diagram illustrating the concept of start-up (e.g., fast start-up) of a crystal oscillator 10 (XO) by means of an external clock injection according to an embodiment of the application. For oscillators with a high quality factor (which can be referred to as high-Q oscillators), the performance related to noise (e.g., phase noise) is much better than for oscillators with a low quality factor (which can be referred to as low-Q oscillators), but the start-up time required for high-Q oscillators can be much longer than the start-up time required for low-Q oscillators. Examples of high-Q oscillators can include, but are not limited to, Pierce XO and Colpitts XO. Examples of low-Q oscillators can include, but are not limited to, ring oscillators and resistor-capacitor (RC) oscillators. Figure 1 The fast start-up technique shown in INJ turns on an injection switch coupled between a low-Q oscillator and a high-Q oscillator during a time period T INJ ​Energy injection into a high-Q oscillator (e.g., including an active device 11 (wherein having a transconductance Gm and a load capacitor C)). L ), capacitor C m and C o resistor R m and inductor L m This increases the energy (e.g., V) of the intrinsic oscillation signal of the high-Q oscillator during the XO startup process. m,ss and I m,ss This accelerates the startup of the XO and allows the XO to output its inherent oscillation signal.

[0031] In practice, at the start of the startup process, the injection frequency of the low-Q oscillator is typically different from the intrinsic frequency of the high-Q oscillator, for example, by ±6000 ppm (parts per million). Therefore, the phase error between the injected signal and the intrinsic oscillation signal may gradually accumulate. In some embodiments, Figure 1 The fast-start technique illustrated can also utilize a feedback control mechanism that detects the intrinsic frequency and modifies the low-Q oscillator accordingly to bring the injected frequency close to the intrinsic frequency. Specifically, the injection switch can be turned on during the first injection period, and the energy of the intrinsic oscillator signal can be increased, whereby the injected signal can dominate the overall waveform at the connection node of the low-Q and high-Q oscillators (e.g., a combination of the injected signal and the intrinsic oscillator signal) because the intrinsic oscillator signal is initially insufficiently strong. To detect the intrinsic frequency, the injection switch is then turned off during a lock / synchronization period following the first injection period to allow the intrinsic frequency to be detected for control of the low-Q oscillator. After the injected frequency approaches the intrinsic frequency, the injection switch is turned on again during a second injection period following the lock / synchronization period, and clock injection continues.

[0032] Figure 2 This is a schematic diagram illustrating an XO 20 according to an embodiment of the present invention. (As shown) Figure 2 As shown, XO 20 may include XO core circuit 100, external oscillator 200 of XO core circuit 100 (in particular, external oscillator 200 is located outside XO core circuit 100), and at least one injection switch (e.g., one or more, collectively referred to as the one controlled by signal INJ). EN The injection switch is coupled to the injection node N of the XO 20, and the frequency controller is 300. INJ and the output terminal N of the XO core circuit OUTBetween, the external oscillator is coupled to the injection node N. INJ Furthermore, the frequency controller 300 is coupled to the external oscillator 200. In this embodiment, the quality factor of the external oscillator 200 is lower than that of the XO core circuit 100. The XO core circuit 100 may be an example of a high-Q oscillator, while the external oscillator 200 may be an example of a low-Q oscillator. Figure 3 This illustrates a rapid startup method using an external clock injection according to an embodiment of the invention. Figure 2 The flowchart of the XO 20 method is shown. It should be noted that... Figure 3 The illustrated workflow is for illustrative purposes only and is not intended to limit the scope of the invention. Figure 3 In the workflow shown, one or more steps can be added, deleted, or modified. Furthermore, if the same result can be obtained, it is not necessary to follow the steps exactly. Figure 3 These steps are performed in the exact order shown. For a better understanding, please refer to [the diagram / reference]. Figure 2 refer to Figure 3 .

[0033] In step S310, the external oscillator 200 may generate an injection signal (e.g., a low-Q signal) within the external oscillator 200. In this embodiment, the operating frequency of the frequency controller 300 is controlled by the external oscillator (e.g., the operating frequency of the frequency controller 300 may be equal to the injection frequency of the injection signal), but the invention is not limited thereto.

[0034] In step S320, the system including XO 20 (e.g., a duty cycle wireless / wired system) can utilize signal INJ EN The injection switch is turned on to inject energy of the injection signal into the XO core circuit 100, thereby increasing the energy of the inherent oscillation signal of the XO core circuit 100 (e.g., the energy Im(t) of the resonator) during the startup process of XO 20. When the injection switch is turned on, the output terminal N... OUT Coupled to injection node N INJ Both the injected signal and the inherent oscillation signal exist at the injection node N. INJ At the injection node N, and based on the combination of the injected signal and the inherent oscillation signal. INJ An amplitude-modulated (AM) signal is generated. For example, the injected signal (e.g., an output square wave) can be modulated by an inherent oscillation signal to generate an AM signal, such as... Figure 4 The signal V shown GATE The waveform of (t) is shown.

[0035] In step S330, the frequency controller 300 can receive the AM signal and, according to a signal such as V, GATEThe AM signal of the waveform of (t) controls the external oscillator 200 to selectively change the injection frequency of the injection signal. More specifically, during the start-up process, the injection switch is always on (e.g., not off) or at least on for a period of time when the external oscillator selectively changes the injection frequency of the injection signal.

[0036] It should be noted that the different relative phase (e.g., phase error) between the injection signal and the inherent oscillation signal can cause Figure 4 The signal V GATE (t) is shown, where the energy I m (t) of the resonator within the XO core circuit 100 is also shown. For example, when the injection frequency (e.g., F INJ ) is not equal to the inherent frequency (e.g., F XO ), the phase error can accumulate over time, and a beating behavior can occur, where the envelope period T envelope of the beating behavior can be calculated as follows:

[0037]

[0038] The Δf can represent the frequency difference between the injection frequency and the inherent frequency. In this embodiment, the waveform of the signal V GATE (t) can be considered as a square wave from the external oscillator 200 being distorted by the inherent oscillation signal (which can be represented by I m (t)) from the XO core circuit 100, and the different distortion (e.g., the envelope of the beating) can correspond to the different relative phase between the injection signal and the inherent oscillation signal. Therefore, the information about the relative phase between the injection signal and the inherent oscillation signal is carried by the AM signal such as the signal V GATE (t).

[0039] Figure 5 The relationship between the growth rate of the inherent oscillation signal and the relative phase is shown according to an embodiment of the present application. As Figure 5 shown, when the relative phase falls in the interval between +90 degrees and -90 degrees, the growth rate of the inherent oscillation signal can be positive in response to the external clock injection. When the relative phase falls outside of this interval (e.g., relative phase > +90° or relative phase < -90°), the growth rate can be negative in response to the external clock injection, which means that the low-Q oscillator hinders the start-up of the XO when the relative phase falls outside of the interval between +90° and -90°.

[0040] Based on this, in Figure 2In the illustrated embodiment, the injection switch is not turned off until the start-up process of the XO 20 is completed (e.g., after the injection switch is turned on). Although the present application does not interrupt the clock injection of the XO 20 during the required lock / synchronization period, the frequency controller 300 can extract the information related to the relative phase from the signal V GATE (t) to control the injection frequency. In addition, the frequency controller 300 can utilize a control mechanism to ensure that the relative phase always falls in the interval between +90° and -90°, thereby preventing the injection signal from hindering the start-up process. As a result, the efficiency of the clock injection is improved, and the start-up time can be greatly reduced.

[0041] In one embodiment, Figure 2 The frequency controller 300 illustrated in FIG. 3 can include a demodulation circuit, wherein the demodulation circuit can be configured to receive the AM signal and generate a demodulation voltage sequence according to the AM signal. Figure 6 is a schematic diagram illustrating a detailed implementation of generating the demodulation voltage sequence by the demodulation circuit 310 according to an embodiment of the present application, wherein the demodulation circuit 310 can be an example of the demodulation circuit described above. In this embodiment, Figure 2 The external oscillator 200 illustrated in FIG. 2 can include Figure 6 a low-Q oscillator 210 (e.g., a ring oscillator or an RC oscillator) and at least one output buffer (e.g., one or more output buffers, collectively referred to as output buffers 220), wherein the buffers 220 can be coupled between the low-Q oscillator 210 and the injection node N INJ In some embodiments, the buffers 220 can be omitted.

[0042] In this embodiment, the demodulation circuit 310 can be implemented by using a diode with a sample-and-hold mechanism, as illustrated in FIG. 4, to extract the information related to the relative phase (e.g., the jitter envelope) from the AM signal such as the signal V Figure 6 (t). In detail, the demodulation circuit 310 can include a diode D0, a reset switch controlled by a signal RST, a sample switch controlled by a signal RSTB, and a sample capacitor C GATE , wherein the cathode of the diode D0 is coupled to a sampling node of the demodulation circuit 310. In the demodulation circuit 310, the reset switch is coupled between the sampling node and a reference terminal (e.g., a ground voltage terminal) of the demodulation circuit 310, the sample switch is coupled between the anode of the diode D0 and the injection node N S , and the sample capacitor C INJ is coupled between the anode of the diode D0 and the output terminal N OUT of the XO core circuit 100 (or in other embodiments, it is coupled between the anode of the diode D0 and the output terminal N SIt is coupled between the sampling node and the reference terminal. For example, during the reset period of the demodulation circuit 310, when the reset switch is turned on and the sampling switch is turned off, the voltage level of the sampling node is reset to the reference level of the reference terminal. When the reset switch is off and the sampling switch is turned on during the sampling period, in response to the voltage level of the AM signal exceeding the threshold corresponding to diode D0, charge accumulates on the sampling node (e.g., in response to signal V). GATE The voltage level of (t) causes the voltage difference between the cathode and anode of diode D0 to be greater than the threshold voltage of diode D0, so as to generate the demodulated voltage in the demodulated voltage sequence at the sampling node. The operation of demodulation circuit 310 is similar to that of an integrator, so information related to distortion can correspond to the demodulated voltage sequence, which can be generated by signal V. De-MOD This indicates that each demodulated voltage in the demodulated voltage sequence is generated using the same diode (i.e., diode D0), and no mismatch problem is introduced in the demodulated voltage sequence.

[0043] Figure 7 Some details regarding the relationship between relative phase and distortion (e.g., jitter envelope) according to embodiments of the present invention are illustrated. For better understanding, assume a signal such as V XO The energy of the inherent oscillating signal (e.g., signal V) XO The amplitude remains unchanged. They have different relative phases. The jumping envelope can be calculated as follows:

[0044]

[0045] According to this equation, when When the angles are -90°, -45°, 0°, +45°, and 90° respectively, by The jump envelope can be 0. -2A0, And 0, where A0 can represent signal V XO The amplitude. Based on this, it leads to a pulsating envelope. Minimum relative phase It can be 0°. Therefore, as... Figure 8 As shown, when the relative phase At times, such as signal V De-MOD The demodulated voltage sequence can have a minimum voltage.

[0046] In fact, such as Figure 9 As shown, such as signal V XO The energy of the inherent oscillating signal (e.g., signal V) XO The amplitude may increase over time. They have different relative phases. The jumping envelope can be modified as follows:

[0047]

[0048] with the signal V XO The beat envelope with the increased amplitude can be represented by According to this equation, when -90°, -45°, 0°, +45° and +90°, respectively, the beat envelope can be 0, and 0, where k can represent the rate of increase of the amplitude of the signal V XO Based on this, when the relative phase accumulates in the positive direction, when A0and k are positive values, the beat envelope the minimum relative phase may fall within the interval of 0° to 90°. Therefore, as Figure 10 indicated, when , the demodulated voltage sequence such as the signal V De-MOD may have the minimum voltage. Similarly, when the relative phase accumulates in the negative direction, when A0and k are positive values, the beat envelope the minimum relative phase may fall within the interval of 0° to -90°. According to the above description, it can be known that the relative phase between the injected signal and the inherent oscillation signal that causes the minimum voltage (more specifically, the local minimum voltage) in the demodulated voltage sequence to occur falls within the interval between +90° and -90°. Among them, the local minimum voltage can be the voltage at which the change trend of the demodulated voltage decreasing in the demodulated voltage sequence is reversed.

[0049] Figure 11 is a schematic diagram illustrating a detailed implementation of the XO 20 according to an embodiment of the present application. Note that the injection switch is turned on in the start-up process, which is omitted in Figure 11 for the sake of brevity. In addition to the demodulation circuit 310 shown in Figure 6 , the frequency controller 300 shown in Figure 3 may further include a monitoring circuit 320 coupled to the demodulation circuit, and a finite state machine (FSM) 330 (FSM with a counter) coupled to the monitoring circuit 320 and the external oscillator 200 (e.g., the low-Q oscillator 210). In this embodiment, the FSM 330 can utilize the injected signal as a counting clock (e.g., CLK counting), but the present application is not limited thereto. In this embodiment, the monitoring circuit 320 can be configured to generate the monitoring result from the demodulation voltage sequence, and the FSM 330 can be configured to control the external oscillator 200 (e.g., the low-Q oscillator 210) by the signal V control to selectively change the injection frequency according to the monitoring result to ensure that the relative phase falls in the interval between +90 degrees and -90 degrees. In Figure 11 the embodiment, the monitoring circuit 320 can include an amplifier AMP COMP , a capacitor C COMP and a loop switch controlled by a signal LOOP EN , wherein a first input of the amplifier AMP COMP labeled as "+" on the amplifier AMP Figure 11 shown in COMP may be coupled to the demodulation circuit 310 (e.g., a sampling node therein), the capacitor C COMP may be coupled between a reference terminal and a second input of the amplifier AMP COMP labeled as "-" on the amplifier AMP Figure 11 shown in COMP , and the loop switch can be coupled between the second input and an output of the amplifier AMP COMP . In this embodiment, a D flip-flop (DFF) 322 controlled by the signal LOOP EN may be included in the monitoring circuit 320, wherein the DFF is coupled between the output of the amplifier AMP COMP and the FSM 330 to make the FSM 330 receive only a digital result, but the present application is not limited thereto.

[0050] In detail, the amplifier AMP COMP may be configured to receive the demodulation voltage sequence through its first input, the capacitor C COMP may be configured to sequentially store the demodulation voltage sequence, and the loop switch is configured to control the configuration of the monitoring circuit 320. For better understanding, please refer to Figure 12 and Figure 13 , wherein, Figure 12 shows the operation of the monitoring circuit 320 shown in Figure 11 in the pre-setting phase. Figure 13 shows the operation of the monitoring circuit 320 shown in Figure 11 in the evaluation phase. During the pre-setting phase of the monitoring circuit 320, the loop switch is turned on, and the monitoring circuit 320 is configured as a unity gain buffer to pass the demodulation voltage sequence from the first input of the amplifier AMP COMP to the capacitor C COMP (e.g., the amplifier AMPCOMP the first demodulation voltage within the sequence of demodulation voltages. In the evaluation phase, the loop switch is opened and the monitoring circuit 320 is configured as a comparator to compare the second demodulation voltage on the first input of the amplifier AMP COMP the first demodulation voltage stored on the capacitor with the second demodulation voltage on the second input of the amplifier AMP COMP and generate a comparison result, wherein the monitoring result comprises the comparison result. In this way, successive comparison results for the sequence of demodulation voltages can be generated, wherein these successive comparison results can represent the monitoring result.

[0051] It is assumed that a comparison result of "0" of the monitoring circuit 320 indicates that a previous demodulation voltage (e.g. the first demodulation voltage described above) of two successive demodulation voltages within the sequence of demodulation voltages is greater than a following demodulation voltage (e.g. the second demodulation voltage described above) of the two successive demodulation voltages within the sequence of demodulation voltages, and a comparison result of "1" of the monitoring circuit 320 indicates that the previous demodulation voltage of the two successive demodulation voltages is smaller than the following demodulation voltage. Thus, when the comparison result changes from "0" to "1", it means that a local minimum of the sequence of demodulation voltages is detected.

[0052] In practice, there can be an inherent offset V COMP caused by the mismatch of the first input and the second input of the amplifier AMP OS . Based on the operations shown in FIGS. Figure 12 and Figure 13 , the influence from the inherent offset V OS can be removed from the comparison result. For example, when the first demodulation voltage (which can be represented by "V[n]") is transferred from the first input of the amplifier AMP COMP to the second input of the amplifier AMP COMP in the pre-setup phase, the inherent offset V OS can be stored on the capacitor C COMP together with the first voltage, thus the capacitor C COMP can store the voltage V[n]-V OS ; in the evaluation phase, the second demodulation voltage (which can be represented by V[n+1]) can exist on the first input of the amplifier AMP COMP together with the inherent offset V COMP . Since both the first input and the second input of the amplifier AMP RESULT have the inherent offset, the comparison result (e.g. the AD Figure 13 shown in FIG. counting will not be affected by the inherent offset.

[0053] It should be noted that the monitoring circuit 320 is not limited to the AD Figure 11The XO 20 shown is used. Any system requiring continuous comparison operations (e.g., generating comparison results about adjacent data (or voltages) within a data (or voltage) sequence) can be implemented by the monitoring circuit 320.

[0054] In another embodiment, the diode D0 in the demodulation circuit 310 can be used as follows: Figure 14 The transistor M0 shown is replaced by an N-type transistor, wherein the gate terminal of transistor M0 is coupled to the drain terminal of transistor M0, so that the transistor functions as a diode, but the invention is not limited thereto. Note that the injection switch is turned on during startup, and... Figure 11 The middle part has been omitted for the sake of brevity.

[0055] In another embodiment, monitoring circuit 320 can be replaced by monitoring circuit 320A, such as... Figure 15 As shown in the XO30 diagram, the monitoring circuit 320A may include a comparator COMP, a first sampling switch controlled by the signal SH, a second sampling switch controlled by the signal SHB, a first sampling capacitor C1, and a second sampling capacitor C2. Note that the injection switch is on during startup, and for simplicity... Figure 11 The middle part is omitted. For example... Figure 15 As shown, the first sampling switch and the first sampling capacitor C1 form a first sampling and holding circuit, which is coupled to the first input terminal of the comparator COMP (marked as "+" on the comparator COMP). The second sampling switch and the second sampling capacitor C2 form a second sampling and holding circuit, which is coupled to the second input terminal of the comparator COMP (marked as "-" on the comparator COMP). The signals VA and VB represent the voltages at the first and second input terminals of the comparator COMP.

[0056] Figure 16 This is illustrated in the embodiments of the present invention. Figure 15 Some signals within XO 20 shown (e.g., the counting clock CLK) counting The timing diagram shows signals RST, RSTB, SH, SHB, VA, and VB. In this embodiment, signals RST, RSTB, SH, and SHB can be generated by a timing controller (not shown) according to a counting clock CLK, but the invention is not limited thereto. Figure 16As shown in the timing, the demodulation voltages of the demodulation voltage sequence can be sampled on the sampling capacitors C1 and C2 alternately / sequentially, and the corresponding monitoring results of the demodulation voltage sequence can be output from the comparator COMP. For example, the sampling capacitor C1 samples the first demodulation voltage, the sampling capacitor C2 samples the second demodulation voltage, the sampling capacitor C1 samples the third demodulation voltage, and the sampling capacitor C2 samples the fourth demodulation voltage.

[0057] In another embodiment, as shown in the XO 40 in Figure 17 , the monitoring circuit 320 can be replaced by an analog-to-digital converter (ADC) 320B. Please note that the injection switch is on during the start-up process, and is omitted in Figure 17 for brevity. For example, the ADC 320B can sequentially convert the demodulation voltage sequence into digital codes, where the digital codes can represent the aforementioned monitoring results, and the FSM 330 can control the low-Q oscillator 210 to selectively change the injection frequency according to the digital codes.

[0058] Figure 18 Some details related to the control of the injection frequency according to embodiments of the present application are shown. As shown in Figure 18 , the FSM 330 can control the external oscillator (e.g., the low-Q oscillator 210) to alternately switch the injection frequency to one or more target frequencies among a plurality of candidate frequencies, to make the injection frequency stepwise approach the natural frequency of the natural oscillation signal, where the plurality of candidate frequencies respectively correspond to a plurality of states of the FSM 330. In this embodiment, it is assumed that the natural frequency (which can be considered as a target frequency) is equal to a center frequency among the plurality of candidate frequencies (e.g., has a frequency error of 0 ppm with respect to the center frequency). When the injection frequency is initially at a first frequency, which has a frequency error of -5000 ppm with respect to the center frequency among the plurality of candidate frequencies, the relative phase (e.g., phase error) between the natural oscillation signal and the injection signal can start to accumulate in the positive direction, where the energy of the natural oscillation signal is increasing, and the level of the demodulation voltage sequence (e.g., the signal V De-MOD ) is decreasing, thus, the comparison result of the monitoring circuit 320 remains “0” at the beginning. When the monitoring result indicates that the following demodulation voltage is greater than the previous demodulation voltage at the time point t1 (e.g., the comparison result from the monitoring circuit 320 changes from “0” to “1”), it means that the local minimum voltage of the demodulation voltage sequence (e.g., the signal V De-MODIn this process, the FSM 330 can determine that candidate frequencies lower than a first frequency are unavailable and control the external oscillator 200 (e.g., a low-Q oscillator) to switch the injection frequency from the first frequency to a second frequency, which has a frequency error of +5000ppm relative to the center frequency, and then the comparison result returns to "0". Similarly, when the monitoring result indicates that the comparison result changes from "0" to "1" at time point t2, the FSM 330 can determine that candidate frequencies higher than the second frequency are unavailable and control the external oscillator 200 (e.g., a low-Q oscillator) to switch the injection frequency from the second frequency to a third frequency, which has a frequency error of -4000ppm relative to the center frequency. And so on, the injection frequency can be switched to a fourth, fifth, sixth, and seventh frequency at time points t3, t4, t5, and t6, respectively. For the sake of brevity, similar descriptions will not be repeated here. Accordingly, whenever the demodulated voltage in the demodulated voltage sequence reaches its minimum value, the injection frequency can be adjusted appropriately so that the relative phase can accumulate in alternating directions, thereby ensuring that the relative phase is limited to within ±90° (usually within ±40° or less), so that the energy of the inherent oscillation signal will always increase.

[0059] Figure 19 Some details relating to the control of the injection frequency according to another embodiment of the invention are shown. In this embodiment, it is assumed that the inherent frequency (which can be considered as the target frequency) has a frequency error of +4500 ppm relative to the center frequency. Figure 19 As shown, the monitoring results indicate that the comparison result changes from "0" to "1" at time t7 (i.e., the demodulation voltage V1 is less than the demodulation voltage V2). The FSM 330 can determine that candidate frequencies less than this third frequency (with a frequency error of -4000ppm) are unavailable and control the external oscillator 200 (e.g., a low-Q oscillator) to switch the injection frequency from the third frequency to a fourth frequency with a frequency error of +4000ppm relative to the center frequency. However, because the demodulation voltage V3 is greater than the demodulation voltage V2, the comparison result remains "1" at time t8, meaning that the switch from the third frequency to the fourth frequency cannot change the accumulation direction of the relative phase. Therefore, the FSM 330 can control the external oscillator 200 (e.g., a low-Q oscillator) to further switch the injection frequency from the fourth frequency to an eighth frequency (with a frequency error of +4500ppm) greater than the fourth frequency (with a frequency error of +4000ppm) to change the accumulation direction of the relative phase. Similarly, if the comparison result remains "1" after the injection frequency is switched from the ninth frequency to the tenth frequency, which is less than the ninth frequency, the FSM 330 can control the external oscillator 200 (e.g., a low-Q oscillator) to further switch the injection frequency from the tenth frequency to the eleventh frequency, which is less than the tenth frequency.

[0060] In some embodiments, according to the monitoring result, the FSM 330 can control the external oscillator 200 (e.g., the low-Q oscillator 210) to alternately switch the injection frequency to a first candidate frequency (e.g., the first frequency has a -5000 ppm frequency error) or a second candidate frequency (e.g., the second frequency has a +5000 ppm frequency error). Note that the first frequency is greater than the natural frequency of the natural oscillation signal, and the second frequency is less than the natural frequency, so that each switch between the first candidate frequency and the second candidate frequency is indeed capable of changing the cumulative direction of the relative phase. Therefore, the relative phase can still be limited within ±90°, and it can be ensured that the energy of the natural oscillation signal is always increasing during the start-up process only by means of the two candidate frequencies.

[0061] In some embodiments, the injection switch can be turned on for a predetermined period of time. That is, the time point at which the injection switch is turned off (or the time at which the start-up process is completed) can be predetermined. In other embodiments, the system including the XO 20 can monitor at least one signal within the XO 20 to trigger the system to complete the start-up process (e.g., turn off the injection switch) in response to the at least one signal satisfying a certain condition. In one embodiment, assuming that the initial demodulation voltage represents a first demodulation voltage of a demodulation voltage sequence at the start of the start-up process, when a target demodulation voltage of the demodulation voltage sequence is detected, the system can determine that the start-up process is completed, and the injection switch can be turned off, where a voltage difference between the target demodulation voltage and the initial demodulation voltage is greater than or equal to a predetermined value. Therefore, when the energy of the natural oscillation signal grows to a certain value that causes the target demodulation voltage to appear, it can be considered that the start-up process has been completed, and the injection switch is turned off.

[0062] The start-up method and related XO architecture provided by the embodiments of the present application can control the switching of the injection frequency based on the distortion square wave caused by the amplitude modulation of the injection signal and the natural oscillation signal, so that the relative phase between the injection signal and the natural oscillation signal is limited within a desired interval (e.g., ±90°). Based on this, the injection switch does not need to be turned off in the aforementioned lock / synchronization period, and it is further ensured that the energy of the natural oscillation signal is always increasing. Assuming that the start-up process requires a reference period of time when the injection frequency of the injection signal is the same as the natural frequency of the XO core circuit. As for the method of temporarily interrupting clock injection during the previous lock / synchronization period, it can require 17.4 times to 90.6 times the reference period of time for the start-up process. As for the start-up method of turning off the injection only after the start-up process is completed, it can require 1.05 to 1.5 times the reference period of time, which means that the present application indeed greatly improves the efficiency of clock injection, and the start-up time can be greatly reduced.

[0063] Those skilled in the art will readily observe that numerous modifications and changes in the devices and methods can be made without departing from the teachings of the present application. Accordingly, the above disclosure is intended to be illustrative only and not limiting of the scope of the application as set forth in the following claims.

Claims

1. A method for starting a crystal oscillator XO by means of an external clock injection, characterized in that, The method includes: An injection signal is generated using an external oscillator located outside the XO core circuit of the XO, wherein the XO includes an XO core circuit, the external oscillator located outside the XO core circuit, and at least one injection switch coupled between an injection node of the XO and the output of the XO core circuit, the external oscillator being coupled to the injection node, and the quality factor of the external oscillator being lower than that of the XO core circuit. By activating at least one injection switch, the energy of the injection signal is injected into the XO core circuit, thereby increasing the energy of the inherent oscillation signal of the XO core circuit, wherein a modulation signal is generated at the injection node based on a combination of the injection signal and the inherent oscillation signal; and The external oscillator is controlled according to the modulation signal to selectively change the injection frequency of the injection signal; wherein, when the external oscillator selectively changes the injection frequency of the injection signal, the at least one injection switch is turned on.

2. The method according to claim 1, characterized in that, The step of controlling the external oscillator according to the modulation signal to selectively change the injection frequency of the injected signal includes: The demodulation circuit of the XO generates a demodulation voltage sequence based on the modulation signal, and the demodulation voltage sequence carries information about the relative phase between the injected signal and the inherent oscillation signal; Using the monitoring circuit of the XO, a monitoring result is generated based on the demodulated voltage sequence; and Based on the monitoring results, the external oscillator is controlled to selectively change the injection frequency.

3. The method according to claim 2, characterized in that, The step of controlling the external oscillator to selectively change the injection frequency based on the monitoring results includes: The injection frequency is alternately switched to a first frequency or a second frequency based on the monitoring results, so that the relative phase falls within an interval between +90 degrees and -90 degrees, wherein the first frequency is greater than the inherent frequency of the inherent oscillation signal, and the second frequency is less than the inherent frequency; Alternatively, the injection frequency may be alternately switched to a frequency in a first group of frequencies or a frequency in a second group of frequencies based on the monitoring results, wherein the first group of frequencies is greater than the inherent frequency of the inherent oscillation signal, and the second group of frequencies is less than the inherent frequency.

4. The method according to claim 2, characterized in that, The step of controlling the external oscillator to selectively change the injection frequency based on the monitoring results includes: Based on the monitoring results, the injection frequency is switched among multiple candidate frequencies to make the injection frequency close to the inherent frequency of the inherent oscillation signal, wherein the multiple candidate frequencies correspond to multiple states of the finite state machine (FSM).

5. The method according to claim 2, characterized in that, The demodulation voltage sequence includes a first demodulation voltage and a second demodulation voltage following the first demodulation voltage, and the step of controlling the external oscillator to selectively change the injection frequency based on the monitoring result includes: In response to the monitoring result indicating that the second demodulation voltage is greater than the first demodulation voltage, the injection frequency is switched from the first frequency to the second frequency.

6. The method according to claim 5, characterized in that, The demodulation voltage sequence further includes a third demodulation voltage following the second demodulation voltage, and the step of controlling the external oscillator to selectively change the injection frequency based on the monitoring result further includes: In response to the monitoring result indicating that the third demodulation voltage is greater than the second demodulation voltage, the injection frequency is switched from the second frequency to the third frequency; Wherein, the first frequency is greater than the second frequency, and the second frequency is greater than the third frequency; or, the first frequency is less than the second frequency, and the second frequency is less than the third frequency.

7. The method according to claim 2, characterized in that, The demodulated voltage sequence includes a first demodulated voltage and a second demodulated voltage following the first demodulated voltage. The monitoring circuit includes an amplifier and a capacitor. The step of generating a monitoring result based on the demodulated voltage sequence using the monitoring circuit includes: By switching on a loop switch coupled between the second input and output of the amplifier, the monitoring circuit is configured as a unity-gain buffer to transfer the first demodulated voltage from the first input of the amplifier to a capacitor coupled to the second input of the amplifier; and The monitoring circuit is configured as a comparator to compare a second demodulated voltage at the first input of the amplifier with a first demodulated voltage stored on the capacitor by disconnecting the loop switch, and to generate a comparison result accordingly, wherein the monitoring result includes the comparison result.

8. The method according to claim 2, characterized in that, The step of generating the demodulated voltage sequence based on the modulation signal using the demodulation circuit includes: Turn on the reset switch of the demodulation circuit and turn off the sampling switch of the demodulation circuit, so as to reset the voltage level of the sampling node of the demodulation circuit to the reference level during the reset period; and During the sampling period, in response to the voltage level of the modulation signal exceeding the threshold corresponding to the diode of the demodulation circuit, the reset switch is turned off and the sampling switch is turned on to accumulate charge at the sampling node to generate the demodulation voltage of the demodulation voltage sequence at the sampling node.

9. The method according to claim 2, characterized in that, The initial demodulation voltage represents the first demodulation voltage in the demodulation voltage sequence, and the method further includes: In response to the detection of a target demodulated voltage in the demodulated voltage sequence to indicate the completion of the startup process, at least one injection switch is disconnected, wherein the voltage difference between the target demodulated voltage and the initial demodulated voltage is greater than or equal to a predetermined value.

10. A crystal oscillator XO, characterized in that, include: The XO core circuit is used to generate the inherent oscillation signal; An external oscillator, coupled to the injection node of the XO, is used to generate an injection signal, wherein the quality factor of the external oscillator is lower than the quality factor of the XO core circuit. At least one injection switch is coupled between the injection node and the output of the XO core circuit, wherein when the at least one injection switch is turned on, the energy of the injection signal is injected into the XO core circuit to increase the energy of the inherent oscillation signal, and a modulation signal is generated at the injection node according to the combination of the injection signal and the inherent oscillation signal; and A frequency controller, coupled to the external oscillator, is used to control the external oscillator to selectively change the injection frequency of the injected signal according to the modulation signal; Specifically, when the external oscillator selectively changes the injection frequency of the injection signal, the at least one injection switch is turned on.

11. The XO according to claim 10, characterized in that, The frequency controller includes: A demodulation circuit is used to receive a modulated signal and generate a demodulated voltage sequence based on the modulated signal, wherein the demodulated voltage sequence carries information about the relative phase between the injected signal and the inherent oscillation signal; A monitoring circuit, coupled to the demodulation circuit, is used to generate a monitoring result based on the demodulated voltage sequence; and A finite state machine (FSM), coupled to the monitoring circuit and the external oscillator, is configured to control the external oscillator to selectively change the injection frequency based on the monitoring results.

12. The XO according to claim 11, characterized in that, The FSM controls the external oscillator to alternately switch the injection frequency to a first frequency or a second frequency based on the monitoring results, so that the relative phase falls within the interval between +90 degrees and -90 degrees, wherein the first frequency is greater than the inherent frequency of the inherent oscillation signal, and the second frequency is less than the inherent frequency.

13. The XO according to claim 11, characterized in that, The FSM controls the external oscillator to switch the injection frequency among multiple candidate frequencies based on the monitoring results, so that the injection frequency is close to the inherent frequency of the inherent oscillation signal, wherein the multiple candidate frequencies correspond to multiple states of the FSM.

14. The XO according to claim 11, characterized in that, The demodulation voltage sequence includes a first demodulation voltage and a second demodulation voltage following the first demodulation voltage; and when the monitoring result indicates that the second demodulation voltage is greater than the first demodulation voltage, the FSM controls the external oscillator to switch the injection frequency from the first frequency to the second frequency.

15. The XO according to claim 14, characterized in that, The demodulation voltage sequence also includes a third demodulation voltage following the second demodulation voltage. When the monitoring result indicates that the third demodulation voltage is greater than the second demodulation voltage, the FSM controls the external oscillator to switch the injection frequency from the second frequency to the third frequency, wherein the first frequency is greater than the second frequency and the second frequency is greater than the third frequency; or, the first frequency is less than the second frequency and the second frequency is less than the third frequency.

16. The XO according to claim 11, characterized in that, The demodulated voltage sequence includes a first demodulated voltage and a second demodulated voltage following the first demodulated voltage, and the monitoring circuit includes: An amplifier, coupled to the demodulation circuit, is used to receive the demodulated voltage sequence through a first input terminal of the amplifier; A capacitor, coupled to the second input terminal of the amplifier, is used to sequentially store the demodulated voltage sequence; and A loop switch, coupled between the second input terminal and the output terminal of the amplifier, is used to control the configuration of the monitoring circuit; Wherein, when the loop switch is turned on, the monitoring circuit is configured as a unity-gain buffer to transmit the first demodulated voltage from the first input terminal of the amplifier to the capacitor; and when the loop switch is turned off, the monitoring circuit is configured as a comparator to compare the second demodulated voltage at the first input terminal of the amplifier with the first demodulated voltage stored on the capacitor and generate a comparison result, wherein the monitoring result includes the comparison result.

17. The XO according to claim 11, characterized in that, The demodulation circuit includes: A diode, the cathode of which is coupled to the sampling node of the demodulation circuit; A reset switch is coupled between the sampling node and the reference terminal of the demodulation circuit; A sampling switch, coupled to the anode of the diode; and A sampling capacitor is coupled to the sampling node; Specifically, when the reset switch is turned on and the sampling switch is turned off during the reset period, the voltage level of the sampling node is reset to the reference level of the reference terminal; and when the reset switch is turned off and the sampling switch is turned on during the sampling period, in response to the voltage level of the modulation signal exceeding the threshold corresponding to the diode, charge accumulates on the sampling node, and the demodulation voltage of the demodulation voltage sequence is generated on the sampling node.

18. The XO according to claim 11, characterized in that, The initial demodulation voltage represents the first demodulation voltage in the demodulation voltage sequence; when a target demodulation voltage in the demodulation voltage sequence is detected to indicate that the startup process is complete, the at least one injection switch is turned off, wherein the voltage difference between the target demodulation voltage and the initial demodulation voltage is greater than or equal to a predetermined value.

19. A monitoring circuit, characterized in that, For generating successive comparison results of a demodulated voltage sequence, the demodulated voltage sequence carrying information about the relative phase between the injected signal and the inherent oscillation signal of XO, the monitoring circuit includes: An amplifier for receiving the demodulated voltage sequence through a first input terminal of the amplifier, wherein the demodulated voltage sequence includes a first voltage and a second voltage following the first voltage; A capacitor, coupled to the second input terminal of the amplifier, is used to sequentially store the demodulated voltage sequence; and A loop switch, coupled between the second input terminal and the output terminal of the amplifier, is used to control the configuration of the monitoring circuit; When the loop switch is closed, the monitoring circuit is configured as a unity-gain buffer to transfer the first voltage from the first input terminal of the amplifier to the capacitor; when the loop switch is open, the monitoring circuit is configured as a comparator to compare the second voltage at the first input terminal of the amplifier with the first voltage stored on the capacitor and generate a comparison result in the continuous comparison results; wherein the comparison result carries information about the relative phase between the injected signal and the inherent oscillation signal of XO, and is used to control the injection frequency of the injected signal.

20. The monitoring circuit according to claim 19, characterized in that, When the loop switch is turned on, the inherent offset caused by the mismatch between the first and second input terminals of the amplifier is stored on the capacitor along with the first voltage, thereby preventing the comparison result from being affected by the inherent offset.

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