Crystal oscillator circuit and electronic device

Abstract

This application relates to the field of crystal oscillator technology, and discloses a crystal oscillator circuit and electronic device. The crystal oscillator circuit includes a quartz crystal, an adjustable gain oscillation amplifier circuit, a feedback resistor, and two adjustable negative capacitor circuits. The oscillation amplifier circuit is connected in parallel with the quartz crystal; the feedback resistor is also connected in parallel with the oscillation amplifier circuit; the two capacitor circuits are respectively connected between the first terminal of the quartz crystal and signal ground, and between the second terminal of the quartz crystal and signal ground. The embodiments of this application can simultaneously achieve low phase noise and a wide crystal resonant frequency range, and are applicable to various quartz crystals.

Description

Technical Field

[0001] This application relates to the field of crystal oscillator technology, and in particular to a crystal oscillator circuit and electronic device. Background Technology

[0002] A crystal oscillator is an electronic component that uses the piezoelectric effect of a quartz crystal to generate a stable frequency signal. It is widely used in electronic devices that require high-precision and high-stability clock signals. However, current crystal oscillators suffer from limitations in their applicable frequency range or high phase noise, and cannot simultaneously achieve both low phase noise and a wide crystal resonant frequency range. Utility Model Content

[0003] The purpose of this application is to provide a crystal oscillator circuit and electronic device that can simultaneously achieve low phase noise and a wide crystal resonant frequency range, and is applicable to a variety of quartz crystals.

[0004] This application provides a crystal oscillator circuit, including: Quartz crystal; An adjustable gain oscillating amplifier circuit is connected in parallel with the quartz crystal; A feedback resistor is connected in parallel with the oscillation amplifier circuit; Two load capacitor circuits with adjustable capacitance values ​​are respectively connected between the first end of the quartz crystal and the signal ground, and between the second end of the quartz crystal and the signal ground.

[0005] In some embodiments, the load capacitor circuit includes at least two load capacitor branches, each including a load capacitor and a switching device, wherein the load capacitor and the switching device are connected in series.

[0006] In some embodiments, the load capacitor circuit includes an adjustable capacitor.

[0007] In some embodiments, the oscillation amplifier circuit includes at least two parallel oscillation amplifier branches, each branch including an inverting amplifier and a switching device, wherein the inverting amplifier and the switching device are connected in series.

[0008] In some embodiments, the amplification gain of each oscillation amplification branch is different.

[0009] In some embodiments, the crystal oscillator circuit further includes: A low-dropout linear regulator is used to provide the operating voltage source for the oscillation amplifier circuit.

[0010] In some embodiments, the crystal oscillator circuit further includes: A bandgap reference source is used to provide a reference current for the oscillation amplifier circuit.

[0011] In some embodiments, the crystal oscillator circuit further includes: An output amplifier circuit is used to amplify and output the output signal of the oscillation amplifier circuit.

[0012] In some embodiments, the quartz crystal is selected as an AT-cut crystal.

[0013] This application also provides an electronic device, characterized in that it includes the crystal oscillator circuit described above.

[0014] The beneficial effects of this application are as follows: The oscillator design, based primarily on the Pierce oscillator topology, features low phase noise. By configuring an adjustable gain oscillation amplifier circuit and a two-capacitor circuit with adjustable values, it can be adapted to quartz crystals with different resonant frequencies. Furthermore, the adjustable load capacitor circuit allows for flexible expansion of the crystal oscillation circuit's output frequency, covering multiple frequency bands without replacing the quartz crystal. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the crystal oscillator circuit provided in the first embodiment of this application.

[0016] Figure 2 This is a schematic diagram of the crystal oscillator circuit provided in the second embodiment of this application.

[0017] Figure 3 This is a schematic diagram of the crystal oscillator circuit provided in the third embodiment of this application. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0019] It should be noted that the terms "first," "second," "third," "fourth," etc. (if present) in the specification and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that embodiments of this application can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a system, product, or device that includes a series of circuits is not necessarily limited to those explicitly listed, but may include other circuits not explicitly listed or inherent to such systems, products, or devices.

[0020] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing embodiments of this application only and is not intended to limit this application.

[0021] This application provides a crystal oscillator circuit.

[0022] See Figure 1 In one embodiment, the crystal oscillator circuit includes a quartz crystal 1, an oscillation amplifier circuit 2, a feedback resistor 3, and a two-load capacitor circuit 4.

[0023] The amplification gain of the oscillating amplifier circuit 2 is adjustable, and it is connected in parallel with the quartz crystal 1. The quartz crystal 1 refers to a resonant element with a piezoelectric effect. The adjustable-gain oscillating amplifier circuit 2 is a circuit module capable of dynamically adjusting the signal amplification gain. Specifically, it can be implemented using multiple amplification branches. By switching different amplification branches, the overall amplification gain of the oscillating amplifier circuit 2 can be changed to provide appropriate phase shift and current gain, compensating for the energy loss of the resonant circuit.

[0024] Feedback resistor 3 is connected in parallel with oscillation amplifier circuit 2. It can be understood that feedback resistor 3 is used to establish the DC bias point of oscillation amplifier circuit 2, and its resistance value must satisfy the Barkhausen oscillation criterion.

[0025] The capacitance values ​​of the two load capacitor circuits 4 are adjustable. The two load capacitor circuits 4 are connected between the first terminal of the quartz crystal 1 and the signal ground, and between the second terminal of the quartz crystal 1 and the signal ground, respectively. It can be understood that the load capacitor circuit 4 refers to a capacitive network connected between the crystal port and ground. Specifically, it can be implemented using a structure of multiple capacitive branches connected in parallel. By controlling the switching state of each capacitive branch, the equivalent capacitance value of the load capacitor circuit 4 is changed, thereby adjusting the resonant frequency to match the crystal resonant frequency of the quartz crystal 1.

[0026] A Pierce oscillator topology is constituted by a quartz crystal 1, an oscillator amplifier circuit 2, a feedback resistor 3, and two load capacitor circuits 4. In practical applications, the quartz crystal 1 is connected as a resonant element between the input and output terminals of the oscillator amplifier circuit 2, forming a closed oscillation loop. The quartz crystal 1 generates mechanical vibration when an alternating electric field is applied, forming a stable resonant frequency. To accommodate different crystal resonant frequencies of the quartz crystal 1, the amplification gain of the oscillator amplifier circuit 2 is adjusted to match the crystal resonant frequency of the quartz crystal 1. The oscillator amplifier circuit 2 feeds the output signal back to its own input terminal through inverting amplification, forming a positive feedback loop. Simultaneously, the equivalent capacitance values ​​of the two load capacitor circuits 4 are changed so that, while matching the crystal resonant frequency of the quartz crystal 1, the output frequency of the crystal oscillator circuit matches the target output frequency. Furthermore, the feedback resistor 3 provides DC bias to the oscillator amplifier circuit 2, ensuring it operates in the linear amplification region. Simultaneously, by being connected in parallel with the oscillator amplifier circuit 2, it reduces the impact on the input impedance of the oscillator amplifier circuit 2. Therefore, the oscillator design based on the Pierce oscillator topology features low phase noise. By configuring an adjustable gain oscillation amplifier circuit 2 and a two-capacitor adjustable load capacitor circuit 4, it can be adapted to quartz crystals 1 with different crystal resonant frequencies. Simultaneously, the adjustable load capacitor circuit 4 allows for flexible expansion of the crystal oscillation circuit's output frequency, covering multiple frequency bands without replacing the quartz crystal 1.

[0027] See Figure 2 In one embodiment, the load capacitor circuit 4 includes at least two load capacitor branches 41, each of which includes a load capacitor and a switching device connected in series.

[0028] Load capacitor branch 41 refers to one of the capacitive circuit branches constituting load capacitor circuit 4, and all load capacitor branches 41 are connected in parallel. Load capacitor refers to the capacitive element used to form the equivalent load capacitance, which can be implemented using multilayer ceramic capacitors or film capacitors, and its capacitance value can range from 0.5 picofarads to 20 picofarads.

[0029] When the required resonant frequency needs to be adjusted according to the quartz crystal 1, the switching states of different load capacitor branches 41 are controlled to selectively turn on a corresponding number of load capacitor branches 41. For example, when it is necessary to reduce the resonant frequency, a larger number of load capacitor branches 41 can be turned on, increasing the total load capacitance value of the load capacitor circuit 4 and reducing the resonant frequency. The series connection structure of the switching devices and load capacitors in each load capacitor branch 41 avoids parallel interference caused by multiple branches being turned on simultaneously, while ensuring complete isolation of the corresponding load capacitor branch 41 in the off state. When digitally controlling the switching devices of the load capacitor branches 41, the VCXO (voltage-controlled crystal oscillator) function can be realized. Thus, by using multiple independently controllable load capacitor branches 41, the total load capacitance value of the load capacitor branches 41 can be adjusted in the smallest step, thereby accurately matching different frequency requirements.

[0030] In some embodiments, the load capacitor circuit 4 includes an adjustable capacitor.

[0031] Adjustable capacitors are capacitive components whose capacitance can be changed by electrical signals or mechanical structures. Specifically, they can be implemented using varactor diodes or microelectromechanical systems (MEMS) adjustable capacitor structures. By changing the voltage applied across them or the amount of mechanical displacement, the capacitance can be continuously or incrementally adjusted, thereby precisely matching the load capacitance requirements at different frequencies.

[0032] In practical applications, the adjustable capacitor is integrated into the load capacitor circuit 4 across the quartz crystal 1. When the oscillation frequency needs to be adjusted, the capacitance value of the adjustable capacitor is changed, causing a corresponding change in the overall capacitance value of the load capacitor circuit 4. This change directly affects the equivalent load capacitance of the quartz crystal 1, causing a shift in the resonant frequency of the quartz crystal 1. Thus, continuous adjustment without mechanical contact is achieved through an electrically controlled adjustable capacitor, reducing the circuit layout area.

[0033] See Figure 2 In one embodiment, the oscillation amplifier circuit 2 includes at least two parallel oscillation amplifier branches 21, each including an inverting amplifier and a switching device connected in series.

[0034] When it is necessary to adjust the overall amplification gain of the oscillation amplifier circuit 2, the inverting amplifier of the corresponding oscillation amplifier branch 21 can be connected to the circuit by controlling the conduction state of the switching devices of different oscillation amplifier branches 21. When the switching device of a certain oscillation amplifier branch 21 is in the conduction state, the inverting amplifier of that oscillation amplifier branch 21 is connected to the reference current input from the outside ( Figure 2 I in REF ) and working voltage source ( Figure 2 V in REFWhen the operating voltage source is connected, the circuit is powered on and starts, applying a preset gain value to the reference current and outputting a corresponding gain current. The total gain of multiple oscillation amplification branches 21 connected in parallel is determined by the sum of the total gain currents of each activated oscillation amplification branch 21. Thus, by selecting different numbers or different gain values ​​of branch combinations, step-wise adjustment of the gain can be achieved. For example, the oscillation amplification circuit 2 may be configured with three sets of oscillation amplification branches 21. When each set of oscillation amplification branches 21 is turned on, the output gain current of the oscillation amplification circuit 2 is 600μA. When the crystal oscillation frequency of the connected quartz crystal 1 is 32M-64M, one set of oscillation amplification branches 21 is turned on, and the overall gain current of the oscillation amplification circuit 2 is 600μA. When the crystal oscillation frequency of the connected quartz crystal 1 is 66M-100M, all three sets of oscillation amplification branches 21 are turned on, and the overall gain current of the oscillation amplification circuit 2 is 1.8mA. Therefore, by configuring the oscillation amplifier circuit 2 with a parallel multi-branch structure, the crystal oscillation circuit can maintain low phase noise characteristics while quickly switching the branch combination through switching devices to adapt to the gain requirements of different quartz crystals 1.

[0035] exist Figure 2 Furthermore, based on the embodiment, the amplification gain of each oscillation amplification branch 21 is different.

[0036] Multiple parallel oscillation amplification branches 21 are configured in the crystal oscillation circuit, each equipped with an inverting amplifier with a different amplification gain. When the oscillation conditions need to be adjusted, a branch with a specific gain can be selected to be connected to the circuit by controlling the switching device. For example, in low-frequency oscillation scenarios, a high-gain branch can be enabled to enhance the oscillation start-up capability, while in high-frequency scenarios, a low-gain branch can be switched to suppress phase noise. Thus, the combination of oscillation amplification branches 21 with different amplification gains can dynamically match the equivalent impedance characteristics of the quartz crystal 1, maintaining the loop gain stable in the critical oscillation state.

[0037] See Figure 3 In one embodiment, the crystal oscillator circuit further includes a low-dropout linear regulator 5.

[0038] The low-dropout linear regulator 5 is used to provide the operating voltage source for the oscillation amplifier circuit 2.

[0039] The low-dropout linear regulator 5 refers to a linear voltage regulator with a low voltage drop between the input and output. Specifically, it can be implemented using an LDO chip with low noise characteristics, capable of converting the input voltage into a stable output voltage with low ripple. In the crystal oscillator circuit, the low-dropout linear regulator 5 ensures the stability of the amplifier circuit's operating point by suppressing the impact of power supply voltage fluctuations on the oscillation amplifier circuit 2.

[0040] The input of the low-dropout linear regulator 5 is connected to an external power supply, and its output is connected to the power supply pin of the oscillation amplifier circuit 2. When there are voltage fluctuations or noise interference in the external power supply, the low-dropout linear regulator 5 adjusts its output through an internal feedback loop to maintain a constant supply voltage to the oscillation amplifier circuit 2. For example, when the external power supply voltage fluctuates due to load changes, the low-dropout linear regulator 5 adjusts the conduction state of its internal power transistor to maintain the output voltage at a preset value, thereby preventing the oscillation amplifier circuit 2 from experiencing frequency shifts or increased phase noise due to unstable power supply. Thus, by providing the operating voltage source for the oscillation amplifier circuit 2 through the low-dropout linear regulator 5, efficient voltage regulation can be achieved under relatively small voltage drop conditions, reducing power loss in the power supply path. At the same time, by optimizing the design of the internal reference and error amplifier, the influence of high-frequency noise on the crystal oscillator circuit is further suppressed.

[0041] See Figure 3 In one embodiment, the crystal oscillator circuit further includes a bandgap reference source 6.

[0042] The bandgap reference source 6 is used to provide a reference current for the oscillation amplifier circuit 2.

[0043] Bandgap reference source 6 refers to a reference voltage generation circuit built based on the bandgap voltage characteristics of semiconductor materials. Specifically, it can be implemented using a combination of bipolar transistors and resistor networks, outputting a stable reference voltage independent of temperature changes through a temperature compensation mechanism. Reference current refers to the constant current value formed by converting the voltage generated by bandgap reference source 6 through a resistor. Specifically, it can be implemented using a current mirror circuit composed of an operational amplifier and a field-effect transistor, used to provide bias current to the transistors in the oscillation amplifier circuit 2.

[0044] The bandgap reference source 6 uses an internal temperature compensation circuit to offset the effects of temperature changes on the output voltage, generating a stable reference voltage. This reference voltage is converted into a reference current by a resistor network and then input to the oscillation amplifier circuit 2 as the basis for generating the oscillation signal. Since the reference current is unaffected by temperature fluctuations or power supply voltage changes, the transconductance gain and phase characteristics of the oscillation amplifier circuit 2 are stabilized, thereby suppressing frequency shift and phase noise degradation caused by bias current drift. Thus, by eliminating temperature dependence through its internal compensation mechanism, the bandgap reference source 6 improves the stability of the reference current, thereby reducing the noise component introduced by current fluctuations in the oscillation signal.

[0045] See Figure 3 In one embodiment, the crystal oscillator circuit further includes an output amplifier circuit 7.

[0046] Output amplifier circuit 7 is used to amplify and output the output signal of oscillation amplifier circuit 2.

[0047] Output amplifier circuit 7 refers to the circuit module that amplifies the amplitude of the polarization signal generated by oscillation amplifier circuit 2. Specifically, it can be implemented using an operational amplifier or a transistor amplifier circuit. By adjusting the amplification factor to match the requirements of the back-end circuit, the phase noise during signal transmission can be reduced.

[0048] In this embodiment, the output amplifier circuit 7 is a push-pull drive circuit based on a CMOS circuit topology. It amplifies the output signal and converts it into a square wave before outputting it. The output amplifier circuit 7 receives the initial oscillation signal generated by the oscillation amplifier circuit 2, adjusts the signal amplitude through an internal gain module, and outputs it to the external circuit after buffering and isolation. During this process, the signal amplitude is boosted to a level suitable for subsequent circuit processing, while impedance matching reduces signal reflection and loss, ensuring the stability and accuracy of the output frequency. The output amplifier circuit 7 can employ a multi-stage amplification structure, such as a combination of a preamplifier stage and a power amplifier stage, progressively improving signal quality. Therefore, by introducing the output amplifier circuit 7, signal driving capability is enhanced while maintaining frequency stability, effectively suppressing noise interference, and adapting to more complex load environments.

[0049] In the above embodiments, the quartz crystal 1 is selected as an AT-cut crystal.

[0050] AT-cut crystals refer to quartz crystals 1 processed at a specific cutting angle, specifically using quartz wafers with a cutting angle of 35°15'. This cutting method causes the crystal frequency to exhibit a cubic curve characteristic as a function of temperature. Specifically, AT-cut crystals have stable frequency output characteristics over a wide temperature range, with their temperature coefficient showing a gradual change in the range of -40℃ to 85℃. By employing AT-cut crystals, the crystal oscillator circuit utilizes their inherent temperature compensation characteristics to ensure that the oscillation frequency remains relatively stable even when the ambient temperature fluctuates. The load capacitor circuit 4 and the amplification gain adjustment mechanism in the crystal oscillator circuit further coordinate with the frequency-temperature characteristics of the AT-cut crystal, compensating for minor shifts in the crystal's resonant frequency by adjusting the combination of capacitance and amplification gain.

[0051] In some specific implementations, the fundamental frequency mode of the AT-cut crystal can be set to a nominal frequency in the range of 16MHz to 48MHz, and its thickness is inversely proportional to the target frequency value. The crystal package can adopt a surface-mount metal housing structure with internal vacuum sealing to isolate it from the influence of external humidity.

[0052] This application also provides an electronic device.

[0053] The electronic device includes the crystal oscillator circuit described above. The specific structure of the crystal oscillator circuit is as described in the above embodiments. Since the electronic device provided in this application adopts all the technical solutions of all the above embodiments, it has at least all the beneficial effects brought about by the technical solutions of the above embodiments, which will not be described in detail here.

[0054] In summary, the crystal oscillator circuit and electronic device provided in this application adopt an oscillator design based on a Pierce oscillator topology, resulting in low phase noise. By configuring an oscillator amplifier circuit with adjustable amplification gain and a load capacitor circuit with two adjustable capacitor values, it can be adapted to quartz crystals with different crystal resonant frequencies. Furthermore, the adjustable load capacitor circuit allows for flexible expansion of the crystal oscillator circuit's output frequency, covering multiple frequency bands without replacing the quartz crystal.

[0055] It should be understood that in this application, "at least one (item)" means one or more, and "more than" means two or more. "And / or" is used to describe the relationship between related objects, indicating that three relationships can exist. For example, "A and / or B" can represent three cases: only A exists, only B exists, and both A and B exist simultaneously, where A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects are in an "or" relationship. "At least one (item) of the following" or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, at least one (item) of a, b, or c can represent: a, b, c, "a and b", "a and c", "b and c", or "a and b and c", where a, b, and c can be single or multiple.

[0056] The preferred embodiments of the present application have been described above with reference to the accompanying drawings, but this does not limit the scope of the claims of the present application. Any modifications, equivalent substitutions, and improvements made by those skilled in the art without departing from the scope and substance of the embodiments of the present application shall be within the scope of the claims of the present application.

Claims

1. A crystal oscillator circuit, characterized by comprising: The crystal oscillator circuit comprises: a quartz crystal; an oscillation amplification circuit with adjustable amplification gain, connected in parallel with the quartz crystal; a feedback resistor, connected in parallel with the oscillation amplification circuit; a load capacitance circuit with two adjustable capacitance values, connected between a first end of the quartz crystal and a signal ground and between a second end of the quartz crystal and the signal ground, respectively.

2. The crystal oscillator circuit of claim 1, wherein The load capacitance circuit comprises at least two load capacitance branches, each of which comprises a load capacitor and a switching device connected in series.

3. The crystal oscillator circuit of claim 1, wherein, The load capacitance circuit comprises an adjustable capacitor.

4. The crystal oscillator circuit of claim 1, wherein, The oscillation amplification circuit comprises at least two oscillation amplification branches connected in parallel with each other, each of which comprises an inverting amplifier and a switching device connected in series.

5. The crystal oscillator circuit of claim 4, wherein, The amplification gains of the oscillation amplification branches are different.

6. The crystal oscillator circuit of claim 1, wherein, The crystal oscillator circuit further comprises: a low-dropout linear voltage regulator for providing a working voltage source for the oscillation amplification circuit.

7. The crystal oscillator circuit of claim 1, wherein The crystal oscillator circuit further comprises: a bandgap reference source for providing a reference current for the oscillation amplification circuit.

8. The crystal oscillator circuit of claim 1, wherein, The crystal oscillator circuit further comprises: an output amplification circuit for amplifying and outputting an output signal of the oscillation amplification circuit.

9. The crystal oscillator circuit according to any one of claims 1 to 8, characterized by, The quartz crystal is an AT-cut crystal.

10. An electronic device, comprising: The crystal oscillator circuit comprises the crystal oscillator circuit according to any one of claims 1 to 9.

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