Voltage-controlled oscillator, phase-locked loop and temperature compensation method for frequency of voltage-controlled oscillator

Abstract

The invention provides a voltage-controlled oscillator, a phase-locked loop and a temperature compensation method for the frequency of the voltage-controlled oscillator, and the voltage-controlled oscillator comprises an adjustable capacitor and a temperature compensation circuit. The first end of the adjustable capacitor is connected with control voltage, the second end of the adjustable capacitor is connected with the temperature compensation circuit, and the temperature compensation circuit provides temperature compensation voltage changing along with temperature for the adjustable capacitor. According to the technical scheme, the temperature compensation circuit is used for providing the temperature compensation voltage for the voltage-controlled oscillator of the phase-locked loop, so that in and Ip of a charge pump Cp of the phase-locked loop can still be kept approximately equal when the temperature is changed and the control voltage provided by the loop filter of the phase-locked loop is kept unchanged, and the control voltage of the phase-locked loop is kept constant. Compared with a voltage-controlled oscillator in the related technology, the circuit structure in the application can reduce periodic jitter introduced in the PLL by temperature change.

Description

Technical Field

[0001] The present application belongs to the field of chip technology, and in particular relates to a voltage-controlled oscillator, a phase-locked loop, and a temperature compensation method for the frequency of a voltage-controlled oscillator. Background Art

[0002] A phase-locked loop (PLL) is a closed-loop negative feedback control system that can keep the phase of two periodic signals in a certain phase relationship. Therefore, the phase-locked loop has a wide range of uses, including measuring and tracking signal frequency, extracting a given frequency component of the original signal while eliminating noise and spurious components, or synthesizing a new signal based on the input signal. However, when the ambient temperature changes, the frequency of the PLL's voltage-controlled oscillator will change, causing the PLL to easily generate fixed periodic jitter during frequency locking. Summary of the invention

[0003] The purpose of the present application is to provide a voltage-controlled oscillator, a phase-locked loop and a temperature compensation method for the voltage-controlled oscillator frequency, aiming to solve the technical problem that the frequency of the voltage-controlled oscillator changes when the ambient temperature changes, and causes the PLL to generate periodic jitter during frequency locking.

[0004] According to a first aspect of the present application, a voltage-controlled oscillator is provided, comprising: an adjustable capacitor and a temperature compensation circuit; the first end of the adjustable capacitor is connected to a control voltage, and the second end is connected to the temperature compensation circuit, and the temperature compensation circuit provides a temperature compensation voltage that changes with temperature for the adjustable capacitor.

[0005] In an optional embodiment, the temperature compensation circuit includes a transistor; the emitter and base of the transistor are connected, the base is also connected to the second end of the adjustable capacitor, and the collector of the transistor is grounded.

[0006] In an optional implementation, the temperature compensation voltage is negatively correlated with temperature.

[0007] In an optional implementation, the capacitance value of the adjustable capacitor is negatively correlated to the voltage difference between the control voltage and the temperature compensation voltage.

[0008] According to a second aspect of the present application, a phase-locked loop is provided, comprising: the voltage-controlled oscillator described in the first aspect.

[0009] In an optional implementation, the phase-locked loop further includes: a phase frequency detector, a charge pump and a loop filter; wherein,

[0010] The phase frequency detector receives a reference clock and a frequency signal output by the voltage-controlled oscillator, and outputs a phase difference between the reference clock and the frequency signal; the charge pump is used to convert the phase difference into a current signal, and the loop filter outputs a control voltage for adjusting the frequency of the voltage-controlled oscillator based on the current signal.

[0011] According to a third aspect of the present application, a method for temperature compensation of a voltage controlled oscillator frequency is provided, comprising:

[0012] receiving a control voltage;

[0013] The capacitance value of the adjustable capacitor of the voltage-controlled oscillator is adjusted by utilizing the voltage difference between the control voltage and the temperature compensation voltage provided by the temperature compensation circuit of the voltage-controlled oscillator; the temperature compensation voltage changes with the change of temperature.

[0014] In an optional embodiment, the temperature compensation circuit includes a transistor; the emitter and base of the transistor are connected, the base is connected to the second end of the adjustable capacitor, and the collector of the transistor is grounded.

[0015] In an optional implementation, the temperature compensation voltage is negatively correlated with temperature.

[0016] In an optional implementation, the capacitance value of the adjustable capacitor is negatively correlated to the voltage difference between the control voltage and the temperature compensation voltage.

[0017] In an optional implementation, receiving a control voltage includes:

[0018] A control voltage outputted by a loop filter of a phase-locked loop is received; wherein,

[0019] The phase frequency detector of the phase-locked loop receives a reference clock and a frequency signal output by the voltage-controlled oscillator, and outputs a phase difference between the reference clock and the frequency signal; the charge pump of the phase-locked loop is used to convert the phase difference into a current signal, and the loop filter outputs a control voltage for adjusting the frequency of the voltage-controlled oscillator based on the current signal.

[0020] Compared with the related art, the technical solution of this application has the following advantages:

[0021] In the embodiment of the present application, a temperature compensation circuit is used to provide a temperature compensation voltage for a voltage-controlled oscillator of a phase-locked loop, so that when the temperature changes, the control voltage provided by the loop filter of the phase-locked loop remains unchanged, and the In and Ip of the charge pump Cp of the phase-locked loop can still be kept nearly equal. Compared with the voltage-controlled oscillator in the related art, the circuit structure in the present application can reduce the periodic jitter introduced into the PLL by temperature changes. Other features and advantages of the present application will be described in the subsequent description, and will partially become apparent from the description, or can be understood by implementing the present application. The purposes and other advantages of the present application can be achieved and obtained through the structures and processes indicated in the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the related technologies, the drawings required for use in the embodiments or the related technical descriptions are briefly introduced below. It is obvious that the drawings described below are certain embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0023] Figure 1 It is a schematic diagram of the circuit connection effect of a phase-locked loop according to the related technology.

[0024] Figure 2A It is a schematic diagram of the curve effect of the control voltage of a voltage-controlled oscillator changing with temperature according to the related technology.

[0025] Figure 2B The present invention is a schematic diagram of the circuit connection effect of a voltage-controlled oscillator and a control voltage providing circuit according to the related technology.

[0026] Figure 3A It is a schematic diagram of the circuit connection effect of a voltage-controlled oscillator and a control voltage providing circuit according to an exemplary embodiment of the present application.

[0027] Figure 3B It is a schematic diagram of the curve effect of the temperature compensation voltage output by the temperature compensation circuit of the voltage-controlled oscillator according to the exemplary embodiment of the present application changing with temperature. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0029] like Figure 1 It is the basic structure of PLL, where the function of PFD (Phase Frequency Detector) is to identify the frequency and phase difference between the reference clock and the feedback clock of PLL, and then transmit this difference to CP (Charge Pump). CP generates current according to this difference and outputs it to LPF (Loop Filter). LPF generates voltage VC (control voltage) to adjust the frequency of VCO (Voltage Control Oscillator). DIVIDER (divider) divides the clock frequency generated by VCO to obtain the feedback clock. After locking, the output frequency is N times the input frequency, where N is the division ratio of DIVIDER.

[0030] like Figure 1 As shown, the relationship between VC and frequency is a linear relationship, so if the output clock frequency of the PLL is certain, the value of VC will also be determined. After the VC value is determined, the entire PLL is in a locked state, that is, the output clock is N times the reference clock.

[0031] like Figure 1 This is the working condition of PLL at room temperature. However, when the ambient temperature changes, the frequency of VCO will change, so it is necessary to change the VC value to adjust the frequency. If the VC value reaches a certain limit, PLL will lose the ability to lock to the target frequency, resulting in PLL unlocking, that is, the output frequency is no longer equal to N times the input frequency.

[0032] like Figure 2A As shown, when the temperature increases, the VC relative to frequency curve will move upward. In this way, when achieving the same target frequency, the VC value must become larger to lock the target frequency. Therefore, the VC value will increase when the temperature increases.

[0033] like Figure 2B As shown, under normal circumstances, if VC is at a relatively medium voltage, the input current In and output current Ip of CP are relatively close, because the voltage difference of vdsn (equivalent to the voltage difference between VC and ground) and vdsp (equivalent to the voltage difference between power supply and VC) are relatively close. When the VC value becomes larger, as shown in the CP circuit on the left side of Figure 2, the vdsp voltage difference will be larger than the vdsn voltage difference, which will cause the input current In and Ip to deviate too much, resulting in fixed periodic jitter when the PLL is locked.

[0034] In the related art, in order to avoid the periodic jitter of the PLL introduced by the excessive VC when locked, the value of C_var in the VCO is increased, that is, the value of the C_var capacitor is increased, so that the deviation of VC will become smaller when the temperature changes, thereby reducing the introduced PLL periodic jitter.

[0035] However, the related technologies have the following problems:

[0036] 1) If C_var is too large, it will cause VC to change, which will increase the variation of VCO frequency.

[0037] If C_var is too large, then the same amplitude of VC change will increase the amplitude of VCO frequency change. When the PLL has other non-ideal introductions that cause VC changes, the amplitude of VCO frequency change will increase. Ultimately, when the PLL is locked, the periodic jitter introduced by the VC disturbance will increase, deteriorating the locking performance of the PLL.

[0038] 2) Increasing C_var cannot completely avoid changes in VC

[0039] Although increasing C_var can effectively reduce the amplitude of VC changes, simply reducing the amplitude of VC changes cannot completely avoid VC changes. This cannot completely eliminate the frequency change when the PLL is locked, so periodic jitter still exists.

[0040] Based on the above analysis, the present application exemplarily proposes a voltage-controlled oscillator, including: an adjustable capacitor and a temperature compensation circuit; the first end of the adjustable capacitor is connected to a control voltage, and the second end is connected to the temperature compensation circuit, and the temperature compensation circuit provides the adjustable capacitor with a temperature compensation voltage that changes with temperature.

[0041] See also Figure 3A As shown in the circuit on the right, for example, the control voltage VC comes from the loop filter LPF of the PLL, the first end of the adjustable capacitor C_var is connected to the control voltage, and the second end is connected to the temperature compensation circuit, and the temperature compensation voltage VBE provided by the temperature compensation circuit is connected to the second end of the adjustable capacitor. Figure 2B Compared with the VCO in the related art shown, the second end of the adjustable capacitor is no longer grounded, but connected to the temperature compensation circuit. In this application, the capacitance value of the adjustable capacitor is related to the voltage difference between the control voltage VC and the temperature compensation voltage VBE.

[0042] Exemplarily, the temperature compensation voltage output by the temperature compensation circuit may vary with changes in ambient temperature. Any temperature compensation circuit capable of achieving an output voltage that varies with temperature is applicable to the present application, and the present application does not impose any specific limitation on this.

[0043] In some optional implementations, the temperature compensation circuit includes a transistor; the emitter and base of the transistor are connected, the base is also connected to the second end of the adjustable capacitor, and the collector of the transistor is grounded.

[0044] Exemplarily, a temperature compensation circuit may be implemented using a transistor, that is, the present application uses the characteristics of the transistor to provide temperature compensation for the frequency output by the VCO.

[0045] like Figure 3A As shown, the emitter of the transistor is connected to a current source, and the emitter is also connected to a base, and the collector is grounded. The base of the transistor is also connected to a second end of the adjustable capacitor, thereby providing a temperature compensation voltage that varies with temperature for the adjustable capacitor.

[0046] Exemplarily, the temperature compensation voltage is negatively correlated with the temperature. Figure 3B As shown, the higher the ambient temperature, the smaller the temperature compensation voltage VBE, which is determined by the characteristics of the transistor; and the lower the ambient temperature, the higher the temperature compensation voltage VBE.

[0047] Normally, the control voltage will increase with the increase of temperature. This is because the control voltage comes from the loop filter of the phase-locked loop. As mentioned above, when the temperature rises, the curve of VC relative to frequency will move upward. Therefore, in order to achieve the same target frequency, the value of VC needs to be increased to lock at the target frequency. Therefore, the value of VC will become larger after the temperature rises. In this application, since a temperature compensation circuit is set up, the PLL can be locked at the target frequency without increasing VC.

[0048] Exemplarily, the capacitance value of the adjustable capacitor is negatively correlated with the pressure difference between the control voltage and the temperature compensation voltage. That is, the greater the pressure difference between the control voltage and the temperature compensation voltage, the smaller the capacitance value of the adjustable capacitor, and the smaller the pressure difference between the control voltage and the temperature compensation voltage, the larger the capacitance value of the adjustable capacitor. Therefore, if the ambient temperature rises, the capacitance value of the adjustable capacitor will increase, and at the same time, because the temperature compensation voltage decreases, the pressure difference between the control voltage and the temperature compensation voltage increases when the control voltage does not change, which in turn causes the capacitance value of the adjustable capacitor to decrease, thereby compensating for the part of the capacitance value of the adjustable capacitor that increases due to the increase in temperature, so that it can be ensured that the control voltage does not need to increase with the increase in temperature.

[0049] Similarly, if the ambient temperature drops, the capacitance value of the adjustable capacitor will decrease. At the same time, the temperature compensation voltage will increase, so that when the control voltage does not change, the voltage difference between the control voltage and the temperature compensation voltage will decrease, which will cause the capacitance value of the adjustable capacitor to increase, thereby compensating for the part of the capacitance value of the adjustable capacitor that decreases due to the temperature drop. Therefore, it can be ensured that the control voltage does not need to increase with the increase in temperature.

[0050] Therefore, if Figure 3A The lower end of C_var shown is not directly connected to the ground, but connected through VBE. Here, VBE is injected into the emitter of a transistor through a current source. At the same time, the characteristic of VBE is that VBE also changes when the temperature changes. By utilizing the characteristic of VBE changing with temperature, when the temperature changes, although the voltage across C_var changes, since VBE is a value that changes with temperature, the absolute value of VC can be kept almost unchanged when the temperature changes. In this way, the Ip and In of the CP of the phase-locked loop can remain close when the temperature changes, that is, almost equal. In this way, the phase-locked loop will not cause periodic jitter due to temperature changes.

[0051] Therefore, in the embodiment of the present application, a temperature compensation circuit is used to provide a temperature compensation voltage for the voltage-controlled oscillator of the phase-locked loop, so that when the temperature changes, the control voltage provided by the loop filter of the phase-locked loop remains unchanged, and the In and Ip of the charge pump Cp of the phase-locked loop can still be kept nearly equal, and the PLL will not be caused to generate periodic jitter. Compared with the voltage-controlled oscillator in the related art, the circuit structure in the present application can reduce the periodic jitter introduced in the PLL by temperature changes.

[0052] Accordingly, the present application exemplarily provides a phase-locked loop, including: the voltage-controlled oscillator proposed in the above embodiment.

[0053] For details of the above phase-locked loop, please refer to the description of the voltage-controlled oscillator above, which will not be repeated here.

[0054] In some optional implementations, the phase-locked loop further includes: a phase frequency detector, a charge pump, and a loop filter; wherein,

[0055] The phase frequency detector receives a reference clock and a frequency signal output by the voltage-controlled oscillator, and outputs a phase difference between the reference clock and the frequency signal; the charge pump is used to convert the phase difference into a current signal, and the loop filter outputs a control voltage for adjusting the frequency of the voltage-controlled oscillator based on the current signal.

[0056] Exemplarily, in a phase-locked loop, a phase frequency detector PFD, a charge pump CP and a loop filter LPF are connected in sequence. The PFD has two input signals, one of which is a reference clock, and the other input signal is a frequency signal output by a voltage-controlled oscillator. The PFD compares the reference clock and the frequency signal to output a phase difference between the reference clock and the frequency signal. After the phase difference is output to the CP, it is converted into a current signal by the CP and provided to the LPF. The LPF outputs a control voltage based on the current signal to control the frequency of the voltage-controlled oscillator, thereby finally locking the frequency of the voltage-controlled oscillator at the target frequency.

[0057] Accordingly, the present application exemplarily provides a method for temperature compensation of a voltage-controlled oscillator frequency, comprising:

[0058] receiving a control voltage;

[0059] The capacitance value of the adjustable capacitor of the voltage-controlled oscillator is adjusted by utilizing the voltage difference between the control voltage and the temperature compensation voltage provided by the temperature compensation circuit of the voltage-controlled oscillator; the temperature compensation voltage changes with the change of temperature.

[0060] In some optional implementations, the temperature compensation circuit includes a transistor; the emitter and base of the transistor are connected, the base is connected to the second end of the adjustable capacitor, and the collector of the transistor is grounded.

[0061] In some optional implementations, the temperature compensation voltage is negatively correlated with temperature.

[0062] In some optional implementations, the capacitance value of the adjustable capacitor is negatively correlated with the voltage difference between the control voltage and the temperature compensation voltage.

[0063] In some optional implementations, receiving a control voltage includes:

[0064] A control voltage outputted by a loop filter of a phase-locked loop is received; wherein,

[0065] The phase frequency detector of the phase-locked loop receives a reference clock and a frequency signal output by the voltage-controlled oscillator, and outputs a phase difference between the reference clock and the frequency signal; the charge pump of the phase-locked loop is used to convert the phase difference into a current signal, and the loop filter outputs a control voltage for adjusting the frequency of the voltage-controlled oscillator based on the current signal.

[0066] The above method can perform temperature compensation for the voltage-controlled oscillator frequency provided in the above embodiment, thereby ensuring that when the temperature changes, the control voltage provided to the voltage-controlled oscillator by the loop filter of the phase-locked loop remains unchanged, and the phase-locked loop can still lock the target frequency without periodic jitter. For specific details, please refer to the description in the above embodiments of the voltage-controlled oscillator and the phase-locked loop, which will not be repeated here.

[0067] It is understood that the circuit structures, names and parameters described in the above embodiments are only examples. Those skilled in the art can also easily combine and adjust the structural features of the above embodiments according to the use requirements, and should not limit the concept of the present application to the specific details of the above examples.

[0068] Although the present application has been described in detail with reference to the aforementioned embodiments, a person skilled in the art should understand that he or she may still modify the technical solutions described in the aforementioned embodiments, or make equivalent substitutions for some of the technical features therein; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A voltage-controlled oscillator, characterized in that: include: An adjustable capacitor and a temperature compensation circuit; the first end of the adjustable capacitor is connected to a control voltage, and the second end is connected to the temperature compensation circuit, and the temperature compensation circuit provides a temperature compensation voltage that changes with temperature for the adjustable capacitor.

2. The voltage controlled oscillator according to claim 1, characterized in that: The temperature compensation circuit comprises a transistor; the emitter and the base of the transistor are connected, the base is also connected to the second end of the adjustable capacitor, and the collector of the transistor is grounded.

3. The voltage controlled oscillator according to claim 1 or 2, characterized in that: The temperature compensation voltage is negatively correlated with temperature.

4. The voltage controlled oscillator according to claim 1 or 2, characterized in that: The capacitance value of the adjustable capacitor is negatively correlated with the voltage difference between the control voltage and the temperature compensation voltage.

5. A phase-locked loop, characterized in that: include: The voltage controlled oscillator according to any one of claims 1 to 4.

6. The phase-locked loop according to claim 5, characterized in that: The phase-locked loop also includes: a phase frequency detector, a charge pump and a loop filter; wherein, The phase frequency detector receives a reference clock and a frequency signal output by the voltage-controlled oscillator, and outputs a phase difference between the reference clock and the frequency signal; the charge pump is used to convert the phase difference into a current signal, and the loop filter outputs a control voltage for adjusting the frequency of the voltage-controlled oscillator based on the current signal.

7. A method for temperature compensation of a voltage controlled oscillator frequency, characterized in that: include: receiving a control voltage; The capacitance value of the adjustable capacitor of the voltage-controlled oscillator is adjusted by utilizing the voltage difference between the control voltage and the temperature compensation voltage provided by the temperature compensation circuit of the voltage-controlled oscillator; the temperature compensation voltage changes with the change of temperature.

8. The method according to claim 7, characterized in that The temperature compensation circuit comprises a transistor; the emitter and base of the transistor are connected, the base is connected to the second end of the adjustable capacitor, and the collector of the transistor is grounded.

9. The temperature compensation method according to claim 7 or 8, characterized in that: The temperature compensation voltage is negatively correlated with temperature.

10. The temperature compensation method according to claim 7 or 8, characterized in that: The capacitance value of the adjustable capacitor is negatively correlated with the voltage difference between the control voltage and the temperature compensation voltage.

11. The temperature compensation method according to claim 7 or 8, characterized in that: Receive control voltage, including: A control voltage outputted by a loop filter of a phase-locked loop is received; wherein, The phase frequency detector of the phase-locked loop receives a reference clock and a frequency signal output by the voltage-controlled oscillator, and outputs a phase difference between the reference clock and the frequency signal; the charge pump of the phase-locked loop is used to convert the phase difference into a current signal, and the loop filter outputs a control voltage for adjusting the frequency of the voltage-controlled oscillator based on the current signal.

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