Alternating current coupling voltage-controlled oscillator and phase-locked loop circuit

Abstract

The invention provides an alternating-current coupling voltage-controlled oscillator and a phase-locked loop circuit. The alternating-current coupling voltage-controlled oscillator comprises an active circuit, an inductance-capacitance oscillating circuit and a cross coupling circuit, the inductance-capacitance oscillation circuit is used for generating an oscillation frequency signal; the active circuit is connected with the inductance-capacitance oscillation circuit and is used for supplementing energy loss when the inductance-capacitance oscillation circuit oscillates; and the cross coupling circuit is connected to the active circuit and is used for generating a negative capacitance effect so as to reduce a critical condition for generating oscillation by the inductance-capacitance oscillation circuit. According to the technical scheme, the cross coupling circuit generating the negative capacitance effect is introduced on the basis of the voltage-controlled oscillator, so that the oscillation starting condition of the voltage-controlled oscillator is reduced, namely the critical condition for generating oscillation is reduced, and the oscillation starting robustness of the voltage-controlled oscillator is enhanced.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of chips, and particularly relates to an AC coupling voltage controlled oscillator and a phase-locked loop circuit. BACKGROUND

[0002] A VCO (voltage controlled oscillator) is a control object of a phase-locked loop, and constitutes a frequency synthesizer together with the phase-locked loop. Figure 1 As shown in the figure, the phase-locked loop is composed of a frequency discriminator, a charge pump, a loop filter, a frequency divider and a voltage controlled oscillator. The function of the frequency discriminator is to identify the frequency and phase difference between the reference clock and the feedback clock of the phase-locked loop, and then transmit the difference to the charge pump. The charge pump generates a current output to the loop filter according to the difference, and the loop filter generates a voltage to adjust the frequency of the voltage controlled oscillator. The frequency divider divides the clock frequency generated by the voltage controlled oscillator to obtain the feedback clock. SUMMARY

[0003] The application aims to provide an AC coupling voltage controlled oscillator and a phase-locked loop circuit, and aims to solve the problem of high starting condition of the AC coupling voltage controlled oscillator in the related art, thereby causing unstable starting.

[0004] According to a first aspect of the application, an AC coupling voltage controlled oscillator is provided, comprising: an active circuit, an inductor-capacitor oscillation circuit and a cross-coupling circuit;

[0005] The inductor-capacitor oscillation circuit is configured to generate an oscillation frequency signal.

[0006] The active circuit is connected to the inductor-capacitor oscillation circuit, and is configured to supplement energy loss when the inductor-capacitor oscillation circuit oscillates.

[0007] The cross-coupling circuit is connected to the active circuit, and is configured to generate a negative capacitance effect to reduce the critical condition of oscillation of the inductor-capacitor oscillation circuit.

[0008] In order to avoid that the field effect transistor (such as a PMOS transistor) of the active circuit of the voltage controlled oscillator works in a deep triode region, an AC coupling capacitor is inserted in the active circuit. However, the insertion of the AC coupling capacitor causes the starting condition of the voltage controlled oscillator to be high, thereby causing instability of the voltage controlled oscillator. In order to solve this problem, the cross-coupling circuit generating the negative capacitance effect is introduced on the basis of the above-mentioned voltage controlled oscillator, thereby reducing the starting condition of the voltage controlled oscillator, that is, the critical condition of oscillation, and enhancing the robustness of the starting of the voltage controlled oscillator.

[0009] In an optional embodiment, the active circuit comprises a first field effect transistor, a second field effect transistor, a first AC coupling capacitor and a second AC coupling capacitor; the first AC coupling capacitor is connected between the drain of the first field effect transistor and the gate of the second field effect transistor, and the second AC coupling capacitor is connected between the gate of the first field effect transistor and the drain of the second field effect transistor; the gate of the first field effect transistor and the gate of the second field effect transistor are connected to a bias voltage through a bias resistor, respectively.

[0010] In an optional embodiment, the LC oscillation circuit comprises a capacitor and an inductor, which are connected in parallel, and the two ends of the parallel connection are connected to the drain of the first field effect transistor and the drain of the second field effect transistor, respectively.

[0011] In an optional embodiment, the inductor comprises a first inductor and a second inductor connected in series, and the middle connection of the first inductor and the second inductor is grounded.

[0012] In an optional embodiment, the cross-coupled circuit comprises a third field effect transistor, a fourth field effect transistor, a first cross capacitor, a second cross capacitor, a first current source and a second current source; the gate of the third field effect transistor is connected to the drain of the fourth field effect transistor, and the drain of the third field effect transistor is connected to the gate of the fourth field effect transistor; the first cross capacitor and the second cross capacitor are connected in series, and the first end of the series connection is connected between the source of the third field effect transistor and the first current source, and the second end of the series connection is connected between the source of the fourth field effect transistor and the second current source.

[0013] In an optional embodiment, the drain of the third field effect transistor of the cross-coupled circuit is connected between the first AC coupling capacitor of the active circuit and the gate of the second field effect transistor, and the drain of the fourth field effect transistor of the cross-coupled circuit is connected between the second AC coupling capacitor and the gate of the first field effect transistor.

[0014] In an optional embodiment, the first field effect transistor and the second field effect transistor are PMOS transistors.

[0015] In an optional embodiment, the third field effect transistor and the fourth field effect transistor are NMOS transistors.

[0016] According to a second aspect of the present application, a phase-locked loop circuit is provided, comprising the AC coupled voltage controlled oscillator of the first aspect.

[0017] Other features and advantages of the present application will be set forth in the following description, and in part will become apparent from the description, or can be learned by practice of the present application. The objects and other advantages of the present application will be realized and attained by the structure and processes particularly pointed out in the description and the appended drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present application or related technologies, the following is a brief introduction to the drawings required for use in the embodiments or related technical descriptions. 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 any creative work.

[0019] Figure 1 It is a structural diagram of a phase-locked loop according to related technology.

[0020] Figure 2 2 is a schematic structural diagram of a voltage-controlled oscillator according to related art.

[0021] Figure 3 It is a circuit structure diagram of an AC-coupled voltage-controlled oscillator according to related technology.

[0022] Figure 4 1 is a schematic diagram of an equivalent circuit of an AC-coupled voltage-controlled oscillator according to related art.

[0023] Figure 5 is a structural block diagram of an AC-coupled voltage-controlled oscillator according to an exemplary embodiment of the present application.

[0024] Figure 6 1 is a connection diagram of an AC-coupled voltage-controlled oscillator and a cross-coupling circuit according to an exemplary embodiment of the present application.

[0025] Figures 7A-7B 1 is a schematic diagram of a circuit structure and an equivalent circuit of a cross-coupling circuit according to an exemplary embodiment of the present application.

[0026] Figure 7C 1 is a circuit structure diagram of an AC-coupled voltage-controlled oscillator according to an exemplary embodiment of the present application.

[0027] Figure 8 is a structural block diagram of a phase-locked loop circuit according to an exemplary embodiment of the present application. DETAILED DESCRIPTION

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

[0029] like Figure 2As shown, the voltage controlled oscillator can be regarded as a lossy resonator, in which the resonator is connected with an active circuit, in which the active circuit composed of the current source Iss, PMOS tubes M1 and M2 can replenish the energy consumed by the resonator. In order to enable the oscillation to occur, g m The equivalent negative resistance needs to offset the loss of the resonant cavity.

[0030] Figure 2 The critical condition for the voltage controlled oscillator shown to generate oscillation is as follows:

[0031]

[0032] In which, g m is the transconductance of the PMOS tube, R p is the equivalent resistance of the resonator. The negative resistance offsets the loss of the resonant cavity, and the critical condition for the oscillation to occur is:

[0033] g m R p ≥1

[0034] In order to avoid the PMOS tube working in the deep field effect tube area in the design of the voltage controlled oscillator, an alternating coupling capacitor C0 can be inserted in the voltage controlled oscillator, so that an alternating coupling voltage controlled oscillator is designed, and the circuit structure is as shown in Figure 3 As shown, the equivalent circuit of the alternating coupling voltage controlled oscillator VCO is as shown in Figure 4

[0035] From Figure 4 It can be seen that the critical condition for the voltage controlled oscillator to generate oscillation, i.e. the starting condition, changes after the insertion of C0. The starting condition changes from gm*Rp≥1 to gm*Rp≥(C0+C1) / C0, and the starting condition becomes higher, which is not conducive to starting. The calculation process of the starting condition after the insertion of C0 is as follows:

[0036] V x =V3-V1

[0037] I x =g m V4=-g m V2

[0038] V3=A*V2

[0039] V1=A*V4

[0040]

[0041] In which, V x represents the added power voltage value; V1-V4 represents the voltage value at the position shown in the figure, I x ​I represents the current value generated after the power voltage is added, A represents the voltage division ratio from V3 to V2, that is, the capacitive attenuation ratio.

[0042] The starting condition calculated from the above formula is as follows:

[0043]

[0044] g m R p ≥A

[0045]

[0046] wherein, R p represents the equivalent resistance of the entire AC coupling voltage-controlled oscillator.

[0047] The following is an example: assuming that before C0 is inserted, the starting condition of the voltage-controlled oscillator is g m *R p ≥ 1, after C0 is added, the starting condition of the AC coupling voltage-controlled oscillator is g m *R p > 1.2. It can be seen that, compared with the voltage-controlled oscillator without the insertion of the AC coupling capacitor, the AC coupling voltage-controlled oscillator needs to meet a higher condition to reach the critical point of starting, that is, the starting condition of the AC coupling voltage-controlled oscillator is higher than that of the voltage-controlled oscillator without the insertion of the AC coupling capacitor.

[0048] Based on the above analysis, as Figure 5 shown, the application exemplarily proposes an AC coupling voltage-controlled oscillator, which comprises an inductor-capacitor oscillation circuit 501, an active circuit 502, and a cross-coupling circuit 503. The inductor-capacitor oscillation circuit 501 is used to generate an oscillation frequency signal; the active circuit 502 is connected with the inductor-capacitor oscillation circuit and is used to supplement the energy loss of the inductor-capacitor oscillation circuit during oscillation; and the cross-coupling circuit 503 is connected with the active circuit and is used to generate a negative capacitance effect to reduce the critical condition of oscillation of the inductor-capacitor oscillation circuit.

[0049] Exemplarily, the inductor-capacitor oscillation circuit generates an oscillation frequency signal after power-on, and energy loss occurs during oscillation. In order to maintain the inductor-capacitor oscillation circuit to continuously generate the oscillation frequency signal, the active circuit is equivalent to a negative resistance, thereby supplementing the energy of the inductor-capacitor circuit. As described above, the active circuit comprises two PMOS tubes, in order to prevent the PMOS tube from working in the deep triode region, an AC coupling capacitor is inserted, and the inserted AC coupling capacitor will cause the active circuit to generate a parasitic capacitance (as Figure 4The parasitic capacitance C1 is inserted into the active circuit of the voltage-controlled oscillator, which results in a higher starting condition of the voltage-controlled oscillator, and thus causes the voltage-controlled oscillator to be unstable, i.e., the voltage-controlled oscillator can not generate the oscillation frequency signal in some scenarios due to the failure to meet the starting condition.

[0050] Therefore, the application introduces a cross-coupling circuit into the AC-coupled voltage-controlled oscillator, the cross-coupling circuit is connected in parallel to the active circuit, and thus generates a negative capacitance effect, which can offset part or all of the parasitic capacitance generated by the AC-coupling capacitance inserted into the active circuit, and thus can reduce the starting condition of the voltage-controlled oscillator.

[0051] Suppose that the negative capacitance value generated by the cross-coupling circuit is C2, the parasitic capacitance value is C1, and the AC-coupling capacitance value is C0, the starting condition without the cross-coupling circuit is: The starting condition after the cross-coupling circuit is introduced is: It can be seen that the starting condition after the cross-coupling circuit is introduced is significantly reduced.

[0052] In order to avoid the field effect transistor (such as a PMOS transistor) of the active circuit of the voltage-controlled oscillator from working in the deep triode region, the AC-coupling capacitance is inserted into the active circuit, however, the insertion of the AC-coupling capacitance results in a higher starting condition of the voltage-controlled oscillator, and thus causes the voltage-controlled oscillator to be unstable. In order to solve this problem, the application introduces the cross-coupling circuit generating the negative capacitance effect on the basis of the above voltage-controlled oscillator, and thus reduces the starting condition of the voltage-controlled oscillator, i.e., the critical condition of generating the oscillation, and enhances the robustness of the starting of the voltage-controlled oscillator.

[0053] In some optional implementations, the active circuit includes a first field effect transistor, a second field effect transistor, a first AC-coupling capacitance, and a second AC-coupling capacitance. The first AC-coupling capacitance is connected between the drain of the first field effect transistor and the gate of the second field effect transistor, and the second AC-coupling capacitance is connected between the gate of the first field effect transistor and the drain of the second field effect transistor. The gate of the first field effect transistor and the gate of the second field effect transistor are respectively connected to a bias voltage through a bias resistor.

[0054] Exemplarily, as shown in FIG. 2, the active circuit of the voltage-controlled oscillator includes a first field effect transistor 21, a second field effect transistor 22, a first AC-coupling capacitance 23, and a second AC-coupling capacitance 24. Figure 6As shown, the gate of the first field effect transistor M1 is connected with the drain of the second field effect transistor M2, and a second AC coupling capacitor is connected between the gate of the first field effect transistor M1 and the drain of the second field effect transistor M2; the gate of the second field effect transistor M2 is connected with the drain of the first field effect transistor M1, and a first AC coupling capacitor is connected between the gate of the second field effect transistor M2 and the drain of the first field effect transistor M1; the gates of the first field effect transistor M1 and the second field effect transistor M2 are respectively connected with a bias voltage through bias resistors, and the bias voltage is used to maintain the continuous and stable oscillation frequency signal generated by the LC oscillation circuit after the AC coupled voltage controlled oscillator generates the oscillation frequency signal.

[0055] Exemplarily, the gates of the first field effect transistor and the second field effect transistor are respectively connected with a current source Iss, which is used to provide a current signal to the LC oscillation circuit after the voltage controlled oscillator is powered on, so that the LC oscillation circuit generates a continuous oscillation frequency signal.

[0056] Exemplarily, the first field effect transistor and the second field effect transistor are PMOS transistors.

[0057] In this way, two AC coupling capacitors are inserted in the active circuit, but due to the existence of the cross-coupled circuit, the start-up condition of the voltage controlled oscillator is relatively reduced, thereby enhancing the robustness of the voltage controlled oscillator.

[0058] In some optional implementations, the LC oscillation circuit includes a capacitor and an inductor, and the capacitor and the inductor are connected in parallel, and the two ends after being connected in parallel are respectively connected with the drains of the first field effect transistor and the second field effect transistor.

[0059] Further, the inductor includes a first inductor and a second inductor connected in series, and the middle connection of the first inductor and the second inductor is grounded.

[0060] Exemplarily, as shown in the figure, Figure 6 the oscillation frequency signal of the voltage controlled oscillator is generated by the capacitor and the inductor connected in parallel, and the inductor is composed of two inductors connected in series, and the middle connection of the two inductors connected in series is grounded.

[0061] In some optional implementations, the cross-coupled circuit includes a third field effect transistor, a fourth field effect transistor, a first cross-over capacitor, a second cross-over capacitor, a first current source and a second current source; the gate of the third field effect transistor is connected with the drain of the fourth field effect transistor, the drain of the third field effect transistor is connected with the gate of the fourth field effect transistor, the first cross-over capacitor and the second cross-over capacitor are connected in series, and the first end after being connected in series is connected between the source of the third field effect transistor and the first current source, and the second end after being connected in series is connected between the source of the fourth field effect transistor and the second current source.

[0062] Exemplarily, as shown in the figure, Figure 7AAs shown, the gate of the third field effect transistor M3 is connected with the drain of the fourth field effect transistor M4, the gate of the fourth field effect transistor M4 is connected with the drain of the third field effect transistor M3, the source of the third field effect transistor M3 is connected with the first current source Iss1, and the source of the fourth field effect transistor M4 is connected with the second current source Iss2.

[0063] Further, the drain of the third field effect transistor M3 is connected between the first AC coupling capacitor C0 and the gate of the second field effect transistor M2, and the drain of the fourth field effect transistor M4 is connected between the second AC coupling capacitor C0' and the gate of the first field effect transistor M1.

[0064] Further, the third field effect transistor and the fourth field effect transistor are NMOS transistors.

[0065] The application connects the cross-coupling circuit in parallel at the gate end of the PMOS of the active circuit, which can generate the effect of negative capacitance during operation, thereby neutralizing and canceling the parasitic capacitance generated by the active circuit, so that the starting condition of the inductance-capacitance oscillation circuit is low.

[0066] As shown in Figure 7B and Figure 7C As shown in the application, the critical condition of the voltage-controlled oscillator starting is changed after introducing the cross-coupling circuit, and the calculation is as follows:

[0067] I x ′=V x ′·sC2=g m2 (-ΔV-V x ′)

[0068]

[0069] V x ′(g m2 +sC2)=-g m2 ·ΔV

[0070]

[0071] Wherein, g m2 represents the transconductance at the third field effect transistor M3 and the fourth field effect transistor M4, V x ' represents the power supply voltage value between the third field effect transistor and the first AC coupling capacitor or between the fourth field effect transistor and the second AC coupling capacitor; ΔV represents the small signal change of voltage; I x ' represents the current value generated after applying a power supply voltage of V x ', A represents the capacitive attenuation ratio; C2 is the equivalent capacitance value of the cross-coupling circuit.

[0072] As can be seen from the above calculation process, the introduction of the cross-coupling circuit is equivalent to connecting a negative capacitance in parallel with the active circuit, which can effectively neutralize the parasitic capacitance generated by the active circuit.Figure 4 The V2, V4 nodes of the equivalent circuit shown approximately introduce a negative capacitance value C2, so a new capacitive attenuation coefficient A=(C0+C1-C2) / C0 can be obtained, and the following calculation formula can be obtained:

[0073]

[0074] g m R p ≥A

[0075]

[0076] Wherein, C1 is the capacitance value of the parasitic capacitance generated in the active circuit, and C0 is the capacitance value of the first AC coupling capacitor and the second AC coupling capacitor.

[0077] It can be seen that after the cross-coupling circuit is introduced, compared with before the cross-coupling circuit is introduced, there is a negative C2 in the starting condition, so that the starting condition is reduced.

[0078] Correspondingly, the application also exemplarily provides a phase-locked loop circuit, comprising any one of the AC coupled voltage controlled oscillators described above.

[0079] In some optional implementation manners, the phase-locked loop further comprises a frequency discriminator, a loop filter and a frequency divider; wherein,

[0080] The frequency discriminator receives a reference clock and an oscillation frequency signal generated by the AC coupled voltage controlled oscillator, and outputs a phase difference between the reference clock and the oscillation frequency signal; the loop filter outputs a control voltage for adjusting the oscillation frequency signal based on the phase difference, and the frequency divider is used to feedback the oscillation frequency signal after frequency division to the frequency discriminator.

[0081] Exemplarily, in the phase-locked loop, the frequency discriminator PFD and the loop filter LPF are connected in sequence, the input signals of the PFD are two, one of which is a reference clock, and the other input signal is an oscillation frequency signal generated by the AC coupled voltage controlled oscillator, the PFD compares the reference clock and the oscillation frequency signal, and outputs a phase difference between the reference clock and the oscillation frequency signal, the LPF outputs a control voltage based on the phase difference, which is used to control the oscillation frequency signal of the AC coupled voltage controlled oscillator, and finally lock the oscillation frequency signal of the AC coupled voltage controlled oscillator on the target frequency, and the frequency divider feedbacks the oscillation frequency signal after frequency division to the frequency discriminator.

[0082] The specific details of the AC coupled voltage controlled oscillator in the phase-locked loop circuit can be referred to the embodiment description of the AC coupled voltage controlled oscillator in the above, which will not be described here.

[0083] It can be understood that the circuit structure, name and parameter described in the above embodiments are only examples. Those skilled in the art can also easily think of combinations and adjustments of the structural features of the above multiple embodiments according to the use needs, and the concept of the present application should not be limited to the specific details of the above examples.

[0084] Although the present application is described in detail with reference to the foregoing embodiments, it should be understood by those skilled in the art that the technical solutions recorded in the foregoing embodiments can be modified, or some technical features can be replaced by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. An AC-coupled voltage-controlled oscillator, characterized in that: include: Active circuits, LC oscillator circuits and cross-coupled circuits; The LC oscillation circuit is used to generate an oscillation frequency signal; The active circuit is connected to the LC oscillation circuit and is used to compensate for energy loss during oscillation of the LC oscillation circuit; The cross-coupling circuit is connected to the active circuit and is used to generate a negative capacitance effect to reduce a critical condition for the LC oscillation circuit to generate oscillation.

2. The AC-coupled voltage-controlled oscillator according to claim 1, wherein: The active circuit includes: a first field-effect transistor, a second field-effect transistor, a first AC coupling capacitor, and a second AC coupling capacitor; the first AC coupling capacitor is connected between the drain of the first field-effect transistor and the gate of the second field-effect transistor, and the second AC coupling capacitor is connected between the gate of the first field-effect transistor and the drain of the second field-effect transistor; the gate of the first field-effect transistor and the gate of the second field-effect transistor are respectively connected to a bias voltage through a bias resistor.

3. The AC-coupled voltage-controlled oscillator according to claim 2, wherein: The LC oscillator circuit includes a capacitor and an inductor. The capacitor and the inductor are connected in parallel, and both ends of the parallel connection are respectively connected to the drain of the first field effect transistor and the second field effect transistor.

4. The AC-coupled voltage-controlled oscillator according to claim 3, wherein: The inductor includes a first inductor and a second inductor connected in series, and a middle connection point between the first inductor and the second inductor is grounded.

5. The AC-coupled voltage-controlled oscillator according to any one of claims 1 to 4, wherein: The cross-coupling circuit includes a third field-effect transistor, a fourth field-effect transistor, a first cross-over capacitor, a second cross-over capacitor, a first current source, and a second current source; the gate of the third field-effect transistor is connected to the drain of the fourth field-effect transistor, the drain of the third field-effect transistor is connected to the gate of the fourth field-effect transistor, the first cross-over capacitor and the second cross-over capacitor are connected in series, the first end of the series connection is connected between the source of the third field-effect transistor and the first current source, and the second end of the series connection is connected between the source of the fourth field-effect transistor and the second current source.

6. The AC-coupled voltage-controlled oscillator according to claim 5, wherein: The drain of the third field effect transistor of the cross-coupling circuit is connected between the first AC coupling capacitor of the active circuit and the gate of the second field effect transistor, and the drain of the fourth field effect transistor of the cross-coupling circuit is connected between the second AC coupling capacitor and the gate of the first field effect transistor.

7. The AC-coupled voltage-controlled oscillator according to any one of claims 2 to 4, wherein: The first field effect transistor and the second field effect transistor are PMOS transistors.

8. The AC-coupled voltage-controlled oscillator according to claim 5, wherein: The third field effect transistor and the fourth field effect transistor are NMOS transistors.

9. A phase-locked loop circuit, characterized in that: The AC-coupled voltage-controlled oscillator comprises the AC-coupled voltage-controlled oscillator according to any one of claims 1 to 8.

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