Noise improved differential oscillator

Abstract

The invention provides a noise improved differential oscillator which comprises a power supply end, a current source, a resonant cavity circuit unit and an active network, and the resonant cavity circuit unit and the active network are arranged between the power supply end VDD and the current source IB. The two circuit nodes are respectively connected to two output ends (a first output end and a second output end) of the differential oscillator; the active network is used for providing negative resistance to compensate the loss of the resonant cavity circuit unit, the active network comprises two active branches, each active branch is provided with an inductor to eliminate the phase difference between an input current pulse and an output signal peak, and accurate current injection at the peak is realized. And the current source IB is grounded and is used for providing stable current for the circuit.

Description

Technical Field

[0001] The present disclosure relates to the technical fields of radio frequency circuits and integrated circuits, and in particular to a noise-improved differential oscillator. Background Art

[0002] With the rapid growth of demand for wireless data services, new generation wireless communication standards such as 5G and Wi-Fi 7 with high speed, low latency and large bandwidth have been proposed one after another. In order to achieve these characteristics in limited spectrum resources, the new generation of wireless communication adopts high-order quadrature amplitude modulation technology, which requires the RF clock to have extremely low phase noise to avoid deteriorating modulation accuracy. As the core module of the frequency synthesizer based on the phase-locked loop system, the phase noise characteristics of the integrated voltage-controlled oscillator directly determine the out-of-band phase noise performance of the phase-locked loop system, and play a key role in the RF system. With the continuous improvement of communication standards, it is of great significance to realize oscillators with lower phase noise. However, the current low-noise oscillators cannot minimize phase noise. Summary of the invention

[0003] In view of this, in order to at least partially solve at least one of the above-mentioned technical problems, the present disclosure provides a noise-improved differential oscillator.

[0004] The disclosed embodiment provides a noise-improved differential oscillator, including a power supply terminal, a current source, and a resonant cavity circuit unit and an active network arranged between the power supply terminal and the current source, wherein: two circuit nodes are arranged at both ends of the resonant cavity circuit unit, and the two circuit nodes are respectively connected to two output ends of the differential oscillator; the active network is used to provide a negative resistance to compensate for the loss of the resonant cavity circuit unit, and the active network includes two active branches, and an inductor is arranged in each active branch to eliminate the phase difference between the input current pulse and the output signal peak, so as to realize accurate current injection at the peak. The current source is grounded to provide a stable current for the circuit.

[0005] According to the embodiment of the present disclosure, two active branches introduce positive feedback by means of cross-coupling.

[0006] According to the embodiment of the present disclosure, each active branch includes: a transistor branch, including two transistors connected in series between the power supply terminal and the current source, wherein the gate of one transistor is connected to a circuit node, and the gate of the other transistor is connected to another circuit node. Each active branch also includes: a capacitor branch, including two capacitors connected in series between the circuit node and the ground. Each active branch also includes: an inductor, one end of which is connected between the two transistors of the transistor branch, and the other end of which is connected between the two capacitors of the capacitor branch, for eliminating the phase difference between the current pulse and the output signal peak.

[0007] According to the embodiment of the present disclosure, by selecting an inductor with a suitable inductance value, the phase difference between the current pulse and the output signal peak is eliminated. Assuming that the capacitance values ​​of the two capacitors are C1 and C2 respectively, the inductance value of the inductor is .

[0008] An input end of the resonant cavity circuit unit is connected to the control voltage input node and is configured to tune the frequency of the oscillator under the action of the control voltage.

[0009] According to an embodiment of the present disclosure, the resonant cavity circuit unit includes a resonant cavity inductor and two capacitors, wherein the center tap of the resonant cavity inductor is connected to the power supply terminal, the two capacitors are respectively connected to the two ends of the resonant cavity inductor and then connected to the control voltage input node, and circuit nodes are respectively provided between the resonant cavity inductor and the two capacitors. The two capacitors are variable capacitors, and the capacitance values ​​are adjusted under the action of the control voltage to tune the frequency of the oscillator. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The above and other objects, features and advantages of the present disclosure will become more apparent through the following description of the embodiments of the present disclosure with reference to the accompanying drawings, in which:

[0011] Figure 1 The structure diagram of the noise improved differential oscillator circuit according to the embodiment of the present disclosure is schematically shown;

[0012] Figure 2 The simulation results of the current pulse and output waveform of the conventional transconductance enhanced differential oscillator circuit are schematically shown;

[0013] Figure 3 The simulation results of the current pulse and the output waveform of the noise improved differential oscillator circuit according to the embodiment of the present disclosure are schematically shown;

[0014] Figure 4 A comparison diagram of phase noise simulation results of a conventional transconductance enhanced differential oscillator and a noise improved differential oscillator according to an embodiment of the present disclosure is schematically shown. DETAILED DESCRIPTION

[0015] The present disclosure provides a noise-improved differential oscillator, which can achieve accurate injection of current pulses at the peak of an output signal without increasing power consumption, thereby reducing phase noise and improving the quality factor of the oscillator.

[0016] In order to make the objectives, technical solutions and advantages of the present disclosure more clearly understood, the present disclosure is further described in detail below in combination with specific embodiments and with reference to the accompanying drawings.

[0017] In an embodiment of the present disclosure, a noise-improved differential oscillator is provided, such as Figure 1As shown, the noise improved differential oscillator includes: a power supply terminal, a current source, and a current source arranged between the power supply terminal VDD and the current source I B A resonant cavity circuit unit and an active network are provided between the two ends of the resonant cavity circuit unit, wherein: two circuit nodes are provided at both ends of the resonant cavity circuit unit, and the two circuit nodes are respectively connected to two output ends (a first output end and a second output end) of the differential oscillator; the active network is used to provide a negative resistance to compensate for the loss of the resonant cavity circuit unit, and the active network includes two active branches, and an inductor is provided in each active branch to eliminate the phase difference between the input current pulse and the output signal peak, so as to realize accurate current injection at the peak. Current source I B Ground, used to provide a steady current to the circuit.

[0018] An input terminal of the resonant cavity circuit unit is connected to the control voltage input node Vctrl and is configured to tune the frequency of the oscillator under the action of the control voltage.

[0019] According to the embodiment of the present disclosure, the resonant cavity circuit unit includes a resonant cavity inductor L and two capacitors C, wherein the center tap of the resonant cavity inductor is connected to the power supply terminal VDD, the two capacitors C are respectively connected to the two ends of the resonant cavity inductor L and then connected to the voltage input node Vctrl, and a first circuit node N1 and a second circuit node N2 are respectively provided between the resonant cavity inductor L and the two capacitors C. The two capacitors C are variable capacitors, and the capacitance value is adjusted under the action of the control voltage to tune the frequency of the oscillator.

[0020] In the disclosed embodiment, two active branches introduce positive feedback by cross-coupling. Each active branch includes: a transistor branch, including two transistors connected in series between a power supply terminal and a current source, wherein a gate of one transistor is connected to a circuit node, and a gate of the other transistor is connected to another circuit node. Each active branch also includes: a capacitor branch, including two capacitors connected in series between a circuit node and a ground. Each active branch also includes: an inductor, one end of which is connected between two transistors of the transistor branch, and the other end of which is connected between two capacitors of the capacitor branch, for eliminating the phase difference between the current pulse and the output signal peak.

[0021] Specifically, Figure 1As shown, the active branch on the left side includes two transistors connected in series between the power supply terminal and the current source, namely, a first transistor MN1 and a third transistor MN3, the gate of the first transistor MN1 is connected to the first circuit node N1, and the gate of the third transistor MN3 is connected to the second circuit node N2; the active branch on the right side includes two transistors connected in series between the power supply terminal and the current source, namely, a second transistor MN2 and a fourth transistor MN4, the gate of the second transistor MN2 is connected to the second circuit node N2, and the gate of the fourth transistor MN4 is connected to the first circuit node N1. The left side capacitor branch includes two first capacitors C1 and second capacitors C2 connected in series between the circuit node and the ground, the first capacitor C1 is connected to the first circuit node N1, and the second capacitor C2 is grounded. The right side capacitor branch includes two third capacitors C3 and fourth capacitors C4 connected in series between the circuit node and the ground, the third capacitor C3 is connected to the second circuit node N2, and the fourth capacitor C4 is grounded. One end of the inductor L1 in the left side active branch is connected to the node V between the first transistor MN1 and the third transistor MN3. S1 The other end of the inductor L1 is connected to the node between the first capacitor C1 and the second capacitor C2. One end of the inductor L2 in the right active branch is connected to the node V between the second transistor MN2 and the fourth transistor MN4. S2 , the other end of the inductor L2 is connected to the node between the third capacitor C3 and the fourth capacitor C4. The first transistor MN1, the second transistor MN2, the third transistor MN3, the fourth transistor MN4 and the first capacitor C1, the second capacitor C2, the third capacitor C3, and the fourth capacitor C4 form an active network for providing a negative resistance to compensate for the loss of the resonant cavity; the third transistor MN3 and the fourth transistor MN4 introduce positive feedback by cross-coupling, thereby increasing the small signal gain of the active network, thereby increasing the negative conductance of the active network circuit and reducing power consumption. It should be noted that the left and right active branches are configured in the same manner, for example, the types and parameters of the transistors in the transistor branch are the same, the capacitance parameters in the capacitance branch are the same, and the parameters of the inductance are also the same.

[0022] For a conventional transconductance enhanced differential oscillator, the current pulse (I D ) and the output signal peak value, the simulation diagram is as follows Figure 2 In order to obtain better phase noise, it is necessary to accurately inject the current pulse at the peak, so as to minimize the phase noise without increasing the extra power consumption and improve the quality factor of the oscillator. Figure 1 As shown, the left active branch is taken as an example, and the output voltage of the first output terminal is recorded as V out1 , the node voltage between the first transistor MN1 and the third transistor MN3 is recorded as V S1, since the switch transistor MN1 works in saturation state when it is turned on, its current value I D1 satisfy:

[0023] ;

[0024] where μ n is the electron mobility, C ox is the gate oxide capacitance per unit area, W and L are the gate width and gate length respectively, V TH is the threshold voltage of the NMOS tube. Therefore, I D1 With V out1 The phase difference between them depends on the voltage V out1 With V S1 The phase difference between them. Through the small signal model analysis, we get:

[0025] ;

[0026] Where r is the left active branch transistor at node V S1 The output resistance, , g m1 is the transconductance of the first transistor MN1, r o3 is the output resistance of the third transistor MN3, ω is the oscillation frequency of the circuit, and it can be seen that V out1 With V S1 The phase difference between them is related to the first capacitor C1 and the second capacitor C2, and is mainly caused by the first capacitor C1.

[0027] By selecting the inductance value of the first inductor L1, the above phase difference can be eliminated. Re-analyze the circuit with a small signal model to eliminate V out1 With V S1 The imaginary part of the relationship can be obtained:

[0028] ;

[0029] Similarly, the suitable inductance value of the second inductor L2 can also be obtained by the following formula:

[0030] ;

[0031] Through experimental verification, after selecting the first inductor L1 and the second inductor L2 with suitable inductance values, there is no phase difference between the current pulse and the output signal peak value, and the current can be accurately injected at the output signal peak value. The simulation diagram is as follows Figure 3 shown.

[0032] It should also be noted that, through simulation verification, if a resonator is used to realize the function of the resonant cavity inductor L, the output frequency is 2.45 GHz, and the power consumption is 0.5 mW, the phase noise simulation results of the traditional transconductance enhanced differential oscillator and the noise improved differential oscillator of the embodiment of the present disclosure are compared. Figure 4 As shown in the figure, it can be seen that the phase noise of the noise-improved differential oscillator of the embodiment of the present disclosure at 1 kHz and 1 MHz frequency offset is reduced by 15.8 dBc / Hz and 6.5 dBc / Hz respectively, which is equivalent to the quality factor of the oscillator being improved by 15.8 dB and 6.5 dB respectively. The structure is also applicable to LC oscillators using inductors as resonant devices.

[0033] So far, the embodiments of the present disclosure have been described in detail in conjunction with the accompanying drawings. It should be noted that the implementation methods not shown or described in the drawings or the body of the specification are all forms known to ordinary technicians in the relevant technical field and are not described in detail. In addition, the above definitions of each element and method are not limited to the various specific structures, shapes or methods mentioned in the embodiments, and ordinary technicians in the field can simply change or replace them.

[0034] According to the above description, those skilled in the art should have a clear understanding of the noise improved differential oscillator circuit disclosed in the present invention.

[0035] In summary, the present disclosure provides a noise-improved differential oscillator circuit, which eliminates the phase difference between the current pulse and the output signal peak, achieves precise current injection at the peak, minimizes phase noise, and does not increase additional power consumption, thereby improving the quality factor of the oscillator.

[0036] It should be noted that, in this document, unless otherwise specified, “a” element is not limited to a single element, but may include one or more elements.

[0037] In addition, in this document, unless otherwise specified, ordinal numbers such as "first" and "second" are only used to distinguish multiple components with the same name, and do not indicate that there is a hierarchy, level, execution order, or process order between them. A "first" component and a "second" component may appear together in the same component, or appear in different components. The presence of a component with a larger ordinal number does not necessarily indicate the presence of another component with a smaller ordinal number.

[0038] In this document, unless otherwise specified, the so-called feature A "or" or "and / or" (and / or) feature B means that A exists alone, B exists alone, or A and B exist at the same time; the so-called feature A "and" (and) or "and" (and) or "and" (and) feature B means that A and B exist at the same time; the so-called "include", "comprise", "have" and "contain" mean including but not limited to these.

[0039] In addition, in this document, the terms "upper", "lower", "left", "right", "front", "back", or "between" are only used to describe the relative positions between multiple elements, and can be extended to include translation, rotation, or mirroring. In addition, in this document, unless otherwise specified, "an element is on another element" or similar descriptions do not necessarily mean that the element contacts the other element.

[0040] In addition, unless the steps are specifically described or must occur in sequence, the order of the above steps is not limited to the above list, and can be changed or rearranged according to the required design. And the above embodiments can be mixed and matched with each other or with other embodiments based on design and reliability considerations, that is, the technical features in different embodiments can be freely combined to form more embodiments.

[0041] The specific embodiments described above further illustrate the purpose, technical solutions and beneficial effects of the present disclosure. It should be understood that the above description is only a specific embodiment of the present disclosure and is not intended to limit the present disclosure. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present disclosure should be included in the protection scope of the present disclosure.

Claims

1. A noise-improved differential oscillator, comprising a power supply terminal, a current source, and a resonant cavity circuit unit and an active network arranged between the power supply terminal and the current source, wherein: Two circuit nodes are arranged at two ends of the resonant cavity circuit unit, and the two circuit nodes are respectively connected to two output ends of the differential oscillator; The active network is used to provide negative resistance to compensate for the loss of the resonant cavity circuit unit. The active network includes two active branches, and an inductor is set in each active branch to eliminate the phase difference between the input current pulse and the output signal peak, thereby achieving accurate current injection at the peak. 2 . The oscillator according to claim 1 , wherein the two active branches introduce positive feedback by cross-coupling.

3. The oscillator according to claim 1 or 2, each active branch comprising: The transistor branch includes two transistors connected in series between a power supply terminal and a current source, wherein a gate of one transistor is connected to a circuit node, and a gate of the other transistor is connected to another circuit node.

4. The oscillator according to claim 3, each active branch further comprising: The capacitor branch includes two capacitors connected in series between the circuit node and the ground.

5. The oscillator according to claim 4, each active branch further comprising: The inductor has one end connected between the two transistors of the transistor branch and the other end connected between the two capacitors of the capacitor branch, and is used to eliminate the phase difference between the current pulse and the output signal peak.

6. The oscillator according to claim 1, by selecting an inductor with a suitable inductance value, the phase difference between the current pulse and the output signal peak is eliminated. Assuming that the capacitance values ​​of the two capacitors are C1 and C2 respectively, the inductance value of the inductor is . 7 . The oscillator according to claim 1 , wherein an input terminal of the resonant cavity circuit unit is connected to a control voltage input node and is configured to tune the frequency of the oscillator under the action of the control voltage.

8. The oscillator according to claim 1 or 7, wherein the resonant cavity circuit unit comprises a resonant cavity inductor and two capacitors, wherein: The center tap of the resonant cavity inductor is connected to the power supply end, the two capacitors are respectively connected to the two ends of the resonant cavity inductor and then connected to the control voltage input node, and circuit nodes are respectively arranged between the resonant cavity inductor and the two capacitors. 9 . The oscillator according to claim 8 , wherein the two capacitors are variable capacitors, and the capacitance values ​​are adjusted under the action of a control voltage to tune the frequency of the oscillator.

10. The oscillator of claim 1, wherein the current source is connected to ground and provides a stable current to the oscillator circuit.

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