Noise improved differential oscillator

Abstract

The present disclosure provides a noise improved differential oscillator, comprising a power supply end, a current source, and a resonant cavity circuit unit and an active network arranged between the power supply end VDD and the current source I B The two ends of the resonant cavity circuit unit are provided with two circuit nodes, 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 for providing a negative resistance to compensate for the loss of the resonant cavity circuit unit, the active network comprises two active branches, and an inductor is arranged in each active branch to eliminate the phase difference between an input current pulse and an output signal peak, so as to realize accurate current injection at the peak. The current source I B is grounded to provide a stable current for the circuit.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to the field of radio frequency circuit, integrated circuit technology, and in particular to a noise improved differential oscillator. BACKGROUND

[0002] With the rapid growth of wireless data service demand, new generation of wireless communication standards such as 5G and Wi-Fi 7 with high speed, low delay and large bandwidth characteristics are proposed in succession. In order to realize these characteristics in limited frequency spectrum resources, new generation of wireless communication adopts high order quadrature amplitude modulation technology, which requires radio frequency clock to have extremely low phase noise to avoid deterioration of modulation accuracy. As the core module of frequency synthesizer based on phase-locked loop system, the phase noise characteristics of integrated voltage-controlled oscillator directly determine the out-of-band phase noise performance of phase-locked loop system, and play a key role in radio frequency system. With the continuous improvement of communication standards, it is of great significance to realize an oscillator with lower phase noise. However, the current low noise oscillator cannot realize the minimization of phase noise. SUMMARY

[0003] Therefore, 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 present disclosure provides a noise improved differential oscillator, which comprises a power supply end, a current source, and a resonant cavity circuit unit and an active network arranged between the power supply end 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 connected to two output ends of the differential oscillator respectively; the active network is used to provide negative resistance to compensate for the loss of the resonant cavity circuit unit, the active network comprises 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 and is used to provide stable current for the circuit.

[0005] According to the present disclosure, the two active branches introduce positive feedback in a cross-coupled manner.

[0006] According to the present disclosure, each active branch comprises: a transistor branch comprising two transistors arranged in series between the power supply end and the current source, wherein one transistor gate is connected to one circuit node, and the gate of the other transistor is connected to the other circuit node. Each active branch further comprises: a capacitor branch comprising two capacitors arranged in series between the circuit node and the ground. Each active branch further comprises: 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 proper 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] The input end 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.

[0009] According to the embodiment of the present disclosure, the resonant cavity circuit unit includes a resonant cavity inductor and two capacitors. The center tap of the resonant cavity inductor is connected to the power supply end. The two capacitors are connected to the control voltage input node after being connected to the two ends of the resonant cavity inductor respectively. Circuit nodes are arranged between the resonant cavity inductor and the two capacitors respectively. The two capacitors are variable capacitors, and the capacitance values thereof are adjusted under the action of the control voltage to tune the frequency of the oscillator. BRIEF DESCRIPTION OF DRAWINGS

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

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

[0012] Figure 2 Simulation results of a current pulse and an output waveform of a conventional transconductance-enhanced differential oscillator circuit are schematically shown;

[0013] Figure 3 Simulation results of a current pulse and an output waveform of a 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 the embodiment of the present disclosure is schematically shown. DETAILED DESCRIPTION

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

[0016] To make the objectives, technical solutions and advantages of the present disclosure clearer, the present disclosure is further described in detail below with reference to specific embodiments and the accompanying drawings.

[0017] In the embodiment of the present disclosure, a noise-improved differential oscillator is provided, which includes a resonant cavity circuit unit and a control voltage input node. Figure 1As shown, the noise improved differential oscillator comprises a power supply end, a current source, and a resonant cavity circuit unit and an active network arranged between the power supply end VDD and the current source I B The two circuit nodes of the resonant cavity circuit unit 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. The active network comprises 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, thereby achieving accurate current injection at the peak. B The ground is used to provide a stable current for the circuit.

[0018] An input end of the resonant cavity circuit unit is connected to a 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 comprises a resonant cavity inductor L and two capacitors C. The center tap of the resonant cavity inductor is connected to the power supply end 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. The resonant cavity inductor L and the two capacitors C are respectively provided with a first circuit node N1 and a second circuit node N2. The two capacitors C are variable capacitors, and the capacitance values thereof are adjusted under the action of the control voltage to tune the frequency of the oscillator.

[0020] In the embodiment of the present disclosure, the two active branches introduce positive feedback through cross-coupling. Each active branch comprises a transistor branch comprising two transistors arranged in series between the power supply end and the current source. One transistor gate is connected to a circuit node, and the gate of the other transistor is connected to another circuit node. Each active branch further comprises a capacitor branch comprising two capacitors arranged in series between the circuit node and the ground. Each active branch further comprises an inductor connected between the two transistors of the transistor branch at one end and between the two capacitors of the capacitor branch at the other end, for eliminating the phase difference between the current pulse and the output signal peak.

[0021] Specifically, as Figure 1As shown, the left active branch includes two transistors arranged in series between the power supply end and the current source, which are the first transistor MN1 and the 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 right active branch includes two transistors arranged in series between the power supply end and the current source, which are the second transistor MN2 and the 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 capacitor branch includes the first capacitor C1 and the second capacitor C2 arranged 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 capacitor branch includes the third capacitor C3 and the fourth capacitor C4 arranged 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 active branch is connected to the node V S1 between the first transistor MN1 and the third transistor MN3, and 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 S2 between the second transistor MN2 and the fourth transistor MN4, and 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, the first capacitor C1, the second capacitor C2, the third capacitor C3, and the fourth capacitor C4 form an active network for providing negative resistance to compensate for the loss of the resonant cavity; the third transistor MN3 and the fourth transistor MN4 introduce positive feedback through cross coupling, increase the small signal gain of the active network, and thus increase the negative conductance of the active network circuit and reduce power consumption. It should be noted that the left and right active branches are configured identically, for example, the types and parameters of the transistors in the transistor branch are the same, the parameters of the capacitors in the capacitor branch are the same, and the parameters of the inductors are the same.

[0022] For a conventional transconductance-enhanced differential oscillator, there is a phase difference between the current pulse (I D ) and the peak value of the output signal, as shown in the simulation diagram Figure 2 . In order to obtain better phase noise, precise injection of the current pulse at the peak is required, so as to minimize the phase noise while not increasing additional power consumption and improving the quality factor of the oscillator. In combination with Figure 1 , the left active branch is taken as an example for illustration, the output voltage of the first output end is denoted as V out1 , and the voltage at the node between the first transistor MN1 and the third transistor MN3 is denoted as V S1Since the switch transistor MN1 works in saturation state when it is turned on, its current value I D1 satisfies:

[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, and V TH is the threshold voltage of the NMOS transistor. Therefore, the phase difference between I D1 and V out1 depends on the phase difference between V out1 and V S1 . Through small signal model analysis, it is obtained that:

[0025] ;

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

[0027] By selecting the inductance value of the first inductor L1, the above phase difference can be eliminated. Re-analyzing the small signal model of the circuit, the imaginary part in the relationship between V out1 and V S1 can be eliminated, and it is obtained that:

[0028] ;

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

[0030] ;

[0031] Through experiments, after selecting the suitable inductance values of the first inductor L1 and the second inductor L2, 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 shown in Figure 3 .

[0032] It is also necessary to point out that through simulation verification, if the resonator is used to realize the function of the resonant cavity inductance L, the output frequency is 2.45 GHz, and the power consumption is 0.5 mW, the simulation results of the phase noise of the traditional transconductance enhanced differential oscillator and the noise improved differential oscillator of the embodiment of the present disclosure are compared as shown in the following table. Figure 4 As can be seen from the figure, 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 an increase of 15.8 dB and 6.5 dB in the quality factor of the oscillator. The structure is also applicable to LC oscillators using inductance as resonant devices.

[0033] So far, the embodiment of the present disclosure has been described in detail in combination with the drawings. It should be noted that the implementation modes not shown or described in the drawings or the text are known to those skilled in the art, and are not described in detail. In addition, the definitions of the elements and methods described above are not limited to the various specific structures, shapes or ways mentioned in the embodiments, and can be simply changed or replaced by those skilled in the art.

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

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

[0036] It should be noted that, in this document, unless specifically indicated, having "one" element is not limited to having only one of the element, but can have one or more of the element.

[0037] In addition, in this document, unless specifically indicated, the ordinal numbers "first", "second", etc. are only used to distinguish multiple elements with the same name, and do not mean that there is a hierarchy, level, execution order, or process order between them. A "first" element and a "second" element can appear together in the same component, or separately in different components. The presence of an element with a larger ordinal number does not necessarily mean the presence of another element with a smaller ordinal number.

[0038] In this document, the terms "comprises", "comprising", "includes", "including", "has", "having" or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a process, method, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements but can include other elements not expressly listed or inherent to such process, method, article, or apparatus.

[0039] Also, in this document, relational terms such as "first", "second", and the like can be used solely to distinguish one entity or action from another entity or action, without necessarily requiring or implying any actual such relationship or order between such entities or actions. The terms "comprises", "comprising", "includes", "including", or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can include other elements not expressly listed or inherent to such process, method, article, or apparatus. Additionally, unless otherwise specified, the steps of a process, method, or the like can be performed in any order or sequence and need not be performed in the order or sequence in which they are recited.

[0040] Also, unless specifically stated otherwise, or as can be clearly inferred from the specification, steps of a process, method, or the like can be performed in any order or sequence and need not be performed in the order or sequence in which they are recited. Also, the above-described embodiments can be mixed and matched with each other or with other embodiments, based on design and reliability considerations, i.e., technical features of different embodiments can be freely combined with each other to form further embodiments.

[0041] The specific embodiments described above have been shown by way of example, and it should be understood by those skilled in the art that the application is not limited to these embodiments. Rather, other modifications, uses, and substitutions of manufacturing processes, machine elements, operational techniques and design parameters of the application, can be made without departing from the spirit and scope of the 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 disposed between the power supply terminal and the current source, wherein: The resonant cavity circuit unit has two circuit nodes at both ends, and these two circuit nodes are respectively connected to the two output terminals of the differential oscillator; An active network is used to provide negative resistance to compensate for the losses 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 peak of the output signal, so as to achieve precise current injection at the peak. Each active branch includes a transistor branch, a capacitor branch, and an inductor. The transistor branch includes two transistors connected in series between the power supply and the current source, with the gate of one transistor connected to a circuit node and the gate of the other transistor connected to another circuit node. The capacitor branch includes two capacitors connected in series between the circuit node and ground. One end of the inductor is connected between the two transistors in the transistor branch, and the other end is connected between the two capacitors in the capacitor branch. By selecting an inductor with an appropriate inductance value to eliminate the phase difference between the current pulse and the peak of the output signal, let the capacitance values ​​of the two capacitors be C1 and C2, then the inductance value of the inductor is... ω is the oscillation frequency.

2. The oscillator according to claim 1, wherein the two active branches introduce positive feedback through cross-coupling.

3. The oscillator according to claim 1, wherein one 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.

4. The oscillator according to claim 1 or 3, wherein the resonant cavity circuit unit comprises a resonant cavity inductor and two resonant cavity capacitors, wherein, The center tap of the resonant cavity inductor is connected to the power supply terminal. Two resonant cavity capacitors are connected in series and respectively to the two ends of the resonant cavity inductor. Then, the node between the two resonant cavity capacitors is connected to the control voltage input node. Circuit nodes are set between the resonant cavity inductor and each resonant cavity capacitor.

5. The oscillator according to claim 4, wherein the two resonant cavity capacitors are variable capacitors, and the capacitance value of the resonant cavity capacitors is adjusted under the action of the control voltage to tune the frequency of the oscillator.

6. The oscillator according to claim 1, wherein the current source is grounded and provides a stable current to the oscillator circuit.

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