An active multi-mode VCO mode switching method based on mode suppression and a voltage controlled oscillator

Abstract

The application relates to an active multi-mode VCO mode switching method based on mode suppression and a voltage-controlled oscillator, and belongs to the technical field of electronic circuits. The oscillator comprises a mode composition network, an active mode suppression network and a switched capacitor array. The mode composition network is constructed by two pairs of coupled inductors and four coupled capacitors to build four phase relationships, utilizes inductance-capacitance hybrid tuning to generate four discrete frequency base points, and is free of switching devices in a resonant cavity. The active mode suppression network is composed of four Gmc units in a ring topology, and the admittance matrix is adjusted by configuring an enable signal EN1-EN4 to provide a maximum negative conductance for a target mode to meet a starting condition, while suppressing non-target modes, and the coupling path is free of passive resistance. The switched capacitor array and the variable capacitance module receive external digital codes and analog voltages to realize continuous fine adjustment of frequency. The application avoids the deterioration of the Q value caused by the switching on resistance in the traditional scheme, realizes a wide tuning range, and guarantees low phase noise in the whole frequency band.

Description

Technical Field

[0001] This invention belongs to the field of electronic circuit technology, specifically relating to an active multimode VCO mode switching method based on mode suppression and a voltage-controlled oscillator. Background Technology

[0002] Voltage-controlled oscillators (VCOs) are core modules in broadband communication equipment such as RF transceivers, phase-locked loops, and radar systems. Their tuning range and phase noise performance directly determine the system's communication bandwidth and signal quality. With the increasing demand for multi-band coverage and high data rates in applications such as 5G / 6G communication and automotive radar, VCOs are required to maintain low phase noise while achieving wide frequency coverage.

[0003] To extend the tuning range of VCO chips, existing technologies mainly employ the following solutions:

[0004] (1) Switched capacitor or switched inductor scheme based on single-core structure. This scheme expands the frequency tuning range by introducing a switched capacitor array or switched inductor into the resonant cavity of the single-core oscillator to change the equivalent capacitive reactance or inductive reactance. However, the switches on the chip are not ideal devices. Their inherent on-resistance reduces the quality factor (Q value) of the resonant cavity and deteriorates the phase noise; while the off-capacitor limits the upper limit of the frequency tuning range. This inherent trade-off between on-resistance and off-capacitor fundamentally limits the potential of a single-core VCO to achieve both a wide tuning range and low phase noise.

[0005] (2) Dual-core coupling resistor switching scheme. This scheme introduces two VCO cores and a coupling capacitor or coupling inductor between them. By controlling the phase relationship between the two cores, two oscillation modes are achieved, thereby increasing the frequency tuning range. However, this scheme can only use a single inductor tuning or capacitor tuning, and the two modes alone are still insufficient to meet the requirement of wide frequency coverage. To further increase the number of modes, more switches need to be introduced, which will further exacerbate the contradiction between the switch Q value and the tuning range, essentially an extension of the shortcomings of single-core technology. Therefore, this scheme has obvious limitations in achieving a wide frequency tuning range and low phase noise in tandem.

[0006] (3) Dual-core mode suppression scheme. This scheme introduces two VCO cores and uses an active mode suppression network composed of transconductance cells (GMCs) to control the phase relationship between the two cores, thereby selecting between two oscillation modes. Compared with the resistive coupling scheme, this scheme avoids the losses of passive switches in the mode switching path. However, the mode suppression architecture of this scheme is only optimized for dual-core dual-mode scenarios: its coupling topology is designed to provide sufficient equivalent admittance difference between the two modes to ensure stable oscillation in a single operating mode, without further multi-core expansion. Therefore, this scheme still has architectural limitations in achieving wide frequency coverage and low phase noise in a coordinated manner.

[0007] (4) A scheme based on passive switching of four-core coupling resistors. To achieve wider frequency coverage, this scheme uses four VCO cores and couples them through a passive resistor network controlled by switches to form multiple oscillation modes. However, this scheme has three main drawbacks: First, the coupling resistors and switches introduce additional thermal noise, directly deteriorating the phase noise of the VCO; second, the parasitic effects of the resistors and switches become more pronounced at high frequencies, introducing additional energy loss, effectively reducing the quality factor (Q value) of the resonant cavity, further limiting the frequency tuning range and exacerbating the deterioration of phase noise; third, when the number of cores increases to four or more, the connection complexity of the resistor-coupled network in the layout increases sharply, and it may even be impossible to route, limiting its ability to expand to more core architectures. In summary, this scheme inevitably sacrifices phase noise and scalability when achieving wide frequency coverage, making it difficult to meet the performance requirements of wide-tuning-range communication systems for low phase noise and highly scalable frequency sources. Summary of the Invention

[0008] The purpose of this invention is to address the problem in existing VCO chip technology where phase noise or scalability must be sacrificed to achieve a wide tuning range. This invention provides an active multimode VCO mode switching method based on mode suppression and a voltage-controlled oscillator (VCO). It proposes an active multimode (four oscillation modes) VCO mode switching scheme that combines an active mode suppression network with a mode-composition network for hybrid inductor-capacitor tuning, along with a corresponding wide-tuning-range on-chip inductor-capacitor VCO. This achieves a wide frequency coverage while theoretically ensuring low phase noise and strong scalability.

[0009] (1) To address the two root causes of phase noise degradation in existing single-core switching schemes (due to the introduction of switches within the resonant cavity) and resistive-coupled multi-core schemes (due to the introduction of thermal noise by coupling resistors), this invention employs two networks: a mode-forming network with hybrid inductor-capacitor tuning and a novel active mode suppression network, working in tandem. The mode-forming network generates four oscillation modes through hybrid coupling of coupled inductors and fixed capacitors, and its resonant cavity contains no switching devices. The active mode suppression network achieves mode selection through the conductance differences of distributed transconductance units, and its coupling path also contains no switches or resistors. This dual-network collaborative architecture structurally eliminates the switching on-resistance loss within the resonant cavity and the resistive thermal noise on the coupling path, which is why this invention achieves low phase noise across the entire frequency band while ensuring wide frequency coverage.

[0010] (2) To address the bottleneck of existing resistive-coupled multi-core schemes, which are difficult to expand to more cores due to the high complexity of physical wiring of passive devices, this invention adopts a ring active mode suppression network composed of distributed transconductance units connected end to end. In this network, the coupling between cores is achieved entirely through the transconductance connection of transistors, rather than the traditional switch-controlled resistor network and its physical connections. Increasing the number of VCO cores only requires directly expanding the Gmc module on the ring topology, without introducing the complexity and parasitic effects of resistor network layout wiring. This allows the VCO to be smoothly expanded to six cores, eight cores, or even more cores, exchanging better phase noise performance for the linearly increased power consumption. This is the reason why this invention has strong scalability.

[0011] To achieve the above objectives, the technical solution of the present invention is: an active multimode VCO mode switching method based on mode suppression, comprising:

[0012] A pattern-forming network is constructed, which includes four VCO cores, two pairs of coupled inductors, and four coupled capacitors. By controlling the output voltage phase relationship of the four VCO cores, the frequency base points of four oscillation modes are defined.

[0013] An active mode suppression network is constructed, which consists of four Gmc networks connected end to end to form a ring topology. The four-port admittance matrix is ​​adjusted by configuring the enable signal of the Gmc network to make the target oscillation mode meet the oscillation condition, while suppressing non-target oscillation modes.

[0014] By connecting the switched capacitor array and the variable capacitor module to the output of the VCO core, the frequency of the selected mode is continuously tuned in response to external control signals.

[0015] Furthermore, the four oscillation modes include even-even mode, odd-even mode, even-odd mode, and odd-odd mode; the angular frequency ω of each mode is calculated using the following formula:

[0016]

[0017]

[0018]

[0019]

[0020] Where L is the self-inductance of the coupled inductor, and M is the mutual inductance. This represents the sum of the load capacitance of the resonant cavity. This is the capacitance value of the coupling capacitor.

[0021] Furthermore, the four-port admittance matrix Y is characterized by the following voltage-current equation:

[0022]

[0023] Among them, V1, V2, V3, and V4 are the output voltages of the four VCO cores, respectively. , , , These represent the currents at the corresponding ports; elements Y in the admittance matrix Y. ij The equivalent transconductance of the voltage at port j to port i is determined by the transconductance of the VCO core cross-coupled pair and the transconductance of the Gmc unit in the Gmc network.

[0024] Furthermore, when configured in even-even mode, the admittance matrix... Specifically:

[0025]

[0026] Where gm is the absolute value of the equivalent transconductance of the active part of the VCO core, and gmc is the transconductance value of the Gmc unit in the Gmc network when it is working.

[0027] Furthermore, for any port, its equivalent negative conductance Gm for a specific oscillation mode is calculated using the following formula:

[0028]

[0029] Where V is the reference voltage amplitude. Let gm be the voltage amplitude at the j-th port; by adjusting the ratio of gm to gmc, the oscillation start-up condition is met in the target mode. Satisfy in non-target mode ;in, This is a general representation of the equivalent admittance of an LC oscillator. This is the equivalent parallel resistance of the resonant cavity at the oscillation frequency.

[0030] Furthermore, the enable signals include EN1, EN2, EN3, and EN4, and their correspondence with the four oscillation modes is as follows:

[0031] even-even mode: EN1=1, EN2=0, EN3=1, EN4=0;

[0032] Odd-even mode: EN1=0, EN2=1, EN3=1, EN4=0;

[0033] even-odd mode: EN1=1, EN2=0, EN3=0, EN4=1;

[0034] Odd-odd mode: EN1=0, EN2=1, EN3=0, EN4=1.

[0035] This invention also provides a voltage-controlled oscillator, employing the above-described active multimode VCO mode switching method based on mode suppression, comprising:

[0036] The pattern constitutes a network, including four VCO cores, two pairs of coupled inductors, and four coupled capacitors (CM).

[0037] The active mode suppression network includes four Gmc networks, which are respectively connected to adjacent VCO cores and connected end to end to form a ring topology.

[0038] There are four groups of switched capacitor arrays and variable capacitor modules. Each group is connected to the output of a VCO core to receive digital control code Vsw and analog tuning voltage Vctrl.

[0039] Furthermore, the active part of the VCO core is composed of NMOS transistors M4 and M5 and PMOS transistors M6 and M7. M4 and M5 form an NMOS cross-coupled pair, and M6 and M7 form a PMOS cross-coupled pair, providing negative transconductance -gm. The Gmc network is composed of four Gmc units, of which the upper two Gmc units are connected in the forward direction and the lower two Gmc units are connected in the reverse direction. The upper or lower units are controlled by an enable signal to generate transconductance values ​​of +gmc or -gmc.

[0040] Furthermore, the switched capacitor array and variable capacitor module includes a 3-bit binary weighted capacitor array and two symmetrical variable capacitors. The four VCO cores share the same digital control code Vsw<2:0> and analog tuning voltage Vctrl.

[0041] Furthermore, the coupling paths in the active mode suppression network do not contain passive switches or resistors, and the resonant cavity of the mode-forming network does not contain switching devices.

[0042] Compared with the prior art, the present invention has the following beneficial effects:

[0043] (1) Synergistic optimization of wide bandwidth and low phase noise: As described in the working principle, the mode construction network in the mode switching method of the present invention achieves wide frequency coverage by inductor-capacitor hybrid coupling, and the active mode suppression network controls the mode switching in an active manner. The two work together to avoid introducing switches or resistors that degrade the Q value in the oscillation cavity, thus achieving both wide frequency coverage and low phase noise at the same time.

[0044] (2) Strong scalability: As described in the working principle, the mode suppression network in the mode switching method of this invention is based on the "ring transconductance" topology and conductance matrix control. The coupling between modes is completely achieved by the connection of active devices, which gets rid of the physical bottleneck of traditional resistive coupling schemes in multi-core wiring. Therefore, this architecture can be smoothly expanded to more cores, and better phase noise performance is obtained at the cost of linearly increased power consumption.

[0045] use:

[0046] This invention addresses the urgent need for high-performance frequency sources in broadband communication systems by proposing an active multimode VCO mode switching method based on mode suppression, along with its corresponding wide-tuning-range on-chip inductor-capacitor voltage-controlled oscillator. This method can be widely applied in 5G / 6G communications, automotive radar, satellite communications, and other fields. While achieving a wide tuning range, this invention retains excellent phase noise performance, making it particularly suitable for RF front-end systems with stringent signal quality requirements and compatibility with multiple communication frequency bands. Specific applications include broadband frequency synthesizers in 5G / 6G terminal RF transceivers, automotive multimode radar systems, and satellite communication and microwave backhaul equipment. Attached Figure Description

[0047] Figure 1 This is a block diagram of the overall architecture of an active multimode VCO mode switching method based on mode suppression and its corresponding wide-tuning-range on-chip inductor-capacitor voltage-controlled oscillator.

[0048] Figure 2 for Figure 1 Circuit diagram of the Gmc network and its Gmc unit;

[0049] Figure 3 for Figure 1 Core circuit diagram of VCO oscillator;

[0050] Figure 4 for Figure 1 The network circuit structure diagram of the mixed inductor-capacitor tuning mode;

[0051] Figure 5 for Figure 1 Circuit diagram of switched capacitor array and variable capacitor module;

[0052] Figure 6 A schematic diagram of the core phase of each VCO under four oscillation modes (based on...) Figure 1 );

[0053] Figure 7 This is a circuit diagram of an active mode suppression network. Detailed Implementation

[0054] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings.

[0055] This invention provides a mode switching method for an active multimode VCO based on mode suppression, comprising:

[0056] A pattern-forming network is constructed, which includes four VCO cores, two pairs of coupled inductors, and four coupled capacitors. By controlling the output voltage phase relationship of the four VCO cores, the frequency base points of four oscillation modes are defined.

[0057] An active mode suppression network is constructed, which consists of four Gmc networks connected end to end to form a ring topology. The four-port admittance matrix is ​​adjusted by configuring the enable signal of the Gmc network to make the target oscillation mode meet the oscillation condition, while suppressing non-target oscillation modes.

[0058] By connecting the switched capacitor array and the variable capacitor module to the output of the VCO core, the frequency of the selected mode is continuously tuned in response to external control signals.

[0059] This invention also provides a voltage-controlled oscillator, employing the above-described active multimode VCO mode switching method based on mode suppression, comprising:

[0060] The pattern constitutes a network, including four VCO cores, two pairs of coupled inductors, and four coupled capacitors (CM).

[0061] The active mode suppression network includes four Gmc networks, which are respectively connected to adjacent VCO cores and connected end to end to form a ring topology.

[0062] There are four groups of switched capacitor arrays and variable capacitor modules. Each group is connected to the output of a VCO core to receive digital control code Vsw and analog tuning voltage Vctrl.

[0063] The following is a detailed implementation process of the present invention.

[0064] The active multimode VCO mode switching method based on mode suppression of this invention and its corresponding wide-tuning-range on-chip inductor-capacitor voltage-controlled oscillator circuit composition and connection method are described below:

[0065] (1) The active mode suppression network consists of four such Figure 2 The Gmc network shown has four such Figure 3 The active portion (M4-M7) in the VCO oscillation core shown is, according to Figure 1 The topological structure is formed by the connections within. The circuit structure of the Gmc unit is as follows: Figure 2 As shown, each Gmc unit consists of NMOS transistors M1, M2, and M3. M1 acts as the bias transistor, with its gate connected to the external control signal EN, its source grounded, and its drain connected to the sources of M2 and M3. M2 and M3 form a differential pair; the gate of M2 serves as the input signal terminal IP, and its drain as the output terminal OP; the gate of M3 serves as the input signal terminal IN, and its drain as the output terminal ON. The circuit structure of the VCO oscillation core is as follows: Figure 3 As shown, its active part consists of transistors M4-M7. Among them, the two NMOS transistors M4 / 5 and the two PMOS transistors M6 / 7 form cross-coupled pairs. The specific connection method is as follows: M4 and M5 form an NMOS cross-coupled pair. The drain of M4 is connected to the core positive output OSCxP and the gate is connected to the core inverted output OSCxN. The drain of M5 is connected to OSCxN and the gate is connected to OSCxP. The sources of the two are interconnected and then connected to the tail current source ground, x=1,2,3,4. M6 and M7 form a PMOS cross-coupled pair. The source of M6 is connected to the power supply VDD, the gate is connected to OSCxN and the drain is connected to OSCxP. The source of M7 is connected to VDD, the gate is connected to OSCxP and the drain is connected to OSCxN. This cross-coupled structure provides negative transconductance -gm to maintain the oscillation of the resonant cavity.

[0066] Four GMC networks Figure 1A ring-coupled link is formed by connecting the first and last connections: the first input of the first Gmc network is connected to the output of the first VCO core (OSC1P, OSC1N), and the output is connected to the output of the second VCO core (OSC2P, OSC2N); the second Gmc network is connected to the outputs of the second and third VCO cores; the third Gmc network is connected to the outputs of the third and fourth VCO cores; and the fourth Gmc network is connected to the outputs of the fourth and first VCO cores. The enable terminals of the four Gmc networks are connected to external mode selection signals EN1, EN2, EN3, and EN4, respectively. By configuring the high and low level combinations of the four EN signals, the operating mode of each Gmc network is switched, thereby adjusting the overall admittance matrix to achieve mode selection.

[0067] (2) The specific structure of the network formed by the inductor-capacitor hybrid tuning mode is as follows: Figure 4 As shown, the network consists of coupled inductors 1 and 2 and coupled capacitors C1-C4 as shown in the figure, with each capacitor having a capacitance value of C. M .

[0068] (3) The structure of the switched capacitor array and the variable capacitor module is as follows: Figure 5 As shown, the module consists of a 3-bit binary weighted capacitor array and two symmetrical variable capacitors. Four identical switched capacitor arrays and variable capacitor modules are connected to the output of each oscillator core. The four switched capacitor arrays and variable capacitor modules share the Vsw<2:0> and Vctrl signals, which are control codes from outside the oscillator.

[0069] The specific connection method of the switched capacitor array and variable capacitor module structure is as follows: the output terminals OSC1P and OSC1N of each VCO core (such as the first core) are respectively connected to a set of switched capacitor arrays and variable capacitor modules. In each set, the common terminal of two back-to-back connected variable capacitors is connected to the Vctrl signal, the other end of one variable capacitor is connected to OSC1P, and the other end of the other variable capacitor is connected to OSC1N; the capacitance values ​​of these two variable capacitors are controlled by the externally input analog tuning voltage Vctrl. The 3-bit binary weighted capacitor array contains three sets of capacitor units. The two ends of each set of capacitor units are selectively connected between OSC1P and OSC1N via a switching transistor. The control gate of the switching transistor receives a 3-bit digital control code Vsw<2:0> (i.e., the high-order Vsw). <2> Median Vsw <1> Low-position Vsw <0> The four sets of switched capacitor arrays corresponding to the four VCO cores and the variable capacitor module share the same set of external control signals Vsw<2:0> and Vctrl to ensure that the four cores maintain strict symmetry during the tuning process.

[0070] The working principle and function of the active multimode VCO mode switching method based on mode suppression and its corresponding wide-tuning-range on-chip inductor-capacitor voltage-controlled oscillator of this invention are described below:

[0071] The working process of the active multimode VCO mode switching method based on mode suppression in this invention is based on the collaborative principle of "mode constituting network defining frequency base point, active mode suppression network selecting oscillation mode, and switched capacitor array and variable capacitor module realizing continuous tuning". The working mechanism of the two core networks in the scheme will be described in detail below, and it will be demonstrated how they necessarily lead to the advantages claimed by this invention.

[0072] (1) Working principle of the inductor-capacitor hybrid tuning mode network in the active multimode VCO mode switching method

[0073] This network generates four oscillation modes using a hybrid inductor-capacitor coupling method. The frequency tuning method for each mode is determined by the inherent characteristics of the coupled inductor and capacitor.

[0074] This invention primarily controls the operating frequency of the oscillator by altering the operating phase of each VCO core to control the values ​​of the equivalent capacitance and inductance connected to the resonant cavity. For example... Figure 4 As shown, let the self-inductance of the two ports of the coupled inductor be L, and the mutual inductance be M. Based on the properties of the coupled inductor itself, when a voltage signal with equal amplitude and frequency but opposite phase is applied across the coupled inductor, the equivalent inductance at the two input ports is LM. Conversely, when two voltage signals with equal amplitude, frequency, and phase are applied, the equivalent inductance at the input ports is L+M. For a capacitor with capacitance C, when a voltage signal with equal amplitude, frequency, and phase is applied across the capacitor, the capacitor is effectively short-circuited, and its equivalent capacitance in the circuit is 0. Similarly, when a voltage signal with equal amplitude and frequency but opposite phase is applied across the capacitor, the midpoint between the capacitor's plates is virtually grounded. In this case, the capacitor can be considered equivalent to having a capacitance to ground of twice C at each of its two input terminals.

[0075] Furthermore, based on the above principles, it can be concluded that by changing the loading... Figure 4 By understanding the phase relationship between the voltages across the coupling inductor and capacitor, the values ​​of the equivalent inductance and capacitance connected in the circuit can be flexibly controlled. The following analysis will further illustrate this. Figure 6 As shown, when all cores operate in phase (even-even mode), the voltages at the two input terminals of the coupling inductor are in phase. According to inductor coupling theory, the equivalent inductance of each core is... Meanwhile, the coupling capacitor C M With the voltages at both ends being the same, it is equivalent to a short circuit and does not contribute any additional capacitance. The oscillation frequency at this time is:

[0076]

[0077] Among them, C L This is the sum of the capacitances of all other load capacitors in the resonant cavity. When cores 1 and 3 are in phase with cores 2 and 4, but cores 1 and 2 are out of phase with cores 3 and 4 (odd-even mode), the voltages across the coupled inductor are in phase, and the equivalent inductance remains the same. However, the coupling capacitor C M The voltages across the terminals are out of phase. According to the principle of capacitance impedance, this is equivalent to connecting a capacitor with a capacitance of C in parallel with each core. M The capacitance is C. L +C M The oscillation frequency at this time is:

[0078]

[0079] Similarly, the operating frequencies of the oscillator in even-odd and odd-odd modes are:

[0080]

[0081]

[0082] From equations (1)-(4), we can obtain that by reasonably designing the coupling coefficient k (M=k×L, k can determine the mutual inductance of the coupled inductor) and the coupling capacitance C of the coupled inductor, we can achieve the desired results. M By adjusting the capacitance value, four appropriate frequency base points can be obtained, covering an extremely wide frequency range, thus realizing four oscillation modes.

[0083] Based on this working principle, this invention achieves hybrid tuning of inductors and capacitors. This structural innovation directly brings two advantages: First, in terms of frequency coverage, four oscillation modes are generated using only a simple two-winding coupled inductor, laying the foundation for wide frequency coverage, which is unattainable by existing single-core and dual-core dual-mode solutions; Second, in terms of phase noise, since the mode configuration does not depend on the introduction of switches in the resonant cavity, this invention structurally allows the use of fixed-coupled inductors and capacitors with high Q values, fundamentally ensuring the possibility of achieving low phase noise from the perspective of passive components. This contrasts sharply with single-core switching solutions, which inevitably degrade the Q value due to the introduction of switches.

[0084] (2) Working principle of active mode suppression network in active multimode VCO mode switching method

[0085] After defining four oscillation modes in the mode-forming network, the core task of the active mode suppression network is to ensure that the circuit operates in the target mode while simultaneously suppressing the other modes. Its working mechanism is based on the differential management of the conductance matrix, as detailed below:

[0086] according to Figure 7 The illustrated "ring transconductance" network structure designates the output ports of the four VCO cores as ports 1, 2, 3, and 4. Each port is connected to a VCO oscillation core, whose active part consists of... Figure 3 The diagram shows two pairs of cross-coupled PMOS and NMOS transistors (providing negative transconductance -gm), with adjacent ports coupled via a Gmc module. The admittance matrix is ​​used here to analyze the specific working principle of the active mode suppression network's mode switching. For a four-port network, its voltage-current equations are as follows:

[0087]

[0088] Among them, Y ij Let V1, V2, V3, and V4 represent the equivalent transconductance of the voltage at port j with respect to port i, respectively. In all four oscillation modes, transistors M4-M7 within the VCO core are in the saturation region. Assuming the transconductances of the NMOS and PMOS transistors in the saturation region are -gmn and -gmp, respectively, then the current introduced into port 1 by the voltage applied to port 1 is:

[0089]

[0090] Where -gm is the sum of -gmn and -gmp.

[0091] Further analysis of the GMC unit is performed: such as Figure 2 As shown, a Gmc network is a two-port device composed of four Gmc units. The inputs and outputs of the lower two Gmc units are reversed with the inputs and outputs of the Gmc network, while the inputs and outputs of the upper two Gmc units are not reversed. The two pairs of Gmc units are controlled by the enable signal EN, and only one pair of units is active at any given time. Taking port 1 / 2 as an example, when the upper two Gmc units are active and the lower two Gmc units are off, the current introduced into port 1 by port 2 for the Gmc network is:

[0092]

[0093] Where gmc is the transconductance value of transistor M2 / 3 in the Gmc cell of the Gmc network when it is operating in the saturation region. Similarly, when the two lower Gmc cells are operating and the upper one is off, we can obtain:

[0094]

[0095] For ease of description, the working state corresponding to the Gmc network in equation (7) is defined as the in-phase mode, and similarly, the working state corresponding to equation (8) is defined as the out-of-phase mode.

[0096] Combination Figure 1 As shown, let OSC1P / OSC1N be port 1. Similarly, define the other ports as 2, 3, and 4 respectively.

[0097] Table 1

[0098]

[0099] When the EN signal input of the Gmc unit is 1, Figure 2 When the middle tube M1 is turned on, tubes M2 and M3 enter the saturation region and begin to work, providing a transconductance of value gmc. Meanwhile, in the Gmc unit where the EN signal input is 0, tube M1 is turned off, and no current flows through tubes M2 and M3, so they do not work.

[0100] When the active mode suppression network is like Figure 6 As shown in Table 1, when operating in even-even mode, all Gmc networks operate in in-phase mode. The formula for the total current at each port can be obtained as follows:

[0101]

[0102] At this point, the corresponding admittance matrix can be written as:

[0103]

[0104] At this point, the effectiveness of the active mode suppression network can be determined. By analyzing the target's even-even mode, we first assume the oscillator operates in even-even mode, where the amplitude, frequency, and phase of the four cores are identical. Let:

[0105]

[0106] At this point, the equivalent admittance of the active mode suppression network in the even-even mode can be written as:

[0107]

[0108] Further calculation of the equivalent admittance of the active mode suppression network in the even-even mode to the odd-even mode. In the odd-even mode, cores 1 and 2 are out of phase with cores 3 and 4, and cores 1 and 3 are in phase with cores 2 and 4. At this time, we have:

[0109]

[0110] At this point, the equivalent admittance of the active mode suppression network in the even-even mode for the odd-even mode can be written as:

[0111]

[0112] Similarly, we can obtain the equivalent admittance of the active mode suppression network operating in even-even mode for the remaining two modes:

[0113]

[0114]

[0115] The above calculations show that when the active mode suppression network operates in even-even mode, the network provides the largest absolute negative conductance for the even-even operating mode:

[0116]

[0117] The absolute values ​​of the negative conductance provided for the other three non-target modes are significantly reduced. For an oscillator consisting of a negative resistance element and an RLC resonant cavity, its oscillation start-up condition is:

[0118]

[0119] in R is a general representation of the equivalent admittance of an LC oscillator. p This is the equivalent parallel resistance of the resonant cavity at the oscillation frequency. For example... Figure 4 As shown, different modes have different resonant frequencies, and their corresponding frequencies are... and They also differ. By adjusting the ratio of gm and gmc, the operating states of the four oscillation modes are made to satisfy:

[0120]

[0121]

[0122]

[0123]

[0124] At this point, (19) can guarantee the oscillation of the even-even mode. (20)-(22) can ensure that the other three modes are effectively suppressed. , not vibrating).

[0125] Similar to the example of the even-even mode oscillation above, by switching the Gmc module to the on and off states as shown in Table 1 to change the configuration of the admittance matrix, the other three modes can obtain the negative conductance with the largest absolute value, thereby realizing the flexible switching of multiple modes among the four modes. Equations (23) to (25) give the equivalent admittance matrices corresponding to the other three working modes.

[0126]

[0127]

[0128]

[0129] Based on the above working principle, the active multimode VCO mode switching scheme of this invention relies entirely on the conductance difference of the active transconductance network to achieve mode selection, without requiring any switches or resistors to be connected in series in the resonant cavity or core coupling path. Therefore, it reduces the degrading effect of the passive switch's on-resistance on the resonant cavity's Q value. This is why this invention can achieve low phase noise across the entire frequency band compared to single-core switching schemes and resistively coupled multi-core schemes. Simultaneously, the "ring transconductance" topology of the active mode suppression network can be implemented solely through transistor interconnects, unrestricted by the complex wiring rules of multi-port passive networks. This allows it to be smoothly scaled to six-core, eight-core, or even more-core architectures, trading power consumption for superior phase noise, demonstrating the strong scalability of this invention at the architectural level compared to traditional resistively coupled schemes.

[0130] (3) Overall working principle of active multimode VCO mode switching method based on mode suppression

[0131] Combining the two core networks mentioned above, the complete workflow of this invention's multimode VCO mode switching method, which achieves wide frequency coverage and low phase noise oscillations, is as follows: First, the mode-forming network utilizes electromagnetic hybrid coupling to construct four discrete oscillation modes (multimode) within the target frequency band, establishing a frequency framework for wide frequency coverage; subsequently, the active mode suppression network dynamically ensures that any one mode obtains sufficient negative conductance for oscillation startup by configuring the conductance matrix, while strictly suppressing the other three modes, ensuring the pure spectrum and stable oscillation of the selected mode; finally, Figure 5 The switched capacitor array shown is controlled by the digital signal Vsw<2:0> and the analog voltage signal Vctrl, which continuously changes the equivalent capacitance connected to the resonant cavity, enabling the invention to fully cover the frequency range within each mode and achieve seamless overlap between adjacent modes.

[0132] The three collaborative workflows described above correspond sequentially to the "coarse tuning" (mode configuration), "selection" (mode suppression), and "fine tuning" (capacitor array) of the oscillation frequency. It is precisely because of this collaborative working principle that the active multimode VCO mode switching scheme of this invention achieves wide-frequency continuous tuning while introducing only minimal switching and resistance losses into the resonant cavity, maintaining a high Q-value resonance, and keeping the phase noise across the entire frequency band at an excellent level. Simultaneously, mode switching is controlled by a transconductance matrix, whose entirely active circuitry nature naturally adapts to the on-demand expansion of the core count, giving this architecture enormous potential for evolution towards higher performance.

[0133] This invention relates to an active multimode VCO mode switching method based on mode suppression, and its corresponding wide-tuning-range on-chip inductor-capacitor voltage-controlled oscillator, which can be used as the core frequency generation module in an RF transceiver or phase-locked loop. It operates by being powered by a DC control signal and a power supply. As shown in Table 1, the active mode suppression network is controlled by externally provided digital selection signals EN1-EN4, and the oscillation mode of the VCO is selected by controlling the phase relationship of each core of the VCO. Figure 5 As shown, the externally provided digital control signal Vsw<2:0> and analog control signal Vctrl control the operating states of the switched capacitor array and the variable capacitor module, respectively. First, based on the target operating frequency band, the VCO is configured to enter one of four operating modes via the EN signal. At this time, as described in the previous working principle, the mode rejection network automatically and precisely suppresses all non-operating modes, allowing only the target mode to oscillate. Subsequently, in this mode, continuous and fine tuning of the output frequency is achieved by changing the control word of the capacitor array and the DC voltage on the variable capacitor. In closed-loop phase-locked loop applications, the VCO based on the active multi-mode VCO mode switching scheme of this invention can further receive analog tuning voltage from the loop filter, locking the frequency and phase to preset values, thereby achieving wide tuning range and low phase noise frequency synthesis. This invention is implemented using standard semiconductor CMOS technology and can be directly integrated with other RF modules such as phase-locked loops and mixers on mainstream EDA platforms such as Cadence and Synopsys for integrated chip design, simulation, and integration.

[0134] The above are preferred embodiments of the present invention. Any changes made to the technical solution of the present invention that do not exceed the scope of the technical solution of the present invention shall fall within the protection scope of the present invention.

Claims

1. A mode switching method for an active multimode VCO based on mode suppression, characterized in that, include: A pattern-forming network is constructed, which includes four VCO cores, two pairs of coupled inductors, and four coupled capacitors. By controlling the output voltage phase relationship of the four VCO cores, the frequency base points of four oscillation modes are defined. An active mode suppression network is constructed, which consists of four Gmc networks connected end to end to form a ring topology. The four-port admittance matrix is ​​adjusted by configuring the enable signal of the Gmc network to make the target oscillation mode meet the oscillation condition, while suppressing non-target oscillation modes. By connecting the switched capacitor array and the variable capacitor module to the output of the VCO core, the frequency of the selected mode is continuously tuned in response to external control signals.

2. The active multimode VCO mode switching method based on mode suppression according to claim 1, characterized in that, The four oscillation modes include even-even mode, odd-even mode, even-odd mode, and odd-odd mode; the angular frequency ω of each mode is calculated using the following formula: Where L is the self-inductance of the coupled inductor, and M is the mutual inductance. This represents the sum of the load capacitance of the resonant cavity. This is the capacitance value of the coupling capacitor.

3. The active multimode VCO mode switching method based on mode suppression according to claim 1, characterized in that, The four-port admittance matrix Y is characterized by the following voltage-current equation: Among them, V1, V2, V3, and V4 are the output voltages of the four VCO cores, respectively. , , , These represent the currents at the corresponding ports; elements Y in the admittance matrix Y. ij The equivalent transconductance of the voltage at port j to port i is determined by the transconductance of the VCO core cross-coupled pair and the transconductance of the Gmc unit in the Gmc network.

4. The active multimode VCO mode switching method based on mode suppression according to claim 3, characterized in that, When configured in even-even mode, the admittance matrix Specifically: Where gm is the absolute value of the equivalent transconductance of the active part of the VCO core, and gmc is the transconductance value of the Gmc unit in the Gmc network when it is working.

5. The active multimode VCO mode switching method based on mode suppression according to claim 4, characterized in that, For any port, its equivalent negative conductance Gm for a specific oscillation mode is calculated using the following formula: Where V is the reference voltage amplitude. Let gm be the voltage amplitude at the j-th port; by adjusting the ratio of gm to gmc, the oscillation start-up condition is met in the target mode. Satisfy in non-target mode ;in, This is a general representation of the equivalent admittance of an LC oscillator. This is the equivalent parallel resistance of the resonant cavity at the oscillation frequency.

6. The active multimode VCO mode switching method based on mode suppression according to claim 1, characterized in that, The enable signals include EN1, EN2, EN3, and EN4, and their correspondence with the four oscillation modes is as follows: even-even mode: EN1=1, EN2=0, EN3=1, EN4=0; Odd-even mode: EN1=0, EN2=1, EN3=1, EN4=0; even-odd mode: EN1=1, EN2=0, EN3=0, EN4=1; Odd-odd mode: EN1=0, EN2=1, EN3=0, EN4=1.

7. A voltage-controlled oscillator, characterized in that, The active multimode VCO mode switching method based on mode suppression as described in any one of claims 1 to 6 includes: The pattern constitutes a network, including four VCO cores, two pairs of coupled inductors, and four coupled capacitors (CM). The active mode suppression network includes four Gmc networks, which are respectively connected to adjacent VCO cores and connected end to end to form a ring topology. There are four groups of switched capacitor arrays and variable capacitor modules. Each group is connected to the output of a VCO core to receive digital control code Vsw and analog tuning voltage Vctrl.

8. A voltage-controlled oscillator according to claim 7, characterized in that, The active part of the VCO core consists of NMOS transistors M4 and M5 and PMOS transistors M6 and M7. M4 and M5 form an NMOS cross-coupled pair, and M6 and M7 form a PMOS cross-coupled pair, providing negative transconductance -gm. The Gmc network consists of four Gmc units, with the upper two Gmc units having forward-biased input-output connections and the lower two Gmc units having reverse-biased input-output connections. An enable signal controls the operation of the upper or lower units to generate transconductance values ​​of +gmc or -gmc.

9. A voltage-controlled oscillator according to claim 7, characterized in that, The switched capacitor array and variable capacitor module includes a 3-bit binary weighted capacitor array and two symmetrical variable capacitors. The four VCO cores share the same digital control code Vsw<2:0> and analog tuning voltage Vctrl.

10. A voltage-controlled oscillator according to claim 7, characterized in that, The coupling paths in the active mode suppression network do not contain passive switches or resistors, and the resonant cavity of the mode-forming network does not contain switching devices.

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