Voltage Controlled Oscillator

Abstract

The present invention discloses a voltage-controlled oscillator, comprising a negative resistance circuit and an LC resonant circuit; the negative resistance circuit is connected to a current source, and the negative resistance circuit is connected to the LC resonant circuit; the LC resonant circuit comprises a first capacitor, a transformer, an inductor, and a second capacitor; the first capacitor is connected in parallel with the primary coil of the transformer; the secondary coil of the transformer, the inductor, and the second capacitor are connected in parallel with each other; the first capacitor is a varactor. The voltage-controlled oscillator based on a single transformer and a single inductor of the present invention can effectively reduce the inductance value of the LC resonant circuit, improve the quality factor Q value, and reduce the circuit layout area.

Description

Technical Field

[0001] The present invention relates to the technical field of oscillators, and in particular to a voltage-controlled oscillator. Background Art

[0002] In the prior art, a voltage-controlled oscillator (VCO) is an oscillation circuit in which there is a corresponding relationship between the output frequency and the input control voltage, and its output frequency is a function of the input control voltage. An oscillator is a circuit that can convert direct current power into a periodic alternating current signal without external signal excitation. If the working state of the oscillator and the component parameters of the oscillation circuit are controlled by the input control voltage, the oscillator constitutes a voltage-controlled oscillator. The types of voltage-controlled oscillators include LC voltage-controlled oscillators, RC voltage-controlled oscillators, and crystal voltage-controlled oscillators. The main technical requirements of voltage-controlled oscillators include good frequency stability, high control sensitivity, wide frequency modulation range, linear relationship between frequency deviation and control voltage, and suitable for integration. Among them, the crystal voltage-controlled oscillator has high frequency stability but a narrow frequency modulation range; the RC voltage-controlled oscillator has low frequency stability and a wide frequency modulation range; and the performance of the LC voltage-controlled oscillator is between the two.

[0003] The current mainstream voltage-controlled oscillator is implemented by inductor and capacitor resonance, that is, LC voltage-controlled oscillator. The capacitor includes fixed capacitor and varactor (variable capacitor); the voltage of the varactor is controlled to change the inductor and capacitor resonance frequency, thereby changing the output frequency of the voltage-controlled oscillator. The main performance indicator of the voltage-controlled oscillator is phase noise (PN), and there is a trade-off relationship between the phase noise (PN) and power consumption of the LC voltage-controlled oscillator. If the power consumption of the voltage-controlled oscillator is increased, it is necessary to reduce the parallel equivalent resistance of the LC resonant circuit, that is, reduce the inductance value.

[0004] In the prior art, a common solution to reduce the inductance of an LC voltage-controlled oscillator is to reduce the inductance by using an on-chip inductor with a small number of coils and a small area; when this simple method is used to reduce the inductance, the phase noise (PN) can be reduced by 3dB, while the power consumption of the LC voltage-controlled oscillator is doubled. Another common solution to reduce the inductance of an LC voltage-controlled oscillator is to use two 1:n transformers to reduce the inductance, such as Figure 1 By applying two on-chip transformers T1 and T2 with a ratio of 1:n based on back-to-back connection to the on-chip LC voltage-controlled oscillator, the inductance value L of the LC voltage-controlled oscillator can be increased. p Reduce to L p / (1+n 2 ),like Figure 2 shown.

[0005] However, the inventors have found through research that the first solution in the prior art uses an on-chip inductor with a small number of coils and a small area to reduce the inductance value. Although it is simple and clear, when the inductance value is reduced to a certain extent, the connection resistance of the LC resonant circuit will become the dominant parasitic resistance, which reduces the phase noise (PN) of the LC voltage-controlled oscillator; in the second solution, if Figure 2 As shown, adding two 1:n transformers can effectively reduce the inductance value, but adding two transformers will greatly increase the circuit board area of ​​the LC voltage-controlled oscillator, and because it requires two identical transformers, the flexibility of circuit design becomes poor. At the same time, the quality factor Q value of the transformer is low, which increases the phase noise (PN) of the LC voltage-controlled oscillator. Summary of the invention

[0006] Based on this, in order to solve the technical problems in the prior art, a voltage-controlled oscillator is proposed.

[0007] The voltage-controlled oscillator includes a negative resistance circuit and an LC resonant circuit; the negative resistance circuit is connected to a current source; the LC resonant circuit is connected to the negative resistance circuit; the LC resonant circuit includes a first capacitor, a transformer, an inductor, and a second capacitor; the first capacitor is connected in parallel with the primary coil of the transformer; the secondary coil of the transformer, the inductor, and the second capacitor are connected in parallel with each other; the first capacitor is a varactor.

[0008] In one embodiment, the LC resonant circuit includes a transformer inductor network, the transformer inductor network includes the transformer and the inductor; the transformer is an on-chip transformer, and the inductor is an on-chip inductor; the left side of the transformer inductor network is the primary coil input port of the transformer; the right side of the transformer inductor network is the secondary coil output port of the transformer, the input port of the inductor and the center tap port of the primary coil of the transformer.

[0009] In one embodiment, the inductor and the transformer share a circuit layout area, and the distance between the coil of the inductor and the primary coil and the secondary coil of the transformer exceeds 10 micrometers.

[0010] In one embodiment, the inductor is a single-turn inductor including two thick metal layers.

[0011] In one embodiment, the negative resistance circuit is a cross-coupled tube; the cross-coupled tube is composed of an NMOS tube and / or a PMOS tube; the cross-coupled tube includes an NMOS cross-coupled tube, a PMOS cross-coupled tube, or an NMOS and PMOS complementary cross-coupled tube.

[0012] In one embodiment, the cross-coupled transistor includes a first MOS transistor and a second MOS transistor; the first MOS transistor and the second MOS transistor are MOS transistors of the same size and type; the gate of the first MOS transistor and the drain of the second MOS transistor are connected to each other and to one end of the first capacitor; the gate of the second MOS transistor and the drain of the first MOS transistor are connected to each other and to the other end of the first capacitor; the source of the first MOS transistor and the source of the second MOS transistor are connected to each other and to the current source.

[0013] In one embodiment, the current source is a current source with a tail or a current source without a tail.

[0014] Implementing the embodiments of the present invention will have the following beneficial effects:

[0015] The technical solution of the voltage-controlled oscillator composed of a single transformer and a single inductor according to the present invention effectively reduces the inductance value of the LC resonant circuit, improves the quality factor Q value, and reduces the circuit layout area. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0017] in:

[0018] Figure 1 It is a schematic diagram of an LC resonant circuit circuit for reducing inductance in the prior art;

[0019] Figure 2 It is a schematic diagram of the structure of an LC resonant circuit for reducing inductance in the prior art;

[0020] Figure 3 is a circuit diagram of a voltage-controlled oscillator in the present invention;

[0021] Figure 4 It is a schematic diagram of the structure of the transformer inductor network of the voltage-controlled oscillator in the present invention. DETAILED DESCRIPTION

[0022] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0023] The present invention discloses an LC voltage-controlled oscillator based on a single transformer T1 and a single inductor L. First, the transformer T1 effectively reduces the inductance value of the LC resonant circuit; second, the use of the inductor can improve the quality factor Q value of the entire circuit; finally, the use of a single transformer and the shared area of ​​the inductor and the transformer effectively reduce the circuit layout area.

[0024] like Figure 3 The circuit diagram of the voltage controlled oscillator is shown, the voltage controlled oscillator includes a negative resistance circuit and an LC resonant circuit; a current source is connected to the negative resistance circuit; the negative resistance circuit is connected to the LC resonant circuit; the LC resonant circuit includes a first capacitor C1, a transformer T1, an inductor L, and a second capacitor C2; the first capacitor C1 and the primary coil L of the transformer T1 P connected in parallel with each other; the secondary coil L of the transformer T1 s , the inductor L, and the second capacitor C2 are connected in parallel with each other; the first capacitor C1 is a varactor.

[0025] The current source is a current source with a tail or a current source without a tail.

[0026] The negative resistance circuit is a cross-coupled tube. The basic function of the cross-coupled tube is to compensate for the energy loss in the LC resonant circuit. A cross-coupled tube refers to a structure in which two MOS tubes of the same size and type are connected in a cross-coupled manner, that is, the sources of the two MOS tubes are connected together, and the gate of one MOS tube is connected to the drain of the other MOS tube.

[0027] The cross-coupled tubes are composed of NMOS tubes and / or PMOS tubes; the cross-coupled tubes include NMOS cross-coupled tubes, PMOS cross-coupled tubes or NMOS and PMOS complementary cross-coupled tubes.

[0028] like Figure 3 As shown, in one embodiment, the cross-coupled transistor includes a first MOS transistor M1 and a second MOS transistor M2; the first MOS transistor M1 and the second MOS transistor M2 are two MOS transistors of the same size and the same type, and may be NMOS transistors or PMOS transistors; the gate of the first MOS transistor M1 and the drain of the second MOS transistor M2 are connected to each other and to one end of the first capacitor C1, and the gate of the second MOS transistor M1 and the drain of the first MOS transistor M2 are connected to each other and to the other end of the first capacitor C1; the source of the first MOS transistor M1 and the source of the second MOS transistor M2 are connected to each other and to the current source.

[0029] Depend on Figure 3It can be seen that the ratio of the primary coil to the secondary coil of the transformer T1 is 1:n, and the inductance value from the primary side of the transformer to the transformer is L / n 2 :The inductance value of the transformer viewed from the primary side is L p *L / (n 2 L p +L), in L p >L、n>2, the inductance value is approximately L / n 2 This circuit structure reduces the inductance of the LC voltage-controlled oscillator by about n 2 times, among which L p is the inductance of the primary coil of the transformer.

[0030] Among them, the first capacitor C1 connected to the primary coil of the transformer and the second capacitor C2 connected to the secondary coil of the transformer are two capacitors constituting the LC resonant circuit of the voltage-controlled oscillator. Compared with the LC resonant circuit with only inductance and capacitance in the prior art, the LC resonant circuit of this circuit structure improves the flexibility of resonant frequency control: the capacitance value of the transformer viewed from the primary side of the transformer is n 2 ×C2, and the capacitance value at the input end (left end) of the LC resonant circuit is C1+n 2 ×C2, it can be seen that the second capacitor C2 in the LC resonant circuit amplifies n through this circuit structure. 2 times, compared with the direct use of capacitance value of n 2 ×C2 capacitance, through this circuit structure amplifies n 2 The parasitic capacitance of the second capacitor C2 is smaller, thereby increasing the tuning range of the LC voltage-controlled oscillator.

[0031] Figure 4 It is a schematic diagram of the structure of the transformer inductor network of the voltage-controlled oscillator in the present invention. The transformer inductor network includes the transformer T1 and the inductor L. The transformer inductor network is a part of the LC resonant circuit.

[0032] The transformer T1 is an on-chip transformer; the left side of the transformer inductor network is the primary coil input port 41 of the transformer T1. Figure 4 As shown, in one embodiment, the transformer T1 is an octagonal symmetrical interwinding planar on-chip transformer, and the number of primary inductance coils of the transformer T1 is adjusted according to demand, and the number of primary inductance coils of the transformer T1 can be 2 turns, 3 turns or 4 turns.

[0033] The inductor L is an on-chip inductor. The inductor and the transformer are stacked on each other. The inductor and the transformer share a circuit layout area. The distance between the coil of the inductor and the primary coil and the secondary coil of the transformer exceeds 10 microns.

[0034] In the present invention, in order to improve the performance of the LC voltage-controlled oscillator, the inductor L adopts a single-turn inductor; at the same time, the inductor L adopts a thick metal layer, and the thick metal layer is located at the upper layer of the on-chip inductor; in particular, the inductor L adopts two or three thick metal layers, and the material of the thick metal layer can be copper or aluminum, such as both thick metal layers are copper, or the top layer is aluminum and the two thick metal layers below are copper; the single-layer thickness of the thick metal layer ranges from 1 micron to 5 microns. Figure 1 The primary and secondary coils of the transformer in the prior art shown in the figure usually can only use a single thick metal layer. In the technical solution of the present invention, the inductor L uses two thick metal layers so that the quality factor Q value of the overall circuit including the transformer is improved, and the quality factor Q value of the inductor can be increased by 5-8 relative to the quality factor Q value of the transformer.

[0035] The right side of the transformer inductor network is the secondary coil output port 42 of the transformer T1, the inductor L input port 43 and the primary coil center tap port 44 of the transformer T1. Compared with the LC voltage-controlled oscillator based on two transformers in the prior art to achieve inductance reduction, the LC voltage-controlled transformer structure disclosed in the present invention can reduce the chip circuit board because only a single transformer is used. Figure 1 The area of ​​the transformer is half. The inductor coil in the transformer inductor network is separated from the transformer coil by a certain distance, so the coupling coefficient between the inductor and the transformer is low, thereby reducing the coupling effect between the transformer and the inductor. The ports of the inductor and the transformer secondary coil are in the same position, reducing the loss caused by the connection between the inductor and the transformer.

[0036] Implementing the embodiments of the present invention will have the following beneficial effects:

[0037] The quality factor Q value of a single on-chip inductor is higher than the quality factor Q value of a transformer. The voltage-controlled oscillator based on the inductance reduction technology of a single inductor and a single transformer has a high quality factor, a simple circuit, and overcomes the defect that the connection resistance of the LC resonant circuit will become the dominant parasitic resistance after directly reducing the inductance value. The technical solution of the present invention proposes that the inductor and the transformer share the circuit layout area, which greatly reduces the circuit layout area, thereby reducing the circuit cost.

[0038] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements will not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A voltage-controlled oscillator, characterized in that: The voltage-controlled oscillator comprises a negative resistance circuit and an LC resonant circuit; the negative resistance circuit is connected to a current source; the LC resonant circuit is connected to the negative resistance circuit; the LC resonant circuit comprises a first capacitor, a transformer, an inductor, and a second capacitor; the first capacitor is connected in parallel with the primary coil of the transformer; the secondary coil of the transformer, the inductor, and the second capacitor are connected in parallel with each other; the first capacitor is a varactor; The transformer is an octagonal symmetrical interwinding planar on-chip transformer; The inductor is an on-chip inductor, the inductor and the transformer are stacked on each other, the inductor and the transformer share a circuit layout area, and the distance between the coil of the inductor and the primary coil and the secondary coil of the transformer exceeds 10 microns; The inductor adopts a single-turn inductor; the inductor adopts two or three thick metal layers, and the thickness of a single thick metal layer ranges from 1 micron to 5 microns.

2. The voltage controlled oscillator according to claim 1, characterized in that: in, The LC resonant circuit includes a transformer inductor network, and the transformer inductor network includes the transformer and the inductor; the transformer is an on-chip transformer, and the inductor is an on-chip inductor; the left side of the transformer inductor network is the primary coil input port of the transformer; the right side of the transformer inductor network is the secondary coil output port of the transformer, the input port of the inductor and the center tap port of the primary coil of the transformer.

3. The voltage controlled oscillator according to claim 2, characterized in that: in, The inductor and the transformer share a circuit layout area, and the distance between the coil of the inductor and the primary coil and the secondary coil of the transformer exceeds 10 microns.

4. The voltage controlled oscillator according to claim 2 or 3, characterized in that: in, The inductor is a single-turn inductor comprising two thick metal layers.

5. The voltage controlled oscillator according to any one of claims 1 to 4, characterized in that: in, The negative resistance circuit is a cross-coupled tube; the cross-coupled tube is composed of an NMOS tube and / or a PMOS tube; the cross-coupled tube includes an NMOS cross-coupled tube, a PMOS cross-coupled tube, or an NMOS and PMOS complementary cross-coupled tube.

6. The voltage controlled oscillator according to claim 5, characterized in that: in, The cross-coupled transistor includes a first MOS transistor and a second MOS transistor; the first MOS transistor and the second MOS transistor are MOS transistors of the same size and type; the gate of the first MOS transistor and the drain of the second MOS transistor are connected to each other and to one end of the first capacitor; the gate of the second MOS transistor and the drain of the first MOS transistor are connected to each other and to the other end of the first capacitor; the source of the first MOS transistor and the source of the second MOS transistor are connected to each other and to the current source.

7. The voltage controlled oscillator according to any one of claims 1 to 6, characterized in that: in, The current source is a current source with a tail or a current source without a tail.

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