CN103095217B - Low Phase Noise Voltage-controlled Oscillator - Google Patents

Abstract

The invention discloses a kind of Low Phase Noise Voltage-controlled Oscillator, comprise negative resistance circuit module, differential coupling inductance capacitance resonant cavity and source class feedback inductance.Coupling inductance capacitor resonance chamber is in order to improve the effective quality factor of resonant cavity, magnetic coupling between source class feedback inductance and resonant cavity inductance is as feeding back the amplitude outputed signal to increase resonant cavity, and negative resistance circuit module adopts current multiplexing structure to reduce power consumption and to remove the deterioration of second harmonic to phase noise of common-mode node.Low Phase Noise Voltage-controlled Oscillator of the present invention effectively can reduce phase noise.

Description

Low Phase Noise Voltage Controlled Oscillator

technical field

The invention belongs to the technical field of radio frequency wireless receiver integrated circuits, and in particular relates to a voltage-controlled oscillator with low phase noise.

Background technique

A voltage-controlled oscillator is a module used to generate local oscillator signals in a communication system, and its performance directly determines the performance of the communication system. As a main performance index of the voltage controlled oscillator, the phase noise affects the sensitivity of the receiver and the adjacent channel interference of the transmitter. Therefore, it is particularly important to design a voltage-controlled oscillator with low phase noise for modern wireless communication systems.

The implementation forms of voltage-controlled oscillators mainly include ring oscillators and inductor-capacitor voltage-controlled oscillators. Ring oscillators are mainly used to generate on-chip clock signals due to their poor phase noise performance. The LC-VCO is widely used in the field of wireless communication because of its good phase noise performance.

According to the D.B.Lesson phase noise model formula, the phase noise L(Δf) of the LC voltage-controlled oscillator can be expressed as:

$\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&Delta;f</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&Proportional;</span>\frac{{\mathrm{<span\; class="notranslate">\; Fk</span>}}_{\mathrm{<span\; class="notranslate">\; B</span>}}\mathrm{<span\; class="notranslate">\; T</span>}}{{\mathrm{<span\; class="notranslate">\; Q</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}\frac{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; P</span>}}}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}{\mathrm{<span\; class="notranslate">\; \&Delta;f</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

Where Δf is the offset frequency, f _o is the oscillation frequency, F is the noise figure, k is the Boltzmann constant, T is the absolute temperature value, Q is the quality factor of the resonant cavity, V _p is the oscillation signal amplitude of the resonant cavity, and R _p is the equivalent parallel resistance of the resonant cavity.

It can be seen from formula (1) that in order to optimize the phase noise performance, it can be realized by improving the quality factor Q of the resonant cavity and increasing the amplitude V _p of the oscillation signal. Since the quality factor of the on-chip capacitor is much greater than that of the on-chip inductor, the quality factor of the resonant cavity is mainly determined by the on-chip inductor. However, due to factors such as the skin effect and the high loss of the substrate, the available quality factor of the on-chip inductor is limited. On the other hand, as the feature size of the CMOS process decreases, the power supply voltage decreases accordingly, and the output signal amplitude of the voltage-controlled oscillator also decreases, which makes the optimal design of low phase noise very difficult.

Contents of the invention

The object of the present invention is to provide a kind of low phase noise voltage controlled oscillator, the technical scheme that takes is as follows:

A voltage-controlled oscillator with low phase noise is characterized in that it includes a negative resistance circuit module and a differentially coupled inductor-capacitor resonant cavity, wherein:

The negative resistance circuit module includes a PMOS transistor M _p , an NMOS transistor M _n , and two source-level feedback inductors L _s1 and L _s2 with equal inductance values; the power supply VDD is connected in series with the source-level feedback inductor L _s1 to the source of the PMOS transistor M _p , The source of the NMOS transistor M _n is connected in series with the source feedback inductance L _s2 and grounded, the gate of the PMOS transistor M _p is connected to the drain of the NMOS transistor M _n as the output terminal V _p , and the gate of the NMOS transistor M _n is connected to the PMOS transistor M _p The drain of is used as the output terminal V _n ;

The differential coupled inductance-capacitance resonant cavity includes differential inductance L _d and differential inductance L _c and two variable capacitors C _v ; differential inductance L _d is composed of inductance L _d1 and inductance L _d2 in series, and the inductance of inductance L _d1 and inductance L _d2 The values are equal, the ends of the inductance L _d1 and the inductance L _d2 that are not connected together are respectively connected to the output terminal V _p of the negative resistance circuit module and the output terminal V _n ; the differential inductance L _c is composed of the inductance L _c1 and the inductance L _c2 connected in series, and the inductance The inductance values of L _c1 and inductor L _c2 are equal, and the butt ends of inductor L _c1 and inductor L _c2 are connected to the DC bias voltage V _b ; two variable capacitors C _v are connected back to back, and the butt ends are connected to the analog tuning voltage V _ctrl . The unconnected ends of the variable capacitors C _v are respectively connected to the unconnected ends of the inductance L _c1 and the inductance L _c2 .

The differential inductance L _d , differential inductance L _c , source-level feedback inductance L _s1 and source-level feedback inductance L _s2 are all formed on the substrate, the differential inductance L _d and L _c both adopt a symmetrical differential structure and the inductance L _c is formed on Directly below the inductance L _d , the source feedback inductance L _s1 and L _s2 are symmetrically formed around the differential inductance L _d , the coupling coefficient between the inductance L _d1 and the inductance L _c1 , the inductance L _d2 and the inductance L _c2 is 0.94, the inductance The coupling coefficient between L _d1 and inductor L _s1 , the inductor L _d2 and inductor L _s2 is 0.38, the coupling coefficient between inductor L _c1 and inductor L _s1 , inductor L _c2 and inductor L _s2 is 0.37.

Advantages and beneficial effects of the present invention: Compared with the prior art, the voltage-controlled oscillator with low phase noise provided by the present invention adopts a coupled inductor-capacitor resonant cavity to improve the effective quality factor of the resonant cavity. The magnetic coupling between the source-level feedback inductance and the resonant cavity inductance is used as feedback to increase the effective gate-source overdrive voltage of the MOS transistor in the negative resistance unit circuit and increase the amplitude of the output signal of the resonant cavity. The negative resistance unit circuit adopts a current multiplexing structure to remove the common mode node in the traditional negative resistance unit circuit, thereby eliminating the deterioration of the phase noise caused by the second harmonic of the common mode node in the traditional structure. Therefore, the invention can effectively improve the phase noise performance of the voltage-controlled oscillator.

Description of drawings

FIG. 1 is a schematic structural diagram of a low phase noise voltage-controlled oscillator according to an embodiment of the present invention;

2 is a schematic diagram of a traditional differential complementary structure voltage-controlled oscillator circuit;

3 is a perspective view of the arrangement of inductors L _d , L _c , L _s1 and L _s2 according to an embodiment of the present invention;

FIG. 4 is a schematic diagram of comparing phase noise curves of the low phase noise voltage controlled oscillator of the present invention and the voltage controlled oscillator shown in FIG. 2 at the same output frequency.

Detailed ways

In order to further illustrate the advantages of the present invention and the specific technical means adopted, specific embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings. It is understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. After reading the present invention, those skilled in the art should fall within the protection scope of the claims of the present application to the amendments of various equivalent forms of the present invention .

Referring to Fig. 1, the low-phase-noise voltage-controlled oscillator of the present invention includes a negative resistance circuit module and a differentially coupled inductor-capacitor resonant cavity, wherein:

The negative resistance circuit module includes PMOS transistor M _p and NMOS transistor M _n , the power supply VDD is connected in series with the source feedback inductance L _s1 and then connected to the source of the PMOS transistor M _p , and the source of the NMOS transistor M _n is connected in series with the source feedback inductance L _s2 and grounded , the inductance value of source feedback inductance L _s1 and source feedback inductance L _s2 is equal, the gate of PMOS transistor M _p is connected to the drain of NMOS transistor M _n as the output terminal V _p , and the gate of NMOS transistor M _n is connected to PMOS transistor The drain of M _p serves as the output terminal V _n .

The differentially coupled inductor-capacitor resonant cavity includes a differential inductor L _d , a differential inductor L _c and two variable capacitors C _v . in:

The differential inductance L _d is composed of the inductance L _d1 and the _inductance L _d2 connected in series, and the inductance values of the inductance L _d1 and the inductance L _{d2 are equal} . _Vn connection.

The differential inductance L _c is composed of an inductance L _c1 and an inductance L _c2 connected in series, and the inductance values of the inductance L _c1 and the inductance L _c2 are equal, and the butt ends of the inductance L _c1 and the inductance L _c2 are connected to the DC bias voltage V _b .

The two variable capacitors C _v are connected back to back, the butt ends are connected to the analog tuning voltage V _ctrl , and the unconnected ends of the two variable capacitors C _v are respectively connected to the unconnected ends of the inductor L _c1 and the inductor L _c2 .

The differential inductance L _c is formed directly below the differential inductance L _d ; the source feedback inductance L _s1 and the source feedback inductance L _s2 are symmetrically formed around the differential inductance L _d .

The definition of resonant cavity Q value is the ratio between the stored energy of the resonant cavity and the resonant cavity loss in essence. In order to improve the resonant cavity Q value, the present invention adopts two differential inductances L _d and L _c and two variable capacitors C _v constitutes a differentially coupled inductor-capacitor resonant cavity, and the inductor L _d and the inductor L _c have a coupling coefficient k _dc . Compared with the single-inductor-capacitor resonant cavity used in the traditional voltage-controlled oscillator structure shown in Figure 2, the existence of the coupling effect between the coupled inductors makes the coupled-inductor-capacitor resonant cavity have more magnetic field energy at the resonance frequency, Correspondingly, it has a higher Q value, thereby improving the phase noise performance.

In one embodiment of the present invention, two variable capacitors C _v are used as the analog tuning section. The center tap of L _c is connected to the DC bias voltage V _b to provide a suitable DC bias for the two variable capacitors C _v . By adjusting the analog tuning voltage V _ctrl , the capacitance value connected to the resonant cavity is changed to achieve fine frequency Tune. The differential oscillation signal is output from the output terminal V _p and the output terminal V _n .

In the present invention, the negative resistance circuit module adopts a current multiplexing structure. An NMOS transistor _Mn and a PMOS transistor _Mp are used to cross-couple to provide negative resistance and supplement the energy loss of the resonant cavity. Compared with traditional complementary cross-coupled differential pair transistors (Figure 2), this structure requires only half the bias current to provide the same negative resistance. In addition, since the PMOS transistor and the NMOS transistor are turned on or off at the same time when the voltage-controlled oscillator is working, there is no common-source node in the traditional structure, which makes it possible to avoid the second harmonic frequency-to-phase noise in the common-source node the impact.

The present invention introduces source feedback inductors L _s1 and L _s2 . Using the magnetic coupling between the source feedback inductance L _s1 , L _s2 and the inductance L _d , L _c in the resonant cavity as feedback, the drain voltage and the source voltage of the NMOS transistor M _n and the PMOS transistor M _p change in the same direction, so that the output The output signal amplitude of the terminal V _p and the output terminal V _n is not clamped by the power supply voltage VDD and the ground potential, and a higher oscillation signal amplitude can be obtained under the same bias condition.

The low phase noise VCO provided by the present invention uses multiple inductors, and these inductors require a large layout area. Fig. 3 shows an example of the present invention, a perspective view of inductors L _d , L _c , L _s1 and L _s2 formed on the substrate. Both the inductor L _d and the inductor L _c adopt a symmetrical differential structure and the inductor L _c is formed directly below the inductor L _d so as to reuse the same layout area. The inductance values of the inductor L _d and the inductor L _c are both 1.0nH. The inductance L _s1 and the inductance L _s2 are symmetrically formed on the periphery of the inductance L _d , and the inductance values of the inductance L _s1 and the inductance L _s2 are both 0.2nH. The coupling coefficient k _dc between the inductor L _d1 and the inductor L _c1 , and between the inductor L _d2 and the inductor L _c2 is about 0.94. The coupling coefficient k _ds between the inductance L _d1 and the inductance L _s1 , the inductance L _d2 and the inductance L _s2 is about 0.38, the coupling coefficient k _cs between the inductance L _c1 and the inductance L _s1 , the inductance L _c2 and the inductance L _s2 is about 0.37.

FIG. 4 is a schematic diagram showing the comparison of the phase noise curves of the low phase noise voltage-controlled oscillator of the present invention and the voltage-controlled oscillator shown in FIG. 2 at the same output frequency. Using TSMC0.18-μm CMOS technology, the resonant frequency is 12GHz. With the structure of the present invention, under the condition of the same power consumption and output frequency, the phase noise performance has been greatly improved. At 1MHz frequency deviation, the phase noise The reduction is about 8.8dB, and the phase noise is reduced by about 13.2dB at a frequency offset of 100kHz, which shows that the structure of the present invention can effectively improve the phase noise performance.

Claims (2)

1. a Low Phase Noise Voltage-controlled Oscillator, is characterized in that: comprise negative resistance circuit module, differential coupling inductance capacitance resonant cavity, wherein:

Negative resistance circuit module comprises PMOS M _p, NMOS tube M _n, two source class feedback inductance L that inductance value is equal _s1and L _s2; Power vd D series connection source class feedback inductance L _s1rear connection PMOS M _psource electrode, NMOS tube M _nsource series source class feedback inductance L _s2rear ground connection, PMOS M _pgrid connect NMOS tube M _ndrain electrode as output V _p, NMOS tube M _ngrid connect PMOS M _pdrain electrode as output V _n;

Differential coupling inductance capacitance resonant cavity comprises differential inductance L _dwith differential inductance L _cand two variable capacitance C _v; Differential inductance L _dby inductance L _d1with inductance L _d2be composed in series, and inductance L _d1with inductance L _d2inductance value equal, inductance L _d1with inductance L _d2the one end do not linked together respectively with negative resistance circuit module output V _pwith output V _nconnect; Differential inductance L _cby inductance L _c1with inductance L _c2be composed in series, and inductance L _c1with inductance L _c2inductance value equal, inductance L _c1with inductance L _c2butt end and DC offset voltage V _bbe connected; Two variable capacitance C _vdock back-to-back, butt end and analog tuner voltage V _ctrlbe connected, two variable capacitance C _vthe one end do not linked together respectively with inductance L _c1with inductance L _c2the one end do not linked together connects.

2. Low Phase Noise Voltage-controlled Oscillator according to claim 1, is characterized in that: differential inductance L _d, differential inductance L _c, source class feedback inductance L _s1with source class feedback inductance L _s2all be formed on substrate, differential inductance L _dand L _call adopt symmetric difference structure and inductance L _cbe formed at inductance L _dimmediately below, source class feedback inductance L _s1with L _s2be symmetrically formed in differential inductance L _daround, inductance L _d1with inductance L _c1, inductance L _d2with inductance L _c2between coupling coefficient be 0.94, inductance L _d1with inductance L _s1, inductance L _d2with inductance L _s2between coupling coefficient be 0.38, inductance L _c1with inductance L _s1, inductance L _c2with inductance L _s2between coupling coefficient be 0.37.