CN1889365A - Radio frequency double-channel voltage controlled oscillator based on central tapped inductive switch - Google Patents

Abstract

The invention relates to a radio-frequency dual-band voltage-controlled oscillator based on a center-tapped inductance switch, which belongs to the technical field of integrated circuit design and signal processing. IEEE802.11 is one of the most widely used WLAN protocols in the world today. The RF front-end of the wireless router based on this protocol needs to use a phase-locked loop to generate local oscillator signals working in the 2.4G frequency band and the 5G frequency band. BACKGROUND OF THE INVENTION The dual-band voltage-controlled oscillator with an inductance switch needs four inductors, and its disadvantage is that integrating four on-chip inductors on a chip requires a relatively large chip area. The voltage-controlled oscillator of the present invention uses a center-tap inductor to replace two of the four inductors in the background technology, and its advantage is that the chip area occupied by the integrated center-tap inductor on the chip is smaller than the chip area occupied by the two inductors it replaces. The area is much smaller, and it is especially suitable for use as a radio frequency dual-band voltage-controlled oscillator in the radio frequency front-end chip of a wireless router.

Description

RF dual-band voltage-controlled oscillator based on center-tapped inductive switch

                    

The present invention relates to a radio-frequency dual-band voltage-controlled oscillator based on a center-tap inductance switch, to be precise, relates to a radio-frequency dual-band inductance-capacitance voltage-controlled oscillator based on a center-tap inductance switch, which belongs to the technology of integrated circuit design and signal processing field.

Background technique

In recent years, with the rapid development of radio frequency integrated circuit technology, people have used many wireless communication products in their daily life: mobile phones, Bluetooth communication products, global positioning systems and so on. In addition, with the emergence of wireless local area networks, people can access the Internet through wireless routers, thereby eliminating the inconvenience caused by wired Internet access and bringing great flexibility to users.

IEEE802.11 is one of the most widely used WLAN protocols in the world today. After IEEE promulgated IEEE802.11b and IEEE802.11a in 1999, IEEE promulgated IEEE802.11g in 2003. In order to solve the compatibility problem between protocols, the development of hardware based on multi-protocol has become a hot spot. However, the publications and papers issued by IEEE in 2005 show that there are still many technical difficulties in hardware based on multi-protocol.

Like other wireless products, the RF front-end based on the multi-protocol wireless router needs to use the phase-locked loop to generate the local oscillator signal. The difference is that the operating frequency band selected by IEEE802.11b and IEEE802.11g is 2.4GHz-2.4835GHz, while the operating frequency band selected by IEEE802.11a is 5.15GHz-5.35GHz (can be used indoors and outdoors) or 5.725GHz-5.85 GHz (for outdoor use only). The three sub-protocols select two different working frequency bands: 2.4G segment and 5G segment.

Using lower power consumption and smaller chip area to achieve the best performance is one of the goals of the development of radio frequency integrated circuit technology. Through "hardware multiplexing" technology, that is, using only one circuit and using transistors as switches to switch between two operating frequency bands, about 50% of power consumption and a certain chip footprint can be saved. Therefore, "hardware multiplexing" is an important idea based on multi-protocol hardware development.

The voltage-controlled oscillator (VCO) is the core module in the phase-locked loop circuit, and the local oscillator signal required by the RF front-end is generated by the voltage-controlled oscillator. Among the voltage-controlled oscillators, there is an inductance-capacitance voltage-controlled oscillator (LC VCO), which is widely used in radio frequency integrated circuits due to its relatively good phase noise performance. The oscillation frequency of this oscillator is mainly determined by the inductance and capacitance in the resonant circuit. In traditional radio frequency integrated circuits, voltage-controlled oscillators change the operating frequency band by switching capacitors. However, the power dissipation of the LC VCO increases with the capacitance. Switching from the 5G frequency band to the 2.4G frequency band requires increasing the capacitance in the resonant circuit, and the power consumption of the oscillator will also increase accordingly. Therefore, the power consumption of LC VCOs based on switched capacitors is generally relatively large. However, the power dissipation of an LC VCO is relatively insensitive to changes in the inductor value. In the case of obtaining the same working frequency band switching, the power consumption of the LC VCO switching the working frequency band is generally relatively small by using a switch to switch the inductor.

Since the chip area of the integrated on-chip inductor is relatively large (usually accounting for 60%-80% of the chip area of the entire radio frequency integrated circuit), the method of changing the inductance parameter as the working frequency band switching will occupy a larger chip area. In early 2006, Seong-Mo Yim and Kenneth K.O published a technical solution on inductive switches in "IEEE Transactions on Microwave Theory and Techniques", as shown in Figure 1, see literature [1]. The core part of the inductive switch dual-band voltage-controlled oscillator used in literature [1] (that is, the output buffer circuit is not included, and it is not shown in the figure) requires 4 inductors, and the integration of 4 on-chip inductors requires a large chip area.

Contents of the invention

The technical problem to be solved by the invention is to introduce a radio frequency dual-band inductance-capacitance voltage-controlled oscillator based on a center-tapped inductance switch. The LC VCO has the advantages of low power consumption and relatively small chip footprint, and its performance indicators fully meet the requirements of IEEE802.11a/b/g multi-standards for hardware resources. Since in the 5G frequency band, IEEE802.11a provides the 5.15GHz-5.35GHz frequency band that can be used indoors and outdoors and the 5.725GHz-5.85GHz frequency band that is limited to outdoor use, the present invention only uses the 5.15GHz-5.35GHz frequency band in the 5G frequency band.

In order to solve the above-mentioned technical problems, the present invention adopts the following technical solutions: (1) replace two of the four inductors in the background technology with on-chip integrated center tap inductors. See Figure 2. This kind of on-chip inductance can provide two symmetrical inductances at the same time electrically, and lead out the taps at the center of the two, and the area occupied by the chip is smaller than that of an asymmetric on-chip inductance with the same inductance value (electrically only manifested as one Inductance) is small. (2) Appropriately change the circuit structure, and use the center-tap inductor as the object of switch control, as shown in Figure 3, then the core part of this voltage-controlled oscillator only needs 3 inductors, compared with the voltage-controlled oscillator shown in Figure 1 The oscillator uses one less inductor, and the area occupied by the chip is reduced by about 20%-50%. In addition, the symmetry of the center-tapped inductor helps to improve the quality factor Q of its inductance, which in turn improves the phase noise performance of the VCO. The radio frequency dual-band LCVCO based on a center tap inductive switch includes a negative resistance circuit, a resonant circuit, a resonator switch circuit and a bias circuit. The negative resistance circuit is all composed of PMOS tubes to reduce phase noise; the resonant circuit uses on-chip integrated inductors and on-chip varactor diodes without any off-chip passive devices to reduce production costs; the resonator switch circuit uses NMOS tubes as The switch device changes the total inductance of the resonant circuit by closing the switch to short-circuit the center tap inductance, so as to achieve the purpose of changing the oscillation frequency of the LCVCO; the bias circuit provides the necessary DC bias for the entire voltage-controlled oscillator circuit.

The technical solution of the present invention is now specifically described in conjunction with the accompanying drawings.

A radio frequency dual-band inductance-capacitance voltage-controlled oscillator based on a center-tapped inductance switch, including a negative resistance circuit, a resonant circuit, a bias circuit and seven lead terminals. The negative resistance circuit consists of a first MOS transistor M1 and a second MOS transistor M2 Composition, the first MOS transistor M1 and the second MOS transistor M2 are PMOS transistors, the resonant circuit includes the first varactor diode C1, the second varactor diode C2, the first inductance L1, the second inductance L2, the first varactor diode C1 and the second varactor diode C2 are on-chip integrated NMOS transistors working in the accumulation region-depletion region, the first inductance L1 and the second inductance L2 are asymmetric on-chip integrated inductances, and the bias circuit is composed of the fifth MOS transistor M5 Bias constant current source, the fifth MOS tube M5 is a PMOS tube, the seven lead terminals are Vcc terminal, Vbias terminal, Vout+ terminal, Vout- terminal, Ctrl terminal, SW terminal and ground wire, and the Vcc terminal and ground wire are voltage The input terminal of the source+ terminal and the voltage source- terminal, the Vbias terminal is the input terminal of the bias voltage, the Ctrl terminal is the input terminal of the control voltage, the SW terminal is the frequency band switching voltage input terminal, and the Vout+ terminal and Vout- terminal are respectively the RF signal Non-inverting and inverting output terminals, the source of the first MOS transistor M1 is connected to the source of the second MOS transistor M2, the gate of the first MOS transistor M1 is connected to the drain of the second MOS transistor M2, and the first MOS transistor M2 The gate of the gate is connected to the drain of the first MOS transistor M1, and the first varactor diode C1 and the second varactor diode C2 are connected in series between the drain of the first MOS transistor M1 and the drain of the first MOS transistor M2 , the connection point of the first varactor diode C1 and the second varactor diode C2 is connected to the Ctrl terminal, the drain of the first MOS transistor M1 and the drain of the second MOS transistor M2 are respectively connected to the Vout+ terminal and the Vout- terminal, and the second One end of an inductance L1 is connected to the drain of the first MOS transistor M1, and one end of the second inductance L2 is connected to the drain of the first MOS transistor M2. It is characterized in that it also includes a resonator switch circuit and a third inductance L3, resonant The device switching circuit is composed of a third MOS transistor M3 and a fourth MOS transistor M4, the third MOS transistor M3 and the fourth MOS transistor M4 are NMOS transistors, the third inductor L3 is a symmetrical on-chip integrated inductor with a center tap, and the third The two ends of the inductance L3 are respectively connected to the other end of the first inductance L1 and the second inductance L2, the center tap of the third inductance L3 is connected to the ground, and the sources of the third MOS transistor M3 and the fourth MOS transistor M4 are connected After that, it is connected to the ground wire, the drains of the third MOS transistor M3 and the fourth MOS transistor M4 are respectively connected to the other ends of the first inductor L1 and the second inductor L2, and the gates of the third MOS transistor M3 and the fourth MOS transistor M4 After being connected, it is connected to the SW terminal, and the drain, the gate and the source of the fifth MOS transistor M5 are respectively connected to the source of the first MOS transistor M1, the Vbias terminal and the Vcc terminal. The circuit diagram of the VCO is shown in Figure 3.

The invention has the advantages that the number of inductors used in the voltage-controlled oscillator is reduced by adopting the inductor with a center tap, so as to ensure that the purpose of reducing the area occupied by the entire voltage-controlled oscillator chip can be achieved.

The following table lists the voltage-controlled oscillator of the present invention, that is, the power consumption is 4.08mW, and the dual-band voltage-controlled oscillator based on the center-tapped inductance switch (marked as VCO1) manufactured by the 0.18 μm CMOS process and based on the scheme shown in Figure 1 The comparison results of the dual-band voltage-controlled oscillator (denoted as VCO2): parameter VCO1 VCO2 switch scheme Center tap inductance switch (technical side of the present invention) Standard Inductive Switch (Scheme shown in Figure 1) Power Consumption (mW) 4.08 4.08 Tuning range (GHz) 5G frequency band: 5.135-5.3652.4G frequency band: 2.38-2.52 5G frequency band: 5.128-5.3582.4G frequency band: 2.386-2.53 Chip area(mm ² ) 0.95×0.58 1.4×0.62

It can be seen from the above table that under the same power consumption, the chip area occupied by the voltage-controlled oscillator of the present invention is 0.551mm ² , while the chip area occupied by the voltage-controlled oscillator based on the scheme shown in Figure 1 is 0.868mm ² . In other words, the technical solution of the present invention can save about 36.5% of the occupied chip area.

Figure 4(a) and (b) respectively show the phase noise simulation results of the voltage-controlled oscillator of the present invention as the local oscillator of the radio frequency front-end in the 5G frequency band and the 2.4G frequency band. It can be seen from the figure that in the 5G frequency band, its phase noise is -120.0dBc/Hz@1MHz; in the 2.4G frequency band, its phase noise is -126.2dBc/Hz@1MHz. According to the requirements of the IEEE802.11b/g standard, in the 2.4G frequency band, the phase noise of the local oscillator must be less than -110dBc/Hz@1MHz; according to the requirements of the IEEE802.11a standard, in the 5G frequency band, the phase noise of the local oscillator must also be less than - 110dBc/Hz@1MHz[2]. Therefore, the voltage-controlled oscillator of the present invention fully complies with the requirements of IEEE802.11a/b/g standards.

Description of drawings

Fig. 1 is the circuit diagram of the standard inductance switch dual-band voltage-controlled oscillator adopted in literature [1].

Figure 2(a) is the layout of the on-chip integrated inductor including the center tap.

Figure 2(b) is the circuit symbol of the on-chip integrated inductor including the center tap.

FIG. 3 is a circuit diagram of a radio frequency dual-band voltage-controlled oscillator based on a center-tapped inductive switch of the present invention.

FIG. 4( a ) is a phase noise curve obtained by simulation of the voltage-controlled oscillator of the present invention at a frequency of 5.24 GHz.

FIG. 4( b ) is a phase noise curve obtained by simulation of the voltage-controlled oscillator of the present invention when the frequency is 2.4 GHz.

Detailed ways

The technical solution of the present invention will now be described in detail in conjunction with the accompanying drawings and embodiments.

Example

This embodiment has exactly the same circuit structure as that shown in FIG. 3 . The components and circuit parameters of this embodiment are listed as follows:

The inductances of the first inductor L1, the second inductor L2 and the third inductor L3 are respectively: 0.292nH, 0.292nH and 1.083nH;

The capacitance variation range of the first varactor diode C1 and the second varactor diode C2 is: 568.7fF-764.4fF;

The width-to-length ratios of the first MOS transistor M1 and the second MOS transistor M2 are both (96/0.18) μm/μm;

The width-to-length ratios of the third MOS transistor M3 and the fourth MOS transistor M4 are both (960/0.18) μm/μm;

The width-to-length ratio of the fifth MOS transistor M5 is (1000/1) μm/μm;

The voltage at the + terminal of the voltage source is 1.25V;

The bias voltage at the Vbias terminal is 0V;

The control voltage range of the Ctrl terminal is 0-1.25V;

The input voltage of the SW terminal is: 0V, the voltage controlled oscillator works in the 2.4G frequency band and 1.25V, and the voltage controlled oscillator works in the 5G frequency band.

working principle.

The circuit diagram of the radio frequency dual-band LC voltage-controlled oscillator based on the center-tapped inductive switch of the present invention is shown in FIG. 3 . The third inductor L3 includes a center tap and is a symmetrical on-chip integrated inductor. Half of the coil of the inductor is interlaced with the other half and embedded together. When a differential current flows in from both ends of the inductor, the direction of the current flowing in the coils of the two parts of the inductor is opposite, so that a strong magnetic coupling is formed between the coils of the two parts, and the total inductance is increased. Therefore, an inductor with a center tap only needs to occupy a smaller chip area to obtain a larger inductance.

In the voltage-controlled oscillator of the present invention, the fifth MOS transistor M5 provides the necessary bias current for the oscillator circuit. Since the passive components in the actual resonant circuit: the first inductance L1, the second inductance L2, the third inductance L3, the first varactor diode C1 and the second varactor diode C2 are all lossy during operation, so the first inductance is required A cross-coupled pair composed of a MOS transistor M1 and a second MOS transistor M2 acts as a negative resistance device to supplement energy to the resonant circuit, so as to maintain the oscillation of the resonant circuit.

The input signal at the Ctrl terminal is provided by the charge pump output in the phase-locked loop, which is designed to fine-tune the resonant frequency of the resonant circuit. The first varactor diode C1 and the second varactor diode C2 are actually NMOS transistors working in the accumulation region-depletion region. When the potential of the Ctrl terminal rises, the NMOS transistor enters the accumulation region, at this time, the first varactor diode C1 and the second varactor diode C2 increase, and the resonant frequency of the resonant circuit decreases; when the potential of the Ctrl terminal decreases, the NMOS transistor enters the depletion region. When the first varactor diode C1 and the second varactor diode C2 decrease, the resonant frequency of the resonant circuit rises.

The third MOS transistor M3 and the fourth MOS transistor M4 constitute a resonator switch circuit of the voltage-controlled oscillator, that is, a frequency band switch circuit. When the input signal at the SW terminal is at low level, the third MOS transistor M3 and the fourth MOS transistor M4 are turned off, and at this time, the first varactor diode C1, the second varactor diode C2, the first inductance L1, the second inductance L2 and the The three inductors L3 constitute the resonant circuit of the voltage-controlled oscillator. The voltage-controlled oscillator works in the 2.4G frequency band due to the large LC product of the resonant circuit; when the input signal at the SW terminal is at a high level, the third MOS transistor M3 and the fourth The MOS transistor M4 is turned on. At this time, for the radio frequency, it is equivalent to the third inductance L3 being short-circuited, and the first varactor diode C1, the second varactor diode C2, the first inductance L1, and the second inductance L2 form a voltage-controlled oscillator. The resonant circuit of the voltage-controlled oscillator works in the 5G frequency band because the LC product of the resonant circuit is small.

references

[1] S.M.Yim and K.K.O, "Switched Resonators and Their Applications in a Dual-Band Monolithic CMOS LC-Tuned VCO," IEEETrans.Microw.Theory Tech., vol.54, no.1, pp.74-81, Jan. 2006.

[2] M.Brandolini, P.Rossi, D.Manstretta and F.Svelto, "Toward Multistandard Mobile Terminal-Fully Integrated Receivers Requirements and Architectures," IEEE J.Solid-State Circuits, vol.53, no.3, pp.1026 -1038, Mar. 2005.

Claims (3)

1, a kind of radio frequency double-frequency band inductor electric capacity voltage controlled oscillator based on the centre cap inductance switch, contain negative resistance circuit, resonant circuit, biasing circuit and seven lead ends, negative resistance circuit is made up of first metal-oxide-semiconductor (M1) and metal-oxide-semiconductor (M2), first metal-oxide-semiconductor (M1) and second metal-oxide-semiconductor (M2) are the PMOS pipes, resonant circuit contains first variable capacitance diode (C1), second variable capacitance diode (C2), first inductance (L1), second inductance (L2), first variable capacitance diode (C1) and second variable capacitance diode (C2) are integrated on the sheet, be operated in the NMOS pipe of accumulation area-depletion region, first inductance (L1) and second inductance (L2) are asymmetric and go up integrated inductor, biasing circuit is formed the biasing constant-current source by the 5th metal-oxide-semiconductor (M5), the 5th metal-oxide-semiconductor (M5) is the PMOS pipe, seven lead ends are Vcc ends, the Vbias end, the Vout+ end, the Vout-end, the Ctrl end, SW end and ground wire, Vcc end and ground wire are respectively the inputs of voltage source+end and voltage source-end, the Vbias end is the input of bias voltage, the Ctrl end is the input of control voltage, the SW end is a frequency range switched voltage input, Vout+ end and Vout-end are respectively the positive and the reversed-phase output of radiofrequency signal, the source electrode of first metal-oxide-semiconductor (M1) is connected with the source electrode of second metal-oxide-semiconductor (M2), the grid of first metal-oxide-semiconductor (M1) is connected with the drain electrode of metal-oxide-semiconductor (M2), the grid of metal-oxide-semiconductor (M2) is connected with the drain electrode of first metal-oxide-semiconductor (M1), be connected across after the series connection of first variable capacitance diode (C1) and second variable capacitance diode (C2) between the drain electrode of the drain electrode of first metal-oxide-semiconductor (M1) and second metal-oxide-semiconductor (M2), the tie point of first variable capacitance diode (C1) and second variable capacitance diode (C2) is connected with the Ctrl end, the drain electrode of the drain electrode of first metal-oxide-semiconductor (M1) and second metal-oxide-semiconductor (M2) is connected with the Vout-end with the Vout+ end respectively, one end of first inductance (L1) is connected with the drain electrode of first metal-oxide-semiconductor (M1), one end of second inductance (L2) is connected with the drain electrode of second metal-oxide-semiconductor (M2), it is characterized in that, it also contains resonator switching circuit and the 3rd inductance (L3), the resonator switching circuit is made up of the 3rd metal-oxide-semiconductor (M3) and the 4th metal-oxide-semiconductor (M4), the 3rd metal-oxide-semiconductor (M3) and the 4th metal-oxide-semiconductor (M4) are the NMOS pipes, the 3rd inductance (L3) is to contain integrated inductor on the sheet of centre tapped symmetric form, two terminations of the 3rd inductance (L3) are connected with the other end of first inductance (L1) with second inductance (L2) respectively, the centre cap of the 3rd inductance (L3) is connected with ground wire, the source electrode of the 3rd metal-oxide-semiconductor (M3) and the 4th metal-oxide-semiconductor (M4) is connected the back and is connected with ground wire, the drain electrode of the 3rd metal-oxide-semiconductor (M3) and the 4th metal-oxide-semiconductor (M4) is connected with the other end of first inductance (L1) with second inductance (L2) respectively, the grid of the 3rd metal-oxide-semiconductor (M3) and the 4th metal-oxide-semiconductor (M4) is connected the back and is connected the drain electrode of the 5th metal-oxide-semiconductor (M5) with the SW end, grid and source electrode respectively with the source electrode of first metal-oxide-semiconductor (M1), the Vbias end is connected with the Vcc end.

2, the radio frequency double-frequency band inductor electric capacity voltage controlled oscillator based on the centre cap inductance switch according to claim 1 is characterized in that half of the coil of the 3rd inductance (L3) is with second half interlaced being embedded in.

3, the radio frequency double-frequency band inductor electric capacity voltage controlled oscillator based on the centre cap inductance switch according to claim 1 and 2 is characterized in that the components and parts of this voltage controlled oscillator and circuit parameter are enumerated as follows:

The inductance value of first inductance (L1), second inductance (L2) and the 3rd inductance (L3) is respectively: 0.292nH, 0.292nH and 1.083nH;

The electric capacitance change scope of first variable capacitance diode (C1), second variable capacitance diode (C2) is: 568.7fF-764.4fF;

The breadth length ratio of first metal-oxide-semiconductor (M1), metal-oxide-semiconductor (M2) all is (96/0.18) μ m/ μ m;

The breadth length ratio of the 3rd metal-oxide-semiconductor (M3), the 4th metal-oxide-semiconductor (M4) all is (960/0.18) μ m/ μ m;

The breadth length ratio of the 5th metal-oxide-semiconductor (M5) is (1000/1) μ m/ μ m;

The voltage of voltage source+end is 1.25V;

The bias voltage of Vbias end is 0V;

The control change in voltage scope of Ctrl end is 0-1.25V;

The input voltage of SW end is respectively: 0V, voltage controlled oscillator are operated in 2.4G frequency range and 1.25V, and voltage controlled oscillator is operated in the 5G frequency range.

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