KR20020084776A - Voltage controlled oscillator for multi-band - Google Patents

Abstract

PURPOSE: A voltage controlled oscillator for multi band is provided, which can select a plurality of frequencies with a variable inductor using one oscillator and a MEMS(Micro-Electro Mechanical System) switch. CONSTITUTION: A resonator(10) can select a frequency according to an external control signal, and an oscillator(20) oscillates and amplifies a frequency signal selected in the above resonator. The resonator includes a variable inductor(12) whose synthesized inductance is varied according to the external control signal and a capacitor(C1) connected in parallel with the variable inductor. The variable inductor includes a plurality of inductors(L1,L2,L3) connected serially with different inductances and switches(S1,S2) which are connected between the inductors and are switched by the external control signal and then form a closed loop by the capacitor and more than one inductor selected by the switching.

Description

VOLTAGE CONTROLLED OSCILLATOR FOR MULTI-BAND}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multiband voltage controlled oscillator, and more particularly, to a multiband voltage controlled oscillator capable of selecting a plurality of frequencies with a variable inductor using a single oscillator and a MEMS switch.

Voltage Controlled Oscillator (VCO) is a device that oscillates single frequency with channel selection function in communication system. Conventional voltage controlled oscillators use a positive feedback circuit using mainly an inductor (L) and a capacitor (C) to select a desired frequency and a variable capacitor for band selection.

That is, the resonance frequency The frequency at the time of channel selection by the variable capacitor is to be.

However, the capacitance change amount of the variable capacitor ( ) Is so small that it can oscillate around 10% of the oscillation frequency, which limits the frequency tuning range.

Therefore, in order to greatly change the frequency range, it is necessary to change a fixed capacitor or inductor. In the case of a voltage controlled oscillator module or an RF IC, there is a problem in that the frequency value is limited to one.

There was no switch to enter the voltage controlled oscillator module and there was no technology to finely control the value of the inductor.

Modern mobile communication terminals operate in two or three bands (Dual Band or Tri-Band) or more bands rather than only in one band, and each time two or more oscillators are selected. ) Is being used.

Traditional dual-band voltage controlled oscillators select multiple resonant tanks using two oscillators with separate combiner networks, oscillators with pin diode switches, single oscillators with multiplier circuits, broadband oscillators, and RF MEMS switches There was a way.

However, in the case of two separate oscillators with a combiner network, two complete voltage controlled oscillator circuits are required, and power consumption by the combiner network is severe.

An oscillator with a pin diode switch consumes a lot of current due to the large DC current required to achieve low 'on' impedance, and reduces resonance sharpness (Q) when there is a switch in the resonant circuit. It also has the disadvantage of generating a spurious signal when off.

When using a multiplier such as a doubler or tripler, spurious signals always appear on the output and must be filtered to prevent degradation of the receiver and interference with other wireless services.

Broadband oscillators are sensitive to tuning controls, which makes them more susceptible to noise coming through the control line.

The method of selecting a plurality of resonant tanks of FIG. 1 has the disadvantage that an individual resonant tank is required according to the resonant frequency. In other words, although the inductor and capacitor which determine the oscillation frequency are arranged to select the necessary part, inductors, capacitors, and switches are required as many bands, and the number of bits for controlling increases.

Therefore, if the inductance value is not controlled using the RF MEMS inductor, the implementation itself is difficult, the volume and the area is increased, the practicality is less, and there is a problem that is very sensitive to the change amount of the variable capacitor.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a multi-band voltage controlled oscillator capable of selecting a plurality of frequencies as a variable inductor using one oscillator and a MEMS switch.

In one embodiment of the present invention to achieve the above object, a resonator capable of selecting a frequency in accordance with an external control signal; And an oscillator for oscillating and amplifying the frequency signal selected by the resonator.

The resonator may include a variable inductor whose synthesized inductance is variable according to the external control signal; And a capacitor connected in parallel with the variable inductor.

The variable inductor includes a plurality of inductors connected in series with different inductances; And a switch connected between the inductors, respectively, and switched according to the external control signal to form a closed loop by the capacitor and at least one inductor selected by the switching.

The variable inductor further includes a disconnect switch between each inductor to block mutual inductance generated by another inductor not contributing to the inductance value configuration when the predetermined inductance value is formed by the closed loop. Characterized in that.

The switch and the disconnect switch is characterized in that the MEMS switch.

In another embodiment of the present invention to achieve the above object, the variable inductor has a different inductance, a plurality of inductors connected in parallel with each other; And a switch which is switched according to the external control signal to form a closed loop with the capacitor.

In another embodiment of the present invention to achieve the above object, the variable inductor has a plurality of inductors connected in parallel with different inductances; And a single input multi-output switch having a plurality of switch contacts connected in series to the inductor, and selectively connecting one of the plurality of switch contacts according to the external control signal to form a closed loop with the capacitor. It is characterized by including.

In another embodiment and another embodiment, the switch is a MEMS switch.

1 is a circuit diagram showing a voltage controlled oscillator of the prior art,

2 is a circuit diagram showing an embodiment of a multi-band voltage controlled oscillator according to the present invention,

3 is a circuit diagram showing another embodiment of the multi-band voltage controlled oscillator according to the present invention,

4 is a circuit diagram showing another embodiment of a multi-band voltage controlled oscillator according to the present invention,

FIG. 5 is a circuit diagram illustrating an embodiment using a switch of a single input multi output type.

6 is a gain versus frequency table simulated in cellular and PCS bands.

<Description of the symbols for the main parts of the drawings>

10 resonator 12 variable inductor

20: Oscillator L1, L2, L3: Inductor

C1: Capacitor S, S1, S2, S3: Switch

S11, S12: Disconnect Switch

The objects, features and advantages of the present invention will be more readily understood by reference to the accompanying drawings and the following detailed description.

Hereinafter, the present invention proposes a multiband voltage controlled oscillator for selecting a plurality of frequencies as a variable inductor using one oscillator and a MEMS switch as a preferred embodiment.

2 to 5 are circuit diagrams showing respective embodiments of the multiband voltage controlled oscillator according to the present invention.

2 to 5, the present invention includes a resonator 10 capable of selecting a frequency according to an external control signal, and an oscillator 20 oscillating and amplifying a frequency signal selected by the resonator 10. Here, the external control signal may be a control signal output by a mode conversion or a power supply, etc., and may be implemented in various forms according to the purpose of the multi-band voltage controlled oscillator.

The resonator 10 includes a variable inductor 12 whose synthesis inductance is variable according to an external control signal, and a capacitor C1 connected in parallel to the variable inductor 12.

2 to 3, the variable inductor 12 is connected between a plurality of inductors L1, L2, L3 connected in series with different inductances, and the inductors L1, L2, L3, respectively. And switches S1 and S2 that are switched in accordance with the control signal to form a closed loop by the capacitor C1 and one or more inductors selected by the switching. Here, the switches S1 and S2 are preferably MEMS switches.

In the embodiment of Fig. 3, the variable inductor has a disconnect switch (S11, S12) for blocking mutual inductance generated by another inductor that does not contribute to the inductance value configuration, when forming a predetermined inductance value by the closed loop, respectively. Included between inductors.

In the embodiment of FIG. 4, the variable inductor 12 has a plurality of inductors L1, L2, L3 connected in parallel with different inductances, and is connected in series with the inductors L1, L2, L3, respectively, and has an external control signal. And switches S1, S2, and S3 that are switched according to the capacitor C1 to form a closed loop. In the present embodiment, the switches S1, S2, and S3 are preferably MEMS switches.

In the embodiment of FIG. 5, the variable inductor 12 has a plurality of inductors L1, L2, L3 connected in parallel with different inductances, and a plurality of switches connected in series with the inductors L1, L2, L3, respectively. And a single input multi-output switch S having a contact and selectively connecting one of a plurality of switch contacts according to an external control signal to form a closed loop with the capacitor C1. In FIG. 5, three switching contacts are used as an example, but the number of switching contacts may vary in correspondence with a plurality of inductors.

If described in detail with reference to Figure 2 the operation of the present invention configured as described above.

When the switch S1 connected to the inductor L1 is turned on by an external control signal, the resonance frequency is determined by the inductor L1 and the capacitor C1. In practical implementations, it is desirable to place L1 and L2 perpendicular to each other to eliminate mutual inductance. If the resonant frequency determined as described above is a cellular band, the signal amplified by the oscillator 20 is output only the signal of the cellular band.

When the switch S2 connected to the inductor L2 is turned on by the external control signal and S1 is opened, the resonance frequency due to the inductance of the inductors L1 and L2 connected in series and the capacitance of the capacitor are determined, which can be set to the PCS band.

If the switches S1 and S2 are not turned on by the external control signal, the resonance frequency is determined by the inductance of the inductors L1, L2, L3 connected in series and the capacitance of the capacitor, and can be set to the IMT-2000 band.

Therefore, since the desired frequency band can be selected according to the external control signal, it can be used as a multi-band voltage controlled oscillator.

In the embodiment of FIG. 2, the capacitor C1 is fixed and the switches S1 and S2 connected to the inductors L1, L2, and L3 are switched, and the number of switches and the number of inductors are increased as necessary to multi-band. Implementable to choose

Inductors (L1, L2, L3) and switches (S1, S2) can be made extremely small using RF MEMS technology, and the coil values can be made precise.

As described above, two inductors can be used to select dual bands, while multiple connections can provide a multiband selectable voltage-controlled oscillator.

For example, using an external control signal consisting of 3 bits using software, and outputting an external control signal of 100 to the switch (S) is connected to the inductor L1, if 010 is connected to the inductor L2, if 001 is connected to the inductor L3 Assume that

Then, 100 is selected for cellular band selection, 010 for PCS band selection, and 001 for IMT-2000 band selection, resulting in a voltage controlled oscillator capable of selecting three bands. Expansion in the same manner is multiband, and the same applies to FIG. 3.

3 is a circuit diagram showing another embodiment of a multi-band voltage controlled oscillator according to the present invention. In FIG. 3, the variable inductor further includes a blocking switch between each inductor to block mutual inductance generated by another inductor that does not contribute to the inductance value configuration when forming a predetermined inductance value by the closed loop. Implemented to work.

For example, when the switch S1 is connected, the cutoff switch S11 is included to block the inductor L2 which generates mutual inductance with the inductor L1 from the inductor L1. In addition, the disconnect switch S12 is included in order to block the inductor L3 which generates mutual inductance with the inductors L1 and L2 when the closed loop is formed by the inductors L1 and L2 by connecting the switch S2.

The disconnect switches S11 and S12 are also controlled in the same manner as the switches S1 and S2 described above, and it is preferable to use a MEMS switch.

4 is a circuit diagram showing yet another embodiment of the multiband voltage controlled oscillator according to the present invention.

4, the inductors L1, L2, and L3 are connected in series according to the connection of the switches S1 and S2 in FIG. 2, but the switches S1, S2, and S3 of FIG. Inductors L1, L2, and L3 are connected in parallel according to the connection.

In addition, as shown in FIG. 3, a blocking switch for blocking mutual inductance between the inductors may be further included to implement stable operation.

As shown in FIG. 5, when the switch S having a single input multi output is used, only a band required by a single switch may be selected and used.

6 is a gain versus frequency table simulated in cellular and PCS bands, and shows a result of simulating a multiband voltage controlled oscillator.

In the simulation result of FIG. 6A, it can be seen that the magnitude of the frequency oscillating at 0.9 GHz is 3.6 dBm, and the surrounding outputs are removed in the actual design. Therefore, by adjusting the value of the inductor, it is possible to design with the correct cellular band, and by using the MEMS inductor, very small values can be controlled.

6B is a diagram illustrating the operation at 1.8 GHz, showing that the output at the oscillation frequency is 4.5 dBm. In practice, the output of each band can be adjusted to match the reference specifications.

The present invention is not limited to the embodiments described above, and various modifications and changes can be made by those skilled in the art, which are included in the spirit and scope of the present invention as defined in the appended claims.

As described above, the present invention can implement a multiband voltage controlled oscillator using a variable MEMS inductor and one voltage controlled oscillator, and the overall size is reduced and the price is reduced because the capacitor is commonly used when implementing an LC tank. There is.

In addition, a band selection switch and an inductor can be simply added without changing existing amplifiers and peripheral circuits.

Claims (9)

A resonator capable of selecting a frequency according to an external control signal; And And an oscillator for oscillating and amplifying the frequency signal selected by the resonator. The method of claim 1, wherein the resonator A variable inductor whose composite inductance is variable according to the external control signal; And And a capacitor connected in parallel with the variable inductor. The method of claim 2, wherein the variable inductor A plurality of inductors connected in series with different inductances; And And a switch connected between the inductors, the switches being respectively switched according to the external control signal to form a closed loop by the capacitor and the at least one inductor selected by the switching. . 4. The multiband voltage controlled oscillator of claim 3, wherein the switch is a MEMS switch. The method of claim 3 or 4, wherein the variable inductor is Further, when forming a predetermined inductance value by the closed loop, it further comprises a blocking switch between each inductor for blocking mutual inductance generated by another inductor that does not contribute to the inductance value configuration Voltage controlled oscillator for band. 6. The multiband voltage controlled oscillator of claim 5, wherein the cutoff switch is a MEMS switch. The method of claim 2, wherein the variable inductor A plurality of inductors connected in parallel with different inductances; And And a switch connected in series with each of the inductors and switched according to the external control signal to form a closed loop with the capacitor. The method of claim 2, wherein the variable inductor A plurality of inductors connected in parallel with different inductances; And And a single input multi-output switch having a plurality of switch contacts connected in series to the inductor, and selectively connecting one of the plurality of switch contacts according to the external control signal to form a closed loop with the capacitor. Voltage controlled oscillator for multi-band, characterized in that. 9. The multiband voltage controlled oscillator of claim 7 or 8, wherein the switch is a MEMS switch.