JP2006033803A - Voltage-controlled oscillator, and pll circuit and wireless communications apparatus using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a voltage controlled oscillator capable of including superior phase noise characteristics and approximately equal frequency sensitivity, in all bands when a plurality of bands are used to obtain a wide-frequency variable range. <P>SOLUTION: A voltage-controlled oscillator comprises a parallel resonance circuit including an inductor circuit, a variable capacitance circuit, and a high-frequency switching circuit, a negative resistance circuit, a frequency control section, and a frequency tuning sensitivity control section. The frequency control section shifts the band of the oscillation frequency, by controlling ON/OFF of a switching element included in the high-frequency switching circuit. The frequency tuning sensitivity control section adjusts the change rate of the total capacitance of the variable capacitance circuit with respect to a control voltage, depending on the band used. The frequency tuning sensitivity control section is connected to a virtual ground point of a different signal. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a voltage controlled oscillator, and a PLL circuit and a wireless communication device using the voltage controlled oscillator. More specifically, the present invention relates to a voltage controlled oscillator having a band switching function, and a PLL circuit and a wireless communication device using the voltage controlled oscillator.

  A voltage controlled oscillator is widely used as a means for generating a local oscillation signal of a wireless communication device. When this voltage controlled oscillator is manufactured as a high frequency IC, it is necessary to widen the oscillation frequency range due to variations in components in the semiconductor manufacturing process. In recent years, in order to cope with a communication system using different frequency bands, it is necessary to make the oscillation frequency of the voltage controlled oscillator variable in a wide frequency range.

  FIG. 13 is a diagram showing an example of a configuration of a conventional voltage controlled oscillator 500 having a band switching function. In FIG. 13, a conventional voltage controlled oscillator 500 includes inductors 501, 502, a power supply terminal 503, variable capacitance elements 504, 505, a control voltage terminal 506, oscillation transistors 507, 508, a current source 509, a capacitance. Characteristic elements 511 and 512, switching elements 513 and 514, and a control voltage terminal 515. In FIG. 13, the bias circuit and the like are omitted.

  The operation of the conventional voltage controlled oscillator will be described below with reference to FIG. A voltage controlled oscillator 500 shown in FIG. 13 includes an inductor 501, an inductor 502 connected in series to the inductor 501, and a power supply terminal 503 connected between the inductor 501 and the inductor 502 for supplying a power supply voltage Vdd. 520, a variable capacitance element 504 and a variable capacitance element 505, and a variable capacitance circuit 530 having a control voltage terminal 506 connected to the connection point between them, and two oscillation transistors 507 and 508 are cross-coupled to each other. Control circuit 540, capacitive element 511 and switching element 513, switching element 514 and capacitive element 512, and a control for supplying a control voltage of switching elements 513 and 514 to a connection point between switching element 513 and switching element 514 A high frequency switch circuit (band switching circuit) 510 voltage terminal 515 is connected, an oscillation circuit but connected in parallel with each other.

  The source side of the oscillation transistor 507 and the source side of the oscillation transistor 508 are connected to each other and connected to one side of the current source 509. The other side of the current source 509 is grounded. One side of each of the switching elements 513 and 514 is connected to the capacitive elements 511 and 512, the other side is grounded, and the other side is connected to the control voltage terminal 515.

  When the power supply voltage Vdd is supplied from the power supply terminal 503, the power supply voltage Vdd is supplied to the oscillation transistors 507 and 508 via the inductors 501 and 502, respectively. By returning the output sides of the oscillation transistors 507 and 508 to the gate sides of the other transistors, this oscillation circuit is constituted by a parallel resonance circuit composed of the above-described inductor circuit 520, variable capacitance circuit 530, and high-frequency switch circuit 510. Oscillates near the determined resonance frequency. That is, a difference voltage between the control voltage Vt input from the control voltage terminal 506 and the power supply voltage Vdd is applied to both ends of the variable capacitance elements 504 and 505, and the capacitance of the variable capacitance elements 504 and 505 is determined by this difference voltage. Therefore, the oscillation frequency changes depending on the control voltage Vt input from the control voltage terminal 506. Further, the switching elements 513 and 514 are turned on or off by the control voltage Vctrl input from the control voltage terminal 515, and the capacitance value of the entire band switching circuit 510 is determined. Therefore, the switching elements 513 and 514 are switched on or off. Thus, the oscillation frequency can be shifted.

  FIG. 14A is a diagram showing how the oscillation frequency shifts in a conventional voltage controlled oscillator. Usually, a conventional voltage controlled oscillator uses a plurality of high-frequency switch circuits in order to widen the variable range of the oscillation frequency. In FIG. 14A, the number of bands is nine. As described above, the voltage controlled oscillator 500 shown in FIG. 13 can continuously change the oscillation frequency by controlling the control voltage Vt, and can further change the oscillation frequency band by controlling the control voltage Vctrl. Can be changed.

The oscillation frequency f0 of the voltage controlled oscillator 500 shown in FIG. 13 is that the inductances of the inductors 501 and 502 are L, the capacitance values of the variable capacitance elements 504 and 505 are C1, respectively, and the capacitance values of the capacitive elements 511 and 512 of the high frequency switch circuit. Is C2, and other differential parasitic capacitance components are C3.
f0 = 1 / (2π (2L · C ′ / 2) ^1/2 ) = 1 / (2π (L · C ′) ^1/2 )
Here, C ′ = C1 + C2 + C3
It is expressed.

When the switching elements 513 and 514 are turned off, the switching elements 513 and 514 are cut off, so that the capacitive elements 511 and 512 are not connected to the resonance circuit in the high-frequency signal. Therefore, the oscillation frequency f0_off at this time is
f0_off = 1 / (2π (L · (C1 + C3)) ^1/2 )
It becomes.

On the other hand, when the switching elements 513 and 514 are turned on, the switching elements 513 and 514 conduct, so that the capacitive elements 511 and 512 are connected to the resonance circuit in the high frequency signal. Therefore, the oscillation frequency f0_on at this time is
f0_on = 1 / (2π (L · (C1 + C2 + C3)) ^1/2 )
It becomes.

  Here, the frequency sensitivity (which means the rate of change of the oscillation frequency with respect to the control voltage Vt, hereinafter the same) is determined by the ratio of the capacitance change amount of the variable capacitance circuit to the total capacitance of the resonance circuit. The frequency sensitivity is high. When f0_off is compared with f0_on, the frequency sensitivity is higher in f0_off.

  That is, when the switching elements 513 and 514 are turned off, the oscillation frequency is higher and the frequency sensitivity is higher.

  As shown in FIG. 14A, as the number of bands is increased by using a plurality of switching elements in the high-frequency switch circuit, the difference between the frequency sensitivities of the highest and lowest oscillating frequencies increases.

  However, the relationship between the control voltage Vt of the voltage controlled oscillator and the oscillation frequency is desirably the same in all bands, that is, at all oscillation frequencies. This is because when a PLL (phase-locked loop) circuit is configured using a voltage controlled oscillator, the transient response characteristics and noise band characteristics of the PLL circuit depend on the frequency sensitivity with respect to the control voltage. This is because the characteristics of the circuit itself vary with frequency.

  When the voltage-controlled oscillator is realized on a semiconductor substrate, it is necessary to make it variable in a wide frequency range as described above. In the conventional voltage-controlled oscillator 500 shown in FIG. Although it is possible to obtain a range, it has been difficult to achieve the same frequency sensitivity in the wide variable frequency range.

  A circuit for solving such a problem has already been proposed (see, for example, Patent Document 1 or Patent Document 2).

  FIG. 15 is a circuit diagram of a conventional voltage-controlled oscillator 600 that employs an improvement method for making the frequency sensitivity comparable in a wide frequency variable range.

  15, parts having the same functions as those of the conventional voltage controlled oscillator 500 shown in FIG. 13 are denoted by the same reference numerals, and description thereof is omitted. In FIG. 15, the conventional voltage controlled oscillator 600 is different from the conventional voltage controlled oscillator 500 in that the variable capacitance elements 551, 552, 561, 562, 571, and the switching elements 553, 554, 563, 564, 573. 574 is different.

  In the voltage controlled oscillator 600 shown in FIG. 15, first, second and third variable capacitance circuits 550, 560 and 570 are connected in parallel. The first variable capacitance circuit 550 has a configuration in which switching elements 553 and 554 are connected to both ends of the variable capacitance elements 551 and 552. The second variable capacitance circuit 560 has a configuration in which switching elements 563 and 564 are connected to both ends of the variable capacitance elements 561 and 562. The third variable capacitance circuit 570 has a configuration in which switching elements 573 and 574 are connected to both ends of the variable capacitance elements 571 and 572. A control voltage Vt is input from the control voltage terminal 506 to the first, second, and third variable capacitance circuits 550, 560, and 570.

  When the oscillation frequency is lowered, the ratio of the capacitance change amount of the variable capacitance circuit to the total capacitance of the resonance circuit is reduced, and the frequency sensitivity is lowered. Therefore, as shown below, in the band where the oscillation frequency is low, the switching element of the variable capacitance circuit is turned on to increase the number of variable capacitance circuits connected to the resonance circuit, thereby increasing the capacitance change amount of the variable capacitance element. Thus, even when the oscillation frequency is low, the frequency sensitivity can be made comparable to that when the oscillation frequency is high.

For example, in the band having the highest oscillation frequency in FIG. 14A, only the switching elements 553 and 554 of the first variable capacitance circuit 550 among the first to third variable capacitance circuits 550, 560, and 570 are turned on. Turn off except. For example, when the oscillation frequency in FIG. 14A is the fifth band from the top, switching of the first and second variable capacitance circuits 550, 560 among the first to third variable capacitance circuits 550, 560, 570 is performed. The elements 553, 554, 563, and 564 are turned on, and the others are turned off. For example, in the case of the band having the lowest oscillation frequency in FIG. 14A, all the switching elements 553, 554, 563, 564, 573, and 574 of the first to third variable capacitance circuits 550, 560, and 570 are turned on. . By doing so, the frequency sensitivity is increased over the entire oscillation frequency range by increasing the parallel number of variable capacitance circuits connected to the resonance circuit each time the oscillation frequency is lowered and increasing the capacitance change amount. It can be the same level. FIG. 14B is a diagram illustrating the characteristics of the voltage controlled oscillator 600 when the frequency sensitivity is set to be approximately the same over the entire oscillation frequency range.
JP 2003-174320 A JP 2004-15387 A JP 2003-324316 A

  However, in the conventional improvement method as shown in FIG. 15, the switching elements 553, 554, 563, 564, 573, and 574 are used in the portions where the high-frequency signals of the variable capacitance circuits 550, 560, and 570 flow. There has been a problem that phase noise characteristics deteriorate due to loss in the switching element. For example, when the switching element is a MOS switch, a loss occurs due to the on-resistance, and the phase noise characteristics deteriorate.

  As a voltage controlled oscillator for preventing deterioration of phase noise characteristics, there is a voltage controlled oscillator described in Patent Document 3. FIG. 16A is a circuit diagram showing a configuration of a conventional voltage controlled oscillator 700 described in Patent Document 3. As shown in FIG. FIG. 16B is a graph showing characteristics of the conventional voltage controlled oscillator 700 described in Patent Document 3. The conventional voltage controlled oscillator 700 connects a variable capacitance element in parallel to the inductor 707. The conventional voltage controlled oscillator 700 changes the number of variable capacitance elements by switching on and off the switching elements 708 to 711. Thereby, the capacity | capacitance of LC resonator changes and the band of an oscillation frequency can be changed. In FIG. 16B, A shows the characteristics when CTRL is applied only to the midpoint between the variable capacitance elements 701 and 702 and Vss is applied to the midpoint between the variable capacitance elements 703 and 704 and 705 and 706. B shows the characteristics when either one of the switching elements 708 or 710 is in the ON state. C indicates characteristics when both of the switching elements 708 and 710 are in the on state. In the band A, although the total capacity of the resonance circuit is the largest (even though the oscillation frequency is the lowest), the ratio of the capacitance change amount of the variable capacitance circuit to the total capacity is small. Therefore, the frequency sensitivity of band A is the lowest. Therefore, the problem that the frequency sensitivity for every band will differ arises.

  Therefore, in view of the above problems, the object of the present invention is to suppress the deterioration of the phase noise characteristics and to control the frequency variable range over a wide band. A voltage-controlled oscillator that can be reduced to an extent, and a PLL circuit and a wireless communication device using the same are provided.

  In order to solve the above problems, the present invention has the following features. A first aspect of the present invention is a voltage controlled oscillator composed of a differential circuit for oscillating a high-frequency signal, the inductor circuit having an inductor and a parallel connection to the inductor circuit, and feedback control of the oscillation frequency And n (where n is a natural number greater than or equal to 2) variable capacitance circuits each having a variable capacitance element whose capacitance value varies depending on the control voltage applied to the capacitor, an inductor circuit connected in parallel, a capacitive element, and a capacitance A switching element connected to the active element, a switching control terminal for inputting a switching control voltage for controlling on / off of the switching element, m (m is a natural number of 1 or more) high-frequency switching circuits, and an inductor circuit Controls ON / OFF of switching elements of negative resistance circuit connected in parallel and m high frequency switch circuits By Rukoto includes a frequency control unit that shifts the band of the oscillation frequency, in response to a band to be used, and a frequency sensitivity controller for adjusting the rate of change in n number of variable capacitance circuits overall capacitance with respect to the control voltage. The frequency sensitivity control unit is connected to a virtual ground point for differential signals in n variable capacitance circuits.

  According to the first aspect of the present invention, since the band of the oscillation frequency can be switched using the high frequency switch circuit, a voltage controlled oscillator having a wide frequency variable range is provided. In addition, since the capacity change rate is adjusted according to the band to be used, it is possible to make the frequency sensitivity comparable in the frequency variable range. Further, since the frequency sensitivity control unit is connected to the virtual ground point, the high frequency signal does not flow outside the voltage controlled oscillator. Therefore, since no loss occurs in the frequency sensitivity control unit, the Q value does not deteriorate. Therefore, deterioration of the phase noise characteristic is suppressed.

  For example, the frequency control unit inputs a switching control voltage for controlling on / off of the switching element to the switching control terminal of the high frequency switch circuit according to the band to be used, and the frequency sensitivity control unit is synchronized with the switching control voltage. Thus, the voltage applied to one terminal of each variable capacitance element in the n variable capacitance circuits may be selectively switched between a predetermined reference voltage and a control voltage.

  As a result, a variable capacitance circuit that functions as a fixed capacitor when a reference voltage is input and a variable capacitance circuit that functions as a variable capacitor that receives a control voltage are determined according to the band to be used. By adjusting the number of variable capacitance circuits functioning as variable capacitors, the capacitance change rate with respect to the control voltage can be adjusted, and the frequency sensitivity can be made comparable in the frequency variable range.

  For example, the frequency sensitivity control unit includes n frequency sensitivity control switching elements, and each frequency sensitivity control switching element is connected to each virtual ground point in the n variable capacitance circuits. It is preferable to selectively switch whether the voltage applied to the voltage is a predetermined reference voltage or a control voltage.

  In this way, by using the frequency sensitivity control switching element connected to the virtual ground point, the switching between the reference voltage and the control voltage is efficiently performed, and the phase noise can be suppressed.

  For example, the frequency sensitivity control unit includes n−1 frequency sensitivity control switching elements, and each frequency control switching element is connected to each virtual ground point in the n−1 variable capacitance circuit. The voltage applied to the variable capacitance circuit is selectively switched between a predetermined reference voltage and a control voltage, and a control voltage may be supplied to a virtual ground point of one variable capacitance circuit.

  Thereby, at least one variable capacitance circuit always functions as a variable capacitance.

  For example, the reference voltage may be a midpoint voltage in the change range of the control voltage.

  As a result, a voltage controlled oscillator capable of making the frequency sensitivities the same around the middle point of the control voltage change range is provided.

  For example, the reference voltage may be a control voltage value when the oscillation frequency is fixed by feedback control of the oscillation frequency.

  As a result, the total capacitance value of the resonance circuit does not change before and after the number of variable capacitance circuits functioning as variable capacitors changes. Therefore, even when the feedback control is converged, the output frequency does not change, so that the voltage control can output the desired frequency as it is and the frequency sensitivity can be made comparable in the variable frequency range. An oscillator will be provided.

  For example, the frequency sensitivity control unit applies a control voltage only to one variable capacitance circuit among n variable capacitance circuits when all of the switching elements of the m high frequency switch circuits are off, The frequency sensitivity control switching element may be controlled so that the reference voltage is applied to the remaining n−1 variable capacitance circuits.

  Thereby, at least one variable capacitance circuit functions as a variable capacitance.

  For example, the frequency sensitivity control unit controls the frequency sensitivity control switching element so that the control voltage is applied to all the n variable capacitance circuits when all the switching elements of the m high frequency switch circuits are turned on. Good.

  As a result, when all the switching elements of the high-frequency switch circuit are turned on, a variable capacitance circuit that functions as a fixed capacitance is not necessary, and the circuit scale of the voltage controlled oscillator is reduced.

  For example, the frequency sensitivity control unit determines in advance whether to use each variable capacitance circuit as a variable capacitor or a fixed capacitor for each band shifted by the frequency control unit. A control signal is applied to the capacitor circuit, and a predetermined reference voltage is applied to the variable capacitor circuit used as a fixed capacitor.

  As a result, a variable capacitance circuit that functions as a fixed capacitor when a reference voltage is input and a variable capacitance circuit that functions as a variable capacitor that receives a control voltage are determined according to the band to be used. By adjusting the number of variable capacitance circuits functioning as variable capacitors, the capacitance change rate with respect to the control voltage can be adjusted, and the frequency sensitivity can be made comparable in the frequency variable range.

  Preferably, the voltage controlled oscillator is provided in the PLL circuit, and the control voltage when the PLL circuit is locked may be a predetermined reference voltage.

  As a result, the total capacitance value of the resonance circuit does not change before and after the number of variable capacitance circuits functioning as variable capacitors changes. Therefore, even when the PLL circuit is locked, the frequency output from the PLL circuit does not change, so that it is possible to make the frequency sensitivity the same in the variable frequency range while outputting the desired frequency as it is. A voltage-controlled oscillator that can be provided will be provided.

  According to a second aspect of the present invention, in a voltage controlled oscillator configured with a differential circuit for oscillating a high-frequency signal, an inductor circuit having an inductor, a variable capacitance element connected in parallel to the inductor circuit, Connected in parallel to an n number (n is a natural number of 2 or more) of variable capacitors having both ends of a blocking capacitor for blocking a direct current component, and an inductor circuit, and to a capacitive element and a capacitive element M high-frequency switch circuits (m is a natural number of 1 or more) having a switching element and a switching control terminal for inputting a switching control voltage for controlling on / off of the switching element, and a negative electrode connected in parallel to the inductor circuit The oscillation frequency band is controlled by controlling on / off of the switching element included in the resistive resistor circuit and the m high frequency switch circuits. , A control terminal for inputting a control voltage for feedback control of the oscillation frequency to one terminal of the variable capacitance elements of the n variable capacitance circuits, and a variable capacitance of the n variable capacitance circuits A reference voltage is input to the other terminal of the element, and a reference voltage control unit that adjusts the reference voltage according to the band to be used and adjusts the rate of change of the oscillation frequency with respect to the control voltage.

  According to the second aspect of the present invention, the frequency sensitivity can be made comparable in the variable frequency range by adjusting the reference voltage according to the band to be used.

  For example, the reference voltage control unit may control the voltage applied to the other terminal of the variable capacitance elements of the n variable capacitance circuits in synchronization with the switching control voltage input to the switching control terminal of the high frequency switch circuit.

  As a result, the capacitance of the variable capacitance circuit can be changed.

  For example, the reference voltage control unit sets the (n + 1) / 2th reference voltage as the control voltage when n is an odd number among the reference voltages input to the other terminals of the variable capacitance elements of the n variable capacitance circuits. The voltage at the midpoint of the change range is assumed. When n is an even number, the intermediate voltage between the n / 2th reference voltage and the (n + 2) / 2th reference voltage is the midpoint voltage of the control voltage change range. Good.

  Thereby, in the vicinity of the reference voltage, the frequency sensitivity can be made comparable in the variable capacitance range.

  For example, the reference voltage control unit sets the oscillation frequency to the (n + 1) / 2th reference voltage when n is an odd number among the reference voltages input to the other terminals of the variable capacitance elements of the n variable capacitance circuits. When the oscillation frequency is fixed by feedback control, the value of the control voltage is set. When n is an even number, the intermediate voltage between the n / 2th reference voltage and the (n + 2) / 2th reference voltage is set as the oscillation frequency. It is good to use the control voltage value when the oscillation frequency is fixed by feedback control.

  As a result, even when the feedback control is converged, the output frequency does not change, so that the voltage sensitivity can be made the same in the variable frequency range while outputting the desired frequency as it is. A controlled oscillator will be provided.

  For example, the reference voltage control unit adjusts the reference voltage so that the rate of change of the oscillation frequency with respect to the control voltage is substantially constant over the control voltage when all the switching elements of the m high-frequency switch circuits are off, In a state other than when all the switching elements of the m high frequency switch circuits are off, in the n variable capacitance circuits, when n is an odd number, (n + 1) / 2th reference voltage is set, and n is an even number. In this case, an intermediate voltage between the n / 2th reference voltage and the (n + 2) / 2th reference voltage may be adjusted.

  As a result, in the vicinity of the reference voltage or the intermediate voltage, the capacitance change rate can be adjusted so that the rate of change of the oscillation frequency with respect to the control voltage is approximately the same as when all the switching elements are turned off.

  For example, when the reference voltages input to n variable capacitance circuits among n variable capacitance circuits are arranged in descending order, the variable capacitance of the kth variable capacitance circuit (k is a natural number of 2 or more and n or less). The difference between the reference voltage input to the element and the reference voltage input to the variable capacitance element of the (k−1) th variable capacitance circuit is maximum when all the switching elements of the m high-frequency switch circuits are off. The minimum is when all the switching elements of the m high frequency switch circuits are on, and the maximum and minimum are when the switching elements of the m high frequency switch circuits are all on or all other than off. It should be a value between.

  Any one of the voltage controlled oscillators may be used in a PLL circuit.

  The voltage controlled oscillator may be used for a wireless communication device.

  A third aspect of the present invention is a PLL circuit for fixing an oscillation frequency, which is composed of a differential circuit for oscillating a high-frequency signal, and adjusts the oscillation frequency according to an applied control voltage. The voltage control oscillator includes a voltage control oscillator and a feedback control voltage adjustment circuit that feeds back a high frequency signal output from the voltage control oscillator, compares a phase difference with a reference signal, and adjusts a control voltage applied to the voltage control oscillator. The oscillator includes an inductor circuit having an inductor and n variable capacitor elements each having a capacitance value that is connected in parallel to the inductor circuit and whose capacitance value changes according to an applied control voltage for feedback control of the oscillation frequency (n is 2 or more). (Natural number) of the variable capacitance circuit and the inductor circuit connected in parallel, the capacitive element, and the switched element connected to the capacitive element Negative switching element connected in parallel to an m number (m is a natural number of 1 or more) high-frequency switch circuit having an element and a switching control terminal for inputting a switching control voltage for controlling on / off of the switching element. The n variable capacitance circuits are connected to the virtual grounding point of the resistance circuit and n variable capacitance circuits, and the switching frequency of the m high frequency switch circuits is turned on and off to shift the oscillation frequency. A frequency sensitivity control unit that selectively switches a voltage applied to one terminal of each variable capacitance element between a predetermined reference voltage and a control voltage, and a high-frequency switch circuit according to a fixed oscillation frequency. A frequency control unit that turns on and off the switching element and determines a band to be used. The control voltage output from the control voltage adjustment circuit, characterized in that the reference voltage.

  According to the third aspect of the present invention, the total capacitance value of the resonance circuit does not change before and after the number of variable capacitance circuits functioning as variable capacitors changes. Therefore, even when the PLL circuit is locked, the frequency output from the PLL circuit does not change, so that it is possible to make the frequency sensitivity the same in the variable frequency range while outputting the desired frequency as it is. A PLL circuit that can be used is provided.

  According to the present invention, a voltage-controlled oscillator having good phase noise characteristics, controlling a frequency range over a wide band, and having the same frequency sensitivity, and a PLL circuit and a wireless communication using the same Equipment can be provided.

  These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(First embodiment)
FIG. 1 is a circuit diagram showing a configuration of a voltage controlled oscillator 100 according to the first embodiment of the present invention. In FIG. 1, the bias circuit and the like are omitted.

  In FIG. 1, a voltage controlled oscillator 100 includes an inductor circuit 120, a negative resistance circuit 140, a high frequency switch circuit (band switching circuit) 110, a first variable capacitance circuit 150 (hereinafter referred to as a variable capacitance circuit A), A second variable capacitance circuit 160 (hereinafter referred to as variable capacitance circuit B), a third variable capacitance circuit 170 (hereinafter referred to as variable capacitance circuit C), a frequency sensitivity control unit 180, and a frequency control unit 190 are provided. The inductor circuit 120, the negative resistance circuit 140, the high frequency switch circuit 110, the variable capacitance circuit A, the variable capacitance circuit B, and the variable capacitance circuit C are connected in parallel to each other to constitute an oscillation circuit.

  The inductor circuit 120 includes an inductor 101, an inductor 102 connected in series to the inductor 101, and a power supply terminal 103 connected between the inductor 101 and the inductor 102 for supplying a power supply Vdd.

  The negative resistance circuit 140 is configured by two transistors 107 and 108 being cross-coupled to each other.

  The high frequency switch circuit 110 includes a capacitive element 111, a switching element 113, a switching element 114, and a capacitive element 112. A control voltage terminal 115 for supplying a control voltage Vctrl of the switching elements 113 and 114 is connected to a connection point between the switching element 113 and the switching element 114.

  The variable capacitance circuit A includes a variable capacitance element 151 and a variable capacitance element 152 connected in series to the variable capacitance element 151.

  The variable capacitance circuit B includes a variable capacitance element 161 and a variable capacitance element 162 connected in series to the variable capacitance element 161.

  The variable capacitance circuit C includes a variable capacitance element 171 and a variable capacitance element 172 connected in series to the variable capacitance element 171.

  The variable capacitance circuit A, variable capacitance circuit B, and variable capacitance circuit C constitute a variable capacitance circuit 130 of the voltage controlled oscillator 100.

  The high frequency switch circuit 110, the inductor circuit 120, and the variable capacitance circuit 130 constitute a resonance circuit of the voltage controlled oscillator 100.

  The source side of the transistor 107 and the source side of the transistor 108 are connected to each other and connected to one terminal of the current source 109. The other terminal of the current source 109 is grounded.

  The variable capacitance elements 151, 152, 161, 162, 171, and 172 are variable capacitance elements using a gate capacitance used in the CMOS process.

  A switch 153 for switching a DC voltage is connected to a connection point (hereinafter referred to as a connection point a) between the variable capacitance element 151 and the variable capacitance element 152 in the variable capacitance circuit A.

  A switch 163 is connected to a connection point (hereinafter referred to as a connection point b) between the variable capacitance element 161 and the variable capacitance element 162 in the variable capacitance circuit B.

  A switch 173 is connected to a connection point (hereinafter referred to as a connection point c) between the variable capacitance element 171 and the variable capacitance element 172 in the variable capacitance circuit C.

  One ends of the switches 153, 163, and 173 are connected to each other and connected to the control voltage terminal 181. The other ends of the switches 153, 163, and 173 are connected to each other and to the reference voltage terminal 182. The switches 153, 163, and 173 constitute a frequency sensitivity control unit 180.

  One output of the frequency control unit 190 is connected to the control voltage terminal 115. The frequency control unit 190 supplies the control voltage Vctrl to the control voltage terminal 115. The other output of the frequency control unit 190 is connected to the frequency sensitivity control unit 180. The frequency control unit 190 supplies a control voltage Vsw for switching on and / or off the switches 153, 163, and 173 of the frequency sensitivity control unit 180.

  The control voltage terminal 181 supplies a control voltage Vt. The control voltage Vt is a voltage for controlling (feedback control) the oscillation frequency obtained by feeding back the oscillation frequency and comparing the reference frequency and the oscillation frequency in the PLL circuit. The reference voltage terminal 182 supplies the reference voltage Vs.

  Next, the operation of the voltage controlled oscillator 100 according to the first embodiment configured as described above will be described.

  FIG. 2A is a graph showing the oscillation frequency of the voltage controlled oscillator 100 when the switch 153 is connected to the control voltage terminal 181 side and the switches 163 and 173 are connected to the reference voltage terminal 182 side. In this case, the variable capacitance circuit A operates as a variable capacitance. The variable capacitance circuit B and the variable capacitance circuit C operate as fixed capacitors. Here, it is assumed that there are a plurality of high-frequency switch circuits. In FIG. 2A, a band with the highest oscillation frequency (hereinafter referred to as band H), a band with the lowest oscillation frequency (hereinafter referred to as band L), and an intermediate oscillation frequency. And a band (hereinafter referred to as a band M).

  By changing the control voltage Vt supplied from the control voltage terminal 181, the capacitance value of the variable capacitance circuit 130 is varied, and the oscillation frequency is changed in an analog manner (lateral direction). The frequency control unit 190 changes the control voltage Vctrl supplied to the control voltage terminal 115 to turn on and / or off the switching elements 113 and 114 of the high-frequency switch circuit 110 to digitally change the oscillation frequency (vertical direction). Can be changed.

  When the switch 153 is connected to the control voltage terminal 181 and the switches 163 and 173 are connected to the reference voltage terminal 182, the frequency sensitivity is highest in the band H and decreases in the order of the band M and the band L.

  This is because the frequency sensitivity is determined by the ratio of the capacitance change amount of the variable capacitance circuit to the total capacitance of the resonance circuit. Comparing the total capacity of the resonance circuit between the band H and the band L, all the switching elements of the high-frequency switch circuit are turned off in the band H, and all the bands L are turned on. Is bigger. Therefore, since the ratio of the capacitance change amount of the variable capacitance circuit to the total capacitance of the resonance circuit is larger in the band H than in the band L, the frequency sensitivity is increased.

  Therefore, as in the voltage controlled oscillator 100 in the first embodiment shown in FIG. 1, the frequency sensitivity control unit 180 and the frequency control unit 190 are used to switch the switches 153, 163, and 173 of the frequency sensitivity control unit 180. By synchronizing with the switching of the high-frequency switch circuit 110, the parallel number of variable capacitance elements used as variable capacitance circuits can be varied for each band, and the frequency sensitivity for each band can be made comparable. In this specification, the term “parallel number of variable capacitance circuits” refers to the number of variable capacitance circuits that operate as variable capacitances among the variable capacitance circuits 150 to 170.

  Next, using FIG. 2B, an operation for setting the frequency sensitivity for each band to the same level will be described.

  For example, in the case of the band H, the oscillation frequency is the highest as compared with the bands M and L, and the total capacity of the resonance circuit is the smallest among the three bands. Since the total capacity of the resonant circuit is small, the frequency sensitivity to the change in the capacity of the variable capacity circuit is increased. In this case, only the switch 153 is connected to the control voltage terminal 181, the variable capacitance circuit A is used as a variable capacitance element, and the remaining switches 163 and 173 are connected to the reference voltage terminal 182, and the variable capacitance circuit B and the variable capacitance circuit C is used not as a variable capacitor but as a fixed capacitor. The change in the oscillation frequency with respect to the control voltage Vt in this case is a change in the solid line L1 having the highest oscillation frequency in FIG. 2B.

  In the case of the band L, the oscillation frequency is the lowest as compared with the bands H and M, and the total capacity of the resonance circuit is the largest among the three bands. Therefore, as in the case of the band H described above, when only the switch 153 is connected to the control voltage terminal 181 and the switches 163 and 173 are connected to the reference voltage terminal 182, the frequency sensitivity is lowered as compared with the band H. End up. The change in the oscillation frequency with respect to the control voltage Vt in this case is the change in the broken line L2 having the lowest frequency in FIG. 2B.

  Therefore, in the case of the band L, the switches 153, 163, and 173 are connected to the control voltage terminal 181, and the variable capacitance circuit A, the variable capacitance circuit B, and the variable capacitance circuit C are all used as the variable capacitance elements, so that the resonance circuit The ratio of the capacitance change amount of the variable capacitance circuit with respect to the total capacitance can be made larger than when only the variable capacitance circuit A is used as the variable capacitance, and the frequency sensitivity can be made comparable to the band H. In this case, the change in the oscillation frequency with respect to the control voltage Vt is a solid line L3 having the lowest frequency in FIG. 2B. It can be seen that the frequency sensitivity of the solid line L3 is as high as that of the band H compared to the broken line L2.

  Here, for example, as shown in FIG. 2B, the middle point of the variable range of the control voltage Vt supplied from the control voltage terminal 181 is Vm [V], and the reference voltage Vs supplied from the reference voltage terminal 182 is Vm. To do. Under this condition, in the case of band L, when only switch 153 is connected to control voltage terminal 181 (in the case of broken line L2) and when switches 153, 163 and 173 are connected to the control voltage terminal (solid line L3). ). In this case, as shown in FIG. 2B, the frequency characteristic is centered on the reference voltage Vs (= Vm) supplied from the reference voltage terminal 182. When Vt <Vm, the solid line L3 is better than the broken line L2. The oscillation frequency becomes lower, and when Vt> Vm, the oscillation frequency is higher in the case of the solid line L3 than in the case of the broken line L2. As a result, the frequency sensitivity is higher in the case of the solid line L3 than in the case of the broken line L2. When Vt = Vm, the oscillation frequency does not change.

  In the case of band M, the oscillation frequency is intermediate compared to bands H and L, and the total capacity of the resonance circuit is also intermediate. Therefore, as in the case of the band H described above, when only the switch 153 is connected to the control voltage terminal 181 and the switches 163 and 173 are connected to the reference voltage terminal 182, the frequency sensitivity is the difference between the band H and the band L. Intermediate value. In this case, the change of the oscillation frequency with respect to the control voltage Vt is a change of a broken line L4 having an intermediate oscillation frequency in FIG. 2B.

  Therefore, in the case of the band M, the switches 153 and 163 are connected to the control voltage terminal 181 and the variable capacitance circuit A and the variable capacitance circuit B are used as variable capacitance elements in order to make the frequency sensitivity comparable to that of the band H. The remaining switch 173 is connected to the reference voltage terminal 182, and the variable capacitance circuit C is preferably used as a fixed capacitance element instead of a variable capacitance element. In this case, the change in the oscillation frequency with respect to the control voltage Vt is a change in the solid line L5 having an intermediate oscillation frequency in FIG. 2B. Comparing the broken line L4 and the solid line L5, it can be seen that the frequency sensitivity is a little higher and is about the same as the band H.

  In this way, a plurality of DC voltages to be supplied to a plurality of variable capacitance circuits connected in parallel are connected to the control voltage terminal 181 or the reference voltage terminal 182 for each band by using a switch. The capacity change rate with respect to the control voltage Vt of the entire variable capacity circuit constituted by the variable capacity circuit is adjusted. As a result, the frequency sensitivity of all bands can be made the same level. Here, the capacitance change rate with respect to the control voltage Vt of the entire variable capacitance circuit is obtained by dividing the change amount of the capacitance of the entire variable capacitance circuit when the control voltage Vt changes by a certain amount by the change amount of the control voltage Vt. is there. That is, the capacity change rate with respect to the control voltage Vt of the entire variable capacitance circuit = (change amount of the capacitance of the entire variable capacitance circuit when the control voltage Vt changes by a certain amount) / (change amount of the control voltage Vt).

  The series of operations described above is controlled by the frequency control unit 190. The frequency control unit 190 inputs a control voltage Vsw corresponding to the control voltage Vctrl input to the control voltage terminal 115 of the high frequency switch circuit 110 to the frequency sensitivity control unit 180. The relationship between the control voltage Vctrl and the control voltage Vsw is determined in advance. That is, when obtaining a desired frequency, the frequency control unit 190 determines the control voltage Vctrl in order to determine the band to be used, and determines the control voltage Vsw in synchronization therewith. When the frequency control unit 190 switches the band, the control voltage Vsw for switching the switch of the frequency sensitivity control unit 180 from the control voltage terminal 181 to the reference voltage terminal 182 so that the frequency sensitivity of the band to be used becomes a desired value. Is output. The frequency sensitivity control unit 180 switches the switch according to a predetermined rule according to the control voltage Vsw.

  In the case of the band H, only the variable capacitance circuit A among the variable capacitance circuits 130 is used as the variable capacitance circuit. Therefore, in the case of the band H, the element values of the variable capacitance elements 151 and 152 constituting the variable capacitance circuit A only have to have a magnitude with which the frequency sensitivity is comparable to that of the other bands. That is, it is desirable that the variable capacitance element used in the variable capacitance circuit A is selected to have an element value at which the frequency sensitivity is an appropriate value in the highest frequency band.

  In the case of the band L, of the variable capacitance circuit 130, all of the variable capacitance circuit A, the variable capacitance circuit B, and the variable capacitance circuit C are used as the variable capacitance circuit. Therefore, in the case of the band L, the sum of the element values of the variable capacitance elements used in the variable capacitance circuit 130 only needs to be large enough to make the frequency sensitivity comparable to other bands. That is, it is desirable to select the maximum value of the total of the variable capacitance elements used in the variable capacitance circuit 130 as an element value at which the frequency sensitivity is an appropriate value in the band with the lowest frequency, and the variable constituting the variable capacitance circuit 130. The total element value of the variable capacitance elements of the variable capacitance circuits connected in parallel, such as the capacitance circuit A, the variable capacitance circuit B, and the variable capacitance circuit C, has an appropriate frequency sensitivity when the frequency band is the lowest. You can choose as follows.

  Further, the connection point a between the variable capacitance element 151 and the variable capacitance element 152 in the variable capacitance circuit A, the connection point b between the variable capacitance element 161 and the variable capacitance element 162 in the variable capacitance circuit B, and the variable capacitance circuit C are variable. Since the connection point c between the capacitive element 151 and the variable capacitive element 152 is a virtual ground point for differential signals in the variable capacitive circuit, a high-frequency signal is present outside the connection point a, the connection point b, and the connection point c. Does not flow. Therefore, even if the switches 153, 163, and 173 are used as the frequency sensitivity control unit 180, no high-frequency signal loss occurs. The phase noise characteristic of the voltage controlled oscillator is proportional to the Q value (an index representing loss) of the resonant circuit at the oscillation frequency, so that if the loss of the resonant circuit is large, that is, if the Q value is low, the phase noise deteriorates. End up. In the variable capacitance circuit 130 of FIG. 1, the Q value does not deteriorate by using the frequency sensitivity control unit 180, so that the phase noise does not deteriorate.

  That is, in the variable capacitance circuit 130 used in the voltage controlled oscillator 100 according to the first embodiment, the frequency sensitivity control unit 180 for making the frequency sensitivity of all bands the same level is connected to the connection point a, which is a virtual ground point, Since it is used outside the connection point b and the connection point c, the frequency sensitivity control unit 180 does not cause a loss of the high frequency signal. Therefore, the Q value of the resonance circuit becomes the same value as when the frequency sensitivity control unit 180 is not used, and the phase noise does not deteriorate.

  FIG. 3A is a graph showing oscillation frequency characteristics when the parallel number of variable capacitance circuits in the variable capacitance circuit 130 is N = 1 and the number of bands is 16. At this time, the element value (also referred to as the number of unit transistors or the number of unit basic cells) of the variable capacitance element used in the variable capacitance circuit is 12. FIG. 4 shows the frequency sensitivity for each band at this time by dotted lines. The horizontal axis in FIG. 4 indicates the band number, and 0, 1, 2,..., 15 from the highest oscillation frequency. The vertical axis in FIG. 4 represents frequency sensitivity [MHz / V]. When the variable capacitance circuits are the same in all bands, as shown in FIG. 4, the frequency sensitivity decreases as the band number increases, that is, the oscillation frequency decreases. The frequency sensitivity of band 0 is about 2.4 times that of band 15.

  FIG. 3B is a graph showing oscillation frequency characteristics when the parallel number of variable capacitance circuits of the variable capacitance circuit 130 is N = 5 (variable capacitance circuits A, B, C, D, E) and the number of bands is 16. is there. FIG. 5 is a table showing switching rules for using the variable capacitance circuits A to E as variable capacitors or fixed capacitors at this time. The ratio of the element values of the variable capacitance circuits A to E is A: B: C: D: E = 8: 2: 2: 2: 4. In FIG. 5, ◯ indicates that the variable capacitance circuits A to E are used as variable capacitors. A cross indicates that the variable capacitance circuits A to E are used as fixed capacitors. Here, it is assumed that the control voltage Vt is used in the range of 0 [V] to 1.8 [V]. The reference voltage Vs is assumed to be Vs = 0.9 [V], which is the middle point of the variable range of the control voltage Vt. FIG. 4 shows the frequency sensitivity for each band at this time by a solid line. As shown in FIG. 5, the variable capacity circuit A is used as a variable capacity in the bands 0 to 2, the variable capacity circuits A and B are used as the variable capacity in the bands 3 to 5, and the variable capacity circuits A and B are used in the bands 6 to 8. , C are used as variable capacitors, the variable capacitors A, B, C, D are used as variable capacitors in bands 9 to 12, and the variable capacitors A, B, C, D, E are used as variable capacitors in bands 13-15. Used. As shown by the solid line in FIG. 4, the frequency sensitivity at this time is about ± 10% with 110 [MHz / V] as the center. Therefore, as shown by the dotted line in FIG. 4, it can be seen that the difference in frequency sensitivity for each band is greatly improved as compared with the case where the variable capacitance circuits are the same. As described above, the frequency sensitivity can be made the same in all bands by changing the parallel number of variable capacitance circuits to be used not in all bands but in stages.

  FIG. 3C is a graph showing phase noise characteristics when the parallel number of variable capacitance circuits in the variable capacitance circuit 130 is N = 1 and the number of bands is 16 (corresponding to FIG. 3A). FIG. 3D is a graph showing phase noise characteristics when the parallel number of the variable capacitance circuits of the variable capacitance circuit 130 is N = 5 and the number of bands is 16 (corresponding to FIG. 3B). As can be seen by comparing FIG. 3C and FIG. 3D, even if the parallel number of variable capacitance circuits is increased and the capacitance change rate of the entire variable capacitance circuit is adjusted for each band, the phase noise characteristics do not deteriorate.

  The frequency control unit 190 is realized by, for example, an integrated circuit in which a predetermined operation is programmed in advance, and stores a table as shown in FIG. 5 in advance. The frequency control unit 190 recognizes which variable capacitance circuit is used as a variable capacitance by referring to the table according to the control voltage Vctrl for switching to a desired band, and the variable capacitance circuit used as the variable capacitance is A control voltage Vsw for switching the switch so as to be connected to the control voltage terminal 181 is input to the frequency sensitivity control unit 180. The frequency sensitivity control unit 180 is realized by, for example, an integrated circuit in which a predetermined operation is programmed in advance, and depending on the control voltage Vsw input from the frequency control unit 190, which switch is connected to the control voltage terminal 181 and / or the reference A table indicating whether to connect to the voltage terminal 182 is stored. The frequency sensitivity control unit 180 refers to the table and recognizes which switch should be switched based on the input control voltage Vsw and switches the switch. As a result, the capacitance change amount of the variable capacitance circuit 130 is adjusted according to the band to be used.

  In the first embodiment, in FIG. 1, the variable capacitance circuit 130 is configured by connecting three variable capacitance circuits of the variable capacitance circuit A, the variable capacitance circuit B, and the variable capacitance circuit C in parallel. However, the number is not necessarily limited to three, and may be five in parallel as shown in FIG. 5, or may have a configuration of two parallels, four parallels or more. That is, it is sufficient if there are n (n is a natural number of 2 or more) variable capacitance circuits. In this case, the frequency sensitivity control unit 180 is connected to the virtual ground point of the n variable capacitance circuits, and adjusts the capacitance change rate with respect to the control voltage Vt of the entire variable capacitance circuit configured by the n variable capacitance circuits. You can do it. In either case, the same effect as described above can be obtained.

  In FIG. 1, the high-frequency switch circuit 110 is composed of a high-frequency switch circuit composed of a capacitive element 111 and a switching element 113, and a high-frequency switch circuit composed of a capacitive element 112 and a switching element 114. However, the present invention is not limited to this. The high-frequency switch circuit has a capacitive element, a switching element connected to the capacitive element, and a switching control terminal for inputting a control voltage for controlling on / off of the switching element. It suffices to be composed of high-frequency switch circuits (m is a natural number of 1 or more).

  In the first embodiment, the variable capacitance circuit 130 includes a variable capacitance circuit A, a variable capacitance circuit B, and a variable capacitance circuit C, and switches are connected to the connection point a, the connection point b, and the connection point c, respectively. Although it is assumed that they are connected, it is not always necessary to connect the switches. For example, since the variable capacitance circuit A is always used as a variable capacitance circuit in the configuration of FIG. 5, the connection point a may be directly connected to the control voltage terminal 181 without being connected to the switch 153. Even in this case, the same effect as described above can be obtained. That is, when there are n variable capacitance circuits, the frequency sensitivity control unit includes n−1 switching elements, and the switching elements are connected to the virtual ground points in the n−1 variable capacitance circuits. The voltage applied to each variable capacitance circuit may be selectively switched between the predetermined reference voltage and the control voltage. A control voltage may be supplied to the virtual ground point of one variable capacitance circuit without passing through the switching element.

  Note that in the first embodiment, the frequency control unit 190 has two output terminals, which are connected to the control voltage terminal 115 and the frequency sensitivity control unit 180, and have the control voltage Vctrl and the control voltage Vsw respectively. However, it is not always necessary to output the control voltage Vctrl. For example, the frequency control unit 190 may supply the control voltage Vsw to the frequency sensitivity control unit 180 in synchronization with the control voltage Vctrl output from other components. Even in this case, the same effect as described above can be obtained.

  In the first embodiment, the frequency control unit 190 has two output terminals, which are connected to the control voltage terminal 115 and the frequency sensitivity control unit 180, respectively, and have the control voltage Vctrl and the control voltage Vsw respectively. Although supplied, it is not necessarily limited to this configuration. For example, the frequency control unit 190 has three output terminals, one of which is connected to the reference voltage terminal 182, and may supply the reference voltage Vs to the reference voltage terminal 182. At this time, the frequency control unit 190 may supply the control voltage Vsw and the reference voltage Vs in synchronization with the control voltage Vctrl so that the frequency sensitivity of the band to be used becomes a desired value. Even in this case, the same effect as described above can be obtained.

  In the first embodiment, the ratio of element values of a plurality of variable capacitance circuits is, for example, 8: 2: 2: 2: 4 in the circuit configuration shown in FIG. Although the ratio of the element values is different, it is not limited to this. For example, the ratio of the element values may be all the same value such as 8: 2: 2: 2: 2, or may be all different values such as 8: 2: 3: 4: 5. : A to E may be set to the same value as in 2: 2: 2: 2. Even in this case, the same effect as described above can be obtained.

  In the first embodiment, the high-frequency switch circuit 110 is configured using the capacitive element 111, the switching element 113, the switching element 114, and the capacitive element 112, but is not necessarily limited to this configuration. . Any device that can switch the band of the oscillation frequency in a stepwise manner may be used. Even in this case, the same effect as described above can be obtained.

  In the first embodiment, the reference voltage Vs supplied from the reference voltage terminal 182 is the midpoint Vm of the variable range of the control voltage Vt supplied from the control voltage terminal 181. However, the reference voltage Vs is not necessarily limited to Vm. . For example, the reference voltage Vs may be the ground, the power supply voltage Vdd, or an arbitrary voltage. When the voltage controlled oscillator is used in the PLL circuit, when the oscillation frequency is fixed by feedback control of the oscillation frequency, the value of the control voltage at that time may be used as the reference voltage Vs. In either case, the same effect as described above can be obtained.

  It is assumed that the voltage controlled oscillator is composed of m high frequency switch circuits. As shown in band 0 of FIG. 5, the frequency sensitivity control unit applies to one variable capacitance circuit among the n variable capacitance circuits when all the switching elements of the m high frequency switch circuits are off. It is preferable to control the built-in switching element so that the control voltage is applied only when the reference voltage is applied to the remaining n-1 variable capacitance circuits. The frequency sensitivity control unit applies the control voltage to all the n variable capacitance circuits as shown in the band 15 in FIG. 5 when all the switching elements of the m high frequency switch circuits are turned on. In addition, the built-in switching element may be controlled.

(Second Embodiment)
FIG. 6A is a block diagram showing a configuration of a PLL circuit according to the second embodiment of the present invention. The voltage controlled oscillator according to the first embodiment is mainly used in a PLL circuit as shown in FIG. 6A. 6A, the PLL circuit 300 includes a phase comparator 301, a loop filter 302, a voltage controlled oscillator 303, and a frequency divider 304. The PLL circuit is a circuit that fixes (locks) the oscillation frequency to a desired frequency. The voltage controlled oscillator 303 is the same as the voltage controlled oscillator according to the first embodiment. The phase comparator 301 compares the phase of the input reference signal with the phase of the signal obtained by dividing the output signal of the voltage controlled oscillator 303 by the frequency divider 304. The output signal of the phase comparator 301 is input to the loop filter 302. The loop filter 302 converts the output signal of the phase comparator 301 into a DC component and inputs it to the voltage controlled oscillator 303. A signal output from the loop filter 302 is input to the control voltage terminal 181 of the voltage controlled oscillator 303 as the control voltage Vt. As a result, a desired frequency is output from the voltage controlled oscillator 303.

  FIG. 6B is a flowchart showing the operation of the voltage controlled oscillator 303 in the second embodiment. Hereinafter, the operation of the voltage controlled oscillator 303 will be described with reference to FIG. 6B. Note that when the operation of the PLL circuit 300 starts, the variable capacitance circuits 150, 160, and 170 operate as variable capacitances, and the control voltage Vt is applied to the variable capacitance circuits 150, 160, and 170. And

  First, the frequency control unit 190 of the voltage controlled oscillator 303 detects a desired frequency to be output from the PLL circuit 300 (step S1). At this time, if the PLL circuit 300 is locked, the frequency control unit 190 of the voltage controlled oscillator 303 may perform the operation of step S1 by detecting the frequency of the output signal of the PLL circuit 300, or may be desired. The operation of step S1 may be performed by detecting the frequency from the circuit block that transmits the command to the PLL circuit 300.

  Next, the frequency control unit 190 of the voltage controlled oscillator 303 determines a band to be used by the voltage controlled oscillator 303 according to the frequency to be output from the PLL circuit 300 detected in step S1 (step S2).

  Next, the frequency control unit 190 of the voltage controlled oscillator 303 determines the parallel number of variable capacitance circuits to be used as variable capacitances in the variable capacitance circuit 130 according to the determined band (step S3). Specifically, the frequency control unit 190 of the voltage controlled oscillator 303 stores in advance a table in which bands are associated with the parallel number of variable capacitance circuits used as variable capacitances. The parallel number of the variable capacitance circuit used as is determined.

  After step S3, the PLL circuit 300 locks the oscillation frequency so that the desired frequency is obtained. When the PLL circuit 300 is locked, the frequency control unit 190 of the voltage controlled oscillator 303 detects the control voltage Vt input to the voltage controlled oscillator 303 (step S4).

  Next, the voltage controlled oscillator 303 supplies the reference voltage Vs (= Vt) to the reference voltage terminal 182 as the reference voltage Vs to which the detected control voltage Vt is supplied to the reference voltage terminal 182 (step S5).

  Finally, the frequency control unit 190 of the voltage controlled oscillator 303 connects the switch of the variable capacitance circuit used as the variable capacitance of the variable capacitance circuit 130 to the control voltage terminal 181 to switch the variable capacitance circuit used as the fixed capacitance. Is connected to the reference voltage terminal 182 and the control voltage Vsw is input to the frequency sensitivity control unit 180 (step S6).

  FIG. 7 is a diagram illustrating a state in which the frequency characteristic is changed by the control according to the second embodiment. In this case, as shown in FIG. 7, the oscillation frequency with respect to the control voltage Vt decreases with respect to the reference voltage Vs in the range of Vs> Vt, and increases in the range of Vs <Vt. Thereby, the frequency sensitivity can be set to an appropriate value. In the second embodiment, since the reference voltage Vs is the control voltage Vt when the PLL circuit is locked, before and after changing the parallel number of variable capacitance circuits (before and after the operation of step S6 is performed) The capacitance value does not change. This is because the same control voltage is input to the variable capacitance circuit used as the fixed capacitance and the variable capacitance circuit used as the variable capacitance before and after the parallel number is changed. Therefore, even when the PLL circuit 300 is already locked, the frequency output from the PLL circuit does not change before and after that, and the desired frequency is output as it is. Therefore, it is possible to provide a voltage controlled oscillator that can output the desired frequency as it is and can have the same frequency sensitivity in the variable frequency range.

  As described above, in the PLL circuit according to the second embodiment, by using the control method, the frequency sensitivity can be changed without changing the output frequency even after the PLL circuit is locked. It can be.

  In the second embodiment, the frequency divider 304 is used. However, the frequency divider 304 is not necessarily limited to the frequency divider, and a mixer may be used, or a frequency divider and a mixer may be used. Good.

(Third embodiment)
FIG. 8 is a circuit diagram showing a configuration of a variable capacitance circuit used in the voltage controlled oscillator according to the third embodiment of the present invention. A variable capacitance circuit 200 shown in FIG. 8 is used as the variable capacitance circuit 130 of the voltage controlled oscillator 100 of FIG.

  Since the frequency sensitivity of the voltage controlled oscillator is substantially determined by the characteristics of the variable capacitance element, it is desirable that the variable capacitance element to be used has a characteristic that the capacitance changes gradually over a wide control voltage range. However, in practice, when implementing a voltage controlled oscillator on a semiconductor substrate, it is difficult to use a variable capacitance element having high linearity.

  In the voltage controlled oscillator according to the first embodiment, the frequency sensitivity is approximated to linear, but as described above, the frequency sensitivity may not be approximated to linear depending on the variable capacitance element used. The voltage-controlled oscillator according to the third embodiment relates to a voltage-controlled oscillator that can make frequency sensitivities in the vicinity of a desired frequency the same in all bands even when a variable capacitance element with low linearity is used. .

  In FIG. 8, a variable capacitance circuit 200 includes a variable capacitance circuit 210 (hereinafter referred to as variable capacitance circuit X), a variable capacitance circuit 220 (hereinafter referred to as variable capacitance circuit Y), and a variable capacitance circuit 230 (hereinafter referred to as variable capacitance circuit). Z), high frequency blocking resistors 215, 216, 225, 226, 235, 236, a reference voltage control unit 240, a control voltage terminal 250, and a control voltage terminal 115. The control voltage terminal 115 plays the same role as the control voltage terminal 115 according to the first embodiment. The variable capacitance circuits X, Y, and Z are connected in parallel.

  The variable capacitance circuit X includes variable capacitance elements 211 and 212 and DC cut capacitive elements 213 and 214. The variable capacitance element 211 and the variable capacitance element 212 are connected in series. DC cut capacitive elements 213 and 214 are connected in series at both ends of the series circuit of the variable capacitance element 211 and the variable capacitance element 212 in order to block a direct current component. A variable capacitance circuit X is configured by a series circuit in which a DC cut capacitive element 213, a variable capacitive element 211, a variable capacitive element 212, and a DC cut capacitive element 214 are connected in order.

  The variable capacitance circuit Y includes variable capacitance elements 221 and 222 and DC cut capacitive elements 223 and 224. The variable capacitance element 221 and the variable capacitance element 222 are connected in series. DC cut capacitive elements 223 and 224 are connected in series to both ends of the series circuit of the variable capacitance element 221 and the variable capacitance element 222 in order to block a direct current component. The variable capacitance circuit Y is configured by a series circuit in which the DC cut capacitive element 223, the variable capacitive element 221, the variable capacitive element 222, and the DC cut capacitive element 224 are sequentially connected.

  The variable capacitance circuit Z includes variable capacitance elements 231 and 232 and DC cut capacitive elements 233 and 234. The variable capacitance element 231 and the variable capacitance element 232 are connected in series. DC cut capacitive elements 233 and 234 are connected in series at both ends of the series circuit of the variable capacitance element 231 and the variable capacitance element 232 in order to block a direct current component. The variable capacitance circuit Z is configured by a series circuit in which the DC-cut capacitive element 233, the variable-capacitance element 231, the variable-capacitance element 232, and the DC-cut capacitive element 234 are sequentially connected.

  The variable capacitance elements 211, 212, 221, 222, 231, 232 are variable capacitance elements using a gate capacitance used in, for example, a CMOS process.

  A connection point between the variable capacitance element 211 and the variable capacitance element 212 in the variable capacitance circuit X, a connection point between the variable capacitance element 221 and the variable capacitance element 222 in the variable capacitance circuit Y, and the variable capacitance element 231 and the variable capacitance in the variable capacitance circuit Z. A control voltage terminal 250 is connected to a connection point with the element 232.

  In the variable capacitance circuit X, the connection point between the variable capacitance element 211 and the DC cut capacitive element 213 and the connection point between the variable capacitance element 212 and the DC cut capacitive element 214 are respectively a high frequency blocking resistor 215. , 216 are connected to the first output of the reference voltage control unit 240.

  In the variable capacitance circuit Y, the connection point between the variable capacitance element 221 and the DC cut capacitive element 223 and the connection point between the variable capacitance element 222 and the DC cut capacitive element 224 are the high frequency blocking resistors 225 and 226, respectively. Is connected to the second output of the reference voltage controller 240.

  In the variable capacitance circuit Z, a connection point between the variable capacitance element 231 and the DC cut capacitive element 233 and a connection point between the variable capacitance element 232 and the DC cut capacitive element 234 are the high frequency blocking resistors 235 and 236, respectively. Is connected to the third output of the reference voltage control unit 240. The control voltage terminal 115 is connected to the input terminal of the reference voltage control unit 240.

The operation of the voltage controlled oscillator according to the third embodiment will be described below.
Even when a variable capacitance element with low linearity is used, the method that can improve the linearity and average the frequency sensitivity is described in “Koji Takinami et al.,“ A Wide Tuning Range. gigahertz wireless Lan Yujingu A tuning Sense tee Activity linearization technique (A WIDE tUNING RANGE LC-VCO FOR 5GHZ wIRELESS LAN USING A tUNING SENSITIVITY lINEARIZATION tECHNIQUE) ", 2003 Asia Pacific microwave Conference (2003 Asia-Pacific microwave Conference)" and, JP 2004-147310 A It has already been described in the broadcast.

  9A to 9B are diagrams for explaining the problems of the conventional method. As shown in FIG. 9, in the conventional method, it is possible to average the frequency sensitivity, but there is a problem that the frequency sensitivity between bands cannot be equalized. FIG. 9A shows the variable capacitance characteristics of the band (band H) having the highest oscillation frequency. FIG. 9B shows the variable capacitance characteristics of the band (band L) having the lowest oscillation frequency. 9A and 9B, the horizontal axis indicates the control voltage Vt, the vertical axis indicates the ratio of the capacitance change amount of the variable capacitance circuit to the total capacitance value of the resonance circuit, and the solid line indicates the variable capacitance characteristics of the plurality of variable capacitance circuits. The broken line indicates the total variable capacitance characteristic. In FIG. 9C, the horizontal axis indicates the control voltage Vt, the vertical axis indicates the oscillation frequency, the solid line indicates the oscillation frequency characteristic, and the broken line indicates the frequency sensitivity near the midpoint of the variable range of the control voltage Vt. As described above, the frequency sensitivity as shown in FIG. 9C is the total capacitance value of the resonance circuit in the band L having a lower frequency than the band H having a higher frequency as shown in FIGS. 9A and 9B. This is because the ratio of the capacitance change amount of the variable capacitance circuit with respect to is reduced. Thus, even when the linearity of the frequency sensitivity is improved, the frequency sensitivity between the bands cannot be equalized as shown in FIG. 9C.

  In the third embodiment, the reference voltage control unit 240 is used to switch the voltage output from the reference voltage control unit 240 to the high frequency switch circuit 110 using the control voltage Vctrl input to the control voltage terminal 115. By synchronizing, the frequency sensitivity between bands can be made comparable.

  The voltages output from the reference voltage control unit 240 to the variable capacitance circuit X, the variable capacitance circuit Y, and the variable capacitance circuit Z are Vref, Vref−Vy, and Vref−Vz, respectively. Note that Vy <Vz.

  Here, assuming that Vz = 2 × Vy, three reference voltages that differ by the voltage Vy are output from the reference voltage control unit 240, and each of the variable capacitance element 211 and the variable capacitance element 212 of the variable capacitance circuit X, and the variable capacitance circuit The variable capacitance element 221 and the variable capacitance element 222 of Y, and the variable capacitance element 231 and the variable capacitance element 232 of the variable capacitance circuit Z are applied.

  When the reference voltage is Vref, assuming that the capacitance of each variable capacitance element changes in the vicinity of the control voltage Vth, the capacitance values of the variable capacitance circuit X, the variable capacitance circuit Y, and the variable capacitance circuit Z are relative to the control voltage Vt. As shown by the solid line in FIG. 10A. 10A, 10B, and 10C, the horizontal axis indicates the control voltage Vt, the vertical axis indicates the ratio of the capacitance change amount of the variable capacitance circuit to the total capacitance value of the resonance circuit, and the solid lines indicate the variable capacitance circuit X and the variable capacitance circuit. Y, the variable capacitance characteristics of the variable capacitance circuit Z, and the broken line indicate the total variable capacitance characteristics. Therefore, the total capacitance values of the variable capacitance circuit X, the variable capacitance circuit Y, and the variable capacitance circuit Z change gently with respect to the control voltage Vt as shown by the broken line in FIG. 10A, and as a result, the frequency over a wide control voltage range. Sensitivity can be averaged.

  FIG. 10A is a diagram showing variable capacitance characteristics in the case of band H, which is the band with the highest oscillation frequency. FIG. 10B is a diagram illustrating variable capacitance characteristics in the case of the band M in which the oscillation frequency is intermediate. FIG. 10C is a diagram illustrating a variable capacitance characteristic in the case of the band L, which is the band with the lowest oscillation frequency. Here, the frequency sensitivities of the bands H, M, and L shown in FIGS. 10A, 10B, and 10C are Kh, Km, and Kl, respectively.

  In the band H, which is the band with the highest oscillation frequency, the reference voltage control unit 240 controls the output voltages Vref, Vref−Vy, and Vref−Vz to moderate the capacitance change of the variable capacitance circuit 200 with respect to the control voltage Vt. Thus, the frequency sensitivity Kh is linearized. For example, when the variable capacitance circuit 200 includes three variable capacitance circuits X, Y, and Z as shown in FIG. 8, the voltage output from the reference voltage control unit 240 is Vref> Vref−Vy> Vref−Vz. It becomes. At this time, by setting Vref−Vy, which has an intermediate value among the three voltages, to Vm, which is the midpoint of the variable range of the control voltage Vt, the frequency sensitivity can be linearized around Vm.

  On the other hand, in the band L, which is the lowest oscillation frequency band, the reference voltage control unit 240 makes the frequency sensitivity Kl approximately equal to the frequency sensitivity Kh of the band H with Vm as the center. The ratio of the capacitance change amount of the variable capacitance circuit to the total capacitance value of the resonance circuit of the band L is smaller than that of the band H as shown in FIG. Therefore, for example, as shown in FIG. 10C, the voltage of Vref−Vy is set to the same value as that of band H, and Vy and Vz are set to values smaller than those of band H. That is, the regions where the capacitances of the variable capacitance circuit X, the variable capacitance circuit Y, and the variable capacitance circuit Z change sharply are collected in the vicinity of Vref−Vy as compared with the band H. This increases the frequency sensitivity in the vicinity of Vref−Vy, that is, in the vicinity of Vm, which is the center of the change range of the control voltage Vt, but not in the range of all the control voltages Vt. be able to.

  Further, in the band M in which the oscillation frequency is intermediate, the reference voltage control unit 240 is set so that the frequency sensitivity Km is about the same as the frequency sensitivity Kh of the band H around Vm as in the case of the band L. To do. The ratio of the capacitance change amount of the variable capacitance circuit to the total capacitance value of the resonance circuit of the band M is a value between the band H and the band L as shown in FIG. 9C. Therefore, for example, as shown in FIG. 10B, the voltage Vm of Vref−Vy is set to the same value as that of the band H, and Vy and Vz are set to values between the band H and the band L. As a result, the frequency sensitivity in the vicinity of Vref−Vy, that is, in the vicinity of Vm, which is the center of the change range of the control voltage Vt, is high in a range narrower than the band H and wider than the band L, although not in the entire control voltage Vt range. In addition, the frequency sensitivity can be set to the same level as that of the band H.

  That is, as shown in FIG. 11, in the band H where the oscillation frequency is the highest, the reference voltage control unit 240 gradually changes the capacitance change of the variable capacitance element with respect to the control voltage Vt, and the frequency sensitivity over a wide control voltage range. In the band where Kh is averaged and the oscillation frequency is low, the frequency sensitivity is not averaged, but the output Vref, Vy, and so on are equal to the frequency sensitivity Kh of the band having the highest frequency sensitivity near Vm. Vz is controlled.

  In order to realize the series of operations described above, the reference voltage control unit 240 outputs Vref output from the reference voltage control unit 240 according to the control voltage Vctrl input to the control voltage terminal 115 of the high-frequency switch circuit 110, The values of Vref−Vy and Vref−Vz are determined. This determination may be made by the reference voltage control unit 240 by referring to a correspondence table of the control voltage Vctrl and Vref, Vref−Vy, Vref−Vz stored in advance, for example. That is, when switching the band, the reference voltage control unit 240 specifies the band to be used by the control voltage Vctrl input to the control voltage terminal 115, and the frequency sensitivity is desired when the band is switched in synchronization with the high frequency switch circuit 110. Vref, Vref−Vy, and Vref−Vz applied to the variable capacitance circuit may be adjusted so as to be output so that the value becomes. As a result, the frequency sensitivities of all the bands can be made similar in the vicinity of the control voltage Vt. Thus, phase noise can be suppressed by setting the frequency sensitivities of all bands to the same level. This is because if the frequency sensitivity is high, the influence of phase noise degradation due to noise components riding on Vt becomes large.

  In the third embodiment, when the variable capacitance circuit 200 is configured by three variable capacitance circuits X, Y, and Z, Vref−Vy which is an intermediate value among the voltages output from the reference voltage control unit 240. Is Vm which is the midpoint of the variable range of the control voltage Vt, but Vref−Vy is not necessarily limited to Vm, and may be any voltage. Even in this case, the same effect as described above can be obtained. For example, as shown in the second embodiment, when the voltage controlled oscillator 100 using the variable capacitance circuit 200 is used in the PLL circuit 300, the control input to the voltage controlled oscillator 100 when the PLL circuit 300 is locked. The voltage Vt may be detected, and the detected control voltage Vt may be defined as Vref−Vy. In this case, the frequency sensitivity of each band can be made the same level with the frequency when the PLL circuit 300 is locked as the center. Thereby, even after the PLL circuit 300 is locked, the frequency sensitivity can be changed without changing the output frequency, and an appropriate frequency sensitivity can be obtained.

  In the third embodiment, the variable capacitance circuit 200 is configured by connecting the three variable capacitance circuits of the variable capacitance circuit X, the variable capacitance circuit Y, and the variable capacitance circuit Z in parallel, but is not necessarily limited to three. Instead of this, a configuration of 2 parallels or 4 parallels or more may be adopted. That is, the number of variable capacitance circuits may be n (n is a natural number of 2 or more). In this case, the reference voltage control unit may control the voltage applied to the variable capacitance elements of the n variable capacitance circuits in synchronization with the switching control voltage input to the switching control terminal of the high frequency switch circuit. In either case, the same effect as described above can be obtained.

  In the third embodiment, the reference voltage control unit 240 adjusts Vref, Vref−Vy, and Vref−Vz based on the control voltage Vctrl input to the control voltage terminal 115. It is not necessary to adjust Vref, Vref−Vy, and Vref−Vx based on Vctrl. For example, the reference voltage control unit 240 determines a band having a desired frequency by itself, outputs the control voltage Vctrl to the control voltage terminal 115, and based on the determined band, Vref , Vref−Vy, Vref−Vz may be adjusted. Even in this case, the same effect as described above can be obtained.

  In the third embodiment, the potential difference output from the reference voltage control unit 240 is Vref, Vref−Vy, Vref−Vz, Vz = 2 × Vy, and each potential difference is constant to Vy. Needless to say, different potential differences may be given. Even in this case, the same effect as described above can be obtained.

  Note that the voltage controlled oscillator according to the third embodiment may be used in the PLL circuit according to the second embodiment. In this case, the same effect as that of the second embodiment can be obtained.

  Here, a preferable example of the reference voltage used when there are n variable capacitance circuits will be described. When n is an odd number, the reference voltage control unit may set the (n + 1) / 2th reference voltage as the midpoint voltage of the change range of the control voltage Vt. When n is an even number, the reference voltage control unit assumes that the intermediate voltage between the n / 2th reference voltage and the (n + 2) / 2th reference voltage is the midpoint voltage of the control voltage Vt changing range. Good. As a result, there is an effect that the frequency sensitivity can be made uniform in all bands centering on the intermediate voltage of the control voltage Vt.

  When n is an odd number, the reference voltage control unit may set the (n + 1) / 2th reference voltage to the value of the control voltage Vt when the oscillation frequency is fixed by feedback control of the oscillation frequency. When n is an even number, the reference voltage control unit feedback-controls the oscillation frequency between the n / 2th reference voltage and the (n + 2) / 2th reference voltage, and the oscillation frequency is fixed. It is good to use the value of the control voltage Vt. Thereby, even when the PLL circuit is already locked, the frequency output from the PLL circuit does not change before and after that, and the desired frequency is output as it is.

  The reference voltage control unit adjusts the reference voltage so that the rate of change of the oscillation frequency with respect to the control voltage Vt is substantially constant over the control voltage Vt when all the switching elements of the m high-frequency switch circuits are turned off. Good. Further, in a state other than when all of the switching elements of the m high-frequency switch circuits are off, the reference voltage control unit, when n is an odd number in the n variable capacitance circuits, is (n + 1) / 2nd. In the vicinity of the reference voltage Vt or the intermediate voltage when the reference voltage is locked, it is preferable to adjust so that the rate of change of the oscillation frequency with respect to the control voltage is approximately the same as when all the switching elements are turned off. Further, in the same state, when n is an even number, the reference voltage control unit calculates an intermediate voltage between the n / 2th reference voltage and the (n + 2) / 2th reference voltage as the reference voltage or the intermediate voltage. It is preferable to adjust so that the rate of change of the oscillation frequency with respect to the control voltage is approximately the same as when all the switching elements are turned off. For example, the reference voltage control unit predetermines the reference voltage corresponding to the band to be used, and by outputting the predetermined reference voltage, the ratio of the change in the oscillation frequency with respect to the control voltage is all the switching elements. Adjust to the same level as when turned off. This has the effect of maximizing the range of the control voltage where the frequency sensitivity is averaged.

  When the reference voltages input to the n variable capacitance circuits among the n variable capacitance circuits are arranged in descending order, the variable capacitance of the kth variable capacitance circuit (k is a natural number of 2 or more and n or less). The difference between the reference voltage input to the element and the reference voltage input to the variable capacitance element of the (k−1) th variable capacitance circuit is maximum when all the switching elements of the m high-frequency switch circuits are off. The minimum is when all the switching elements of the m high-frequency switch circuits are on, and the maximum and minimum when the switching elements of the m high-frequency switch circuits are all on or other than the off state. It should be a value between. Thereby, since the ranges of Vref, Vref−Vy, and Vref−Vz output from the reference voltage control unit 240 are limited, an effect of facilitating the control occurs.

(Fourth embodiment)
FIG. 12 is a block diagram showing a configuration of a wireless communication device 400 using the voltage controlled oscillator according to the first to third embodiments of the present invention.

  In FIG. 12, a wireless communication device 400 includes an antenna 401, a power amplifier 402, a modulator 403, a switch 404, a low noise amplifier 405, a demodulator 406, and a PLL circuit 407.

  The PLL circuit 407 is a PLL circuit according to the second embodiment using the first or third voltage controlled oscillator.

  When transmitting a wireless signal in the wireless communication device 400, the modulator 403 modulates a desired high-frequency signal output from the PLL circuit 407 with a baseband modulation signal and outputs the modulated signal. The high frequency modulation signal output from the modulator 403 is amplified by the power amplifier 402 and radiated from the antenna 401 via the switch 404.

  When a radio signal is received, the high frequency modulation signal received from the antenna 401 is input to the low noise amplifier 405 via the switch 404 and amplified, and then input to the demodulator 406. The demodulator 406 demodulates the input high frequency modulation signal into a baseband modulation signal using the high frequency signal output from the PLL circuit 407.

  As shown in FIG. 12, a PLL circuit 407 including a voltage controlled oscillator is an indispensable circuit as means for generating a high frequency signal.

  In the fourth embodiment, the wireless communication device 400 is configured as shown in FIG. 12, but is not necessarily limited to this configuration. For example, different PLL circuits may be used for transmission and reception, or a plurality of PLL circuits may be used for transmission and reception. The PLL circuit may also serve as the modulator.

  In the first to fourth embodiments, each variable capacitor has been described as a variable capacitor using a gate capacitor used in the C-MOS process. However, each variable capacitor has other types. A variable capacitance element may be used, and in this case, the same effect as described above can be obtained.

  In the first to fourth embodiments, the MOS transistor is used as the oscillation transistor. However, a bipolar transistor may be used.

  As described above, according to the present invention, even when a plurality of bands are used in order to obtain a wide frequency variable range, all the bands have good phase noise characteristics and the same frequency sensitivity. It is possible to provide a voltage-controlled oscillator that can be reduced to a level, a PLL circuit using the oscillator, and a wireless communication device.

  Although the present invention has been described in detail above, the above description is merely illustrative of the present invention in all respects and is not intended to limit the scope thereof. It goes without saying that various improvements and modifications can be made without departing from the scope of the present invention.

  The voltage controlled oscillator according to the present invention, the PLL circuit using the voltage controlled oscillator, and the wireless communication device have good phase noise characteristics and can control a frequency range over a wide band. Useful for.

1 is a circuit diagram showing a configuration of a voltage controlled oscillator 100 according to a first embodiment of the present invention. A graph showing the oscillation frequency of the voltage controlled oscillator 100 when the switch 153 is connected to the control voltage terminal 181 side and the switches 163 and 173 are connected to the reference voltage terminal 182 side. Diagram for explaining the operation to make the frequency sensitivity of each band the same level A graph showing the oscillation frequency characteristics when the parallel number of variable capacitance circuits in the variable capacitance circuit 130 is N = 1 and the number of bands is 16. A graph showing oscillation frequency characteristics when the parallel number of variable capacitance circuits of the variable capacitance circuit 130 is N = 5 (variable capacitance circuits A, B, C, D, E) and the number of bands is 16. The graph which shows the phase noise characteristic when the parallel number of the variable capacity circuit in the variable capacity circuit 130 is N = 1 and the number of bands is 16 (corresponding to FIG. 3A). The graph which shows the phase noise characteristic when the parallel number of the variable capacity circuit of the variable capacity circuit 130 is N = 5 and the number of bands is 16 (corresponding to FIG. 3B). Graph showing frequency sensitivity for each band Table showing switching rules for using variable capacitance circuits A to E as variable capacitors or fixed capacitors The block diagram which shows the structure of the PLL circuit which concerns on the 2nd Embodiment of this invention. Flowchart showing the operation of the voltage controlled oscillator 303 in the second embodiment. The figure which shows a mode that a frequency characteristic changes by control by 2nd Embodiment. A circuit diagram showing composition of a variable capacity circuit used with a voltage controlled oscillator concerning a 3rd embodiment of the present invention. Diagram for explaining the problems of the conventional method Diagram for explaining the problems of the conventional method Diagram for explaining the problems of the conventional method The figure for demonstrating the capacitance value of the variable capacity | capacitance by the voltage control oscillator which concerns on 3rd Embodiment. The figure for demonstrating the capacitance value of the variable capacity | capacitance by the voltage control oscillator which concerns on 3rd Embodiment. The figure for demonstrating the capacitance value of the variable capacity | capacitance by the voltage control oscillator which concerns on 3rd Embodiment. The graph which shows the oscillation frequency of the voltage controlled oscillator which concerns on 3rd Embodiment The block diagram which shows the structure of the radio | wireless communication apparatus 400 using the voltage control oscillator which concerns on the 1st-3rd embodiment of this invention. The figure which shows an example of a structure of the conventional voltage controlled oscillator 500 which has a band switching function. A diagram showing how the oscillation frequency shifts in a conventional voltage-controlled oscillator The figure which shows the characteristic of the voltage controlled oscillator 600 at the time of making frequency sensitivity the same over the whole oscillation frequency range. Circuit diagram of a conventional voltage-controlled oscillator 600 that employs an improved method of making the frequency sensitivity comparable in a wide frequency variable range. A circuit diagram showing a configuration of a conventional voltage-controlled oscillator 700 described in Patent Document 3 The graph which shows the characteristic of the conventional voltage control oscillator 700 described in patent document 3

Explanation of symbols

100, 303 Voltage controlled oscillator 101, 102 Inductor 103 Power supply terminal 107, 108 Transistor 109 Current source 110 High frequency switch circuit 111, 112 Capacitive element 113, 114 Switching element 115 Control voltage terminal 120 Inductor circuit 130, 150, 160, 170, 200, 210, 220, 230 Variable capacitance circuit 140 Negative resistance circuit 151, 152, 161, 162, 171, 172, 211, 212, 221, 222, 231, 232 Variable capacitance element 153, 163, 173 Switch 180 Frequency sensitivity Control unit 181 Control voltage terminal 182 Reference voltage terminal 190 Frequency control unit 213, 214, 223, 224, 233, 234 DC cut capacitive element 215, 216, 225, 226, 235, 236 High frequency blocking resistor 240 reference voltage control unit 250 control voltage terminal 300 PLL circuit 301 phase comparator 302 loop filter 304 frequency divider 400 wireless communication device 401 the antenna 402 power amplifier 403 modulator 404 switches 405 low noise amplifier 406 demodulator 407 PLL circuit

Claims (25)

A voltage controlled oscillator composed of a differential circuit for oscillating a high frequency signal,
An inductor circuit having an inductor;
N variable capacitance circuits (n is a natural number of 2 or more) each having a variable capacitance element that is connected in parallel to the inductor circuit and whose capacitance value changes according to a control voltage applied to feedback control the oscillation frequency;
M capacitors connected in parallel to the inductor circuit and having a capacitive element, a switching element connected to the capacitive element, and a switching control terminal for inputting a switching control voltage for controlling on / off of the switching element. A high-frequency switch circuit (m is a natural number of 1 or more);
A negative resistance circuit connected in parallel to the inductor circuit;
A frequency control unit that shifts a band of the oscillation frequency by controlling on / off of the switching element included in the m high-frequency switch circuits;
A frequency sensitivity control unit that adjusts the rate of change of the capacitance of the entire n variable capacitance circuits with respect to the control voltage according to the band to be used;
The frequency sensitivity control unit is a voltage controlled oscillator connected to a virtual ground point of a differential signal in the n variable capacitance circuits. The frequency control unit inputs a switching control voltage for controlling on / off of the switching element to a switching control terminal of the high-frequency switch circuit according to the band to be used,
The frequency sensitivity control unit uses a voltage applied to one terminal of each of the variable capacitance elements in the n variable capacitance circuits in synchronization with the switching control voltage as a predetermined reference voltage or the control voltage. The voltage controlled oscillator according to claim 1, wherein the voltage controlled oscillator is selectively switched. The frequency sensitivity control unit includes n frequency sensitivity control switching elements,
Each of the frequency sensitivity control switching elements is connected to each of the virtual ground points in the n number of variable capacitance circuits, and the voltage applied to each of the variable capacitance circuits is set to the predetermined reference voltage or the control The voltage controlled oscillator according to claim 2, wherein the voltage controlled oscillator is selectively switched. The frequency sensitivity control unit includes n-1 frequency sensitivity control switching elements,
Each of the frequency sensitivity control switching elements is connected to each of the virtual ground points in the n−1 variable capacitance circuits, and a voltage applied to each of the variable capacitance circuits is set as the predetermined reference voltage. Selectively switching the control voltage,
The voltage controlled oscillator according to claim 2, wherein the control voltage is supplied to a virtual ground point of one of the variable capacitance circuits.   The voltage controlled oscillator according to claim 3, wherein the reference voltage is a voltage at a midpoint of a change range of the control voltage.   The voltage controlled oscillator according to claim 4, wherein the reference voltage is a voltage at a midpoint of a change range of the control voltage.   4. The voltage controlled oscillator according to claim 3, wherein the reference voltage is a value of the control voltage when the oscillation frequency is fixed by feedback control of the oscillation frequency.   5. The voltage controlled oscillator according to claim 4, wherein the reference voltage is a value of the control voltage when the oscillation frequency is fixed by feedback control of the oscillation frequency.   When the switching elements of the m high-frequency switch circuits are all turned off, the frequency sensitivity control unit controls the control voltage only for one of the n variable capacitance circuits. 4. The voltage controlled oscillator according to claim 3, wherein the frequency sensitivity control switching element is controlled so that the reference voltage is applied to the remaining n−1 variable capacitance circuits.   When the switching elements of the m high-frequency switch circuits are all turned off, the frequency sensitivity control unit controls the control voltage only for one of the n variable capacitance circuits. 5. The voltage controlled oscillator according to claim 4, wherein the frequency sensitivity control switching element is controlled so that the reference voltage is applied to the remaining n−1 variable capacitance circuits.   The frequency sensitivity control unit is configured to control the frequency sensitivity so that the control voltage is applied to all of the n variable capacitance circuits when all of the switching elements of the m high frequency switch circuits are turned on. The voltage controlled oscillator according to claim 3, wherein the voltage controlled oscillator controls a switching element.   The frequency sensitivity control unit is configured to control the frequency sensitivity so that the control voltage is applied to all of the n variable capacitance circuits when all of the switching elements of the m high frequency switch circuits are turned on. The voltage controlled oscillator according to claim 4, wherein the voltage controlled oscillator controls a switching element.   The frequency sensitivity controller determines in advance whether to use each variable capacitor circuit as a variable capacitor or a fixed capacitor for each band shifted by the frequency controller. The voltage controlled oscillator according to claim 1, wherein the control signal is applied to a variable capacitance circuit to be used, and a predetermined reference voltage is applied to the variable capacitance circuit to be used as the fixed capacitance.   The voltage controlled oscillator according to claim 13, wherein the voltage controlled oscillator is provided in a PLL circuit, and a control voltage when the PLL circuit is locked is the predetermined reference voltage. In a voltage controlled oscillator composed of a differential circuit for oscillating a high frequency signal,
An inductor circuit having an inductor;
N (n is a natural number of 2 or more) variable capacitance circuits that are connected in parallel to the inductor circuit, have variable capacitance elements, and have blocking capacitors for blocking DC components at both ends;
M pieces having a capacitive element connected in parallel with the inductor circuit, a switching element connected to the capacitive element, and a switching control terminal for inputting a switching control voltage for controlling on / off of the switching element. A high-frequency switch circuit (m is a natural number of 1 or more);
A negative resistance circuit connected in parallel to the inductor circuit;
A frequency control unit that shifts a band of the oscillation frequency by controlling on / off of the switching element included in the m high-frequency switch circuits;
A control terminal for inputting a control voltage for feedback control of the oscillation frequency to one terminal of the variable capacitance elements of the n variable capacitance circuits;
A reference voltage is input to the other terminal of the variable capacitance element of the n number of variable capacitance circuits, the reference voltage is adjusted according to the band to be used, and the rate of change in oscillation frequency with respect to the control voltage is determined. A voltage controlled oscillator comprising a reference voltage control unit to be adjusted.   The reference voltage control unit controls a reference voltage applied to the other terminal of the variable capacitance elements of the n variable capacitance circuits in synchronization with a switching control voltage input to a switching control terminal of the high frequency switching circuit. The voltage controlled oscillator according to claim 15.   The reference voltage control unit determines (n + 1) / 2th reference voltage as the control voltage when n is an odd number among the reference voltages input to the other terminals of the variable capacitance elements of the n variable capacitance circuits. In the case where n is an even number, an intermediate voltage between the n / 2th reference voltage and the (n + 2) / 2th reference voltage is used as the midpoint voltage of the control voltage change range. The voltage controlled oscillator according to claim 16.   The reference voltage control unit sets an oscillation frequency to (n + 1) / 2th reference voltage when n is an odd number among reference voltages input to the other terminals of the variable capacitance elements of the n variable capacitance circuits. When the oscillation frequency is fixed by feedback control, the value of the control voltage is set. When n is an even number, the intermediate voltage between the n / 2th reference voltage and the (n + 2) / 2th reference voltage is set as the oscillation frequency. The voltage-controlled oscillator according to claim 16, wherein the control voltage is set to a value when the oscillation frequency is fixed by feedback control. The reference voltage controller is
When all the switching elements of the m high frequency switch circuits are off, the reference voltage is adjusted so that the rate of change of the oscillation frequency with respect to the control voltage is substantially constant over the control voltage,
When the switching elements of the m high-frequency switch circuits are in a state other than when all the switching elements are off, in the n variable capacitance circuits, when n is an odd number, the (n + 1) / 2th reference voltage is The voltage controlled oscillator according to claim 16, wherein when n is an even number, an intermediate voltage between the n / 2th reference voltage and the (n + 2) / 2th reference voltage is adjusted. When the reference voltages input to the n variable capacitance circuits among the n variable capacitance circuits are arranged in descending order, the variable capacitance of the kth (k is a natural number of 2 to n) variable capacitance circuit The difference between the reference voltage input to the element and the reference voltage input to the variable capacitance element of the (k−1) th variable capacitance circuit is
The maximum is when all of the switching elements of the m high-frequency switch circuits are off,
The case where all the switching elements of the m high-frequency switch circuits are on is the minimum,
The voltage controlled oscillator according to claim 16, wherein when all the switching elements of the m high frequency switch circuits are in a state other than on or all off, the voltage controlled oscillator has a value between a maximum and a minimum. A PLL circuit comprising a voltage controlled oscillator composed of a differential circuit for oscillating a high frequency signal,
The voltage controlled oscillator is:
An inductor circuit having an inductor;
N variable capacitance circuits (n is a natural number of 2 or more) each having a variable capacitance element that is connected in parallel to the inductor circuit and whose capacitance value changes according to a control voltage applied to feedback control the oscillation frequency;
M capacitors connected in parallel to the inductor circuit and having a capacitive element, a switching element connected to the capacitive element, and a switching control terminal for inputting a switching control voltage for controlling on / off of the switching element. A high-frequency switch circuit (m is a natural number of 1 or more);
A negative resistance circuit connected in parallel to the inductor circuit;
A frequency control unit that shifts a band of the oscillation frequency by controlling on / off of the switching element included in the m high-frequency switch circuits;
A frequency sensitivity control unit that adjusts the rate of change of the capacitance of the entire n variable capacitance circuits with respect to the control voltage according to the band to be used;
The frequency sensitivity control unit is a PLL circuit connected to a virtual ground point of a differential signal in the n variable capacitance circuits. A PLL circuit comprising a voltage controlled oscillator composed of a differential circuit for oscillating a high frequency signal,
The voltage controlled oscillator is:
An inductor circuit having an inductor;
N (n is a natural number of 2 or more) variable capacitance circuits that are connected in parallel to the inductor circuit, have variable capacitance elements, and have blocking capacitors for blocking DC components at both ends;
M pieces having a capacitive element connected in parallel with the inductor circuit, a switching element connected to the capacitive element, and a switching control terminal for inputting a switching control voltage for controlling on / off of the switching element. A high-frequency switch circuit (m is a natural number of 1 or more);
A negative resistance circuit connected in parallel to the inductor circuit;
A frequency control unit that shifts a band of the oscillation frequency by controlling on / off of the switching element included in the m high-frequency switch circuits;
A control terminal for inputting a control voltage for feedback control of the oscillation frequency to one terminal of the variable capacitance elements of the n variable capacitance circuits;
A reference voltage is input to the other terminal of the variable capacitance element of the n number of variable capacitance circuits, the reference voltage is adjusted according to the band to be used, and the rate of change in oscillation frequency with respect to the control voltage is determined. A PLL circuit comprising a reference voltage control unit to be adjusted. A PLL circuit for fixing an oscillation frequency,
A voltage-controlled oscillator that is composed of a differential circuit for oscillating a high-frequency signal and adjusts an oscillation frequency according to an applied control voltage;
A feedback control voltage adjustment circuit that feeds back a high-frequency signal output from the voltage-controlled oscillator, compares a phase difference with a reference signal, and adjusts the control voltage applied to the voltage-controlled oscillator;
The voltage controlled oscillator is:
An inductor circuit having an inductor;
N (n is a natural number greater than or equal to 2) variable capacitance circuits each having a variable capacitance element that is connected in parallel to the inductor circuit and whose capacitance value changes according to an applied control voltage for feedback control of the oscillation frequency;
M capacitors connected in parallel to the inductor circuit and having a capacitive element, a switching element connected to the capacitive element, and a switching control terminal for inputting a switching control voltage for controlling on / off of the switching element. A high-frequency switch circuit (m is a natural number of 1 or more);
A negative resistance circuit connected in parallel to the inductor circuit;
According to the oscillation frequency, the frequency control unit for turning on and off the switching element of the high-frequency switch circuit and determining a band to be used;
The n variable capacitance circuits are connected to virtual ground points of the n variable capacitance circuits, and the oscillation frequency shifts by turning on and off the switching elements of the m high frequency switch circuits. A frequency sensitivity control unit that selectively switches a voltage applied to one terminal of each of the variable capacitance elements to be a predetermined reference voltage or the control voltage;
The PLL circuit according to claim 1, wherein the frequency sensitivity control unit uses the control voltage output from the feedback control voltage adjustment circuit as the reference voltage. A wireless communication device comprising a voltage-controlled oscillator configured with a differential circuit for oscillating a high-frequency signal,
The voltage controlled oscillator is:
An inductor circuit having an inductor;
N variable capacitance circuits (n is a natural number of 2 or more) each having a variable capacitance element that is connected in parallel to the inductor circuit and whose capacitance value changes according to a control voltage applied to feedback control the oscillation frequency;
M capacitors connected in parallel to the inductor circuit and having a capacitive element, a switching element connected to the capacitive element, and a switching control terminal for inputting a switching control voltage for controlling on / off of the switching element. A high-frequency switch circuit (m is a natural number of 1 or more);
A negative resistance circuit connected in parallel to the inductor circuit;
A frequency control unit that shifts a band of the oscillation frequency by controlling on / off of the switching element included in the m high-frequency switch circuits;
A frequency sensitivity control unit that adjusts the rate of change of the capacitance of the entire n variable capacitance circuits with respect to the control voltage according to the band to be used;
The frequency sensitivity control unit is a wireless communication device connected to a virtual ground point of a differential signal in the n variable capacitance circuits. A wireless communication device comprising a voltage-controlled oscillator configured with a differential circuit for oscillating a high-frequency signal,
The voltage controlled oscillator is:
An inductor circuit having an inductor;
N (n is a natural number of 2 or more) variable capacitance circuits that are connected in parallel to the inductor circuit, have variable capacitance elements, and have blocking capacitors for blocking DC components at both ends;
M pieces having a capacitive element connected in parallel with the inductor circuit, a switching element connected to the capacitive element, and a switching control terminal for inputting a switching control voltage for controlling on / off of the switching element. A high-frequency switch circuit (m is a natural number of 1 or more);
A negative resistance circuit connected in parallel to the inductor circuit;
A frequency control unit that shifts a band of the oscillation frequency by controlling on / off of the switching element included in the m high-frequency switch circuits;
A control terminal for inputting a control voltage for feedback control of the oscillation frequency to one terminal of the variable capacitance elements of the n variable capacitance circuits;
A reference voltage is input to the other terminal of the variable capacitance element of the n number of variable capacitance circuits, the reference voltage is adjusted according to the band to be used, and the rate of change in oscillation frequency with respect to the control voltage is determined. A wireless communication device comprising a reference voltage control unit to be adjusted.

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