JP2008514163A - Apparatus and method for oscillating broadband frequency - Google Patents

Abstract

  An apparatus for oscillating frequency is shown, comprising a phase locked loop and a variable frequency divider (560) as shown in FIG. The variable frequency divider (560) divides the signal of the first frequency by a certain division ratio to generate a signal of the second frequency (Fout), and this frequency division is sent to the phase / frequency detector (510). This is based on a comparison between an input reference frequency clock input (Fref) and a feedback frequency signal input. A charge pump (520) and loop filter (530) are shown with a divider (550) that divides the second frequency signal (355) to allow the correct feedback frequency to be achieved. The VCO (540) includes a resonant circuit including a selected capacitor, a control voltage for setting an operating frequency, and an active circuit (320) for an appropriate gain.

Description

  The present invention relates to generating a frequency signal, and more particularly to an apparatus and method for oscillating a frequency for extending the tuning range by controlling the division ratio of a phase locked loop (PLL).

  A voltage controlled oscillator (VCO) generates a predetermined frequency of the AC signal based on the control voltage. VCOs are widely used in wireless receivers to send and receive signals through one or more predetermined channels, and are therefore generally incorporated in cell phones, television (TV) receivers and wireless modems. .

  Phase locked loop (PLL) circuits are widely used in VCOs in wired / wireless communication systems, for example, to generate a wide band of frequencies from a low reference frequency to a relatively high frequency.

FIG. 1 shows a phase locked loop (PLL) circuit according to the related art. As illustrated, the PLL circuit 100 includes a frequency divider 150, a phase frequency detector 110, a charge pump 120, a loop filter 130, and a voltage controlled oscillator 140. The frequency divider divides the output frequency Fout into a predetermined frequency. The phase frequency detector 110 receives the reference frequency F _ref from the external unit and the frequency divided from the divider 150, and detects the frequency difference between the reference frequency and the phase difference between the divided frequencies. The charge pump 120 receives the phase difference and the frequency difference from the phase frequency detector 110 and charges or discharges the loop filter (LF) 130. The loop filter removes radio frequency components from the output signal from the CP 120. The VCO 140 generates an output frequency F _out that is proportional to the voltage of the LF 130.

The reference frequency F _ref is normally supplied from a crystal resonator having an accuracy of ppm. The VCO oscillates a stable AC signal within the target frequency band through such a PLL circuit.

FIG. 2 shows a tuner for a radio receiver using a VCO according to the related art. This tuner is a direct conversion type, and demodulates a predetermined frequency signal RF _in the I baseband signal and Q baseband signal. That is, the tuner receives the frequency signal RF _in to be controlled to have a constant level throughout the preamplifier 210 and gain controller 220, a frequency signal RF _in which the received oscillating signal and a mixer 230 of local oscillator 250 , 240 to generate an I baseband signal and a Q baseband signal. The local oscillator 250 generates an oscillation signal having a 90 ° phase difference at the same frequency, and the oscillation signal is applied to the mixers 230 and 240.

The local oscillator (LO) 250 includes a VCO and a frequency distributor. The VCO generates a signal having the same frequency as the carrier of the selected channel. The frequency divider distributes the output signal of the VCO as two signals f ₀₁ and f ₀₂ having a 90 ° phase difference. The mixers 230 and 240 mix the input frequency and the LO signal to generate an I signal and a Q signal.

  Low pass filters 260 and 270 remove out-of-band blocking signals and in-band blocking signals from the output signals of mixers 230 and 240, respectively. Thus, when local oscillator 250 generates an oscillating signal having a frequency equal to the carrier of the selected channel, it mixes the oscillating signal with the corresponding carrier frequency signal in mixers 230 and 240, and the I baseband signal and A Q baseband signal is extracted.

US Pat. No. 5,739,730 Korean Patent Application Publication No. 2004-48439 Shinichiro Azma et. Al., “International solid state circuitconference 2004,” pp. 278-279

  As described above, the VCO oscillates a frequency for the reception band of the tuner. That is, the oscillation range of the VCO must match the reception band of the corresponding wireless system.

  For example, the satellite broadcasting system uses a broadcast band of about 950 MHz to about 2.15 GHz. Therefore, the satellite receiver tuner must have an oscillation frequency band of about 950 MHz to about 2.15 GHz (eg, generate a frequency signal).

  When the oscillation range of the VCO is expressed based on the following Equation 1 expressed as a ratio between the maximum value and the minimum value, the VCO must have an oscillation range of 125%.

  However, a conventional VCO having a resonator generally has an oscillation range of about 30%, and as the oscillation range of the VCO becomes wider, the phase noise characteristics may be dramatically deteriorated.

  In order to overcome such problems of conventional VCOs, many studies are underway to expand the oscillation range of VCOs without degrading phase noise characteristics. In these studies, Patent Document 1 introduces a VCO that uses a plurality of varactor diodes to generate a wide-band frequency signal.

  FIG. 3 is a block diagram for explaining the VCO introduced in Patent Document 1. In FIG. As shown in FIG. 3, the VCO 300 includes a resonance circuit 310 for resonating a signal, and an active circuit 320 for oscillating a frequency signal and outputting the generated frequency signal from the resonance circuit 310.

  The resonance circuit 310 includes an inductance element and a capacitance element, and the tuning range of the VCO 300 is determined by the resonance circuit. That is, the oscillation frequency f of the VCO can be calculated according to Equation 2 based on the inductance L and capacitance C of the resonant circuit.

  As shown in the figure, the resonance circuit 310 is structurally provided with a plurality of varactor diodes, and the oscillation range of the VCO 300 is expanded by changing the capacitance C in accordance with the target frequency band.

  There are several deficiencies in the VCO depicted in FIG. First, since the varactor diode has a low quality factor (Q value) with respect to frequency tuning, the phase noise characteristic is extremely deteriorated.

  Second, frequency oscillation may be interrupted from time to time in this circuit. More specifically, the Q value of the resonance circuit 310 is inversely proportional to the capacitance C and the inductance L. To lower the output frequency using a fixed inductance L, the capacitance C must be increased. This gradually reduces the voltage swing, and as a result, the frequency oscillation is interrupted.

  In order to overcome this VCO deficiency, Non-Patent Document 1 proposes a method using a plurality of VCOs having various frequency bands in order to widen the tuning range. To implement this method, a large die area must be used to provide multiple VCOs with various frequency bands. In addition, the use of a plurality of VCOs increases the manufacturing cost. These deficiencies are obstacles to miniaturization of radio receivers and satisfying many manufacturers' low cost policies.

  Japanese Patent Application Laid-Open No. H10-228707 introduces a technique that uses a frequency signal oscillated from a single VCO to extend the frequency tuning range through various frequency dividers. FIG. 4 shows a frequency oscillation device introduced in Patent Document 2.

As shown in FIG. 4, frequency oscillating device 400 includes a VCO410 having a predetermined frequency variation range, the expansion circuit 420 to expand the frequency range by distributing the output signal F _in the VCO.

  The expansion circuit 420 includes a control logic circuit 450 for selecting and controlling the frequency divider according to the target frequency. The frequency divider includes a 1/2 divider 430, a 1/4 divider 440, and a plurality of switches.

  A control logic unit 450 selects one of the ½ and ¼ dividers by controlling a plurality of switches according to the target tuning frequency, and a single VCO 410. The predetermined range of the frequency signal oscillated and output from is expanded to various frequency bands.

  This technique reduces phase noise and current consumption, and broadens the tuning range with VCO switching elements. However, a subharmonic signal is generated during mixing of the signal fed back through the various dividers with the oscillation signal from the VCO 410. As a result of the subharmonic signal, the characteristics are degraded. In particular, this is highly undesirable because removing the subharmonic signal to obtain the target signal element is very complex. Therefore, many difficulties are expected to commercialize the technology introduced in Patent Document 2.

  Accordingly, there is a need for a frequency oscillation device that can achieve an increased tuning range and at the same time maintain low phase noise.

  One object of the present invention is to provide an apparatus and method for oscillating a wideband frequency while maintaining low phase noise by providing a variable frequency divider in a PLL circuit and controlling the variable frequency divider according to a target frequency band. There is.

  Another object of the present invention is to automatically track and control the variable frequency division ratio with respect to the target frequency according to the result of comparing the reference frequency and the feedback signal without requiring an oscillation frequency matching table, An object of the present invention is to provide an apparatus and a method for oscillating a broadband frequency.

  Another object of the present invention is to provide an apparatus and method for oscillating a broadband frequency that prevents the generation of subharmonic signals that degrade the characteristics.

  It is another object of the present invention to provide an apparatus and method for oscillating at a wideband frequency that appropriately generates an I (in-phase) signal and a Q (quadrature) signal.

  According to an embodiment, the present invention is an apparatus that oscillates a broadband frequency, and is oscillated by feeding back a frequency oscillating unit that oscillates a predetermined frequency and a frequency oscillated from the frequency oscillating unit. The frequency is compared with the reference frequency, and the oscillation frequency is divided by changing the division ratio so as to approach the frequency band required by the oscillation frequency and the phase lock loop that fixes the oscillation frequency of the frequency oscillation unit. An apparatus comprising a variable division unit is provided.

  According to another embodiment, the present invention is an apparatus that selectively oscillates a target frequency within a wide frequency band, and a frequency oscillating unit that oscillates an alternating frequency in a stable operating range by a phase-locked loop; A first control unit that controls the variable division ratio based on the oscillated frequency that is close to the target frequency, and a frequency that is controlled by the first control unit and that matches the target frequency is precisely controlled. And a second control unit.

  According to another embodiment, the present invention is a broadband frequency oscillating device that controls the oscillation frequency of a phase-locked loop using a variable divider, an initialization unit that initializes a division ratio of the variable divider; A detection unit for detecting a feedback frequency of the phase-locked loop, a comparison unit for detecting a frequency difference by comparing a reference frequency of the phase-locked loop and a detected feedback frequency, and according to the detected frequency difference Provided is a broadband frequency oscillating device including a division ratio control unit for increasing, decreasing or fixing a division ratio.

  According to another embodiment, the present invention is a method for oscillating a wideband frequency, the step of oscillating a predetermined frequency, and the frequency oscillated by comparing the oscillated frequency and the reference frequency Then, a method is provided that includes fixing an oscillation frequency oscillated in an oscillation of a predetermined frequency, and changing a division ratio to approach a frequency band required by the oscillation frequency.

  According to another embodiment, the present invention is a method of selectively oscillating a target frequency within a wide frequency band, the step of oscillating an alternating frequency in a stable operating range by a phase locked loop, Providing a method comprising: controlling a variable division ratio based on a frequency approaching the target frequency; and precisely controlling a frequency matched to the target frequency controlled in the control of the variable division ratio To do.

  According to another embodiment, the present invention is a method for controlling an oscillation frequency of a phase-locked loop using a variable divider to oscillate a broadband frequency, and initializes a division ratio of the variable divider According to the detected frequency difference, detecting a feedback frequency of the phase locked loop, detecting a frequency difference by comparing a reference frequency of the phase locked loop and the detected feedback frequency, and Increasing, decreasing or fixing the split ratio.

  FIG. 5 is a block diagram illustrating an apparatus for oscillating a broadband frequency according to one embodiment of the present invention. Apparatus 500 includes frequency divider 550, phase frequency detector 510, charge pump 520, loop filter 530, VCO 540, and variable frequency divider 560.

Frequency divider 550 receives a feedback output signal F _out, to a frequency predetermined by dividing the feedback output signal F _out. A phase frequency detector (PFD) 510 receives a reference signal F _ref supplied from an external device and a frequency output from the frequency divider 550, and calculates a phase difference and a frequency difference between the reference signal F _ref and the received frequency. To detect. The charge pump (CP) 520 receives the phase difference and frequency difference output from the PFD 510 and charges / discharges the loop filter (LF) 530. The LF 530 removes radio frequency components from the signal output from the CP 520. The voltage controlled oscillator (VCO) 540 generates a frequency proportional to the voltage of the LF 530. The variable frequency divider 560 divides the radio frequency AC signal output from the VCO 540 by the variable division ratio M and outputs the output frequency F _out .

The apparatus also includes a frequency detector (FD) 570 and a controller 580. The frequency detector compares the feedback frequency divided by the frequency divider 550 with the reference frequency F _ref to extract a frequency difference. The controller controls the variable division ratio M of the variable frequency divider 560 based on the frequency difference extracted from the FD.

  As described above, the PFD 510 detects a frequency difference and a phase difference between the feedback output signal and the reference signal. Instead of using a PFD, a phase detector may be used like a conventional phase locked loop (PLL) circuit element. The PFD generates a pulse signal corresponding to the phase difference and frequency difference between the two signals.

  CP 520 generates a voltage signal for controlling VCO 540 by charging and discharging the charge in LF 530 based on the pulse signal generated from PFD 510.

  The LF 530 performs low-pass filtering to remove harmonic components that may occur during frequency / phase difference detection. The LF is preferably composed of a capacitance element and a resistive element.

  The VCO 540 includes an active circuit for oscillating and outputting a frequency signal generated from the resonance circuit. The resonant circuit has an inductance element and a capacitance element for determining the frequency. The range of the oscillation operation of the VCO 540 is determined by the capacitance value C and the inductance value L in the resonance circuit. The detailed structure of VCO 540 will be described in more detail below.

  Frequency divider 550 and variable frequency divider 560 reduce the frequency from the VCO by counting the frequency. The frequency divider 550 and the variable frequency divider 560 can easily use other circuits, and can be realized as, for example, flip-flops. The frequency divider has a constant division ratio K fixed by the target oscillation frequency. The variable frequency divider has a variable division ratio M that is controlled by the controller 580 to approach the target oscillation frequency band.

Similar to the PFD 510, the FD 570 detects a frequency difference between two frequencies. More specifically, according to the present embodiment, the FD 570 detects the frequency difference by comparing the signal divided based on the variable division ratio M with the reference frequency F _ref . Controller 580 controls variable division ratio M of variable frequency divider 560 according to the frequency difference detected by FD 570.

  The controller 580 can be implemented, for example, as a microprocessor module that generally controls a receiving system having a device 500 for oscillating a broadband frequency.

When the feedback frequency divided based on the controlled variable division ratio M is lower than the reference frequency F _ref , the controller 580 decreases the variable division ratio M and increases the output frequency. When the feedback frequency divided based on the controlled variable division ratio M is larger than the reference frequency F _ref , the controller 580 increases the variable division ratio M and decreases the output frequency. When the output frequency approaches the target oscillation frequency, the controller 580 fixes the variable division ratio M of the variable frequency divider 560 through the control operation performed by the variable division ratio M. According to the present embodiment, as described above, the target output frequency F _out can be oscillated using the VCO, where the target output frequency F _out is operated by the variable frequency divider 560 set to the variable division ratio according to the present embodiment. The range is limited.

  Also, the specific oscillation frequency can be advantageously controlled by changing the capacitance value of the resonant element in the resonant circuit in the VCO 540.

Although not shown in FIG. 5, the apparatus 500 uses the output frequency F _out to _generate an I signal having the same frequency as the output frequency F _out and a Q signal having a 90 ° phase difference with the I signal. A generating unit may be further provided.

  FIG. 6 is a circuit diagram illustrating a voltage controlled oscillator according to an embodiment of the present invention. The VCO 540 includes a resonance circuit 610 having a capacitance element and an inductance element that resonate at a certain frequency, and a plurality of varactor diodes VD1 and VD2 having a capacitance value that varies depending on one or more applied voltages.

  The resonance frequency is determined in inverse proportion to the capacitance value C and the inductance value L of the resonance circuit. Therefore, the oscillation frequency of VCO 540 can be varied by controlling the applied voltage of varactor diodes VD1 and VD2.

  In this embodiment, the resonant circuit 610 comprises two varactor diodes VD1 and VD2. However, the present invention is not limited to this number of diodes, and is not limited to having a varactor diode in the resonant circuit. For example, the resonant circuit is not a varactor diode, but instead may include a plurality of capacitances and a plurality of switches connected to the capacitances. Such resonant circuits oscillate at various resonant frequencies by controlling the switch to variously combine the capacitance values.

  Further, the resonance circuit 610 may be realized by including a plurality of LC tank circuits. Such a resonant circuit having a plurality of LC tanks can generate one resonant frequency, for example, by selecting one of the LC tanks according to a target frequency. Various other techniques may be used to control the resonant frequency in the resonant circuit 610, and there are various ways to apply these techniques to control the resonant frequency in the resonant circuit 610.

  FIG. 7 is a flowchart illustrating steps involved in a method for oscillating a broadband frequency according to an embodiment of the present invention. In this exemplary embodiment, the oscillation frequency is controlled within a band from about 174 MHz to 240 MHz, which is required for digital audio broadcasting (DAB) standardized by ESTI EN 3000074. is there. Those skilled in the art will appreciate that the present invention is not intended to be limited to this frequency range or this application.

Referring to FIG. 7, the variable division ratio M of the variable frequency divider 560 is initialized in operation S710. In order to clearly show this embodiment, the division ratio K of the frequency divider 550 is fixed to 17.4, the VCO 540 oscillates a radio frequency AC frequency in the range of about 2200 MHz to about 3200 MHz, and the reference frequency F _ref It shall be 10 MHz.

  When variable division ratio M is initialized as 12, frequency divider 550 receives a frequency from about 2200/12 MHz to about 3200/12 MHz (ie, 183.33 MHz to 266.66 MHz) and divides by 17.4. The feedback frequency is in the range of about 10.54 MHz to about 15.33 MHz.

In Operation S720, and S730, FD570 is fed back, by detecting the AC frequency operating at a predetermined frequency range, comparing the reference frequency F _ref and the detected AC frequency. Here, various methods can be used to compare the detected AC frequency with the reference frequency F _ref . For example, it is possible to compare the minimum frequency within the operating range of the detected AC frequency and the reference frequency F _ref, may compare the maximum frequency within the operating range of the detected AC frequency and the reference frequency F _ref . However, the present invention is not intended to be limited to any method of comparison. The present invention can operate properly using any method that compares a predetermined one of the frequencies within the operating range of the detected frequency with the reference frequency F _ref .

  In this embodiment, the feedback alternating frequency within the range of about 10.54 MHz to about 15.33 MHz is compared to the reference frequency of 10 MHz. When the above comparison method is applied to the present embodiment, 10.54 MHz that is the minimum frequency within the operating range of the detected AC frequency may be compared with the reference frequency of 10 MHz, and the detected AC frequency The maximum frequency within the operating range of 15.33 MHz may be compared with the reference frequency of 10 MHz. Furthermore, the average frequency of the maximum frequency and the minimum frequency within the operating range, 12.935 MHz, may be compared with the reference frequency of 10 MHz as described above. The average frequency is calculated from (10.54 + 15.33) / 2.

According to a preferred embodiment of the present invention, the minimum frequency within the operating range of the detected AC frequency is compared with the reference frequency F _ref, and in addition, the maximum frequency within the operating range of the detected AC frequency is compared with the reference frequency F _ref. Compare with

If the minimum frequency is greater than the reference frequency F _ref , the variable frequency division ratio M is increased and the feedback frequency band is decreased in operation S740. In the present embodiment, since the minimum frequency 10.54 MHz is larger than the reference frequency 10 MHz, the variable division ratio M is increased to 16. Preferably, the variable division ratio is increased or decreased by 2 degrees or 4 degrees to generate an in-phase (I) signal and a quadrature (Q) signal having a phase difference of 90 ° from the output frequency F _out .

If the maximum frequency of the fed back AC frequency is smaller than the reference frequency F _ref , the variable frequency division ratio M is reduced and the feedback frequency band is increased in operation S750.

As described above, when the reference frequency F _ref is repeatedly controls the variable division ratio M to be included within the operating range of the feedback AC frequency, the reference frequency F _ref is to be included within the operating range of the feedback AC frequency, In step S760, the variable division ratio M is fixed. In the illustrated embodiment, when the variable division ratio M is 16, the feedback AC frequency is in the range of about 7.9 MHz to about 11.49 MHz, and the reference frequency 10 MHz is included in the operating range of the feedback AC frequency. Therefore, the variable division ratio M is fixed at 16.

  After fixing the variable division ratio M, in operation S770, the capacitance value of the resonance circuit in the VCO 540 is controlled to generate an oscillation frequency in the target frequency band. The locking operation after fixing the variable division ratio M is the same as the phase locking in the PLL. For example, when an LC oscillator is used, a predetermined capacitor value is selected for each individual capacitor, and a frequency similar to the target frequency is generated. This is the same as the method for obtaining the variable division ratio M. Thereafter, it is locked to the target frequency by the analog PLL. When the current oscillation frequency is higher than the target frequency, the switch connected to the capacitor operates so as to increase the capacitor value. Conversely, when the current oscillation frequency is lower than the target frequency, the switch operates to decrease the capacitor value.

  The apparatus and method for oscillating at a broadband frequency according to the present invention dynamically controls the variable division ratio according to the result of comparing the reference frequency and the fed back frequency without requiring a predetermined oscillation frequency table. The oscillation frequency can be automatically tracked and controlled so as to be the target frequency band. When a conventional frequency oscillator is manufactured, an oscillation frequency table is set in advance. The conventional frequency oscillator uses the oscillation frequency table to switch to the X LC tank using the X divider or the x division value to oscillate the frequency in the A frequency band, or oscillates the frequency in the B frequency band. To switch to the Y LC tank using the Y divider or y division value, or to switch to the Z LC tank using the Z divider or z division value to oscillate the frequency in the C frequency band. Such a conventional oscillation frequency table is not necessary in the present invention.

  Although not shown in FIG. 7, an operation for generating an I signal and a Q signal used for I / Q demodulation may be included.

  The above-described operation according to the present embodiment may be controlled by the controller 580 or may be controlled by a microprocessor of a wireless reception system in which the device 500 that oscillates a broadband frequency is mounted.

  The apparatus and method for oscillating a broadband frequency according to the present invention can also oscillate a wider band of frequencies while maintaining low phase noise. In order to oscillate a broadband frequency while maintaining excellent phase noise characteristics, the tuning range of the VCO may be narrowed. In some embodiments of the present invention, the tuning range of the VCO may be narrow, but wideband frequencies can be oscillated dynamically by changing the value of the variable divider.

  The apparatus and method for oscillating a broadband frequency according to the present invention preferably uses a single VCO. Since the device of the present invention has a relatively small die area and low manufacturing cost, the integrity of the receiving system comprising the device of the present invention is increased.

  Furthermore, the apparatus and method for oscillating a broadband frequency according to the present invention first oscillates an accurate frequency by controlling the variable division ratio to approach the target frequency band and secondly controlling the capacitance value of the VCO. , Accurate target frequency can be supplied.

  Furthermore, the apparatus and method for oscillating a broadband frequency according to the present invention automatically performs the tracking and control function for supplying the target frequency by controlling the variable division ratio according to the result of comparing the reference frequency and the feedback frequency. Can be done. Therefore, a predetermined oscillation frequency matching table is not necessary. In addition, the apparatus and method for oscillating a broadband frequency according to the present invention can appropriately and more efficiently generate the I signal and the Q signal.

  The apparatus and method for oscillating broadband frequencies according to the present invention can also prevent or avoid the effects of subharmonic signals that occur during signal mixing and cause characteristic degradation.

  Although the invention has been particularly shown and described with reference to illustrative embodiments, workers skilled in the art will recognize that the invention can be practiced without departing from the spirit and scope of the invention as defined by the appended claims. You will understand that various changes can be made to the details.

1 is a block diagram illustrating a phase locked loop (PLL) circuit according to related art. FIG. FIG. 3 is a circuit diagram showing a tuner of a radio receiver using a VCO according to related technology. It is a block diagram showing the conventional voltage controlled oscillator. It is a block diagram showing the conventional voltage controlled oscillator. 1 is a block diagram illustrating an apparatus for oscillating a broadband frequency according to an embodiment of the present invention. FIG. 6 is a circuit diagram illustrating a voltage controlled oscillator (VCO) that can be included in the apparatus of FIG. 5, for example, according to one embodiment of the invention. 6 is a flowchart illustrating steps that may be included in a method for oscillating a broadband frequency according to an embodiment of the present invention.

Claims (20)

A phase locked loop circuit for generating a first frequency signal;
A variable frequency divider that divides the first frequency signal by a division ratio to generate a second frequency signal existing in a predetermined frequency band, and the division ratio is applied to the phase-locked loop circuit. An apparatus for oscillating a frequency, comprising: a variable frequency divider that can be changed based on a comparison between an input reference frequency signal and a feedback frequency signal. The phase-locked loop circuit is
A detector for detecting a phase difference or a frequency difference between the reference frequency signal and the feedback frequency signal;
A signal generator for generating a voltage for controlling the generation of the first frequency signal based on the phase difference or the frequency difference;
The apparatus of claim 1, further comprising a divider that divides the second frequency signal to form the feedback frequency signal. The variable frequency divider is
A frequency detector for detecting a frequency difference between the reference frequency signal and the feedback frequency signal;
The apparatus according to claim 1, further comprising a controller that sets the division ratio in the variable frequency divider based on a frequency difference detected by the frequency detector. The variable frequency divider is
A frequency detector for detecting a frequency difference between a minimum frequency within an operating range of the feedback frequency signal and the reference frequency;
The apparatus according to claim 1, further comprising a controller that sets the division ratio in the variable frequency divider based on a frequency difference detected by the frequency detector. The variable frequency divider is
A frequency detector for detecting a frequency difference between a maximum frequency within an operating range of the feedback frequency signal and the reference frequency;
The apparatus according to claim 1, further comprising a controller that sets the division ratio in the variable frequency divider based on a frequency difference detected by the frequency detector. The phase-locked loop circuit is
A resonant circuit;
The apparatus according to claim 1, further comprising a frequency oscillation circuit having an active circuit that oscillates a signal output from the resonance circuit and forms the first frequency signal. The resonant circuit is:
The apparatus according to claim 6, further comprising a circuit for changing a resonance frequency of the signal output from the resonance circuit, wherein the circuit has a capacitance value that changes in accordance with an applied voltage. The phase-locked loop circuit is
A plurality of LC tank circuits that generate resonant frequencies;
The apparatus according to claim 1, further comprising: a frequency oscillating circuit including a switching circuit that selects one of the plurality of LC tanks and generates the first frequency signal. Generating a first frequency signal from a phase locked loop circuit;
Dividing the first frequency signal by a division ratio to generate a second frequency signal existing in a predetermined frequency band, wherein the division ratio is input to the phase-locked loop circuit A method of oscillating a frequency comprising: changing the frequency signal based on a comparison of the frequency signal and the feedback frequency signal. Generating the first frequency signal comprises:
Detecting a phase difference or a frequency difference between the reference frequency signal and the feedback frequency signal;
Generating a voltage for controlling the generation of the first frequency signal based on the phase or frequency difference;
10. The method of claim 9, comprising splitting the second frequency signal to form the feedback frequency signal. Dividing the first frequency signal comprises:
Detecting a frequency difference between the reference frequency signal and the feedback frequency signal;
The method according to claim 9, further comprising setting the division ratio based on the detected frequency difference. Dividing the first frequency signal comprises:
Detecting a frequency difference between a minimum frequency within an operating range of the feedback frequency signal and the reference frequency signal;
The method according to claim 9, further comprising setting the division ratio based on the detected frequency difference. Dividing the first frequency signal comprises:
Detecting a frequency difference between a maximum frequency within an operating range of the feedback frequency signal and the reference frequency signal;
The method according to claim 9, further comprising setting the division ratio based on the detected frequency difference. The first frequency signal is generated by a phase-locked loop having a frequency oscillation circuit, and the frequency oscillation circuit includes:
A resonant circuit;
The method according to claim 9, further comprising: an active circuit that oscillates a signal output from the resonance circuit to form the first frequency signal. The resonant circuit is:
The method according to claim 14, comprising a circuit for changing a resonance frequency of a signal output from the resonance circuit, wherein the circuit has a capacitance value that changes according to an applied voltage. The first frequency signal is generated by a phase-locked loop having a frequency oscillation circuit, and the frequency oscillation circuit includes:
A plurality of LC tank circuits that generate resonant frequencies;
The method according to claim 9, further comprising a switching circuit that selects one of the plurality of LC tanks to generate the first frequency signal. A frequency oscillator that oscillates an alternating frequency to generate a first frequency signal within a predetermined operating range;
A first controller that sets a division ratio of a first divider and generates a second frequency signal, wherein the first divider divides the first frequency signal by the division ratio. A first controller for generating the second frequency signal to be close to a target frequency;
An apparatus for selectively oscillating a target frequency, comprising: a second controller that controls a second frequency signal so that the second frequency signal is closer to the target frequency.   The apparatus according to claim 17, wherein the first controller controls the division ratio based on a difference between a feedback signal input to a phase-locked loop including the frequency oscillator and a reference frequency signal. .   The apparatus of claim 17, wherein the second controller comprises a circuit having a capacitance value that varies based on an applied control voltage.   The first controller performs coarse tuning control of the second frequency signal, and the second controller performs fine tuning control so that the second frequency signal approaches the target frequency. The apparatus according to claim 17, wherein:

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