Broadband millimeter wave frequency source circuit based on multimode multi-core oscillator

Abstract

The invention discloses a broadband millimeter wave frequency source circuit based on a multimode multi-core oscillator. The broadband millimeter wave frequency source circuit comprises a multimode multi-core voltage-controlled oscillator, a phase frequency detector, a charge pump, a loop filter and a programmable frequency divider, the multi-mode multi-core voltage-controlled oscillator oscillates near the output frequency, an output signal of the multi-mode multi-core voltage-controlled oscillator forms a feedback signal through the programmable frequency divider, the signal and a reference signal are subjected to phase comparison in the phase frequency detector, a voltage in direct proportion to the phase difference of the two signals is output and transmitted to the charge pump, and charging or discharging of the charge pump is controlled. And the corresponding current is transmitted to the loop filter and is converted into a voltage signal to serve as the control voltage of the multimode multi-core voltage-controlled oscillator, and the frequency source is controlled to output the correct frequency. According to the invention, the connecting line loss in the resonant cavity is reduced, the layout of the numerical control oscillator layout is freer, and the output frequency precision of the numerical control oscillator is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of clock frequency sources of millimeter wave communication systems, and in particular to a broadband millimeter wave frequency source circuit based on a multi-mode multi-core oscillator. Background Art

[0002] High-performance frequency sources are key modules in communication systems and must have high stability, flexibility, and adaptability to meet the high requirements of communication systems. In the fifth generation (5G) millimeter wave communication, the frequency generated by the frequency source needs to reach above 28GHz, which is very difficult to achieve. Specifically, high-performance millimeter wave frequency sources must meet the following requirements: wide frequency range, low phase noise, fast locking, low power consumption, and wide temperature operating range. Therefore, it is of great significance for 5G millimeter wave communication to achieve a wide tuning range, low phase noise, and high-precision frequency source without excessively increasing power consumption or occupying too much chip area.

[0003] Traditionally, frequency sources with wide tuning range and high frequency accuracy use multiple oscillators, i.e., multi-core structures, in order to optimize phase noise, but this takes up a larger area and also increases power consumption. On the other hand, in order to cover the wide frequency tuning range of the 5G millimeter wave band, oscillators usually require more switching capacitors, switching inductors, etc. for frequency switching, which will deteriorate the phase noise of the frequency source. Summary of the invention

[0004] The technical problem to be solved by the present invention is: to provide a broadband millimeter-wave frequency source circuit based on a multi-mode multi-core oscillator, adopt a multi-core multi-mode combined structure, reduce phase noise by combining an appropriate number of oscillator cores, and realize a high-frequency frequency source with a wide frequency range and low phase noise by switching the access mode of each oscillator, so as to expand the frequency band, thereby solving the problems of excessive area, complex structure and insufficient performance in the prior art.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0006] A broadband millimeter wave frequency source circuit based on a multi-mode multi-core oscillator comprises the following steps:

[0007] Multi-mode multi-core voltage controlled oscillator, phase frequency detector, charge pump, loop filter and programmable divider.

[0008] The multi-mode multi-core voltage-controlled oscillator oscillates near the output frequency, and its output signal passes through a programmable frequency divider to form a feedback signal f div , the signal is related to the reference signal f refThe two signals are compared in phase frequency detector to output a voltage proportional to the phase difference between them. The voltage is transmitted to the charge pump to control the charging or discharging of the charge pump. The corresponding current is transmitted to the loop filter and converted into a voltage signal as the control voltage of the multi-mode multi-core voltage-controlled oscillator to control the frequency source to output the correct frequency.

[0009] The multi-mode multi-core voltage-controlled oscillator includes a power supply, two oscillator cores distributed up and down, and four mode switching switches SW distributed in the southeast, northwest, and northeast directions. e , SW s , SW w and SW n and 4 coupling capacitors C m ; The mode switching switch is used to control magnetic coupling and electric coupling.

[0010] The charge pump circuit includes eight MOS tubes M1 to M8, a current source I ref , control signal CT, inverse control signal CTB, the first switch SW1, the charging control voltage UP, the inverse UP signal UPB, the second switch SW2, the discharging control voltage DN and the inverse DN signal DNB; M1, M2 and M3 are used to provide a reference for the charge pump output, M6, M7, M8 and M9 constitute a switch array and control the working states of M4 and M5 with different channel widths.

[0011] The programmable dividers include a high-speed divider-by-four and a 2 / 3 divider chain.

[0012] Furthermore, when f ref When it reaches the phase frequency detector first, the phase frequency detector outputs an UP signal to control the charge pump to charge the loop filter, making the voltage V at the output end of the loop filter ref rises, thereby increasing the output frequency of the multi-mode multi-core voltage-controlled oscillator; when f div When it reaches the phase frequency detector first, the phase frequency detector outputs the DN signal, controls the charge pump to discharge the loop filter, and makes the voltage V ref decreases, thereby reducing the output frequency of the multi-mode multi-core voltage-controlled oscillator.

[0013] Furthermore, in the multi-mode multi-core voltage-controlled oscillator, the oscillator core includes 4 transformer coils, 2 tuning capacitor arrays cap <n:0>, 4 varactors C var and 2 negative resistance-G m .

[0014] When the multi-mode multi-core voltage-controlled oscillator is in the magnetically coupled even-mode excitation state, the currents in the upper and lower transformer coils are in phase, and the magnetic flux in the center area of ​​the two transformers is added; the inductance L of the transformer coil itself is the ratio of the magnetic flux Φ in the coil to the current I flowing through the coil, that is, L = Φ / I, and the even-mode equivalent inductance L is obtained. even for:

[0015] L even =L+M,

[0016] Wherein, M represents the mutual inductance between the coils.

[0017] At the same time, since the capacitance C is the ratio between the charge Q on the capacitor and the voltage U across it, that is, C≡Q / U, the coupling capacitance C m The two ends of the circuit have equal potential, and C m There is no charge accumulated on the capacitor, so the even-mode equivalent capacitance is:

[0018] C even =C o

[0019] Among them, C even Represents the even-mode equivalent capacitance, C o Represents the capacitance of the oscillator core.

[0020] When the multi-mode multi-core voltage-controlled oscillator is in the case of magnetically coupled odd-mode excitation, the magnetic flux in the center area of ​​the two transformers is equal in magnitude and opposite in direction, and the obtained odd-mode equivalent inductance L odd for:

[0021] L odd =LM.

[0022] At the same time, C and C m The voltage across the two ends is differential, so the odd-mode equivalent capacitance C odd for:

[0023] C odd =C+C m .

[0024] The four oscillation frequencies generated are:

[0025]

[0026] Among them, ω1, ω2, ω3, and ω4 represent four oscillation frequencies respectively.

[0027] Further, in the circuit of the charge pump, VDD is respectively connected to the positive electrode of the current source Iref, the source of the MOS tube M3, the source of the MOS tube M4, and the source of the MOS tube M7, and the negative electrode of the current source Iref is respectively connected to the drain of the MOS tube M1, the gate of the MOS tube M1, the gate of the MOS tube M2, and the source of the MOS tube M8; the source of the MOS tube M1 and the source of the MOS tube M2 are both grounded; the drain of the MOS tube M2 is respectively connected to the drain of the MOS tube M3, the gate of the MOS tube M3, and the drain of the MOS tube M6; the gate of the MOS tube M6 is connected to the anti-control signal CTB, and the source of the MOS tube M6 is respectively connected to the drain of the MOS tube M7 and the gate of the MOS tube M4; the gate of the MOS tube M7 is connected to the control signal CT; the drain of the MOS tube M4 is connected to the diffusion region of the MOS tube in the first switch SW1 formed by the transmission gate The gate of the NMOS tube in the first switch SW1 is connected to the charging control voltage UP, the gate of the PMOS tube in the first switch SW1 is connected to the inverted UP signal UPB, the other diffusion area of ​​the MOS tube in the first switch SW1 is connected to the diffusion area of ​​the MOS tube in the second switch SW2, and the output current Iout is obtained; the gate of the NMOS tube of the second switch SW2 is connected to the discharge control voltage DN, the gate of the PMOS tube of the second switch SW2 is connected to the inverted DN signal DNB, the other diffusion area of ​​the MOS tube in the second switch SW2 is connected to the drain of the MOS tube M5; the gate of the MOS tube M5 is respectively connected to the drain of the MOS tube M8 and the drain of the MOS tube M9, and the source of the MOS tube M5 and the source of the MOS tube M9 are both grounded; the gate of the MOS tube M8 is connected to the control voltage CT; the gate of the MOS tube M9 is connected to the inverted control voltage CTB.

[0028] Furthermore, in the programmable divider, the 2 / 3 divider chain includes a first-stage 2 / 3 divider, the input of the first-stage 2 / 3 divider comes from a high-speed four-divider, and the output of the first-stage 2 / 3 divider is transmitted to a frequency detector for frequency and phase detection.

[0029] Furthermore, for the 2 / 3 frequency divider, when the input frequency division ratio control signal and the mode control signal are both at high level, frequency division by 3 is achieved, and in other cases, frequency division by 2 is achieved.

[0030] Compared with the prior art, the present invention adopts the above technical solution and has the following technical effects:

[0031] 1. The present invention reduces the connection loss in the resonant cavity and also makes the layout of the digital controlled oscillator more free.

[0032] 2. The digital controlled oscillator of the present invention achieves an oscillation frequency from 8.3 GHz to 12.6 GHz, reaching a tuning range of 41%. Through the combined effect of the digital-to-analog converter and the fine tuning capacitor, a high-precision frequency tuning resolution of 35 kHz is achieved.

[0033] 3. The present invention utilizes the complementary characteristics of NMOS and PMOS varactors to achieve a fine-tuning varactor that is more than 10 times finer than a traditional varactor, thereby improving the output frequency accuracy of the digitally controlled oscillator. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is the overall structural diagram of the present invention.

[0035] Figure 2 is a circuit diagram of the charge pump of the present invention.

[0036] Figure 3 It is a circuit diagram of the multi-mode multi-core voltage-controlled oscillator of the present invention.

[0037] Figure 4 It is an equivalent circuit diagram of a 2-bit mode switching switch of a multi-mode multi-core voltage-controlled oscillator of the present invention.

[0038] Figure 5 It is a structural diagram of the programmable frequency divider of the present invention.

[0039] Figure 6 It is a structural diagram of the 2 / 3 frequency divider chain of the present invention. DETAILED DESCRIPTION

[0040] The present invention will be further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and cannot be used to limit the protection scope of the present invention.

[0041] To achieve the above object, the present invention proposes a broadband millimeter wave frequency source circuit based on a multi-mode multi-core oscillator, such as Figure 1 As shown, specifically including:

[0042] Multi-mode multi-core voltage controlled oscillator, phase frequency detector, high resolution charge pump, loop filter and programmable divider.

[0043] The multi-mode multi-core VCO (Voltage Controlled Oscillator) oscillates near the output frequency, and its output signal passes through a programmable divider to form a feedback signal f div , the signal is related to the reference signal f ref In the PFD (Phase Frequency Detector, phase frequency detector), phase comparison is performed. ref When it reaches PFD first, PFD outputs UP signal to control CP (Charge Pump) to charge LF (Loop Filter), making the voltage V ref rises, thereby increasing the output frequency of the VCO; when f div When it reaches PFD first, PFD outputs DN signal, controls CP to discharge LF, so that the voltage V ref decreases, thereby reducing the output frequency of the VCO.

[0044] Figure 2 is the CP circuit of the present invention, VDD is respectively connected to the current source I ref The positive electrode of the MOS tube M3, the source of the MOS tube M4, and the source of the MOS tube M7 are connected, and the current source I ref The negative electrode is connected to the drain of MOS tube M1, the gate of MOS tube M1, the gate of MOS tube M2, and the source of MOS tube M8 respectively; the source of MOS tube M1 and the source of MOS tube M2 are grounded; the drain of MOS tube M2 is connected to the drain of MOS tube M3, the gate of MOS tube M3, and the drain of MOS tube M6 respectively; the gate of MOS tube M6 is connected to the inverse control signal CTB, the source of MOS tube M6 is connected to the drain of MOS tube M7 and the gate of MOS tube M4 respectively; the gate of MOS tube M7 is connected to the control signal CT; the drain of MOS tube M4 is connected to the diffusion area of ​​MOS tube in the first switch SW1 formed by the transmission gate, the gate of NMOS tube in the first switch SW1 is connected to the charging control voltage UP, the gate of PMOS tube in the first switch SW1 is connected to the inverse UP signal UPB, the other diffusion area of ​​MOS tube in the first switch SW1 is connected to the diffusion area of ​​MOS tube in the second switch SW2, and the output current I is obtained. out The gate of the NMOS tube of the second switch SW2 is connected to the discharge control voltage DN, the gate of the PMOS tube of the second switch SW2 is connected to the inverse DN signal DNB, and the other diffusion region of the MOS tube in the second switch SW2 is connected to the drain of the MOS tube M5; the gate of the MOS tube M5 is respectively connected to the drain of the MOS tube M8 and the drain of the MOS tube M9, and the source of the MOS tube M5 and the source of the MOS tube M9 are both grounded; the gate of the MOS tube M8 is connected to the control voltage CT; the gate of the MOS tube M9 is connected to the inverse control voltage CTB.

[0045] The first input control voltage UP and the second input control voltage DN come from the output of the frequency detector and the phase detector. out Flow to the loop filter. M1, M2 and M3 are used to provide the reference for CP output. M4 and M5 are set with m-1 groups of different channel widths. The switch array composed of M6, M7, M8 and M9 controls the working state of M4 and M5 with different channel widths in the form of m-bit binary code. Then the charge pump can achieve current output in steps of 0.1mA, provide different forward gains, and effectively control the frequency source loop.

[0046] like Figure 3 As shown, the multi-mode multi-core VCO includes a power supply, two oscillator cores distributed up and down, and four mode switching switches SW distributed in the southeast, northwest, and northeast directions. e , SW s , SW w and SW n and 4 coupling capacitors C m The oscillator core consists of 4 transformer coils, 2 tuning capacitor arrays cap <n:0>, 4 varactors C var and 2 negative resistance-G m The mode switch is used to control magnetic coupling and electrical coupling, that is, the capacitor C m access method, thereby realizing frequency switching in four different modes.

[0047] Specifically, the transformer coil L 1u , L 2u , L 1d and L 2d For forming magnetic coupling, K m is the coupling coefficient, C m is the coupling capacitor of electrical coupling, negative resistance -G m Used to provide oscillation energy to the resonant cavity and tune the capacitor array cap <n:0>Used to further extend the frequency range in four modes, the varactor C var By controlling the adjustable voltage V tune Realize continuous frequency adjustment.

[0048] When the multi-mode multi-core VCO is in the magnetically coupled even-mode excitation state, the currents in the upper and lower transformer coils are in phase, so the magnetic flux in the center area of ​​the two transformers is added. Since the inductance L of the transformer coil itself is the ratio of the magnetic flux Φ in the coil to the current I flowing through the coil, that is, L = Φ / I, the even-mode equivalent inductance L is obtained. even , L even =L+M, where M represents the mutual inductance between the coils. At the same time, since the capacitance C is the ratio between the charge Q on the capacitor and the voltage U across it, that is, C≡Q / U, the coupling capacitance C m The two ends of C have equal potential. m There is no charge accumulated on the even-mode equivalent capacitance. even =C o , where C o Represents the capacitance of the oscillator core.

[0049] When the multi-mode multi-core VCO is in the case of magnetically coupled odd-mode excitation, the magnetic fluxes in the center areas of the two transformers are equal in magnitude and opposite in direction. After canceling each other out, there is no magnetic flux in the center area. At this time, the odd-mode equivalent inductance is: L odd =LM. At the same time, C and C m The voltage across the two ends is differential, and the odd-mode equivalent capacitance is: C odd =C+C m .

[0050] This results in the following four oscillation frequencies:

[0051]

[0052] Among them, ω1, ω2, ω3, and ω4 represent four oscillation frequencies respectively.

[0053] Figure 4 It is a schematic diagram of 4 mode switching switches, where S M,e , S M,o , S E,e and S E,o Respectively represent the access of magnetically coupled even mode, odd mode and electrically coupled even mode, odd mode. osc1 ~V osc4 Respectively represent the control voltages of the upper and lower oscillator cores connected. Four working modes can be formed: electromagnetic even mode capacitor odd mode, electromagnetic even mode capacitor even mode, electromagnetic odd mode capacitor odd mode and electromagnetic odd mode capacitor even mode oscillation state. By correctly switching to the four working modes, a wider tuning range can be achieved.

[0054] like Figure 5 As shown, the programmable frequency divider includes a high-speed four-frequency divider and a 2 / 3 frequency divider chain, wherein the high-speed four-frequency divider is connected to the multi-mode multi-core VCO to convert the output frequency f VCO After the frequency is divided by four to 7-9.5 GHz, a 2 / 3 divider chain is used to divide the frequency to match the reference clock frequency.

[0055] In this embodiment, the reference frequency is 100 MHz, and the frequency division ratio is set to 280-380 to cover the frequency band of 28-38 GHz.

[0056] like Figure 6 As shown, the 2 / 3 divider chain includes a 1-stage 2 / 3 divider. The input f in From the high-speed 4-divider, the output f of the 1st stage 2 / 3 divider out Transmitted to PFD for frequency and phase discrimination, P0~P l is the l+1-bit frequency division ratio control word, and mod is the mode control signal. For the i-th 2 / 3 frequency divider, when the input frequency division ratio control signal P i and mode control signal mod in_i When both are high level, 3-division is achieved, and 2-division is achieved in other cases.

[0057] In this embodiment, since the maximum frequency division ratio coverage of a level 1 2 / 3 frequency divider can reach 2 l ~2 l+1 -1, it can be calculated that the use of a 6-level 2 / 3 divider chain can meet the requirement of a division ratio of 280 to 380, that is, l=6.

[0058] The frequency source circuit proposed in the present invention can realize a quad-core oscillator and switch between four working modes while occupying only a dual-core area.

[0059] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A broadband millimeter wave frequency source circuit based on a multi-mode multi-core oscillator, characterized in that: include: Multi-mode multi-core voltage-controlled oscillators, frequency and phase detectors, charge pumps, loop filters, and programmable frequency dividers; The multi-mode multi-core voltage-controlled oscillator oscillates near the output frequency, and its output signal passes through a programmable frequency divider to form a feedback signal f div , the signal is related to the reference signal f ref The two signals are compared in phase frequency detector, and a voltage proportional to the phase difference of the two signals is outputted and transmitted to the charge pump to control the charging or discharging of the charge pump. The corresponding current is transmitted to the loop filter and converted into a voltage signal as the control voltage of the multi-mode multi-core voltage-controlled oscillator to control the frequency source to output the correct frequency. The multi-mode multi-core voltage-controlled oscillator includes a power supply, two oscillator cores distributed up and down, and four mode switching switches SW distributed in the southeast, northwest, and northeast directions. e , SW s , SW w and SW n and 4 coupling capacitors C m ;The mode switching switch is used to control magnetic coupling and electric coupling; The charge pump circuit includes eight MOS tubes M1 to M8, a current source I ref , control signal CT, inverse control signal CTB, first switch SW1, charging control voltage UP, inverse UP signal UPB, second switch SW2, discharge control voltage DN and inverse DN signal DNB; M1, M2 and M3 are used to provide a reference for the charge pump output, M6, M7, M8 and M9 constitute a switch array and control the working state of M4 and M5 with different channel widths; The programmable dividers include a high-speed divider-by-four and a 2 / 3 divider chain.

2. The broadband millimeter wave frequency source circuit based on a multi-mode multi-core oscillator according to claim 1, characterized in that: When f ref When it reaches the phase frequency detector first, the phase frequency detector outputs an UP signal to control the charge pump to charge the loop filter, making the voltage V at the output end of the loop filter ref rises, thereby increasing the output frequency of the multi-mode multi-core voltage-controlled oscillator; when f div When it reaches the phase frequency detector first, the phase frequency detector outputs the DN signal, controls the charge pump to discharge the loop filter, and makes the voltage V ref decreases, thereby reducing the output frequency of the multi-mode multi-core voltage-controlled oscillator.

3. The broadband millimeter wave frequency source circuit based on a multi-mode multi-core oscillator according to claim 1, characterized in that: In the multi-mode multi-core voltage-controlled oscillator, the oscillator core includes 4 transformer coils, 2 tuning capacitor arrays cap <n:0>, 4 varactors C var and 2 negative resistance-G m ; When the multi-mode multi-core voltage-controlled oscillator is in the magnetically coupled even-mode excitation state, the currents in the upper and lower transformer coils are in phase, and the magnetic flux in the center area of ​​the two transformers is added; the inductance L of the transformer coil itself is the ratio of the magnetic flux Φ in the coil to the current I flowing through the coil, that is, L = Φ / I, and the even-mode equivalent inductance L is obtained. even for: L even =L+M Where M represents the mutual inductance between the coils; At the same time, since the capacitance C is the ratio between the charge Q on the capacitor and the voltage U across it, that is, C≡Q / U, the coupling capacitance C m The two ends of the circuit have equal potential, and C m There is no charge accumulated on the capacitor, so the even-mode equivalent capacitance is: C even =C o Among them, C even Represents the even-mode equivalent capacitance, C o represents the capacitance of the oscillator core; When the multi-mode multi-core voltage-controlled oscillator is in the case of magnetically coupled odd-mode excitation, the magnetic flux in the center area of ​​the two transformers is equal in magnitude and opposite in direction, and the obtained odd-mode equivalent inductance L odd for: L odd =L-M; At the same time, C and C m The voltage across the two ends is differential, so the odd-mode equivalent capacitance C odd for: C odd =C+C m ; The four oscillation frequencies generated are: Among them, ω1, ω2, ω3, and ω4 represent four oscillation frequencies respectively.

4. The broadband millimeter wave frequency source circuit based on a multi-mode multi-core oscillator according to claim 1, characterized in that: In the circuit of the charge pump, VDD is respectively connected to the positive electrode of the current source Iref, the source of the MOS tube M3, the source of the MOS tube M4, and the source of the MOS tube M7, and the negative electrode of the current source Iref is respectively connected to the drain of the MOS tube M1, the gate of the MOS tube M1, the gate of the MOS tube M2, and the source of the MOS tube M8; the source of the MOS tube M1 and the source of the MOS tube M2 are both grounded; the drain of the MOS tube M2 is respectively connected to the drain of the MOS tube M3, the gate of the MOS tube M3, and the drain of the MOS tube M6; the gate of the MOS tube M6 is connected to the anti-control signal CTB, the source of the MOS tube M6 is respectively connected to the drain of the MOS tube M7 and the gate of the MOS tube M4; the gate of the MOS tube M7 is connected to the control signal CT; the drain of the MOS tube M4 is connected to the diffusion region of the MOS tube in the first switch SW1 formed by the transmission gate, and the first The gate of the NMOS tube in the switch SW1 is connected to the charging control voltage UP, the gate of the PMOS tube in the first switch SW1 is connected to the inverted UP signal UPB, the other diffusion region of the MOS tube in the first switch SW1 is connected to the diffusion region of the MOS tube in the second switch SW2, and the output current Iout is obtained; the gate of the NMOS tube in the second switch SW2 is connected to the discharge control voltage DN, the gate of the PMOS tube in the second switch SW2 is connected to the inverted DN signal DNB, the other diffusion region of the MOS tube in the second switch SW2 is connected to the drain of the MOS tube M5; the gate of the MOS tube M5 is respectively connected to the drain of the MOS tube M8 and the drain of the MOS tube M9, and the source of the MOS tube M5 and the source of the MOS tube M9 are both grounded; the gate of the MOS tube M8 is connected to the control voltage CT; the gate of the MOS tube M9 is connected to the inverted control voltage CTB.

5. The broadband millimeter wave frequency source circuit based on multi-mode multi-core oscillator according to claim 1, characterized in that: In the programmable divider, the 2 / 3 divider chain includes a 1-stage 2 / 3 divider, the input of the 1-stage 2 / 3 divider comes from a high-speed 4-divider, and the output of the 1-stage 2 / 3 divider is transmitted to a frequency detector for frequency and phase detection.

6. The broadband millimeter wave frequency source circuit based on multi-mode multi-core oscillator according to claim 5, characterized in that: For the 2 / 3 frequency divider, when the input frequency division ratio control signal and the mode control signal are both at high level, frequency division by 3 is achieved, and in other cases, frequency division by 2 is achieved.

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