Modulation device and modulation method

Abstract

To provide a modulation device and a modulation method capable of generating a wideband FM signal by suppressing frequency variation with a low cost electric component.SOLUTION: According to the present invention, a modulation device includes a multiplication PLL for generating a multiplication FM signal by multiplying N times a center frequency fck / L of an original FM signal generated on the basis of a system clock being a frequency fck and a frequency band W, an LO generation heterodyne PLL for controlling a VCO such that a difference frequency between a local frequency-divided signal of a frequency fLO / M generated from a local signal of a frequency fLO outputted by the VCO and a clock frequency-divided signal of a frequency fck / K approaches a frequency fxo of a reference signal, and a mixer for lowering the multiplication FM signal only by the frequency fLO to output it as a wideband FM signal.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a modulation device and a modulation method for converting a multi-channel signal such as a video signal into a broadband FM signal.

Background Art

[0002] Patent Document 1 discloses an optical heterodyne broadband FM modulation method. This method generates a broadband FM signal as follows. An electrical signal amplitude-modulated by a transmission signal is input and an optically frequency-modulated signal is output, and a local oscillation light having an optical frequency different from that of this optically frequency-modulated signal is multiplexed with this optically frequency-modulated signal. By outputting an electrical signal having a frequency equal to the difference between the optical frequencies of these two multiplexed optical signals from these two multiplexed optical signals, the amplitude-modulated electrical signal is converted into a frequency-modulated electrical signal. Noise caused by fluctuations in the optically frequency-modulated signal and the local oscillation light is removed from this electrical signal.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] The method of Patent Document 1 has problems in that expensive optical components are required and the circuit configuration becomes complicated for compensating for characteristic variations. Specifically, in the method of Patent Document 1, in order to obtain a broadband FM modulation signal, it is necessary to multiplex two optical frequencies and perform heterodyne detection, which is composed of expensive optical components and it is difficult to reduce the cost. And, in order to suppress FM frequency fluctuations, temperature control of the laser diode and a pilot signal for FM modulation are required, an increase in power consumption is inevitable, and a separation circuit for the pilot signal is also indispensable.

[0005] On the other hand, a technique for generating a broadband FM signal using low-cost electrical components instead of optical components that cause the above problems is also known (see, for example, Patent Document 2). The method of Patent Document 2 generates a broadband FM signal using electrical components (voltage-frequency conversion of a VCO oscillator). However, the characteristic variations of the VCO directly result in variations in the characteristics of the generated FM signal, and it is difficult to suppress FM frequency variations only with the method of Patent Document 2.

[0006] Therefore, an object of the present invention is to provide a modulation device and a modulation method that can generate a broadband FM signal with suppressed frequency variations using low-cost electrical components in order to solve the above problems.

Means for Solving the Problems

[0007] In order to achieve the above object, the modulation device and modulation method according to the present invention generate a low-frequency original FM signal with a digital modulation circuit (DDS) and convert it into a target high-frequency broadband FM signal using a frequency multiplication circuit based on a PLL.

[0008] Specifically, the modulation device according to the present invention Original FM signal center frequency f ck Generated based on the system clock of f, multiplied by N times the frequency band W of the original FM signal to generate a multiplied FM signal, and a multiplied phase-locked loop (PLL), ck / L and frequency band W to generate a multiplied FM signal, and a multiplied phase-locked loop (PLL), A local divided signal of frequency f LO Generated from the local signal output by the voltage-controlled oscillator (VCO), and a clock divided signal of frequency f LO / M and a clock divided signal of frequency f ck / K generated from the system clock, and the difference frequency (f ck / K - f LO / M) approaches the reference signal frequency f xo To control the VCO so that the frequency f of the local signal LO Changes, and a LO generation heterodyne PLL that changes the frequency f of the local signal, The center frequency of the multiplied FM signal is lowered by the frequency f of the local signal LO And a mixer that outputs it as a broadband FM signal. comprises. However, the K, the L, the M, and the N are positive numbers.

[0009] Also, the modulation method according to the present invention frequency f ck generates a multiplied FM signal by multiplying the center frequency f of the original FM signal generated based on the system clock that is ck / L by N times the frequency band W, The frequency f output by the voltage controlled oscillator (VCO) LO generates a local divided signal of frequency f LO / M from the local signal and the frequency f ck / K of the clock divided signal generated from the system clock, and the difference frequency (f ck / K - f LO / M) is used to control the VCO so as to approach the frequency f of the reference signal xo and change the frequency f of the local signal, and LO output a wideband FM signal obtained by reducing the center frequency of the multiplied FM signal by the frequency f of the local signal by that amount. LO This is characterized by. However, the K, the L, the M, and the N are positive numbers. However, the K, the L, the M, and the N are positive numbers.

[0010] This modulation device and method generate an FM signal using a low-frequency DDS and multiply it using a PLL in order to obtain a wideband FM modulation signal, and can be realized with low-cost electrical components. And, in order to suppress FM frequency fluctuations, a heterodyne PLL is used in combination, and the FM frequency can be controlled with a high-precision electrical signal source.

[0011] Therefore, the present invention can provide a modulation device and a modulation method that can generate a wideband FM signal with suppressed frequency fluctuations using low-cost electrical components.

[0012] In addition, the modulation device and method according to the present invention are characterized in that the K, the L, the M, and the N can be arbitrarily changed from a setter. Parameters such as the division frequency and the FM modulation degree (modulation index) can be switched, and the versatility is high.

[0013] In particular, when the K, the L, the M, and the N are in the relationship of N:L = M:K, the center frequency of the wideband FM modulation signal can be set only by the division frequency M of the LO generation heterodyne PLL regardless of the system clock of the device.

[0014] Note that the above inventions can be combined as much as possible.

Effect of the Invention

[0015] The present invention can provide a modulation device and a modulation method capable of generating a wideband FM signal with suppressed frequency fluctuation using low-cost electrical components.

Brief Description of the Drawings

[0016]

Figure 1

Figure 2

Embodiment for Carrying Out the Invention

[0017] Embodiments of the present invention will be described with reference to the accompanying drawings. The embodiments described below are examples of the present invention, and the present invention is not limited to the following embodiments. In the present specification and drawings, components having the same reference numerals indicate the same components as each other.

[0018] [Embodiment 1] FIG. 1 is a diagram for explaining the modulation device 301 of the present embodiment. The modulation device 301 is the center frequency f of the original FM signal Sig2 generated based on the clock signal Sig1 of the frequency f from the system clock 11 ck of ckA multiplication phase-locked loop (PLL) 16 that multiplies / L and the frequency band W by N to generate a multiplied FM signal Sig3, The frequency f output by the voltage-controlled oscillator (VCO) 157 LO From the local signal Sig6 of, the frequency f LO / M local divided signal Sig7 and the frequency f generated from the clock signal Sig1 ck / K clock divided signal Sig4 of, and the difference frequency (f ck / K - f LO / M) controls the VCO 157 so as to approach the frequency f of the reference signal Sig5 from the high-precision signal source 13, and changes the frequency f of the local signal Sig6 XO LO generation heterodyne PLL 15 that, LO And a mixer 17 that lowers the center frequency of the multiplied FM signal Sig3 by the frequency f of the local signal Sig6 LO And outputs it as a wideband FM signal Sig8, CK Is provided. However, in this embodiment, f CK / K = f CK / L = 750 MHz, M = N = 16 will be described as an example.

[0019] The system clock 11 outputs a clock signal Sig1 having a frequency f CK . The direct digital synthesis (DDS) 12 collectively FM-modulates a plurality of input signals nch and outputs the original FM signal Sig2. The center frequency (carrier frequency) of the original FM signal Sig2 is 1 / L of the frequency f of the clock signal Sig1 CK And is 750 MHz. The frequency band W of the original FM signal Sig2 is ±125 MHz (250 MHz).

[0020] The multiplication PLL 16 multiplies the original FM signal Sig2 by 16 and outputs a multiplied FM signal Sig3. That is, the multiplied FM signal Sig3 has the center frequency f of the original FM signal Sig2 CKThe center frequency (carrier frequency) is 12 GHz, which is 16 times that of / L (= 750 MHz), and the frequency band is 2 GHz, which is 16 times the frequency band W (±125 MHz) of the original FM signal Sig2.

[0021] The LO generation heterodyne PLL15 includes a frequency divider 151, a mixer 152, a low-pass filter 153, a comparator 154, a phase comparator and charge pump 155, a loop filter 156, and a VCO 157.

[0022] The frequency divider 151 divides the frequency f of the local signal Sig6 output by the VCO 157 by 1 / M. In this embodiment, f LO = 9 GHz (desired value) and M = 16. Therefore, the frequency of the signal Sig7 is f LO / M, which is 562.5 MHz. LO / M is 562.5 MHz. The frequency divider 14 divides the frequency f of the clock signal Sig1 output by the system clock 11 by 1 / K and outputs the signal Sig4. In this embodiment, the frequency of the signal Sig4 is f CK / K, which is 750 MHz. CK / K is 750 MHz.

[0023] The mixer 152 mixes the signal Sig4 and the signal Sig7. The low-pass filter 153 transmits only the difference component (f CK / K - f LO / M = 750 MHz - 562.5 MHz = 187.5 MHz) among the signals mixed by the mixer 152. The comparator 154 converts the difference component (sine wave) output from the low-pass filter 153 into a rectangular wave.

[0024] The high-precision signal source 13 is, for example, a crystal oscillator and outputs the frequency f of the reference signal Sig5. In this embodiment, the frequency f XO = 187.5 MHz. XO = 187.5 MHz. The phase comparator and charge pump 155 compare the rectangular wave output by the comparator 154 with the reference signal Sig5, and output a current according to the deviation between the frequency of the rectangular wave output by the comparator 154 and the frequency of the reference signal Sig5. The loop filter 156 converts the current into a voltage such that the deviation becomes small and inputs it to the VCO 157.

[0025] The LO generation heterodyne PLL 15 can output a stable local signal Sig6 at a desired frequency f LO (9 GHz in the case of this embodiment) to the mixer 17.

[0026] The mixer 17 mixes the frequency-multiplied FM signal Sig3 from the frequency-multiplier PLL 16 and the local signal Sig6 from the LO generation heterodyne PLL 15, and outputs the difference component as a wideband FM signal Sig8. In the case of this embodiment, since the frequency-multiplied FM signal Sig3 is 12 GHz ± 2 GHz and the local signal Sig6 is 9 GHz, the wideband FM signal Sig8 has a center frequency of 3 GHz and a frequency band of 4 GHz (± 2 GHz).

[0027] That is, the modulation device 301 can output a wideband FM signal Sig8 centered on the frequency obtained by multiplying the frequency of the reference signal Sig5 output by the high-precision signal source 13 by the frequency multiplication factor of the frequency-multiplier PLL 16.

[0028] The modulation device 301 can be composed of only an electric circuit. That is, since the modulation device 301 does not use expensive optical components, a temperature adjustment circuit and a pilot signal separation circuit are not required, and low power consumption and miniaturization can be achieved. In particular, the modulation device 301 can integrate the configuration shown by the broken line A in FIG. 1, and further miniaturization is possible. Furthermore, since the modulation device 301 has a configuration in which a low-frequency FM signal generated by a commercially available DDS is multiplied by a PLL, cost reduction can be achieved. In particular, the modulation device 301 can suppress variations in the frequency of the wideband FM signal Sig8 at low cost by operating based on the high-precision signal source 13.

[0029] [Embodiment 2] In Embodiment 1, for the sake of easy understanding of the operation of the modulation device of the present invention, M = N = 16, f CK / L = f CK / K = 750 MHz was described. In the present embodiment, a modulation device 302 with generalized parameters will be described. FIG. 2 is a diagram for explaining the modulation device 302. The modulation device 302 further includes a setter 18 for arbitrarily changing the parameters K, L, M, and N with respect to the modulation device 301 in FIG. 1. Note that K, L, M, and N are positive numbers.

[0030] As described in the explanation of Embodiment 1, since the frequency f XO of the reference signal Sig5 of the high-precision signal source 13 is the difference between the signal Sig4 and the signal Sig5,

Equation

Equation

[0031] Since the center frequency (carrier frequency) of the original FM signal Sig2 output by the DDS 12 is f CK / L, the center frequency (carrier frequency) of the broadband FM signal Sig8 output by the mixer 17 is

Equation

[0032] By appropriately adjusting the parameters (division ratio K, FM modulation index L, division ratio M, and multiplication factor N) with the setter 18, the frequency of the broadband FM signal Sig8 can be changed, and a hard function corresponding to the application requirements can be realized.

[0033] In particular, if N:L = M:K, the frequency of the broadband FM signal Sig8 is Mf XO so that it can be determined only by the frequency f XO of the reference signal Sig5 and the division ratio M. That is, the frequency (fCK / K) = center frequency (f CK / L) of the original FM signal Sig2 (i.e., if L = K), by setting the division ratio M = multiplication factor N, the influence of the frequency fluctuation of the system clock 11 can be avoided.

Industrial Applicability

[0034] The present invention can be applied to a transmitter for transmitting a broadband FM optical signal for cable television and a broadband FM signal transmitter for collectively transmitting multiplexed large-capacity data.

Explanation of Signs

[0035] 11: System clock 12: Direct Digital Synthesis (DDS) 13: High-precision signal source 14: Divider 15: LO generation heterodyne PLL 16: Multiplication PLL 151: Divider 152: Mixer 153: Low-pass filter 154: Comparator 155: Phase comparator and charge pump 156: Loop filter 157: VCO 301, 302: Modulator

Claims

1. frequency f ｃｋ The center frequency f of the original FM signal generated based on the system clock is ｃｋ a multiplication phase-locked loop (PLL) for multiplying the frequency band W by N to generate a multiplied FM signal; The frequency f output by the voltage controlled oscillator (VCO) ＬＯ The frequency f generated from the local signal ＬＯ / M and the frequency f generated from the system clock ｃｋ / K clock division signal (f ｃｋ / K-f ＬＯ / M) is the frequency f of the reference signal ｘｏ and controlling the VCO so that the frequency of the local signal approaches ＬＯ an LO generating heterodyne PLL that varies The multiplied FM signal is converted to a frequency f ＬＯ a mixer for reducing the frequency by a factor of 10 and outputting the resulting wideband FM signal; A setting device for arbitrarily changing the K, L, M, and N; A modulation device comprising: Here, K, L, M, and N are positive numbers.

2. The K, the L, the M, and the N N:L=M:K 2. The modulation device according to claim 1, wherein the relationship is:

3. frequency f ｃｋ The center frequency f of the original FM signal generated based on the system clock is ｃｋ / L and frequency band W are multiplied by N to generate a multiplied FM signal; The frequency f output by the voltage controlled oscillator (VCO) ＬＯ The frequency f generated from the local signal ＬＯ / M and the frequency f generated from the system clock ｃｋ / K clock division signal (f ｃｋ / K-f ＬＯ / (M) is the frequency f of the reference signal ｘｏ control the VCO so as to approach the frequency f ＬＯ of the local signal and change the frequency f of the local signal, output a wideband FM signal obtained by reducing the multiplied FM signal by the frequency f ＬＯ of the local signal, and arbitrarily change the K, the L, the M, and the N from a setter A modulation method characterized by the above. However, the K, the L, the M, and the N are positive numbers.

4. The modulation method according to claim 3, characterized in that the K, the L, the M, and the N satisfy N:L = M:K ​

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