JP2007103986A - Stereo modulator and fm stereo modulator employing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a stereo modulator capable of autonomously decreasing a phase difference between a pilot signal and a subcarrier, and to provide an FM stereo modulator employing the same. <P>SOLUTION: The stereo modulator in an embodiment disclosed herein includes: (1) a multiplexer for generating a multiplexed signal resulting from multiplexing a left side signal and a right side signal on the basis of the subcarrier; (2) a mixer for generating a composite signal resulting from the composition of the multiplexed signal with the pilot signal; (3) a first frequency divider for generating a frequency-divided subcarrier resulting from the application of 1/2 frequency division to the subcarrier; (4) a phase comparison unit for generating a phase comparison signal representing a phase difference between the frequency-divided subcarrier and the pilot signal; (5) a phase shifter for generating an adjusted subcarrier resulting from the adjustment of the phase of the subcarrier to decrease the phase difference on the basis of the phase comparison signal; and (6) a second frequency divider for generating the pilot signal resulting from the application of 1/2 frequency division to the adjusted subcarrier. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a stereo modulator and an FM stereo modulator using the stereo modulator.

  There is known an FM stereo transmitter that multiplex-modulates two left and right audio signals and wirelessly transmits the modulated signals. A pilot tone method is known as a multiplex modulation method. An FM stereo transmitter using this pilot tone method has an FM stereo modulator, and this FM stereo modulator is composed of a stereo modulator and a frequency modulator. The stereo modulator amplitude-modulates the difference signal (LR) between the left signal L and the right signal R based on the 38 kHz subcarrier, and the amplitude-modulated difference signal (LR) and sum signal (L + R). And a 19 kHz pilot signal to generate a composite signal. The frequency modulator frequency-modulates the main carrier according to the composite signal.

  By the way, the FM stereo receiver using the pilot tone method reproduces a 38 kHz reproduction subcarrier from the pilot signal extracted from the reception signal, and based on the reproduction subcarrier, a difference signal (LR) and a sum signal (L + R) are reproduced. The reproduction left signal Lr and the reproduction right signal Rr are reproduced. Therefore, if the phase of the pilot signal is shifted from the phase of the subcarrier for generating the difference signal (L−R) and the sum signal (L + R) in the stereo modulator, the reproduced left signal is output in the FM stereo receiver. The channel separation characteristics between Lr and the reproduction right signal Rr are degraded. That is, not only the left signal L but also the right signal R is mixed in the reproduced left signal Lr, and not only the right signal R but also the left signal L is mixed in the reproduced right signal Rr.

In order to reduce deterioration of channel separation characteristics in the FM stereo receiver, the stereo modulator may match the phase of the pilot signal and the phase of the subcarrier. Patent Document 1 describes an FM stereo transmitter having a stereo modulator capable of adjusting the phase of a pilot signal.
JP 2000-228635 A

  However, since the stereo modulator described in Patent Document 1 has an external variable capacitance element and adjusts the phase of the pilot signal by changing the capacitance of this element, it takes time for the phase adjustment work. In addition, the phase separation between the pilot signal and the subcarrier is caused by an external factor such as temperature fluctuation, so that the channel separation characteristic in the FM stereo receiver is deteriorated.

  Accordingly, an object of the present invention is to provide a stereo modulator capable of autonomously reducing the phase difference between a pilot signal and a subcarrier, and an FM stereo modulator using the stereo modulator.

  The first stereo modulator of the present invention includes (1) a sum signal representing a sum of a left signal and a right signal, and a difference signal obtained by amplitude-modulating a difference between the left signal and the right signal with a subcarrier. A multiplexer that generates a multiplexed signal by multiplexing based on the subcarrier; and (2) a mixer that generates a composite signal by combining the multiplexed signal and the pilot signal output from the multiplexer; (3) a first divider that generates a divided subcarrier by dividing the subcarrier by 1/2, and (4) a divided subcarrier and a pilot signal output from the first divider. A phase comparison unit that generates a phase comparison signal that represents a phase difference between the subcarrier and an adjustment sub-phase that adjusts the phase of the subcarrier to reduce the phase difference based on the phase comparison signal output from the phase comparison unit The shift that generates the carrier wave And vessels, and a (6) by circumferential 1/2 adjustment subcarriers output from the phase shifter, a second frequency divider for generating a pilot signal.

  According to the first stereo modulator, the phase comparison signal output from the phase comparison unit is obtained by dividing the subcarrier divided by 1/2 by the first frequency divider and the pilot signal. It is changed according to the phase difference. The phase of the input subcarrier is adjusted by the phase shifter so as to reduce this phase difference, and an adjusted subcarrier is generated. The adjusted subcarrier output from the phase shifter is divided by ½ by the second frequency divider to generate a pilot signal. Therefore, according to the first stereo modulator, the phase difference between the subcarrier and the pilot signal is reduced by the processing in the loop including the phase comparator, the phase shifter, and the second frequency divider. The phase of the pilot signal is adjusted autonomously.

  According to the first stereo modulator, a composite signal in which a multiplexed signal multiplexed based on an input subcarrier and a pilot signal having a small phase difference with respect to the subcarrier is generated is generated. Can do.

  The phase comparison unit in the first stereo modulator generates a phase comparison signal having a pulse width corresponding to the phase difference between the frequency-divided subcarrier output from the first frequency divider and the pilot signal. The phase shifter includes (1) a lock detector that outputs a first level detection signal when the pulse width of the phase comparison signal output from the phase comparison unit is greater than the period of the reference clock, and (2) a lock detector. And a counter that outputs a digital signal representing a count value counted at a reference clock period interval when the detection signal output from the first level is (3) a phase comparison signal output from the phase comparison unit; A shift register that generates an adjusted subcarrier by shifting the phase of the subcarrier by a phase shift amount corresponding to the value of the digital signal output from the counter so that the pulse width is narrowed. Good.

  According to this configuration, the pulse width of the phase comparison signal output from the phase comparison unit is equal to the phase difference between the divided subcarrier obtained by dividing the subcarrier by 1/2 by the first frequency divider and the pilot signal. Will be changed according to The phase of the input subcarrier is adjusted by the phase shifter so that the pulse width of the phase comparison signal is narrowed, and the adjusted subcarrier is generated. Therefore, according to this configuration, the phase difference between the pilot signal generated from the adjusted subcarrier and the subcarrier becomes small.

  The second stereo modulator of the present invention includes (1) a sum signal representing the sum of the left signal and the right signal, and a difference signal obtained by amplitude-modulating the difference between the left signal and the right signal with a subcarrier. A multiplexer that generates a multiplexed signal by multiplexing based on the subcarrier; and (2) a mixer that generates a composite signal by combining the multiplexed signal and the pilot signal output from the multiplexer; (3) a phase comparator that generates a phase comparison signal representing the phase difference between the subcarrier and the adjusted subcarrier; and (4) the phase difference is reduced based on the phase comparison signal output from the phase comparator. A phase shifter that generates an adjusted subcarrier in which the phase of the subcarrier is adjusted; and (4) a frequency divider that generates a pilot signal by dividing the adjusted subcarrier output from the phase shifter by 1/2. With There.

  According to the second stereo modulator, the phase comparison signal output from the phase comparison unit is changed according to the phase difference between the subcarrier and the adjusted subcarrier obtained by adjusting the phase of the subcarrier. The phase of the input subcarrier is adjusted by the phase shifter so as to reduce this phase difference, and an adjusted subcarrier is generated. This adjusted subcarrier is divided by ½ by the frequency divider to generate a pilot signal. Therefore, according to the second stereo modulator, the phase of the pilot signal is autonomously set so that the phase difference between the subcarrier and the pilot signal is reduced by the processing in the loop including the phase comparison unit and the phase shifter. Adjusted.

  According to the second stereo modulator, a composite signal in which a multiplexed signal multiplexed based on an input subcarrier and a pilot signal having a small phase difference with respect to the subcarrier is generated is generated. Can do.

  The phase comparison unit in the second stereo modulator generates a phase comparison signal having a pulse width corresponding to the phase difference between the subcarrier and the adjusted subcarrier. The phase shifter includes (1) a lock detector that outputs a first level detection signal when the pulse width of the phase comparison signal output from the phase comparison unit is greater than the period of the reference clock, and (2) a lock detector. And a counter that outputs a digital signal representing a count value counted at a reference clock period interval when the detection signal output from the first level is (3) a phase comparison signal output from the phase comparison unit; A shift register that generates an adjusted subcarrier by shifting the phase of the subcarrier by a phase shift amount corresponding to the value of the digital signal output from the counter so that the pulse width is narrowed. Good.

  According to this configuration, the pulse width of the phase comparison signal output from the phase comparison unit is changed according to the phase difference between the subcarrier and the adjusted subcarrier obtained by adjusting the phase of the subcarrier. The phase of the input subcarrier is adjusted by the phase shifter so that the pulse width of the phase comparison signal is narrowed, and the adjusted subcarrier is generated. Therefore, according to this configuration, the phase difference between the pilot signal generated from the adjusted subcarrier and the subcarrier becomes small.

  The FM stereo modulator of the present invention includes (1) any one of the above stereo modulators, and (2) frequency-modulating the main carrier according to the composite signal output from the stereo modulator. And a frequency modulator to be generated.

  According to the FM stereo modulator, the main carrier is frequency-modulated in accordance with the composite signal in which the pilot signal having a small phase difference with respect to the input subcarrier is synthesized, and a frequency modulation signal is generated. , It is possible to reduce deterioration of channel separation characteristics in the FM stereo receiver.

  ADVANTAGE OF THE INVENTION According to this invention, the stereo modulator which can make small the phase difference of a pilot signal and a subcarrier autonomously, and FM stereo modulator using the same are provided.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals.

[First Embodiment]
FIG. 1 is a circuit diagram of an FM stereo transmitter including a stereo modulator and an FM stereo modulator according to the first embodiment of the present invention. The FM stereo transmitter 10 includes two audio units 12 and 14, an oscillation unit 16, two frequency dividers 18 and 20, an FM stereo modulator 22, an amplifier 24, and an antenna 26.

  The audio unit 12 is an audio unit for the left audio signal. The audio unit 12 includes a pre-emphasis unit 30, a limiter 32, and a low-pass filter (hereinafter referred to as LPF) 34.

  The pre-emphasis unit 30 increases the level of the high-frequency component of the input left audio signal Lin. That is, the pre-emphasis unit 30 amplifies the high frequency component of the left audio signal Lin. When the FM stereo transmitter 10 includes the pre-emphasis unit 30, the S / N ratio of the reproduced left audio signal reproduced by the FM stereo receiver can be improved. Specifically, when the level of the high frequency component of the left audio signal Lin is increased in the FM stereo transmitter 10 and the level of the high frequency component of the reproduced left audio signal is decreased (deemphasis) in the FM stereo receiver, the reproduced left audio is reproduced. Since the level of the noise component superimposed on the signal and distributed in the high range is also weakened, the S / N ratio of the reproduced left audio signal is improved. The output terminal of the pre-emphasis unit 30 is connected to the input terminal of the limiter 32.

  The limiter 32 limits the output signal from the pre-emphasis unit 30 to a predetermined value or less. Specifically, when the level of the high frequency component of the left audio signal Lin strengthened in the pre-emphasis unit 30 is higher than a predetermined value, the level of the high frequency component is limited to a predetermined value and output. The predetermined value may be determined as appropriate. The output terminal of the limiter 32 is connected to the input terminal of the LPF 34.

  The LPF 34 generates the left signal L by reducing high frequency noise of the output signal from the limiter 32. The output terminal of the LPF 34 is connected to the FM stereo modulator 22.

  The audio unit 14 is an audio unit for the right audio signal. The audio unit 14 includes a pre-emphasis unit 31, a limiter 33, and a low-pass filter (hereinafter referred to as LPF) 35.

  The pre-emphasis unit 31 is the same as the pre-emphasis unit 30 and increases the level of the high frequency component of the input right audio signal Rin. That is, the pre-emphasis unit 31 amplifies the high frequency component of the input right audio signal Rin. If the FM stereo transmitter 10 has the pre-emphasis unit 31, the S / N ratio of the reproduced right audio signal reproduced by the FM stereo receiver can be improved. The output terminal of the pre-emphasis unit 31 is connected to the input terminal of the limiter 33.

  The limiter 33 is the same as the limiter 32, and outputs an output signal from the pre-emphasis unit 31 by limiting it to a predetermined value or less. The output terminal of the limiter 33 is connected to the input terminal of the LPF 35.

  The LPF 35 is the same as the LPF 34 and generates the right signal R by reducing the high frequency noise of the output signal from the limiter 33. The output terminal of the LPF 35 is connected to the FM stereo modulator 22.

  The oscillation unit 16 includes an oscillator 36, a crystal resonator 37, and two capacitive elements 38 and 39. A crystal resonator 37 is connected between the two terminals of the oscillator 36. A capacitive element 38 is connected between one terminal of the oscillator 36 and a power supply line (for example, ground line) 40, and a capacitive element 39 is connected between the other terminal of the oscillator 36 and the power supply line 40. Has been. The oscillator 16 generates a reference clock C of 19 MHz, for example. The output terminal of the oscillating unit 16 is connected to the input terminal of the frequency divider 18.

  The frequency divider 18 divides the reference clock C output from the oscillation unit 16 to generate a 38 kHz subcarrier Ws. The output terminal of the frequency divider 18 is connected to the input terminal of the frequency divider 20. The frequency divider 20 divides the 38 kHz sub-carrier wave Ws to generate a divided clock of 20 kHz, for example. The frequency-divided clock, the reference clock C, and the subcarrier Ws are input to the FM stereo modulator 22.

  The FM stereo modulator 22 multiplexes the left signal L output from the audio unit 12 and the right signal R output from the audio unit 14 based on the subcarrier Ws from the frequency divider 18, and then multiplexes the multiplexed signal. The composite signal and the pilot signal Sp are combined to generate a composite signal, and the main carrier is frequency-modulated based on the composite signal to generate a frequency modulation signal. Details of the FM stereo modulator 22 will be described later. The output terminal of the FM stereo modulator 22 is connected to the input terminal of the amplifier 24.

  The amplifier 24 amplifies the frequency modulation signal output from the FM stereo modulator 22. The output terminal of the amplifier 24 is connected to the input terminal of the antenna 26. The antenna 26 outputs an electromagnetic wave corresponding to the amplified frequency modulation signal.

  Next, an FM stereo modulator according to the first embodiment of the present invention will be described. The FM stereo modulator 22 includes a stereo modulator 50 and a frequency modulator 52 according to the first embodiment of the present invention.

  The stereo modulator 50 multiplexes the left signal L and the right signal R based on the subcarrier Ws, and then synthesizes the multiplexed signal and the pilot signal Sp to generate a composite signal. For this purpose, the stereo modulator 50 includes a multiplexer (MPX) 54, a mixer (MIX) 56, a first frequency divider 58, a phase comparator 60, a phase shifter 62, and a second frequency divider 64. ing.

  The multiplexer 54 receives the left signal L, the right signal R, and the subcarrier Ws. The multiplexer 54 generates a sum signal (L + R) representing the sum of the left signal L and the right signal R, and a difference signal (LR) obtained by amplitude-modulating the difference between the left signal L and the right signal R with the subcarrier Ws. Then, a multiplexed signal is generated by multiplexing based on the subcarrier Ws. When the frequency range of the left signal L and the right signal R is, for example, 50 Hz to 15 kHz, the frequency range of the sum signal (L + R) is 50 Hz to 15 kHz, and the frequency of the amplitude-modulated difference signal (LR) The range is 38 kHz ± 15 kHz (23 kHz to 53 kHz).

  The multiplexer 54 is, for example, a left / right switching type multiplexer. That is, the multiplexer 54 includes a changeover switch for switching the connection between the output terminal and the two input terminals. This change-over switch switches the connection between the output terminal and the two input terminals based on the subcarrier Ws so that the left signal L and the right signal R are alternately output. Here, when the angular velocity corresponding to the changeover cycle is ω, the left signal passing through the changeover switch is expressed as “L (1 + cosωt)”, and the right signal passing through the changeover switch is expressed as “R (1-cosωt)”. Is done. The multiplexed signal generated at the output terminal is represented by the sum of these signals, and is represented as “(L + R) + (LR) cosωt”. As apparent from this, the multiplexer 54 multiplexes the sum signal (L + R) and the amplitude-modulated difference signal “(LR) cosωt”. The output terminal of the multiplexer 54 is connected to the input terminal of the mixer 56.

  In addition to the multiplexed signal output from the multiplexer 54, the pilot signal Sp is input to the mixer 56. The mixer 56 generates a composite signal by synthesizing the multiplexed signal and the pilot signal Sp. The output terminal of the mixer 56 is connected to the frequency modulator 52.

  The pilot signal Sp is generated from the subcarrier Ws by the first frequency divider 58, the phase comparison unit 60, the phase shifter 62, and the second frequency divider 64.

  The first frequency divider 58 generates a divided subcarrier Wsd by dividing the subcarrier Ws by 1/2. The output terminal of the first frequency divider 58 is connected to one input terminal of the phase comparison unit 60.

  The pilot signal Sp is input to the other input terminal of the phase comparison unit 60. The phase comparison unit 60 generates a phase comparison signal Spc that represents the phase difference between the frequency-divided subcarrier Wsd output from the first frequency divider 58 and the pilot signal Sp. For example, the phase comparison unit 60 generates a pulse corresponding to the phase difference between the frequency-divided subcarrier Wsd and the pilot signal Sp based on the frequency-divided subcarrier Wsd and the pilot signal Sp output from the first frequency divider 58. A phase comparison signal Spc having a width is generated. Details of the phase comparison unit 60 will be described later. The output terminal of the phase comparison unit 60 is connected to the phase shifter 62.

  The subcarrier Ws is input to the input terminal of the phase shifter 62. Based on the phase comparison signal Spc output from the phase comparator 60, the phase shifter 62 adjusts the phase of the subcarrier Ws so that the phase difference between the divided subcarrier Wsd and the pilot signal Sp becomes small. An adjusted subcarrier Wsa is generated. For example, the phase shifter 62 adjusts the phase of the subcarrier Ws so that the pulse width of the phase comparison signal Spc output from the phase comparator 60 is narrowed, and generates the adjusted subcarrier Wsa. Details of the phase shifter 62 will be described later. The output terminal of the phase shifter 62 is connected to the input terminal of the second frequency divider 64.

  The second frequency divider 64 divides the adjusted subcarrier Wsa output from the phase shifter 62 by 1/2 to generate a pilot signal Sp.

  In this manner, a 19 kHz pilot signal Sp obtained by dividing the 38 kHz subcarrier Ws by 1/2 is generated. The phase comparison unit 60, the phase shifter 62, and the second frequency divider 64 constitute a feedback circuit, and the phase of the pilot signal Sp is reduced so that the phase difference between the pilot signal Sp and the subcarrier Ws becomes small. Adjust.

  Next, the phase comparison unit 60 will be described in detail. FIG. 2 is a circuit diagram of the phase comparison unit. The phase comparison unit 60 includes two comparators 70 and 72 and a phase comparator 74. The frequency-divided subcarrier Wsd is input to the plus input terminal of the comparator 70. The negative input terminal of the comparator 70 is connected to one terminal of the reference voltage source 76, and the reference voltage output from the reference voltage source 76 is input to the negative input terminal of the comparator 70. The other terminal of the reference voltage source 76 is connected to the power supply line 40. The comparator 70 generates a rectangular wave by comparing the level of the divided subcarrier Wsd with the level of the reference voltage. The output terminal of the comparator 70 is connected to one input terminal of the phase comparator 74.

  The pilot signal Sp is input to the plus input terminal of the comparator 72. The negative input terminal of the comparator 72 is connected to one terminal of the reference voltage source 76, and the reference voltage output from the reference voltage source 76 is input to the negative input terminal of the comparator 72. The comparator 72 generates a rectangular wave by comparing the level of the pilot signal Sp with the level of the reference voltage. The output terminal of the comparator 72 is connected to the other input terminal of the phase comparator 74.

  The phase comparator 74 generates a phase comparison signal Spc having a pulse width corresponding to the phase difference between the rectangular wave output from the comparator 70 and the rectangular wave output from the comparator 72. The output terminal of the phase comparator 74 is connected to the phase shifter 62.

  FIG. 3 shows signal waveforms of main parts of the phase comparison unit 60 and the phase shifter 62. FIG. 3A shows a rectangular wave output from the comparator 70, and FIG. 3B shows a rectangular wave output from the comparator 72. FIG. 3C shows an example of the waveform of the phase comparison signal Spc output from the phase comparator 74.

  Next, the phase shifter 62 will be described in detail. FIG. 4 is a circuit diagram of the phase shifter 62. The phase shifter 62 includes a lock detector 80, a counter 82, and a shift register 84.

  The phase comparison signal Spc output from the phase comparison unit 60 is input to the input terminal of the lock detector 80. Further, the reference clock C from the oscillation unit 16 is also input to the lock detector 80. When the pulse width of the phase comparison signal Spc is larger than one cycle of the reference clock C, the lock detector 80 outputs a HIGH level (first level) detection signal. When the pulse width of the phase comparison signal Spc is equal to or less than one cycle of the reference clock C, the lock detector 80 outputs a LOW level detection signal (see FIGS. 3C to 3E). The output terminal of the lock detector 80 is connected to the input terminal of the counter 82.

  The reference clock C from the oscillation unit 16 is also input to the counter 82. When the detection signal output from the lock detector 80 is at a high level, the counter 82 counts at the cycle interval of the reference clock C and outputs a digital signal representing this count value. When this detection signal changes from HIGH level to LOW level, the counter 82 holds the value of the digital signal. The counter 82 continues to hold the value of the digital signal when the detection signal is at the LOW level. The output terminal of the counter 82 is connected to the input terminal of the shift register 84.

  The shift register 84 generates the adjusted subcarrier Wsa by shifting the phase of the subcarrier Ws by the phase shift amount corresponding to the value of the digital signal output from the counter 82. The reference clock C from the oscillating unit 16 is also input to the shift register 84, and the shift register 84 shifts the phase of the subcarrier Ws at the periodic interval of the reference clock C. The output terminal of the shift register 84 is connected to the second frequency divider 64.

  The phase difference between the pilot signal Sp and the subcarrier Ws is made to be one cycle or less of the reference clock C by the processing in the loop including the phase comparison unit 60, the phase shifter 62, and the second frequency divider 64. The phase of the pilot signal Sp is adjusted.

  With reference to FIG. 1 again, the frequency modulator 52 will be described. The frequency modulator 52 generates a frequency modulation signal by frequency modulating the main carrier based on the composite signal output from the stereo modulator 50. Therefore, the frequency modulator 52 constitutes a PLL modulator. That is, the frequency modulator 52 includes a voltage controlled oscillator (hereinafter referred to as VCO) 90, a frequency divider 92, a phase comparator 94, and a low-pass filter (hereinafter referred to as LPF) 96.

  A modulation signal in which a composite signal is superimposed on an output signal from the LPF 96 is input to an input terminal (control terminal) of the VCO 90. The VCO 90 generates a frequency modulated signal obtained by frequency-modulating a main carrier having an oscillation frequency corresponding to the level of the output signal from the LPF 96 with the level of the composite signal. The frequency range of the center frequency of the frequency modulation signal is set to an arbitrary range from 76 MHz to 110 MHz. The output terminal of the VCO 90 is connected to the input terminal of the frequency divider 92.

  The frequency divider 92 divides the frequency modulation signal output from the VCO 90. The output terminal of the frequency divider 92 is connected to one input terminal of the phase comparator 94.

  The frequency-divided clock output from the frequency divider 20 is input to the other input terminal of the phase comparator 94. The phase comparator 94 generates a signal having a pulse width corresponding to the phase difference between the output signal from the frequency divider 92 and the divided clock in accordance with the output signal from the frequency divider 92 and the divided clock. . The output terminal of the phase comparator 94 is connected to the input terminal of the LPF 96.

  The LPF 96 smoothes the output signal from the phase comparator 94 into a direct current, thereby generating a signal having a level corresponding to the pulse width of the output signal from the phase comparator 94.

  In this manner, the frequency modulator 52 generates a main carrier having a frequency corresponding to the frequency of the divided clock, and frequency-modulates the main carrier according to the level of the composite signal.

  Next, the operation of the FM stereo transmitter 10 will be described. First, when the left audio signal Lin and the right audio signal Rin are input to the FM stereo transmitter 10 from the outside, the audio unit 12 pre-emphasizes the left audio signal Lin to generate the left signal L, and the audio unit 14 The right audio signal Rin is pre-emphasized to generate the right audio signal R. The oscillation unit 16 generates a 19 MHz reference clock C. The reference clock C is divided to generate a 38 kHz subcarrier Ws and a 20 kHz divided clock.

  The left signal L, the right signal R, and the subcarrier Ws are input to the stereo modulator 50, and the left signal L and the right signal R are multiplexed by the multiplexer 54 based on the subcarrier Ws. (L + R) + (LR) cosωt ”is generated. This multiplexed signal is input to the mixer 56, and the multiplexed signal and the 19 kHz pilot signal Sp are combined by the mixer 56 to generate a composite signal.

  The pilot signal Sp is also input to the phase comparison unit 60, and a phase comparison signal Spc having a pulse width corresponding to the phase difference between the divided subcarrier Wsd obtained by dividing the subcarrier Ws by 1/2 and the pilot signal Sp is generated. The This phase comparison signal Spc is input to the phase shifter 62. When the pulse width of the phase comparison signal Spc is larger than one period of the reference clock C, a HIGH level detection signal is generated by the lock detector 80 in the phase shifter 62. The When this detection signal is at a HIGH level, the counter 82 in the phase shifter 62 counts at the period interval of the reference clock C, and a digital signal representing this count value is generated. This digital signal is input to a shift register 84 in the phase shifter 62, and the phase of the subcarrier Ws is shifted by the amount of the phase shift corresponding to the value of the digital signal to generate the adjusted subcarrier Wsa. This adjusted subcarrier Wsa is divided by ½ by the second frequency divider 64 to generate a pilot signal Sp. As described above, the processing in the loop including the phase comparison unit 60, the phase shifter 62, and the second frequency divider 64 shifts the phase of the pilot signal Sp, and the phase difference between the pilot signal Sp and the subcarrier Ws is This is one cycle or less of the reference clock C (see FIGS. 3A to 3D).

  When the phase difference between the pilot signal Sp and the subcarrier Ws is equal to or less than one period of the reference clock C, the pulse width of the phase comparison signal Spc output from the phase comparison unit 60 is equal to or less than one period of the reference clock C, and the phase shifter The level of the detection signal output from the lock detector 80 in 62 is the LOW level (see FIGS. 3C to 3E). As a result, the value of the digital signal is held by the counter 82, and the phase of the adjusted subcarrier Wsa, that is, the phase of the pilot signal Sp is fixed.

  In the frequency modulator 52, a main carrier having a frequency corresponding to the reference clock C is output from the VCO 90, and the frequency of the main carrier is obtained by processing in a loop including the VCO 90, the frequency divider 92, the phase comparator 94, and the LPF. It is fixed almost constant. The composite signal output from the stereo modulator 50 is input to the input terminal (control terminal) of the VCO 90 in the frequency modulator 52, the main carrier is frequency-modulated according to the amplitude level of the composite signal, and the frequency modulated signal Is generated. This frequency modulation signal is amplified by the amplifier 24 and then converted into an electromagnetic wave by the antenna 26.

  In the stereo modulator 50 of the present embodiment, the phase difference between the subcarrier Ws and the pilot signal Sp is reduced by the processing in the loop including the phase comparison unit 60, the phase shifter 62, and the second frequency divider 64. In addition, the phase of the pilot signal Sp is adjusted autonomously. As described above, according to the stereo modulator 50 of the present embodiment, the composite signal in which the multiplexed signal multiplexed based on the subcarrier Ws and the pilot signal Sp having a small phase difference with respect to the subcarrier Ws is synthesized. A signal can be generated. Therefore, by transmitting a frequency modulation signal based on this composite signal in the FM stereo transmitter, it is possible to reduce deterioration in channel separation characteristics in the FM stereo receiver.

  Further, according to the FM stereo modulator 22 of the present embodiment, the main carrier is frequency-modulated in accordance with the composite signal obtained by synthesizing the pilot signal Sp having a small phase difference with respect to the subcarrier Ws to generate a frequency modulation signal. can do. As a result, it is possible to reduce deterioration in channel separation characteristics in the FM stereo receiver.

  Further, according to the stereo modulator 50 and the FM stereo modulator 22 of the present embodiment, it is not necessary to manually adjust the phase difference between the subcarrier Ws and the pilot signal Sp as in the prior art. Further, since the phase difference between the pilot signal Sp and the subcarrier Ws is autonomously reduced, the phase between the subcarrier Ws and the pilot signal Sp is not shifted due to an external factor such as temperature fluctuation.

[Second Embodiment]
FIG. 5 is a circuit diagram of an FM stereo transmitter including a stereo modulator and an FM stereo modulator according to the second embodiment of the present invention. The FM stereo transmitter 10A is different from the FM stereo transmitter 10 of the first embodiment in a configuration including an FM stereo modulator 22A instead of the FM stereo modulator 22. The other configuration of the FM stereo transmitter 10A is the same as that of the FM stereo transmitter 10.

  The FM stereo modulator 22A is different from the FM stereo modulator 22 in a configuration including the stereo modulator 50A instead of the stereo modulator 50. Other configurations of the FM stereo modulator 22A are the same as those of the FM stereo modulator 22.

  The stereo modulator 50A includes a phase comparison unit 60A instead of the phase comparison unit 60, and includes a frequency divider 98 instead of the first frequency divider 58 and the second frequency divider 64. Different from the stereo modulator 50. Other components of the stereo modulator 50A are the same as those of the stereo modulator 50. Hereinafter, differences from the first embodiment will be described.

  The output terminal of the frequency divider 18 is connected to one input terminal of the phase comparison unit 60A without going through the first frequency divider 58. The other input terminal of the phase comparison unit 60A is connected to the output terminal of the phase shifter 62 without passing through the second frequency divider 64. Therefore, the phase comparison unit 60A generates the phase comparison signal Spc that represents the phase difference between the subcarrier Ws output from the frequency divider 18 and the adjusted subcarrier Wsa output from the phase shifter 62. For example, the configuration of the phase comparison unit 60A may be the same as the configuration of the phase comparison unit 60 shown in FIG. Such a phase comparison unit 60 </ b> A has a phase difference between the subcarrier Ws and the adjusted subcarrier Wsa based on the subcarrier Ws output from the frequency divider 18 and the adjusted subcarrier Wsa output from the phase shifter 62. A phase comparison signal Spc having a pulse width in accordance with is generated. The output terminal of the phase comparison unit 60A is connected to the phase shifter 62.

  The output terminal of the phase shifter 62 is also connected to the frequency divider 98. The frequency divider 98 divides the adjusted subcarrier Wsa output from the phase shifter 62 by 1/2 to generate the pilot signal Sp. The output terminal of the frequency divider 98 is connected to the mixer 56, and the frequency divider 98 outputs the pilot signal Sp to the mixer 56.

  In the stereo modulator 50A of the present embodiment, the phase comparator 60A and the phase shifter 62 constitute a feedback circuit, and the subcarrier Ws and the adjusted subcarrier are processed by processing in a loop including the phase comparator 60A and the phase shifter 62. The phase of the adjusted subcarrier Wsa is adjusted so that the phase difference from the carrier wave Wsa is small. Specifically, the processing in the loop including the phase comparison unit 60A and the phase shifter 62 causes the phase difference between the subcarrier Ws and the adjusted subcarrier Wsa to be equal to or less than one cycle of the reference clock C. The phase is adjusted. Since the pilot signal Sp is generated from the adjusted subcarrier Wsa by the frequency divider 98, the phase difference between the subcarrier Ws and the pilot signal Sp becomes small.

  Thus, according to the stereo modulator 50A of the present embodiment, the phase difference between the subcarrier Ws and the pilot signal Sp is obtained by the processing in the loop including the phase comparison unit 60A and the phase shifter 62 and the frequency divider 98. The phase of pilot signal Sp is adjusted autonomously so as to decrease. Therefore, the stereo modulator 50A of this embodiment has the same advantages as the stereo modulator 50 of the first embodiment.

  Further, the FM stereo modulator 22A of this embodiment having this stereo modulator 50A has the same advantages as the FM stereo modulator 22 of the first embodiment.

  The present invention is not limited to the above-described embodiment, and various modifications can be made.

  In the present embodiment, a circuit for adjusting the phase of the pilot signal Sp (first embodiment: phase comparison unit 60, phase shifter 62, first frequency divider 58, second frequency divider 64, second frequency Embodiment: The phase comparison unit 60A, the phase shifter 62, and the frequency divider 98) are applied to the stereo modulator 50 and the FM stereo modulator 22 of the left / right switching system (also referred to as switching system). The present invention can also be applied to stereo modulators and FM stereo modulators other than the left / right switching system.

  In the present embodiment, the phase comparison units 60 and 60A represent the phase difference between the subcarrier and the pilot signal by the pulse width of the phase comparison signal. However, the phase comparison unit represents this phase difference as a pulse of the phase comparison signal. It may be expressed by other than the width. For example, the phase comparison unit may represent this phase difference with the voltage level of the phase comparison signal. In this case, the phase shifter may adjust the phase of the pilot signal by performing analog processing instead of digital processing.

  In this embodiment, the oscillation frequency of the oscillating unit 16 is 19 MHz. However, the oscillation frequency of the oscillating unit is not limited to this as long as it can generate a 38 kHz sub-carrier wave Ws.

  In this embodiment, the frequency of the divided clock output from the frequency divider 20 is 20 kHz, but the frequency of the divided clock is not limited to this.

It is a circuit diagram of the FM stereo transmitter provided with the stereo modulator and FM stereo modulator which concern on the 1st Embodiment of this invention. It is a circuit diagram of a phase comparison part. It is a figure which shows the signal waveform of the principal part of a phase comparison part and a phase shifter. It is a circuit diagram of a phase shifter. It is a circuit diagram of the FM stereo transmitter provided with the stereo modulator and FM stereo modulator which concern on the 2nd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Stereo transmitter, 12, 14 ... Audio part, 16 ... Oscillation part, 18, 20 ... Frequency divider, 22 ... FM stereo modulator, 24 ... Amplifier, 26 ... Antenna, 50 ... Stereo modulator, 52 ... Frequency Modulator 54... Multiplexer (MPX) 56. Mixer (MIX) 58. First frequency divider 60... Phase comparison unit 62 62 Phase shifter 64.

Claims (5)

Multiplexing is performed by multiplexing, based on the subcarrier, a sum signal representing the sum of the left signal and the right signal, and a difference signal obtained by amplitude-modulating the difference between the left signal and the right signal with a subcarrier. A multiplexer for generating a signal;
A mixer that generates a composite signal by combining the multiplexed signal output from the multiplexer and a pilot signal;
A first divider for generating a divided subcarrier by dividing the subcarrier by 1/2;
A phase comparison unit that generates a phase comparison signal representing a phase difference between the frequency-divided subcarrier output from the first frequency divider and the pilot signal;
Based on the phase comparison signal output from the phase comparison unit, a phase shifter that generates an adjusted subcarrier that adjusts the phase of the subcarrier so that the phase difference is reduced,
A second frequency divider for generating the pilot signal by dividing the adjusted subcarrier output from the phase shifter by half;
Comprising
Stereo modulator. The phase comparison unit generates a phase comparison signal having a pulse width corresponding to a phase difference between the divided subcarrier output from the first frequency divider and the pilot signal,
The phase shifter is
A lock detector that outputs a first level detection signal when the pulse width of the phase comparison signal output from the phase comparison unit is greater than a period of a reference clock;
A counter that outputs a digital signal representing a count value counted at a cycle interval of the reference clock when the detection signal output from the lock detector is at a first level;
Shifting the phase of the subcarrier by a phase shift amount corresponding to the value of the digital signal output from the counter so that the pulse width of the phase comparison signal output from the phase comparison unit is narrowed. A shift register for generating the adjusted subcarrier,
Having
The stereo modulator according to claim 1. Multiplexing is performed by multiplexing, based on the subcarrier, a sum signal representing the sum of the left signal and the right signal, and a difference signal obtained by amplitude-modulating the difference between the left signal and the right signal with a subcarrier. A multiplexer for generating a signal;
A mixer that generates a composite signal by combining the multiplexed signal output from the multiplexer and a pilot signal;
A phase comparator that generates a phase comparison signal representing a phase difference between the subcarrier and the adjusted subcarrier;
Based on the phase comparison signal output from the phase comparison unit, a phase shifter that generates the adjusted subcarrier in which the phase of the subcarrier is adjusted so that the phase difference is reduced,
A frequency divider that generates the pilot signal by dividing the adjusted subcarrier output from the phase shifter by a half;
Comprising
Stereo modulator. The phase comparator generates a phase comparison signal having a pulse width corresponding to a phase difference between the subcarrier and the adjusted subcarrier;
The phase shifter is
A lock detector that outputs a first level detection signal when the pulse width of the phase comparison signal output from the phase comparison unit is greater than a period of a reference clock;
A counter that outputs a digital signal representing a count value counted at a cycle interval of the reference clock when the detection signal output from the lock detector is at a first level;
Shifting the phase of the subcarrier by a phase shift amount corresponding to the value of the digital signal output from the counter so that the pulse width of the phase comparison signal output from the phase comparison unit is narrowed. A shift register for generating the adjusted subcarrier,
Having
The stereo modulator according to claim 3. The stereo modulator according to any one of claims 1 to 4,
A frequency modulator that generates a frequency-modulated signal by frequency-modulating the main carrier according to the composite signal output from the stereo modulator;
Comprising
FM stereo modulator.

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