JP3957312B2 - FM transmitter - Google Patents

Description

  The present invention relates to an FM transmitter for FM-stereo modulating an audio signal and transmitting it wirelessly.

  Conventionally, FM transmitters have been developed and used for FM stereo modulation and wireless transmission of audio signals. The configuration of a conventional FM transmitter is shown in FIG.

  In FIG. 2, the FM transmitter is configured as follows. That is, from the audio unit 10 for the right audio including the pre-emphasis circuit 11, the volume 12, the limiter 13, the low-pass filter 14, and the mute circuit 15, the pre-emphasis circuit 21, the volume 22, the limiter 23, the low-pass filter 24, and the mute circuit 25. The left audio unit 20, the audio signal 31 from the audio unit 10, the audio amplifier circuit 31 that amplifies the audio signal from the audio unit 20, and the external crystal oscillator Xosc 1 (basic vibration frequency 38 KHz) are combined. Stereo modulation comprising an oscillating circuit 32 for oscillating and outputting a frequency signal, a multiplexer 33 for switching the left and right audio signals amplified by the audio amplifying circuit 31 with an oscillation output of 38 KHz from the oscillating circuit 32, and an RF (radio frequency) amplifying circuit 34 Part 30 and multiplex 33, a modulation level adjustment circuit 41 that adjusts the output level of the oscillator 33, a pilot level adjustment circuit 42 that adjusts the level of the 18 KHz pilot signal divided by half of the oscillation circuit 32, a modulation level adjustment circuit 41, and a pilot level adjustment. The mixing circuit 43 that receives the level-adjusted output of the circuit 42 and outputs a composite signal is coupled to the external crystal resonator Xosc2 (basic vibration frequency 7.2 MHz) and the RF output of the RF amplifier circuit 34 is input. A PLL frequency synthesizer 44 for outputting a frequency control signal, a low pass filter 45 for low-pass filtering the output of the PLL frequency synthesizer 44, and a composite signal from the signal of the PLL frequency synthesizer 44 and the mixing circuit 43 to output an oscillation modulation signal. An oscillation control unit 47 comprising a mixing circuit 46 that performs An oscillation modulating circuit 48 which is controlled by the output signal of the oscillation control unit 47, an RF output level adjusting circuit 49 and outputting the level adjusted the RF output of the RF amplifier circuit 34, FM transmitter and a.

  Here, the stereo modulation unit 30 and the PLL frequency synthesizer 44 are integrated into an integrated circuit. The PLL frequency synthesizer 44 is shown as a single block in the figure, but actually includes a frequency divider, a phase comparator, a program counter, and the like. Then, the 7.2 MHz oscillation frequency output from the oscillation circuit to which the external crystal resonator Xosc2 (basic oscillation frequency 7.2 MHz) is coupled is divided into various frequencies, and the frequency signal thus divided is used as a reference. One input of the phase comparator is used as a frequency signal. Further, the RF frequency signal oscillated by the oscillation modulation circuit 48 is appropriately divided by a program counter or the like, and this divided RF frequency signal is used as the comparison frequency signal and the other input of the phase comparator. Then, the phase comparison output of this phase comparator is supplied to the oscillation control unit 47, and the RF frequency is determined according to the frequency division ratio in the program counter or the like and the reference frequency signal.

  This PLL frequency synthesizer 44 is used for radio and the like, and it is necessary to divide and output various frequency signals such as 100 KHz, 50 KHz, 25 KHz, 10 KHz, 9 KHz, 5 KHz, 1 KHz, etc. as a reference frequency. Therefore, an external crystal resonator Xosc2 having a fundamental vibration frequency of 7.2 MHz is employed.

  As described above, the conventional FM transmitter is separated into the audio unit 10, the audio unit 20, the stereo modulation unit 30, the PLL frequency synthesizer 44, the oscillation control unit 47, the oscillation modulation circuit 48, and the like. In particular, the stereo modulation unit 30 and the PLL frequency synthesizer 44 are configured as an assembly of various components such as an integrated circuit.

  For this reason, when integrating as an FM transmitter, the exchange of signal lines and control lines between each component increases, and the arrangement and wiring of each component become complicated. The required area has become large.

  Further, the stereo modulation unit 30 and the PLL frequency synthesizer 44 are integrated circuits. Further, in order to obtain different frequencies required for the respective circuits, the crystal resonator Xosc1 for stereo modulation has a fundamental vibration frequency of 38 KHz. On the other hand, the crystal oscillator Xosc2 of the PLL frequency synthesizer has a fundamental vibration frequency of 7.2 MHz and is separately prepared and used.

  SUMMARY OF THE INVENTION In view of the problems of conventional FM transmitters, an object of the present invention is to provide an FM transmitter that reduces the number of components such as an expensive crystal resonator, reduces costs, and reduces the mounting area. .

The FM transmitter according to claim 1 is coupled to a crystal resonator, a fundamental vibration frequency oscillation circuit that outputs a fixed fundamental vibration frequency coupled to the crystal resonator, a reactor, and the reactor, and the oscillation frequency is controlled. FM broadcast wave oscillating circuit, a program counter for variably dividing the oscillation frequency of the FM broadcast wave oscillating circuit, a reference frequency dividing circuit for dividing the fundamental vibration frequency, an output of the program counter and the reference frequency dividing A PLL frequency synthesizer comprising a phase comparison circuit that compares the output of the circuit and outputs a signal for oscillation control of the FM broadcast wave oscillation circuit, and a clock generated from the fundamental vibration frequency for two left and right audio signals. And a stereo modulation circuit that outputs a signal for oscillation control of the FM broadcast wave oscillation circuit, wherein the fundamental vibration frequency is 1 9 MHz, an integer multiple of 3.8MHz or 7.6 MHz, the output frequency of the reference frequency divider and 100kHz or 50 kHz, the PLL frequency synthesizer is characterized in that it is formed by a CMOS circuit.

According to the configuration of claim 1 of the present invention, the frequency signal for stereo modulation and the frequency signal of the PLL frequency synthesizer are examined, frequency division is adopted for the former, and necessary frequency classification is reviewed for the latter. Since the PLL frequency synthesizer is formed of a CMOS circuit with a frequency that is an integral multiple of 1.9 MHz, 3.8 MHz , or 7.6 MHz as a reference frequency, conventionally, the PLL frequency synthesizer has been separately required for each frequency. The oscillator and the vibrator used therefor can be made single.

  In addition, the arrangement and wiring of each component constituting the FM transmitter are unified and arranged to improve reliability, the number of parts can be greatly reduced, and the effective area can be reduced.

  An embodiment of the present invention will be described with reference to FIG. FIG. 1 is a diagram illustrating a configuration of an FM transmitter according to an embodiment of the present invention.

  In FIG. 1, the FM transmitter includes an FM transmitter semiconductor integrated circuit device 100 and some external components such as a crystal resonator Xosc.

  In FIG. 1, the right audio input R is input and passed through the audio unit 50 including the volume 51, the pre-emphasis circuit 52, the limiter 53, and the low-pass filter 54 and is input to the multiplexer 71. Similarly, the left audio input L is input and passed through the audio unit 60 including the volume 61, the pre-emphasis circuit 62, the limiter 63, and the low-pass filter 64, and is used as the other input of the multiplexer 71.

  The two inputs of the multiplexer 71 are switched by a switching signal which is a 38 KHz subcarrier supplied from the reference frequency oscillating unit 80-1 and input to the stereo modulation level adjusting circuit 73. In the stereo modulation level adjusting circuit 73, a 19 KHz frequency signal obtained by further dividing the 38 KHz frequency from the reference frequency oscillating unit 80-1 by 1/2 is supplied to the pilot signal supplied from the variable capacitor 72 for separation adjustment and the signal from the multiplexer 71. Are adjusted in stereo modulation level, and the FM modulation level is adjusted by the FM modulation level adjustment circuit 74 and output as an FM modulation signal.

  The FM modulation level adjustment circuit 74 can turn off the output by an external mute signal. Further, the separation adjusting variable capacitor 72 adjusts the phase of the signal switching of the multiplexer 71 and the phase of the 19 KHz pilot signal. These multiplexer 71, variable capacitor 72, stereo modulation level adjustment circuit 73, and FM modulation level adjustment circuit 74 constitute a stereo modulation unit 70.

  Next, in the phase comparison unit 80-2, a signal having a constant frequency of 50 KHz supplied from the reference frequency oscillation unit 80-1 is given to the reference frequency input terminal of the phase comparison circuit 87. Unlike the 38 KHz and 19 KHz in the stereo modulation unit 70, this constant frequency of 50 KHz is a frequency selected as necessary as a transmitter. On the other hand, the radio frequency output signal is supplied to the program counter 86, divided by the division ratio set in the program counter 86, and supplied as a comparison frequency signal to the comparison frequency input terminal of the phase comparison circuit 87. The phase comparison circuit 87 compares the phases of these two inputs, and the comparison result is output as an oscillation signal via the low-pass filter 88. The program counter 86, the phase comparison circuit 87, and the low-pass filter 88 constitute a phase comparison unit 80-2.

  Next, in the reference frequency oscillating unit 80-1, an external crystal resonator Xosc (basic vibration frequency 7.6 MHz) and capacitors C6 and C7 are coupled to the oscillation circuit 81, and oscillation from the oscillation circuit 81 to 7.6 MHz. The frequency is output. This oscillation frequency is divided by 1/200 by the frequency divider circuit 83 to 38 KHz, supplied to the multiplexer 71, further divided by 1/2 by the frequency divider circuit 84, and supplied to the variable capacitor 72.

The oscillation frequency is divided by 1/76 by the frequency dividing circuit 82 and by 1/2 by the frequency dividing circuit 85, and is supplied to the reference frequency input terminal of the phase comparison circuit 87. The frequency dividing ratio of the frequency dividing circuit 85 is appropriately set in relation to the output radio frequency and the frequency dividing ratio of the program counter 86, and is not limited to 1/2.

  These frequency dividing circuits are configured as T-type flip-flop circuits using CMOS logic circuits, and are accurately supplied with a clock having a duty ratio of 50%. Therefore, the separation adjustment range adjusted by the variable capacitor 72 is reduced. Further, since this duty is not affected by the temperature, the modulation section has a good temperature characteristic, and it is possible to make no adjustment.

  The crystal oscillator Xosc, capacitors C6 and C7, oscillation circuit 81, frequency divider circuit 82, frequency divider circuit 83, frequency divider circuit 84, and frequency divider circuit 85 constitute a reference frequency oscillator 80-1, and a reference frequency oscillator The PLL frequency synthesizer 80 is configured by the 80-1 and the phase comparator 80-2.

  As described above, in the present invention, the crystal resonator Xosc having the fundamental vibration frequency of 7.6 MHz is used, and conventionally, the reference frequency signal for phase comparison (the crystal resonator Xosc2 having the fundamental vibration frequency of 7.2 MHz) and the stereo modulation are used. A separate crystal resonator is required for each frequency signal (crystal resonator Xosc1 having a fundamental vibration frequency of 38 kHz) so that it can be shared by one crystal resonator.

  In order to make it possible to share the above, in the present invention, it is necessary to review the dedicated arrangement of a crystal resonator having a fundamental vibration frequency of 38 KHz including the use of a divided frequency as a frequency signal for stereo modulation, and for phase comparison. Since it is necessary to divide and output various frequency signals such as 100 KHz, 50 KHz, 25 KHz, 10 KHz, 9 KHz, 5 KHz, 1 KHz, etc. for radio, etc. Considering the fact that a vibration frequency of 7.2 MHz is adopted, by reexamining the reference frequency for phase comparison required for the FM transmitter, a crystal resonator that can share a crystal resonator with a basic vibration frequency of 7.6 MHz for the first time It can be recognized as. As the crystal resonator used in the present invention, those having a fundamental vibration frequency of 1.9 MHz, 3.8 MHz, 15.2 MHz, and 22.8 MHz in addition to the integer range of the frequency range and frequency are 7.6 MHz. It becomes possible to use suitably.

  Next, the modulation signal from the stereo modulation unit 70 is input to the oscillation modulation circuit 90 via the resistor r1, and the oscillation signal from the phase comparison unit 80-2 is input to the oscillation modulation circuit 90 via the resistor r2, and oscillates according to this input signal. An RF frequency signal is output from the circuit 90, amplified by the RF amplifier circuit 102 and the RF amplifier circuit 103, and supplied to the outside as an RF output. The oscillation modulation circuit 90 includes voltage variable capacitors Vc1 and Vc2, capacitors C1 to C4, a reactor L, and an oscillation circuit 91 using a transistor circuit, and generates an oscillation-modulated RF signal.

  The shift register 101 receives the chip enable signal CE, the clock signal CK, and the control data DA from the outside, and receives the volume 51, volume 61, stereo modulation level adjustment circuit 73, FM modulation level adjustment circuit 74, program counter 86, RF A control signal or a command signal is supplied to the amplifier circuit 103 in the form of a digital signal. The voltage Vref is a reference voltage formed by the resistors r3, r4, the capacitor C5, and the operational amplifier OP1.

  Further, the resistors r1, r2, capacitors C5, C6, C7, etc., which are externally attached in FIG. 1, can be incorporated in the FM transmitter semiconductor integrated circuit device 100. Although not shown, necessary terminals such as a power supply terminal and a ground terminal are added.

  In the FM transmitter according to the present invention, all the components are integrated in a single semiconductor except for a part such as a crystal resonator Xosc and an oscillation modulation element. Each component is formed using a BiCMOS process. The audio unit 50, the audio unit 60, the stereo modulation unit 70, the oscillation modulation circuit 90, the RF amplification circuit 102, and the RF amplification circuit 103, which are analog signal systems, are bipolar. The PLL frequency synthesizer 80 and the shift register 101, which are formed of a circuit and are pulsed or digital, are mainly formed of a CMOS circuit.

  As described above, in the present invention, the necessary steps of the frequency signal of the frequency signal for stereo modulation, 38 KHz and 19 KHz, and the PLL frequency synthesizer are examined, frequency division is adopted for the former, and the latter is necessary. The frequency classification was reviewed. As a result, if the fundamental vibration frequency of the PLL frequency synthesizer is 7.6 MHz (or an integer multiple of this frequency, or a frequency corresponding to an integer), the crystal oscillation circuit that has been separately required for each frequency can be shared. The present invention has been made by paying attention to the above, and this makes it possible to use a single crystal oscillator and a single crystal resonator.

  Further, since the components of the FM transmitter are integrated in a single semiconductor device except for some external components such as the crystal resonator Xosc and the oscillation modulation elements Vc1 and Vc2, the arrangement of each component And wiring are unified and arranged to improve reliability, the number of parts can be greatly reduced, and the effective area can be reduced.

  Further, when the FM transmitter is integrated into a semiconductor, the whole is formed by a BiCMOS circuit, and its constituent elements are divided into an analog signal system element, a pulse system, and a digital system element. The audio unit 50, the audio unit 60, the stereo modulation unit 70, the oscillation modulation circuit 90, the RF amplification circuit 102, and the RF amplification circuit 103, which are analog signal systems, are formed of bipolar circuits, and are pulse systems and digital PLLs. Since the frequency synthesizer 80 and the shift register 101 are mainly formed of a CMOS circuit, a circuit suitable for the characteristics of each component can be configured.

The figure which shows the structure of the FM transmitter based on the Example of this invention. The figure which shows the structure of the conventional FM transmitter.

Explanation of symbols

DESCRIPTION OF SYMBOLS 50 Audio part 60 Audio part 70 Stereo modulation part 80 PLL frequency synthesizer 80-1 Reference frequency oscillation part 80-2 Phase comparison part 90 Oscillation modulation circuit 100 Semiconductor integrated circuit device for FM transmitter

Claims (1)

A crystal unit,
A fundamental oscillation frequency oscillation circuit coupled to the crystal unit and outputting a fixed fundamental oscillation frequency;
Reactor,
An FM broadcast wave oscillation circuit coupled to the reactor and controlled in oscillation frequency;
A program counter for variably dividing the oscillation frequency of the FM broadcast wave oscillation circuit, a reference frequency divider for dividing the fundamental vibration frequency, and comparing the output of the program counter with the output of the reference frequency divider A PLL frequency synthesizer comprising a phase comparison circuit that outputs a signal for oscillation control of an FM broadcast wave oscillation circuit;
A stereo modulation circuit that stereo-modulates two left and right audio signals using a clock generated from the fundamental vibration frequency, and outputs a signal for oscillation control of the FM broadcast wave oscillation circuit;
The fundamental vibration frequency is an integral multiple of 1.9 MHz, 3.8 MHz, or 7.6 MHz, the output frequency of the reference frequency divider circuit is 100 kHz or 50 kHz, and the PLL frequency synthesizer is formed of a CMOS circuit. FM transmitter characterized by the above.

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