JPH0758649A - Fm modulator - Google Patents

Abstract

PURPOSE:To improve the convenience for use and to prevent the distortion of an audio signal by extending the oscillation frequency range of an FM modulator in the PLL system and extending the linear area. CONSTITUTION:Plural VCOs 1 and 2 constitute a PLL and division-ally take partial charge of a prescribed frequency range. The VCO which should take charge of a used frequency is discriminated by a microcomputer 19 to output a VCI switching signal. The oscillation frequency of the PLL is controlled by the used frequency, and the audio signal is converted to a composite signal of a format of FM broadcast by a COMP 15 and is superposed on an oscillation frequency control voltage VT by a superposing part 16, and the oscillation frequency of the VCO is subjected to FM modulation and is amplified by an RF amplifier 17 and is outputted as ANT OUT and is received, demodulated, and reproduced by an FM radio 20.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an audio device, and more particularly to an FM modulator for an ADD-ON used in a vehicle audio device.

[0002]

2. Description of the Related Art In an on-vehicle audio device equipped with an FM tuner, an audio source such as DCC or MD is to be added in addition to a current audio source. That is, at the time of ADD-ON, when the input terminals provided in the audio device are insufficient, or when the input terminals of the audio device are on the back surface of the device or the like, which makes the connection troublesome, the FM tuner is used. A technique is used in which a signal of an audio source to be added is converted into an FM modulated wave according to an FM broadcast format, input to an FM tuner, demodulated, and reproduced.

[0003]

When a PLL type oscillation circuit is used for this FM modulation and oscillation, V in the PLL circuit is used.
The variable width of the oscillation frequency of the CO (voltage controlled oscillator) is VCO
It is determined by the capacitance variation range of the varicap that composes.
FIG. 6 shows a block diagram of a conventionally used PLL type FM modulator. 61 is a VCO, 6
2 is a PLL controller and 63 is an LPF.
The LL circuit is configured, and an audio signal from the outside is converted into a composite signal by 64 CMP is input to the superimposing section of 67 in the circuit to superimpose it on the control voltage VT, and the oscillation frequency of the VCO 61 is FM-modulated. After being amplified by the RF amplifier 68, it is input to the FM radio 69 originally provided in the audio device as ANT OUT and then demodulated and reproduced. A control unit 65 and a microcomputer 66 input a control signal to the PLL controller 62.

When the oscillation and the modulation are performed by the same PLL circuit as in the configuration of FIG. 6, the audio signal is distorted unless the characteristics of the control voltage of the VCO and the oscillation frequency are linear. , VCO 61, the capacitance change characteristics of the varicap have a wide frequency range, for example, 76-9.
When the VCO 61 is changed at 0 MHz, the linear region is exceeded, and when the audio signals are simultaneously modulated, the problem of distortion occurs. The pattern is shown in FIG. 4, but since the capacitance change of the varicap and the oscillation frequency change are in a proportional relationship, they are shown in the same figure as a relationship between the control voltage VT and the frequency. As can be seen in the figure, for example, the lower limit is 7
If you want to set 6 MHz and the upper limit to 90 MHz, the lower limit is 76
When MHz is used as a reference, it becomes a non-linear region before it reaches 90 MHz, so that it cannot cover the entire frequency range of FM up to 108 MHz.

For the above reasons, the conventional FM modulator has a variable width of the oscillation frequency of only a few MHz. Therefore, when using this, the FM of the area is
If the transmission frequency of the broadcasting station and the oscillation frequency of the FM modulator are different, annoying inter-station noise will occur when the FM modulator is turned off, or the reception frequency of the FM radio will change when the FM broadcasting and the FM modulator are switched. It was complicated because it had to be readjusted each time.
The present invention proposes an FM modulator that eliminates such drawbacks.

[0006]

According to the present invention, there are provided a plurality of voltage controlled oscillators for dividing a predetermined frequency range and sharing the divided frequency range, and a plurality of voltage controlled oscillators corresponding to a desired reception frequency. A microcomputer that selects and operates one of them, or a plurality of coils or varicaps, which are the only constituent factors of the voltage-controlled oscillator and are divided into a predetermined frequency range and shared by each, and a desired reception frequency. According to the present invention, a microcomputer for selecting and operating one of a plurality of coils or varicaps constituting the voltage controlled oscillator is provided, so that the operating frequency range of the FM modulator is the entire frequency range of FM broadcasting, or most of it. Will be solved by covering.

[0007]

[Operation] VC constituting PLL type FM modulator
The user can change the operating frequency range of the FM modulator by covering the entire frequency range of FM broadcasting or most of the frequency range by switching the O itself or the plurality of coils and varicaps constituting the VCO. Since it is possible to match the frequency with the FM broadcast in advance without having to perform the readjustment operation of the reception frequency when switching between the FM broadcast and the FM modulator, which has been conventionally required, the FM broadcast and the FM modulator are not necessary. You can switch only by turning ON / OFF the FM modulator. In addition, it is possible to minimize the influence on the audio signal. Further, since the transmission frequency of the FM broadcasting station and the oscillation frequency of the FM modulator are the same, no unpleasant inter-station noise that is generated when the conventional FM modulator is powered off does not occur.

[0008]

1 is a block diagram of an embodiment of an FM modulator according to the present invention. 11 and 12 are V
CO1 and VCO2 are configured so that a desired oscillation frequency range is divided into two and shared. The PLL controller, 14 is an LPF and forms a PLL circuit by these three parties, and inputs a composite signal of an external audio signal by 15 CMP to the superimposing part of 16 in the same circuit to input the control voltage VT. The oscillation frequencies of the VCOs 11 and 12 are superimposed and FM-modulated, amplified by the RF amplifier 17, output as ANT OUT, and input to the FM radio 20 originally provided in the audio device. 18 is a control unit, 1
Reference numeral 9 denotes a microcomputer, which inputs a control signal to the PLL controller 13 and controls switching for the VCO 1 and VCO 2 to divide the oscillation frequency range into two and share them.

The operation of the FM modulator having the above-described circuit is as follows. The control unit 18 inputs the power to the FM modulator (not shown) to the microcomputer 19 so as to turn it on. The microcomputer 19 outputs a frequency control signal to the PLL controller 13 so as to lock the PLL at a desired frequency, and at the same time, the VCO 1 having a desired frequency of 11 and the VCO 1 having a desired frequency of 12.
2 or which frequency is in charge is determined, and a VCO switching signal is output. By the above, the oscillation frequency of the PLL is controlled to the desired frequency, the audio signal is input to the COMP 15, converted into the composite signal of the FM broadcast format, and superimposed on the oscillation frequency control voltage VT by the superimposing unit 16, and the VCO 1
Alternatively, the oscillation frequency of 2 is frequency-modulated. The modulated output output from the VCO 1 or 2 is amplified to a predetermined antenna output level by the RF amplifier 17 and output from ANT OUT. The above ANT OUT is received by the FM radio 20, demodulated into an audio signal and reproduced as an audio signal from the speaker.

Using the two VCOs shown in FIG.
The characteristic diagram of the PLL circuit of the M modulator shows that the object of the present invention is achieved by switching the characteristics of VCO1 and VCO2 at point A and utilizing them.

In the above-described embodiment of the present invention, the structure having two whole VCO circuit blocks has been described. However, as described above, only a plurality of varicaps and coils forming the VCO are provided and they can be switched. Even with this configuration, the effect of the present invention can be obtained. FIG. 2 shows an embodiment of a circuit provided with two coils and switching them, and FIG. 3 shows an embodiment of a circuit provided with two varicaps and switching them.

In the example of the circuit for switching the coil shown in FIG.
Coil 1 and Coil 2 of 22 are connected in series, and are connected so that a signal from the CONT terminal is input to the connection point. When there is no input signal at the CONT terminal, both coils are It operates with an inductance value obtained by adding the inductance of the coil, but when there is an input signal, the coil 2 of 22 is cut (bypassed) to switch the resonance frequency constituted by the varicap.

In the varicap switching circuit example of FIG. 3, 31 varicaps 1 and 32 varicaps 2 are connected in parallel, and the varicap 2 32 has CONT.
It is connected so that the signal from the terminal is input, and C
When there is an input signal at the ONT terminal, the resonance frequency is switched depending on the voltage applied to the varicap 2 32.

In the above embodiment, the required frequency range is set to 76 to 108 MHz, but this band differs depending on the destination country. In the production for export, it is possible to set all types of regions to be covered by one type of production by using the present invention.

[0015]

As described above, according to the present invention, the VCO itself forming the PLL type FM modulator, or the plurality of coils and varicaps forming the VCO can be switched and switched. The variable width of the output frequency can be made much wider than that of the conventional one, and the influence on the audio signal can be minimized. Therefore, the user needed F
It is possible to match the frequency with the FM broadcast in advance without performing a readjustment operation of the reception frequency when switching between the M broadcast and the FM modulator. Therefore, switching between the FM broadcast and the FM modulator is performed. You only have to turn on / off the, which greatly improves convenience. Furthermore, since the transmission frequency of the FM broadcasting station and the oscillation frequency of the FM modulator are the same, the unpleasant inter-station noise that occurs when the conventional FM modulator is powered off does not occur.

[Brief description of drawings]

FIG. 1 is a block diagram of a circuit of a first embodiment of an FM modulator of the present invention.

FIG. 2 is a partial circuit diagram of a second embodiment of the FM modulator of the present invention.

FIG. 3 is a partial circuit diagram of a third embodiment of the FM modulator of the present invention.

FIG. 4 is a characteristic diagram of a capacitance change of a varicap and an oscillation frequency.

FIG. 5 is a characteristic diagram of an FM modulator embodying the present invention.

FIG. 6 is a block diagram of a circuit of a conventional FM modulator.

[Explanation of symbols]

 11 VCO 1 of the first voltage controlled oscillator 12 VCO 2 of the second voltage controlled oscillator 13 PLL controller 14 LPF 18 control unit 19 microcomputer 20 FM radio 21 coil 1 22 coil 2 31 varicap 1 32 varicap 2

Claims (2)

[Claims] 1. A plurality of voltage-controlled oscillators which operate by dividing a required frequency range into a plurality of continuous frequency ranges and sharing each of them, and one of the plurality of voltage-controlled oscillators corresponding to a set operating frequency. And a microcomputer that operates at the set frequency, thereby expanding the usable frequency range of the PLL system FM modulator. 2. A plurality of coils or varicaps, which are the only constituent factors of the voltage controlled oscillator, and divide the required frequency range into a plurality of continuous frequency ranges and share the divided frequency ranges to operate the voltage controlled oscillator. And a microcomputer that selects one from the plurality of coils or varicaps that configure the voltage controlled oscillator in accordance with the set used frequency and operates the voltage controlled oscillator at the set used frequency. , A PLL type FM modulator characterized by expanding the frequency range used.