JPH09321720A - Fm stereo transmitter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the number of crystal oscillators to one so as to attain cost-down and also to prevent interference to the frequency band of an FM broadcast by the higher harmonics of a PLL reference oscillator by dividing an oscillation frequency so as to adopt it as a pilot signal and, in the meantime, permitting a frequency modulating means to control the frequency of carrier wave through the use of a PLL circuit where the oscillation frequency is adopted as a reference frequency. SOLUTION: The crystal oscillators 1 and capacitors C1 and C2 are connected to an oscillator 2 and the oscillation frequency is decided by the crystal oscillators 1 so as to be 76kHz. The repeated frequency transmits a pulse waveform reference signal being 76kHz from the oscillator 2 to a reference divider 3. Phase difference between a signal outputted from the reference devider 3 and the signal where the oscillation frequency of an RF oscillator 16 is divided in a pre-scaler 6 and the main counter 7 is detected by a phase wave detector 4. The signal corresponding to the phase difference is outputted so as to be a control voltage in LPF 5 and to be given to a variable capacitance diode so that the oscillation frequency of the RF oscillator 16 is controlled.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an FM stereo transmitter, and particularly to an audio signal output from an audio device such as a CD changer, a liquid crystal television, a video tape recorder (hereinafter referred to as "VTR") mounted on an automobile. It relates to an FM stereo transmitter transmitting to an FM receiver.

[0002]

2. Description of the Related Art In-vehicle CD changers, LCD TVs,
In an audio device such as a VTR to be installed in a vehicle later, a car stereo FM receiver is used, and an audio signal output from the audio device is frequency-modulated by an FM stereo transmitter to generate a modulated wave. It is being transmitted to the FM receiver. Then, the FM receiver demodulates the signal and outputs the audio from the car stereo.

FIG. 2 shows a conventional FM stereo transmitter used in such an audio device. L channel signal (left audio signal) and R of the audio signal output from the audio equipment
The channel signal (right audio signal) is first converted into a sum signal (L + R) which is a main channel signal and a difference signal (LR) which is a sub channel signal in a multiplexer (hereinafter referred to as “MPX”) 12. Next, the sine wave having a frequency of 38 kHz oscillated from the pilot signal oscillator 28 is used as a subcarrier, and is amplitude-modulated (A) with the difference signal (LR).
M). However, the subcarrier is suppressed, and the component of the subcarrier is not included after the amplitude modulation. Then, it is combined with the sum signal (L + R) which is the main channel signal and output from the MPX 12.

Further, the 38 kHz signal oscillated from the pilot signal oscillator 28 is divided by the frequency divider 27 into a half frequency of 19 kHz, and is combined with the signal output from the MPX 12 by the combiner 15. However, the 19 kHz signal output from the frequency divider 27 is called a pilot signal, and the signal output from the synthesizer 15 is called a stereo composite signal. Further, the crystal oscillator 29 and the capacitor C3 are connected to the pilot signal oscillator 28, and the oscillation frequency of the pilot signal oscillator 28 is set to 38 k by the crystal oscillator 29.
It becomes Hz.

The stereo composite signal output from the synthesizer 15 is given to the variable capacitance diodes D1 and D2 via the resistors R1 and R3, and the variable capacitance diodes D1 and D2.
The capacitance of 2 is changed. Variable capacitance diodes D1, D
By varying the capacitance of 2, the carrier wave oscillated from the radio frequency oscillator (hereinafter referred to as “RF oscillator”) 16 is frequency-modulated (FM) with a stereo composite signal.
The resulting signal is output from the RF oscillator 16.

This modulated wave is a high frequency amplifier (hereinafter referred to as "RF
It is amplified by an amplifier 17), the frequency band is limited by a band-pass filter (hereinafter referred to as “BPF”) 18, and is radiated from an antenna 19 as shown by an arrow A. In this way, the F of the car stereo (not shown) is wirelessly transmitted.
It is transmitted to the M receiver (not shown). A signal is received by an FM receiver (not shown), and the signal is demodulated, whereby voice is output from a car stereo (not shown).

The modulated wave output from the RF oscillator 16 is sent to the prescaler 6. This modulated wave is converted by the prescaler 6 into a signal having a pulse waveform synchronized with the modulated wave. The main counter 7 counts the pulses, and outputs a pulse waveform signal by a predetermined count. That is, the main counter 7 divides the frequency. The signal output from the main counter 7 is input to the phase detector 4.
The prescaler 6 may be combined with a counting circuit to perform frequency division. The frequency division ratios of the prescaler 6 and the main counter 7 are controlled by the shift register latch 8. For example, the frequency of the signal output from the main counter 7 by the frequency division becomes 1/11 of the oscillation frequency of the RF oscillator 16.

On the other hand, the PLL reference oscillator 26 outputs a reference signal having a pulse waveform whose repetition frequency is 7.2 MHz. A crystal oscillator 25 and capacitors C7 and C8 are connected to the PLL reference oscillator 26, and the frequency of the reference signal is 7.2 MHz due to the crystal oscillator 25. The reference signal is divided by the reference divider 3 and input to the phase detector 4. In addition, reference divider 3
The frequency division ratio is controlled by the shift register latch 8. For example, the signal input to the reference divider 3 is directly input to the phase detector 4 without frequency division.

The phase detector 4 detects the phase difference between the two input signals and outputs a signal corresponding to the phase difference.
This signal is converted into a control voltage by a low pass filter (hereinafter, referred to as "LPF") 5, and given to the variable capacitance diodes D1 and D2 via the resistors R2 and R3. As a result, the oscillation frequency of the RF oscillator 16 is controlled so that the phase difference between the two signals input to the phase detector 4 is reduced, and the oscillation frequency of the RF oscillator 16 is stabilized.

That is, when the frequency division of the RF oscillator 16 is divided by 1/11 by the prescaler 6 and the main counter 7 without dividing by the reference divider 3,
The oscillation frequency of the oscillator 16 is 7.2 MHz × 11 = 79.
It becomes 2MHz. Frequency modulation is performed by the stereo composite signal, and the oscillation frequency of the RF oscillator 16 fluctuates, but fluctuations due to frequency modulation are hardly transmitted to the variable diodes D1 and D2 by the LPF 5. for that reason,
The RF oscillator 16 controls the frequency of the carrier frequency-modulated by the stereo composite signal to 79.2 MHz.

Further, the oscillation frequency of the RF oscillator 16 is recursively controlled in this way, and this is a PLL (Phase
Locked Loop) is a type of circuit. PLL reference oscillator 2
Since the frequency of the reference signal of 6 is 7.2 MHz, each frequency division ratio of the reference device 3, the prescaler 6 and the main counter 7 is controlled by the shift register latch 8. Controlled.

Each of these division ratios is determined by the I / O controller 9
Set by. By inputting the chip enable signal from the terminal CE, the I / O controller 9 is initialized and the frequency of the carrier wave of the RF oscillator 16 can be controlled. Further, by inputting the clock signal from the terminal CK, the I / O controller 9 operates in synchronization with the clock signal. Then, by inputting data from the terminal DA, the I / O controller 9 determines the frequency division ratios of the reference divider 3, the prescaler 6, and the main counter 7, and sets the shift register latch 8.

As described above, the frequency of the carrier wave of the RF oscillator 16 is controlled to 7.2 MHz × 11 = 79.2 MHz. However, if the frequency of the carrier wave is only 79.2 MHz, there is a possibility that the FM receiver (not shown) may interfere with the FM broadcast. In consideration of this, the data is input to the I / O controller 9 from the terminal DA, and the division ratios of the reference divider 3, the prescaler 6, and the main counter 7 are switched.

For example, when the reference divider 3 does not perform frequency division and the prescaler 6 and the main counter 7 divide the frequency into 1/13, the frequency of the carrier wave of the RF oscillator 16 is 7.2 MHz × 13 = 93.6 MHz. Becomes In addition, the reference divider 3 does not perform frequency division, and the prescaler 6 and the main counter 7 reduce the frequency to 1/15.
When the frequency is divided into, the frequency of the carrier wave of the RF oscillator 16 becomes 7.2 MHz × 15 = 108.0 MHz. Carrier frequencies are 79.2MHz, 93.6MHz, 10
From 8.0 MHz, select an FM receiver (not shown) with no interference. Depending on the data input to the terminal DA,
These three frequencies are switched.

In FIG. 2, 10 is an amplifier for amplifying the L channel signal. Reference numeral 11 is an amplifier for amplifying the R channel signal. R1 to R3 are resistors for appropriately combining the stereo composite signal and the control voltage output from the LPF 5. C4 to C6 are RF oscillators 1
6 is a capacitor that determines the oscillation frequency, L1 is RF
This is a coil that determines the oscillation frequency of the oscillator 16.

[0016]

However, in the above-mentioned conventional FM stereo transmitter (FIG. 2), the two crystal oscillators 25 and 29 are required, resulting in an increase in cost. Further, the harmonics of the 7.2 MHz reference signal of the PLL reference oscillator 26 may interfere with the frequency band of FM broadcasting received by the FM receiver (not shown).

The present invention solves such a problem by reducing the cost by using one crystal oscillator and preventing the harmonics of the PLL reference oscillator from interfering with the frequency band of FM broadcasting. The purpose is to

[0018]

In order to achieve the above object, in the first configuration of the present invention, a means for converting an L channel signal, an R channel signal and a pilot signal into a stereo composite signal is provided, and the frequency modulation means is used. In an FM stereo transmitter in which a carrier wave transmits a modulated wave whose frequency is modulated by the stereo composite signal, an oscillator having an oscillation frequency that can obtain 38 kHz by dividing is provided, and by dividing the oscillation frequency, The frequency of the carrier wave is controlled by using a PLL circuit which uses the pilot signal as the pilot signal and the oscillation frequency as the reference frequency.

According to this structure, the oscillator having the oscillation frequency that can obtain 38 kHz by dividing the frequency is provided. By dividing the frequency, 38 kHz is obtained, and by further dividing the frequency, a pilot signal having a frequency of 19 kHz is obtained. The pilot signal, the L channel signal, and the R channel signal are converted into a stereo composite signal by the means for converting into a stereo composite signal.

The carrier wave is frequency-modulated with the stereo composite signal by the frequency modulation means, and the modulated wave is transmitted. The frequency of the carrier wave is controlled using a PLL circuit.
The PLL circuit detects a phase difference between the frequency of the carrier wave divided by a certain dividing ratio and the oscillation frequency of the oscillator divided by a certain dividing ratio, and reduces the phase difference. Control the frequency of the carrier. As a result, the frequency of the carrier wave is controlled and stabilized. In the conventional FM stereo transmitter, two crystal oscillators are required for the PLL circuit and the pilot signal generation. With this configuration, one crystal oscillator is used for the PLL circuit and the pilot signal generation. , Low cost. Also, set the oscillation frequency of the oscillator to 3
If the frequency is set lower than that of the conventional oscillator for PLL circuit such as 8 kHz, 76 kHz ... Even if a harmonic is generated, the level becomes low in the frequency band of FM broadcasting and no interference occurs. The oscillation frequency of the oscillator is not limited to an integral multiple of 38 kHz, and may be an oscillator having an oscillation frequency of 38 kHz by setting the frequency division ratio to a fraction such as 3/5 or 5/7.

Further, in the second structure of the present invention, the first structure
In the above configuration, the L channel signal and the R channel signal are audio signals from the audio equipment mounted on the automobile.

According to this structure, the audio signals from the audio equipment mounted on the automobile such as the CD changer, the liquid crystal television, the VTR and the like are received by the FM stereo transmitter of the first structure by the FM stereo transmitter of the car stereo. Sent to the machine. The signal is demodulated by the FM receiver and the sound is output from the car stereo. As described above, when the audio signal is transmitted from the audio device to the FM receiver, in this configuration, only one crystal oscillator is required for the FM stereo transmitter, which results in low cost.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to FIG. As compared with the conventional FM stereo transmitter (FIG. 2), the present embodiment has only one crystal oscillator 1 as described later. In addition, in FIG.
The same parts as those of are denoted by the same reference numerals, and the description thereof will be omitted.

In this embodiment, the oscillator 2 oscillates at a frequency of 76 kHz. The crystal oscillator 1 and capacitors C1 and C2 are connected to the oscillator 2, and the oscillation frequency is determined by the crystal oscillator 1 and is 76 kHz. The frequency of the reference signal of 76 kHz becomes 38 kHz, which is half the frequency, by the frequency divider 13,
It is sent to PX12.

In the MPX 12, as described in the above-mentioned conventional FM stereo transmitter (FIG. 2), the L channel signal and the R channel signal to be input are first the sum signal (L + R) which is the main channel signal and the sub channel. It is converted into a difference signal (LR) which is a signal. Next, input 38kHz
Is used as a sub-carrier and is amplitude-modulated (AM) in a carrier-suppressing manner with a difference signal (L-R), combined with a sum signal (L + R), and output from the MPX 12. Further, the frequency of the 38 kHz signal output from the frequency divider 13 is further divided in half by the frequency divider 14 to obtain a 19 kHz pilot signal. The signal output from the MPX 12 and the pilot signal are combined by the combiner 15 to form a stereo composite signal.

On the other hand, the repetition frequency is 7 from the oscillator 2.
A reference signal having a pulse waveform of 6 kHz is sent to the reference divider 3. As in the conventional FM stereo transmitter (FIG. 2), the PLL circuit is used, and the signal output from the reference divider 3 and the oscillation frequency of the RF oscillator 16 are frequency-divided by the prescaler 6 and the main counter 7. The phase difference of is detected by the phase detector 4. A signal corresponding to this phase difference is output and becomes a control voltage in the LPF 5,
The oscillation frequency of the RF oscillator 16 is controlled by being applied to the variable capacitance diode.

The frequency of the reference signal is divided into 1/3 by the reference divider 3, and 76 kHz / 3 = 25.333.
kHz. R with prescaler 6 and main counter 7
The carrier wave frequency of the RF oscillator 16 is 25.3333 k by dividing the frequency of the signal output from the F oscillator 16 into 1/3000 and detecting the phase difference by the phase detector 4.
Hz × 3000 = 75.999 MHz.

Comparing this conventional FM stereo transmitter (FIG. 2) with this embodiment, the reference divider 3, the prescaler 6 and the main counter 7 have different frequency division ratios. These frequency division ratios are controlled by the shift register latch 8 and set by the I / O controller 9.
If the FM receiver (not shown) has a 76.0 MHz FM
If it is set to receive a signal, it will be offset by 1 kHz, but there is no problem because the difference is small.

In particular, in Japan, the interval between the reception frequencies of FM broadcasts is 100 kHz, so there is no problem in reception up to a deviation of about 10 kHz. In addition, conventional P
Since the frequency of the crystal oscillator 1 is lower than the frequency of the LL reference oscillator 26 (FIG. 2) of 7.2 MHz, even if harmonics are generated, the level becomes low in the FM broadcast frequency band, and almost no interference occurs. Absent.

However, the frequency of the carrier wave is 76.0 MHz.
By itself, there is a possibility that the FM receiver (not shown) may interfere with the FM broadcast. By inputting data from the terminal DA to the I / O controller 9, the frequency division ratio of the reference divider 3, the prescaler 6 and the main counter 7 is changed, and the carrier frequency of the RF oscillator 16 is switched.

For example, the reference divider 3 is fixed so that the frequency of the input signal is divided into 1/3, and the frequency is set to 1 by the prescaler 6 and the main counter 7.
When the frequency is divided into 3600, the frequency of the carrier wave of the RF oscillator 16 is 76 kHz / 3 × 3600 = 91.2.
MHz. Further, if the frequency is divided into 1/3900 by the prescaler 6 and the main counter 7,
The frequency of the carrier wave of the RF oscillator 16 is 76 kHz / 3 × 3.
900 = 98.8 MHz. Set the carrier frequency to 76.0MHz, 91.2MHz, 9 so that there is no interference.
Select from 8.8 MHz.

The oscillation frequency of the oscillator 2 is 76 kHz.
Alternatively, the crystal oscillator 1 having a frequency of 38 kHz or an integral multiple of 38 kHz may be used. In that case, the frequency division of the frequency divider 13 is changed so that the frequency of the output signal is 38
It may be kHz. For example, the oscillation frequency is 152 kHz
When the frequency is z, if the frequency is divided by the frequency divider 13 to 1/4, a 38 kHz subcarrier is given to the MPX 12, and the frequency divider 14 outputs a 19 kHz pilot signal. Further, the frequency division ratio of the frequency divider 13 is 3/5 or 5
It may be a fraction such as / 7. At this time, the frequency divider 1
The oscillator 2 having an oscillation frequency that can obtain 38 kHz by 3 is provided.

Although the reference divider 3, the prescaler 6 and the main counter 7 were controlled by a pulse waveform signal, the oscillator 2 outputs a sine waveform signal to the reference divider 3, and RF
Even if the reference divider 3, the prescaler 6, and the main counter 7 are frequency dividers that handle a sine-waveform signal with the above-mentioned frequency division ratio, the same operation is performed so that the phase difference from the sine-waveform signal oscillated from the oscillator 16 is detected. It becomes control.

FM stereo transmitter of the present embodiment (FIG. 1)
Is used, for example, in a vehicle-mounted CD changer. C
The D changer is installed in the trunk of the car and operated by remote control. In the CD changer, the L channel signal and the R channel signal of the audio signal from the CD are transmitted to the F of a car stereo (not shown) built in the automobile by the FM stereo transmitter (FIG. 1) of this embodiment.
It is transmitted to the M receiver (not shown). Audio is output from the car stereo by demodulating the signal in the FM receiver (not shown). The FM stereo transmitter (FIG. 1) of this embodiment has only one crystal oscillator 1 and is low in cost. Further, it can be widely used not only for CD changers but also for audio equipment such as in-vehicle liquid crystal televisions and VTRs.

[0035]

<Effect of Claim 1> In the conventional FM stereo transmitter, the crystal oscillators are used separately for the pilot signal generation and the PLL circuit, respectively. However, according to the present invention, one crystal oscillator is used. Since the oscillator is used for generating the pilot signal and for the PLL circuit, the number of crystal oscillators can be reduced to one, resulting in cost reduction. Further, the frequency of the crystal oscillator used for the conventional PLL circuit is a high frequency, but by lowering the oscillation frequency of the crystal oscillator, the level becomes low even if harmonics are generated. It hardly interferes with the broadcasting frequency band.

<Effect of Claim 2> In an audio device mounted on an automobile such as a CD changer, a liquid crystal television, a VTR, etc., an audio signal is transmitted to an FM receiver of a car stereo by using an FM stereo transmitter. It The signal is demodulated by the FM receiver and the sound is output from the car stereo. According to the present invention, an audio signal can be transmitted to an FM receiver at low cost.

[Brief description of drawings]

FIG. 1 is a block diagram of an FM stereo transmitter according to one embodiment of the present invention.

FIG. 2 is a block diagram of a conventional FM stereo transmitter.

[Explanation of symbols]

 1 Crystal Oscillator 4 Phase Detector 8 Shift Register Latch 9 I / O Controller 12 MPX (Multiplexer) 13 Frequency Divider 14 Frequency Divider 16 RF Oscillator (Radio Frequency Oscillator) 19 Antenna D1, D2 Variable Capacitance Diode

Claims (2)

[Claims] 1. An FM stereo transmitter comprising means for converting an L channel signal, an R channel signal and a pilot signal into a stereo composite signal, and transmitting a modulated wave in which a carrier is frequency-modulated by the stereo composite signal by a frequency modulating means. In this case, an oscillator having an oscillating frequency capable of obtaining 38 kHz by dividing is provided, and the oscillating frequency is divided into the pilot signal, while the frequency modulating means uses the oscillating frequency as a reference frequency. An FM stereo transmitter, wherein a frequency of the carrier wave is controlled by using a circuit. 2. The FM stereo transmitter according to claim 1, wherein the L channel signal and the R channel signal are audio signals from an audio device mounted on an automobile.