JP4903633B2 - Tuner for road traffic information communication system - Google Patents

Description

  The present invention relates to a road traffic information communication system tuner for receiving a road traffic information signal included in an FM multiplex broadcast signal.

  The road traffic information communication system multiplexes FM traffic waves and transmits road traffic information such as traffic jams and traffic regulations edited and processed at the VICS center to a wide area in real time. For example, an FM multiplex broadcast signal is received by a dedicated receiver on the vehicle side, a road traffic information signal is extracted, and is overwritten and displayed on a map prepared in a car navigation system.

  In addition, as a method that does not have a dedicated receiver corresponding to the road traffic information communication system, a method can be considered in which the reception frequency band of the television tuner is expanded to the FM band. If a television tuner can be used for road traffic information reception, there is an advantage that the number of parts can be reduced and the size can be reduced as compared with the case of using a dedicated receiver. However, in the future, the shift to digitalization of television broadcasts will make it impossible to receive FM audio multiplex broadcasts. In the digital television broadcasting system, the intermediate frequency signal is input to the digital demodulation circuit and the video and audio are demodulated. Therefore, the intermediate frequency portion is not necessary, and FM audio multiplex broadcasting cannot be received as it is.

On the other hand, recently, FM tuners mounted on mobile phones, car navigation systems, and the like have been downsized due to the use of IC chips. If an FM tuner integrated with IC for mobile use can be used as a tuner for receiving road traffic information broadcast by FM multiplex from the VICS center, it is possible to meet demands for miniaturization, weight reduction and low power consumption. FM tuners integrated into ICs for mobile applications are greatly restricted by built-in electronic components in order to meet the demands for small size, light weight, and low power consumption. For example, as the number of stages of limiter amplifiers that amplify the intermediate frequency signal increases, the signal-to-noise ratio can be improved and the signal level can be greatly amplified, but the number of stages is limited to the minimum number that can be demodulated.
Japanese Patent Application Laid-Open No. 09-200509

  However, in FM tuner ICs for mobile applications in which the number of stages of limiter amplifiers is limited, the absolute signal-to-noise ratio cannot be secured in the voice band (76 kHz in Japan) where road traffic information is multiplexed, and the output level is low. There's a problem.

  The present invention has been made in view of the above points, and is capable of receiving road traffic information signals FM-broadcasted using an FM tuner integrated into an IC for mobile use, and an absolute signal in a voice band. An object of the present invention is to provide a tuner for a road traffic information communication system that can improve the noise-to-noise ratio and the level reduction.

The tuner for road traffic information communication system according to the present invention includes an FM broadcast receiving integrated circuit in which a receiving circuit for receiving FM multiplex broadcast signals is constituted by an integrated circuit for portable devices, and the FM broadcast receiving integrated circuit. A band pass filter connected to the FM detection output terminal for selecting a road traffic information signal included in the FM multiplex broadcast signal, and a road traffic information connected to the band pass filter and selected by the band pass filter And the FM broadcast receiving integrated circuit includes a limiter amplifier limited to a minimum number of stages capable of demodulating the road traffic information signal, and the amplifier circuit includes the limiter amplifier. Amplification is performed so as to correct a decrease in signal level according to the number of stages .

  According to this configuration, an FM broadcast receiving integrated circuit that is integrated into an IC for mobile use is used as an FM tuner to meet the demand for reduction in size, weight, and power consumption. On the other hand, a road selected by a bandpass filter By amplifying the traffic information signal by the amplifier circuit, it is possible to improve the absolute signal-to-noise ratio and level reduction in the FM broadcast audio band.

  The tuner for the road traffic information communication system can be mounted on a vehicle-mounted and portable navigation system. The navigation system may be a navigation system incorporating a digital terrestrial broadcast receiving television tuner.

  According to the present invention, it is possible to receive road traffic information signals that have been FM multiplex broadcasted using an FM tuner that is integrated into an IC for mobile applications, and meet the demands for miniaturization, weight reduction, and low power consumption, as well as VICS data. The absolute signal-to-noise ratio and level reduction in the band can be improved.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a schematic configuration diagram of a tuner for a road traffic information communication system according to an embodiment of the present invention. It is assumed that the tuner for road traffic information communication system shown in the figure is mounted on in-vehicle and portable navigation systems, and that the navigation system has a built-in television tuner for receiving terrestrial digital broadcasting.

  A reception signal is introduced into the input terminal 1 from the antenna device side. The input stage of the FM tuner 2 is connected to the input terminal 1. The FM tuner 2 is an FM broadcast receiving integrated circuit that is integrated into an IC for mobile use, and is configured to receive FM multiplex broadcast signals. A band pass filter 3 is connected to the detection output terminal of the FM tuner 2. The band pass filter 3 has a band pass characteristic for selecting a road traffic information signal included in the FM multiplex broadcast signal. The band pass filter 3 is configured by combining a low pass filter 3a and a high pass filter 3b.

  For example, when the band of the road traffic information signal is 76 kHz, the low pass filter 3a is set to cut a band of 80 kHz or higher, while the high pass filter 3b is set to cut a band of 70 kHz or lower. In the present embodiment, the bandpass filter 3 is configured by a combination of the lowpass filter 3a and the highpass filter 3b, but the bandpass filter 3 is not limited to such a configuration.

  An amplifier circuit 4 that corrects the level drop is connected to the subsequent stage of the band pass filter 3. In the present embodiment, an operational amplifier is used as the amplifier circuit 4. The output terminal of the amplifier circuit 4 is connected to the output terminal 5 of the tuner.

FIG. 2 is a specific circuit configuration diagram of the band-pass filter 3 and the amplifier circuit 4.
The input terminal 10 of the low-pass filter 3 a is connected to the detection output terminal of the FM tuner 2. In the low-pass filter 3a, one end of a resistor 11 is connected to the input terminal 10. The other end of the resistor 11 is connected to the ground via a capacitor 12. One end of another resistor 13 is connected to the other end of the resistor 11. The other end of the resistor 13 is connected to the ground via a capacitor 14. Thus, the low-pass filter 3a has a two-stage configuration of an RC filter. The low pass filter 3a and the high pass filter 3b are connected via a resistor 15.

  In the high-pass filter 3b, the other end of the resistor 15 is connected to the output terminal 20 via the capacitor 16 and the resistor 17 in series, and the resistor 17 is connected between the connection point between the resistor 15 and the capacitor 16 and the ground. ing. Further, a capacitor 19 is connected between the connection point between the resistor 15 and the capacitor 16 and the output terminal 20.

  The operational amplifier 4a constituting the amplifier circuit 4 is connected to an intermediate point of a voltage dividing resistor in which one input terminal (positive) is connected in series, and the other input terminal (negative) is connected to one terminal of the capacitors 16 and 19 and a resistor. 18 is connected to the connection point.

  FIG. 3 is a configuration diagram of the FM tuner 2, the band-pass filter 3, and the amplifier circuit 4 mounted on the substrate. The tuner input terminal 30 is connected to the FM antenna. The FM multiplex broadcast signal introduced from the tuner input terminal 30 is allowed to pass through the RF band pass filter 31. After being amplified by the LNA 32, it is input to the frequency conversion circuit 33, and the FM broadcast signal (RF band) and the local oscillation signal from the local oscillator 34 are combined and frequency-converted to an intermediate frequency. An intermediate frequency AGC circuit 35 and an IF filter 36 are input to a limiter amplifier 37 for amplification.

  The S / N and the signal level are determined by the number of stages of the limiter amplifier 37. However, in an integrated circuit for FM broadcast reception integrated into an IC for mobile use, the number of stages can be demodulated by the demodulator 38 at the subsequent stage. .

  The FM broadcast signal (IF band) amplified by the limiter amplifier 37 is demodulated by the demodulator 38. In the present embodiment, the soft mute circuit 39 is connected to the output terminal of the demodulator 38 serving as the detection output terminal of the FM tuner 2, but it can also be directly connected to the bandpass filter 3.

In the circuit configuration example shown in the figure, the output signal level of the IF filter 36 is sampled by the ADC 41 and sent to the microcomputer outside the substrate 40 via the I ² C bus 42. In addition, the microcomputer controls the operation of the soft mute circuit 39 by transmitting a control signal via the I ² C bus 42 corresponding to the signal level.

Next, the operation of the present embodiment configured as described above will be described.
An FM multiplex broadcast signal in which traffic information is superimposed on 76 kHz of the FM broadcast audio band is received by the FM antenna and input to the tuner input terminal 30. In the FM tuner 2, the frequency conversion circuit 33 frequency-converts the FM multiplex broadcast signal to an intermediate frequency, and then performs gain control and filtering processing to obtain an intermediate frequency signal of the FM multiplex broadcast signal. The level of this intermediate frequency signal is amplified by a limiter amplifier 37. The intermediate frequency signal amplified by the limiter amplifier 37 is input to the demodulator 38 and demodulated from the FM broadcast audio band to the traffic information (76 KHz).

  In the present embodiment, the detection output signal of the demodulator 38 is input to the bandpass filter 3 (3a, 3b) having a passband of 76 kHz of the FM broadcast audio band to remove unnecessary bands, and the bandpass filter 3 The FM broadcast audio band that has passed (3a, 3b) is amplified by the amplifier circuit 4 to correct the level drop.

  As shown in FIG. 4, since the detection output level of the demodulator 38 is limited in the number of stages of the limiter amplifier 37, the signal level near the FM broadcast audio band (76 kHz) is very low, and the traffic information signal can be buried in noise. High nature. FIG. 5 shows the S / N of the detection output itself of the demodulator 38. The S / N of the detection output itself is 4 dB in the FM broadcast audio band, which is a difficult level for decoding traffic information without bit errors.

  On the other hand, as in the present embodiment, when the bandpass filter 3 removes unnecessary frequencies other than the FM broadcast audio band from the detection output signal and amplifies it by the amplifier circuit 4 to correct the level drop, FIG. As indicated by the mark, the signal level near 76 kHz in the FM broadcast audio band is sufficiently high, and the S / N is also improved to about 19 dB as indicated by the circle in FIG.

  As described above, according to the present embodiment, the bandpass for removing unnecessary frequencies other than the FM broadcast audio band from the detection output signal extracted from the demodulator 38 provided in the FM tuner 2 that is integrated into an IC for mobile use. A filter 3 and an amplifying circuit 4 for amplifying the FM broadcast audio band signal output from the bandpass filter 3 are provided, and the FM tuner 2 is made compact by using an FM broadcast receiving integrated circuit integrated into a mobile application. -While meeting the demand for light weight and low power consumption, the absolute signal-to-noise ratio and level reduction in the FM broadcast VICS data band can be improved.

  The present invention is applicable to an FM tuner for receiving a road traffic information signal included in an FM multiplex broadcast signal transmitted from a VICS center of a road traffic information communication system.

Schematic configuration diagram of a tuner for a road traffic information communication system according to an embodiment 1 is a circuit configuration diagram of the bandpass filter and the amplifier circuit shown in FIG. Configuration diagram of FM tuner arranged on a substrate in the above embodiment The figure which shows the frequency characteristic of the signal level in a prior art example and this invention The figure which shows the frequency characteristic of S / N of the FM broadcast audio | voice band signal in a prior art example and this invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Input terminal, 2 ... FM tuner, 3 ... Band pass filter, 3a ... Low pass filter, 3b ... High pass filter, 4 ... Amplifier circuit, 4a ... Operational amplifier, 5 ... Output terminal, 10 ... Input terminal, 11, 13, 15 , 17, resistors, 12, 14, 16, 19, capacitors, 20, output terminals, 30, tuner input terminals, 31, RF bandpass filters, 32, LNA, 33, frequency conversion circuit, 34, local oscillator, 35,. AGC circuit (for IF), 36 ... IF filter, 37 ... limiter amplifier, 38 ... demodulator, 39 ... soft mute circuit, 40 ... substrate, 41 ... ADC, 42 ... I ² C bus

Claims (3)

An FM broadcast receiving integrated circuit in which a receiving circuit for receiving an FM multiplex broadcast signal is composed of an integrated circuit for portable devices;
A band pass filter connected to an FM detection output terminal of the FM broadcast receiving integrated circuit for selecting a road traffic information signal included in the FM multiplex broadcast signal;
An amplification circuit connected to the bandpass filter and amplifying the road traffic information signal selected by the bandpass filter ;
The FM broadcast receiving integrated circuit includes a limiter amplifier limited to a minimum number of stages capable of demodulating a road traffic information signal,
A tuner for a road traffic information communication system , wherein the amplifier circuit amplifies the signal level so as to correct a decrease in signal level according to the number of stages of the limiter amplifier . The tuner for a road traffic information communication system according to claim 1 , wherein the tuner can be mounted on a vehicle-mounted and a portable navigation system. 3. The road traffic information communication system tuner according to claim 2 , wherein the navigation system is a navigation system with a built-in television tuner for receiving digital terrestrial broadcasting.

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