JP3390199B2 - FM tuner - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ARC function and an RDS.
The present invention relates to an FM tuner having a function. 2. Description of the Related Art In FM broadcasting, a subcarrier outside the audible band can be used, and a data signal of about 1 kbit / s can be multiplexed there. For example, the European Broadcasting Union (EBU) F
There is M multiplex data broadcasting (RDS: Radio Data System), and its specification includes usage as a program identification code. That is, when a broadcast station broadcasts, broadcast-related information such as information related to the program contents is transmitted as data by multiplex modulation, and a desired data is demodulated on the receiving side. By making the program content selectable, the service can be provided to radio viewers. In such RDS, 57 kHz, which is the third harmonic of a 19 kHz stereo pilot signal outside the frequency band of the FM modulated wave, is used as a subcarrier, and the subcarrier is filtered and bi-phase coded. A radio data signal is amplitude-modulated by a data signal indicating information related to broadcasting such as contents, and the amplitude-modulated subcarrier is frequency-modulated to a main carrier for broadcasting. A radio data signal is repeatedly multiplexed and transmitted with a group of 104 bits as is clear from FIG. 1 showing its baseband coding structure. One group is composed of four blocks each having a 26-bit structure, and each block includes a 16-bit information word and one block.
It consists of a 0-bit check word. Further, as shown in FIG. 2, block 1 shows program recognition (PI) data representing a network, block 2 shows traffic program recognition (TP) data and traffic announcement recognition (TA) data,
Block 3 is provided with frequency (AF) data of a group of network stations broadcasting the same program, and block 4 is provided with program service name information (PS) data such as a broadcast station name and a network name. [0006] Each group is classified into 16 types of types 0 to 15 by 4 bits according to the contents, and two versions of A and B are defined for each type (0 to 15). These recognition codes are arranged in block 2. The AF data of the network station is transmitted only in the type 0A group. For example, in the case of an in-vehicle receiver, the reception state of a broadcast wave being received may deteriorate as the vehicle travels. However, in the RDS broadcast, as described above, one RDS broadcast wave is received. Then, it is possible to obtain AF data of a group of network stations broadcasting the same program, and it is possible to switch the reception frequency to another same network station frequency having a good reception state by utilizing the AF data. . Also, for example, in a standby state of a TA interrupt due to TA data, a T
By taking in the A data, a TA interrupt is possible. On the other hand, since the FM broadcast radio waves have a strong linearity, the electric field fluctuates greatly due to the influence of the terrain and buildings, the distance from the transmitting station, and the like. In such a case, an ARC (automatic reception control) function for changing a reception state according to a change in a radio wave condition is required. This function performs the original Hi-Fi reception in a strong electric field, and as the electric field level decreases, an auto-separation function that continuously switches the reproduction sound from stereo to monaural, an auto high cut function that reduces high-frequency noise, and a reproduction output. And a soft mute function for reducing the noise. [0009] As for the ARC, for example, Japanese Utility Model Publication No. Sho 59-31077 discloses an FM stereo receiver capable of securing a substantially constant S / N even with a continuous change in electric field strength. . That is, FIG.
Shows the control characteristics of the separation control circuit 21 with respect to the control voltage C in FIG.
The channel and the dotted line show the separation characteristics of the L channel, respectively. FIG. 5 shows the control characteristic of the f characteristic control circuit 22 with respect to the control voltage B in FIG. 3, and shows the attenuation characteristic with respect to 10 kHz. FIG. 6 shows the control characteristics of the variable attenuator 20 with respect to the antenna input level. The solid line shows the non-operating attenuation characteristics, and the dotted line shows the operating attenuation characteristics. Here, the level setting circuits 23 and 24 are appropriately set, and when the antenna input level becomes 45 dB / μV, the separation control circuit 21 starts operating first, and when the level becomes 25 dB / μV, the monaural mode is set. And the antenna input level is 3
At 5 dB / μV, the frequency control circuit 22 operates to increase the attenuation in the high frequency range until it reaches 15 dB / μV. When the antenna input level reaches 25 dB / μV, the variable attenuator 20 operates. Thereafter, the attenuation is continuously increased. In this manner, the characteristics of each circuit can be continuously changed from the operation start point of each circuit as shown in FIGS. 4 to 6 in accordance with the decrease in the input level. Almost constant good S regardless of the size of
/ N can be secured. FIG. 7 shows an example of the configuration of an FM tuner in which the above-described RDS function and ARC function are incorporated. The FM radio wave fetched from the antenna 1 is tuned by the front end unit 2. , The intermediate frequency IF. The tuned intermediate frequency IF is amplified by the intermediate frequency amplifying unit 3 and further demodulated by the FM detection unit 4, and then converted into L and R stereo demodulated signals by the stereo MPX unit 5. The L and R stereo demodulated signals undergo de-emphasis 6 and 7, respectively, and are then amplified and output by low-frequency amplifiers 8 and 9. On the other hand, the ARC circuit 10 monitors the level of the signal detected by the FM detector 4 and activates, for example, the auto-separation function of the stereo MPX 5 when the electric field level of the radio wave currently being received decreases. As a result, the reproduced sound can be continuously switched from stereo to monaural, thereby improving S / N. Also, RD
When detecting the program identification code signal included in the detection signal by the FM detection unit 4, the S detection unit 11 switches the tuning of the front end unit 2 to receive, for example, traffic information currently being broadcast. In the above-mentioned conventional FM tuner, for example, as shown in FIG.
The operating point of the RDS function in the DS detector 11 is A
The operating point of the ARC function in the RC circuit 10 is located on the lower side. This is usually set to a low level range in order to continuously switch the reproduced sound from stereo to monaural as the electric field level decreases. In particular, the operating point of the ARC function is uniquely determined. Therefore, the station currently receiving by the FM tuner is RD
In the case of the S station, the reception switching of the RDS station broadcasting the same program is performed before the operation of the ARC function effectively works, so that the ARC function cannot be effectively used. There was a defect. The present invention has been made in view of such circumstances, and has as its object to provide an FM tuner capable of sufficiently obtaining the effect of the ARC function even when the receiving station is an RDS station. . In order to achieve the above object, an FM tuner of the present invention uses an ARC function to perform FM
Switching control for continuously switching the stereo demodulation operation from stereo to monaural according to the detection output is possible, and the RDS function can switch the reception frequency according to the reception state based on various information included in the RDS data. possible a FM tuner, when the RDS data is detected, the operating point of the ARC feature
It is characterized in that the position is changed to a position higher than the operating point of the RDS function . According to the FM tuner of the present invention, the ARC function and the RD
An attempt is made to effectively use the ARC function when combined with the S function. For example, the operating point of the ARC function which is usually lower than the operating point of the RDS function is set as follows.
When RDS data is detected by the RDS function, R
This is earlier than the operating point of the DS function. Thus, the operating point of the ARC function is earlier than the operating point of the RDS function, so that the ARC function can be effectively activated until the operation of the RDS function starts. Embodiments of the present invention will be described below in detail with reference to the drawings. In the drawings described below, the same parts as those in FIG. 7 are denoted by the same reference numerals, and redundant description will be omitted. FIG. 9 shows an embodiment of the FM tuner according to the present invention. The FM radio wave fetched from the antenna 1 is tuned by the front-end unit 2 to have the intermediate frequency IF. The tuned intermediate frequency IF is
The signal is amplified by the intermediate frequency amplifying unit 3 and further amplified by the FM detecting unit 4
After being demodulated by the stereo MPX unit 5,
This is an R stereo demodulated signal. Each of the L and R stereo demodulated signals undergoes de-emphasis 6 and 7,
The signals are amplified and output by the low-frequency amplifiers 8 and 9. On the other hand, when the reception signal level (SL) detected by the FM detector 4 is lowered and the reception state is deteriorated, the ARC circuit 10 switches the stereo demodulation operation of the stereo MPX 5 to monaural demodulation. Is output. When the RDS detector 11 detects the program identification code signal included in the detection signal of the FM detector 4, it switches the tuning of the front end unit 2 to receive, for example, traffic information currently being broadcast. Further, when detecting the program identification code signal, the RDS detector 11 normally sets the operating point of the ARC function in the ARC circuit 10 located below the operating point of the RDS function in the RDS detector 11 to the RDS function. Outputs a signal to advance the operating point. Next, the operation of the FM tuner having such a configuration will be described with reference to FIGS. First, the tuning of the station to be received in the front end unit 2 is completed (step 1101), and the tuned intermediate frequency IF is amplified by the intermediate frequency amplifying unit 3;
Received signal level (SL) demodulated by M detector 4
Is taken into the ARC circuit 10 (step 110).
2). Next, it is determined whether or not the currently receiving station is an RDS station (step 1103). When determining whether or not an RDS station is present, if the currently receiving station is an RDS station, if the program identification code signal included in the detection signal by the FM detection unit 4 is detected by the RDS detection unit 11, the ARC operation is performed. The set value of the point is changed (step 11
04). That is, it is determined whether the received signal level (SL) is lower than the operating point of the ARC function in the ARC circuit 10 (step 1105). If not, as shown in FIG. 4, the RDS detector 11
A located below the operating point of the RDS function in
The operating point of the ARC function in the RC circuit 10 is changed to a position higher than the operating point of the RDS function. Thus, even if the currently receiving station is an RDS station, since the ARC function operates before the RDS function operates, the reception signal level (SL) decreases immediately before the operating point of the RDS function. However, for example, the auto-separation function can be operated, and the S / N
You can hear a good playback sound. As described above, in the present embodiment, when the currently receiving station is an RDS station, the RDS
ARC circuit 1 located below the operating point of DS function
Since the operating point of the ARC function of 0 is made earlier than the operating point of the RDS function, until the operation of the RDS is started,
The ARC function can be effectively operated. Also, A
Since the RC function can be effectively used, a reproduced sound having a good S / N can be heard even during continuous reception by the RDS station. As described above, according to the FM tuner of the present invention, when RDS data is detected by the RDS function, for example, the ARC function normally located at a position lower than the operating point of the RDS function. Is made earlier than the operating point of the RDS function, and the ARC function is activated effectively until the operation of the RDS function is started, so that even the RDS station can sufficiently obtain the effect of the ARC. be able to.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram illustrating a baseband coding structure in a conventional RDS. FIG. 2 is a diagram showing the contents of each block in the baseband coding structure of FIG. FIG. 3 is a block diagram showing a configuration of a conventional FM stereo receiver having an ARC function. FIG. 4 is a diagram showing control characteristics of a separation control circuit with respect to the control voltage of FIG. 3; FIG. 5 is a diagram showing control characteristics of an f characteristic control circuit with respect to the control voltage of FIG. 3; FIG. 6 is a diagram showing control characteristics of a variable attenuator with respect to the antenna input level of FIG. FIG. 7 is a block diagram showing a configuration example of an FM tuner in a case where the RDS function and the ARC function in FIGS. 1 and 3 are incorporated. 8 shows an ARC function and R in the FM tuner of FIG. 7;
FIG. 3 is a diagram for explaining operating points of a DS function. FIG. 9 is a block diagram illustrating an FM tuner according to an embodiment of the present invention. FIG. 10 is a diagram for explaining operating points of an ARC function and an RDS function in the FM tuner of FIG. 9; FIG. 11 is a diagram for explaining operations of an ARC function and an RDS function in the FM tuner of FIG. 9; [Description of Signs] 1 Antenna 2 Front-end section 3 Intermediate frequency amplification section 4 FM detection section 5 Stereo MPX section 6,7 Tesse emphasis 8,9 Low frequency amplification section 10 ARC circuit 11 RDS detection section

Claims (1)

(57) [Claims 1] An ARC function enables switching control for continuously switching a stereo demodulation operation from stereo to monaural according to FM detection output, and an RDS function by an RDS function. a FM tuner capable of switching a reception frequency according to the reception state based on various information included in, when said RDS data is detected, the operation of the operating point of the ARC feature RDS function
An FM tuner characterized by changing to a position above a point .