RDS receiver

Abstract: A radio data system (RDS) receiver is adapted, when a detection output of a detector circuit of the reception level of a broadcast wave indicates that the reception level of a broadcast wave has fallen below a specified value, to check a flag which indicates permission or prohibition of selection of a broadcasting station designated by frequency data in an AF list. When it is found as the result of the check that the flag is permitting selection of a broadcasting station, the receiver selects the broadcasting station. After the selection of the broadcasting station, the receiver checks its PI code. When its proaram is found to be different as the result of the check of the PI code, the receiver sets the flag into a state prohibiting selection of the broadcasting station and selects the broadcasting station of which the reception level fell below a specified value again.

Description: The present invention relates to a receiver utilizing RDS (Radio Data System) data. In FM broadcasting in Europe, RDS data can be added to a regular audio signal. The RDS data are a collection of digital data related to broadcasting stations, programs, etc. The RDS data include such data as: AF list ... List of frequencies of broadcasting stations in the same network, and PI codes ... Program identification codes. When programs have the same PI code, it is thereby indicated that contents of the programs are the same. The RDS data passes through an encoding process for error correction. A subcarrier signal with a frequency of 57 kHz (three times the frequency 19 kHz of the stereo pilot signal) is balanced-modulated by the RDS data which has passed through the encoding process, the modulated signal is added to a monaural signal or a stereo composite signal to be frequency-multiplexed, and this multiplexed signal is transmitted carried by an FM band. Accordingly, a person in a moving automobile can continuously receive a specific program by utilizing the RDS data and PI code. More specifically, referring to FIG. 5 of the accompanying drawings, we assume that reference characters A to C denote broadcasting stations, SA to SC denote their respective service areas, and the broadcasting stations A to C are included in the same AF list and their PI codes are equal, and, further, that the automobile is traveling along the path through the service areas A to C as indicated by the arrow. Then, the receiver 1 ○ receives the radio wave from the broadcasting station A at the point Pa, 2 ○ thereafter continues to receive the radio wave from the broadcasting station A and meanwhile continues to monitor the reception level, 3 ○ when the automobile reaches the point Pb, checks the AF list because the radio wave from the broadcasting station A becomes weaker, 4 ○ switches channel selection from the broadcasting station A to the broadcasting station B because it is found as the result of the check that the radio wave of the broadcasting station B is included in the AF list of the radio wave of the broadcasting station A, 5 ○ checks the PI code of the newly selected broadcasting station B, 6 ○ thereafter, continues to receive the broadcast from the broadcasting station B because it is found as the result of the check that the radio wave from the broadcasting station B has the same PI code as the broadcast from the broadcasting station A, and 7 ○ thereafter, performs the steps 2 ○ to 6 ○ in the same manner, and when reaching the point Pc, switches channel selection from the broadcasting station B to the broadcasting station C. Accordingly, even if the automobile travels through different service areas, the person on the automobile can continuously receive the specific program by automatic reception. Such a system is described in, for example, "Nikkei Electronics", August 24, 1987. With the operations of the automatic reception as described above, the following problems arise: A. When it is found, as the result of the check of the PI code of the broadcasting station B in the step 5 ○ above, that the PI code is different from the PI code of the broadcast of the broadcasting station A which was being received up to that time, the channel selection is switched back to the broadcasting station A whose program was being received up to that time. B. Upon switching back of the channel selection to the original broadcasting station A, the step 3 ○ is executed because the radio wave from the broadcasting station A is weak, and in the following step 4 ○, the channel selection is switched from the broadcasting station A to the broadcasting station B again. C. Since the PI code of the broadcast of the broadcasting station B is different from that of the broadcasting station A, the channel selection is returned to the original station A again. D. Thereafter, the operations A. to C. are repeated. Thus, in the path beyond the point Pb, the broadcasting station A and the broadcasting station B are selected alternately. In reality, the receiver, while receiving a broadcast from the broadcasting station A, takes scores of seconds to select the broadcasting station B after checking up the AF list and checking the reception level, and it takes 300 msec or so to return the channel selection to the original broadcasting station A after selecting the broadcasting station B and checking its PI code. Accordingly, travelling along the path beyond the point Pb, the person on the automobile, while receiving the radio wave from the broadcasting station A, though it may be weak, will be disturbed, though for an instant, by the broadcasting station B every scores of seconds, or hear a broadcast from the broadcasting station B, though for an instant. DE-C-3 938 269 discloses an RDS system in which this problem can be avoided to a certain extent by inhibiting any switching operation for a time after an unsuccessful switching operation. Thus the previous station is held for a while. JP-A-2 104 133 and JP-A-1090609 disclose RDS systems in which "hunting" of stations in the AF list is avoided by special types of operation during the checking of the strength of the alternative station. The present invention has been made to further improve the RDS system in view of the problems as described above. According to the present invention there is provided a receiver comprising: a tuning circuit for selecting a broadcast wave with a predetermined frequency; a detector circuit for detecting the reception level of said broadcast wave; a decoder circuit for extracting an AF list and a PI code of RDS data from the received signal of said broadcast wave; and a memory circuit for storing said AF list, wherein the receiver is adapted when the output of the detector circuit indicates that the current reception level has fallen below a specified value to check the AF list and select a new broadcasting station therefrom, to subsequently check the PI code and, if its program is different, to deselect that station, characterised in that said receiver is further adapted to store data individually associated with each station in the AF list and indicating permission or prohibition of selection of that broadcasting station; and when the detection output of said detector circuit indicates that the reception level of said broadcast wave has fallen below the specified value, to check said permission or prohibition indicative data, then when it is found as the result of the check that said data is permitting selection of a broadcasting station, to perform said selection of the broadcasting station by means of said tuning circuit, to perform said check said PI code after the selection of said broadcasting station, and when its program is found to be different as the result of the check of said PI code, to set said data into a state prohibiting selection of said broadcasting station and to select another broadcasting station being included in said AF list and not having said data prohibiting selection of this broadcasting station. The apparatus may then select again the broadcasting station of which the reception level fell below a specified value. When a broadcasting station whose program is being received is switched to the next broadcasting station as an automobile moves forward, if the PI code of this broadcasting station is different from the PI code of the original broadcasting station, selection thereafter of this broadcasting station is prohibited even if this broadcasting station is that designated by the frequency data of the AF list. The invention will be further described by way of example only with reference to the accompanying drawings, in which:- FIG. 1 is a system diagram of an example of the present invention; FIG. 2 is a flow chart showing an example of processes performed in the present invention; FIG. 3 is a diagram showing an example of contents of an AF list; FIG. 4 is a diagram explanatory of receive frequencies; and FIG. 5 is a diagram of service areas used for explaining states of reception. Referring to FIG. 1, reference numeral 1 denotes an antenna, 2 denotes an antenna tuning circuit of an electronic tuning type. By this tuning circuit 2, a desired FM broadcast wave signal Sr with a frequency of fr can be obtained. The signal Sr is supplied to a mixer 4 through a high-frequency amplifier 3. Meanwhile, an oscillation signal So, whose frequency fo for example is fo = fr + 10.7 MHz, is taken out from a VCO 11 and this signal So is supplied to the mixer 4 as a local oscillation signal, whereby the signal Sr is converted for frequency to an intermediate-frequency signal Si (the intermediate-frequency being 10.7 MHz). The intermediate-frequency signal Si is supplied, through an intermediate-frequency amplifier 5, to an FM demodulator 6, wherefrom an audio signal (a monaural signal or a stereo composite signal) Sa and a modulated signal Sm by RDS data are taken out. The signal Sa is supplied to a speaker 9 through a low-pass filter 7 and a low-frequency amplifier 8. Here, the VCO 11 and circuits 12 to 15 together constitute a PLL 10. More specifically, the signal So from the VCO 11 is supplied to a variable frequency divider 12 so that its frequency is divided by N. The signal with divided frequency is supplied to a phase comparator 13 and, in the meantime, an oscillation signal Sp with a frequency of 100 kHz serving as a reference is taken out from an oscillator 14 and the signal Sp is supplied to the comparator 13, and a comparison output therefrom is supplied to the VCO 11 as a control voltage therefor through a low-pass filter 15. The output of the low-pass filter 15 is also supplied to the tuning circuit 2 as a tuning voltage. Accordingly, in a steady state, the signal with divided frequency from the frequency divider 12 and the oscillation signal Sp have frequencies equal to each other. Hence, the frequency fo of the oscillation signal So at this time is expressed as fo = 100 kHz x N. At this time, the equality (i) holds. Therefore, as shown in FIG. 4, if the frequency dividing factor N is changed in the range from 982 to 1187 in increments of "1", the local oscillation frequency will vary in the range from 98.2 MHz to 118.7 MHz in increments of 0.1 MHZ, and, accordingly, the receive frequency fr will vary in the range from 87.5 MHz to 108.0 MHz in increments of 0.1 MHz, corresponding to the frequency dividing factor N. Reference numeral 30 denotes a microcomputer for system control (for which, a 4-bit microcomputer MPD 75116 made by NEC Corporation was used), 31 denotes its CPU, 32 denotes a ROM in which for example the processing routine 50 shown in FIG. 2 is written, 33 denotes a RAM for work area, and 41 to 44 denote ports. The memories 32 and 33 and ports 41 to 44 are connected with the CPU 31 through a system bus 36. The port 41 is connected with the frequency divider 12 and the port 43 is connected with various operating keys 49 such as a tuning key. From the intermediate-frequency amplifier 5, a portion of the intermediate-frequency signal Si is taken out, and this signal Si is supplied to a detector circuit 21, wherefrom a reception level detection signal Ss whose D.C. level varies with the reception level of the broadcast wave signal Sr is taken out. This signal Ss is supplied to an A/D converter 22 to be A/D converted to a digital signal and, then, supplied to the port 42. The signals Sa and Sm are supplied to a bandpass filter 24 and the signal Sm is extracted therefrom. This signal Sm is supplied to a demodulator 25 and the RDS data Sd is thereby demodulated. The RDS data Sd is supplied to a decoder 26 and, after passing through an error correction process therein, supplied to the port 42. A muting signal Sx is taken out from the port 44 and this signal Sx is supplied to the amplifier 8. Through the execution of the routine 50 of FIG. 2 by the CPU 31, the following processes are performed. In the step 101, it is checked whether or not an entry is made from a key 49. When no key entry is made, the routine proceeds from the step 101 to the step 102. In the step 102, the level of the detection signal Ss is checked and thereby it is examined whether or not the reception level of the broadcast being currently received is above a specified value. When it is above the specified value, the routine returns from the step 102 to the step 101. Thus, in the steady state, an entry from the key 49 and the reception level of the broadcast being currently received are checked. When an entry is made from a key 49, the routine proceeds from the step 101 to the step 103. In the step 103, the process corresponding to the key entry is executed and the routine returns to the step 101. For example when a station-selector key has been operated, the frequency dividing factor N corresponding to the key operation is established and this frequency dividing factor N is set up in the frequency divider 12 through the port 41, whereby a broadcast station with the frequency corresponding to the factor is selected. Suppose now that an automobile with the receiver mounted thereon is traveling in the service area SA of the broadcasting station A and the broadcasting station A is being selected and that, at this time, the AF list AFLT having M pieces of data as shown in FIG. 3 are written in the RAM 33 because the broadcasting station A is currently selected. In the AF list AFLT, AFD1 to AFDM denote frequency data included in the AF list. Further, PFLG denotes a PI flag, which is set to "1" when the PI code of the broadcast being currently received and the PI code of the broadcast designated by the frequency data AF list AFDi (i = 1 to M) are equal and set to "0" when they are different. When the automobile approaches the circumference of the service area SA of the broadcasting station A, the reception level of the broadcasting station A is lowered and the level of the detection signal Ss becomes lower as the automobile comes closer to the circumference (or goes further away from the broadcasting station A). When the level of the detection signal Ss falls below the specified value upon reaching of the automobile to the limit of the service area Sa, it is detected in the step 102, and the microcomputer 30 proceeds from the step 102 to the step 111. In this step 111, a pointer m designating the frequency data AFDi of the AF list AFLT is set to "1", and in the next step 112, the m th PI flag PFLG of the AF list AFLT is checked. When the PI flag PFLG is "1" (equal), the routine proceeds from the step 112 to the step 113, and in this step 113, the amplifier 8 is muted by a muting signal Sx. In the next step 114, the m th frequency data AFDm is taken out from the AF list AFLT and this frequency data AFDm is, after being converted to a corresponding frequency dividing factor N, set in the frequency divider 12 through the port 41. In the step 115, waiting for example of 10 msec is had until tuning in to the station in the step 114 is stabilized. In the next step 116, the level of the detection signal Ss is checked and it is thereby decided whether or not the reception level of the broadcasting station selected in the step 114 is above the specified value. If the level is below the specified value, the routine proceeds from the step 116 to the step 121 and, in this step 121, the original broadcasting station (the broadcasting station whose broadcast was being received when the steps 101 and 102 were being repeated) is selected. In the next step 122, waiting for example of 5 msec is had until the station selection in the step 121 is stabilized, and in the following step 123, the muting of the amplifier 8 is released by the muting signal Sx. Therefore, from the point of time when the step 123 has been executed onward, it becomes possible to hear for some time the program of the original broadcasting station. In the step 124, the pointer m is incremented by "1", and in the next step 125, m > M is tested for, whereby it is decided whether or not the processes in the steps 112 to 116 have been executed for all of the broadcasting stations of which PFLG = "1" in the frequency data AFD1 to AFDM of the AF list AFLT. When the processes in the steps 112 to 116 have not been executed for all of the broadcasting stations of which PFLG = 1, the routine returns from the step 125 to the step 112. When the processes in the steps 112 to 116 have been executed for all of the broadcasting stations of which PFLG = 1 in the step 125, the routine returns from the step 125 to the step 101. Thus, in the step 116, the reception level is sequentially checked for the broadcasting stations, of which PFLG = 1, in the frequency data AFD1 to AFDM included in the AF list AFLT until a broadcasting station of which the reception level is above the specified value is found. More specifically, while an automobile is receiving a broadcast from a broadcasting station, when the reception level falls as the automobile moves forward, the reception levels of the broadcasting stations, of which PFLG = 1, in the frequency data AFDL to AFDM of the AF list AFLT are sequentially checked so that a broadcasting station whose reception level is above the specified value is selected. When no broadcasting station of which the reception level is above the specified value is detected, the selection is returned to the original broadcasting station, the broadcasting station A in the present example. When, in the step 116, a broadcasting station of which the reception level is above the specified value is found, the routine proceeds from the step 116 to the step 131. In this step 131, the muting of the amplifier 8 is released by the muting signal Sx, and from this point of time on, the broadcast of the mth frequency data AFDM of the AF list is received. For example, when the PFLG is "1" when m = 1, the broadcast corresponding to the first frequency data AFD1 of the AF list is received. Then, the routine proceeds from the step 131 to the step 132. In this step 132, waiting is had until the PI code is obtained from the broadcast selected in the step 114 (the waiting time being 200 to 300 msec). When the PI code is obtained, it is checked in the step 133 whether or not the obtained PI code is equal to the PI code of the broadcast which was being received originally (the broadcast that was being received when the processes in the steps 101 and 102 were being executed), and when they are equal, the routine returns from the step 133 to the step 101. Then, the broadcasting station selected in the step 114 continues to be received and this program is the same as the program which was being received originally. When, in the step 133, the PI code is different from the PI code of the broadcast which was being received originally, the routine proceeds from the step 133 to the step 141. In this step 141, the PI flag PFLG of the frequency data of the broadcasting station which is being currently selected out of the frequency data AFD1 to AFDM of the AF list AFLT, i.e., the PI flag PFLG of the m th frequency data AFDm, is set to "0" (different), and in the next step 142, the amplifier 8 is muted by the muting signal Sx. Then, the routine advances to the step 121, and in the steps 121 to 125, setting for selection of the next broadcasting station is made and, thereafter, the routine returns to the step 112. Thus, even when the broadcasting station selected in the step 114 provides a higher reception level than the specified value, if its PI code is different from the PI code of the broadcast which was being received originally, selection is switched to the next broadcasting station. At this time, the PI flag PFLG of the broadcasting station having the different PI code is set to "0". When the PI flag PFLG is "0" in the check of the m th PI flag PFLG of the AF list AFLT in the step 112, the routine proceeds from the step 112 to the step 124. Thus, even when a broadcasting station has one of the frequency data AFD1 to AFDM of the AF list AFLT, if its PI code is different, the broadcasting station with that frequency data is not selected (rejected) and the next candidate station is searched for. In the described arrangement, suppose that the frequency data of the broadcasting station B is the m th data AFDm of the AF list AFLT. When the automobile reaches the point Pa where the reception level of the broadcast of the broadcasting station A is below the specified value, the following operations are performed: 1. The AF list AFLT is referred to, and if the PI flag PFLG of the frequency data AFDm is "1" (step 112), the broadcasting station B is selected according to the frequency data AFDm (step 114). 2. After this station selection, if the PI code of the broadcast of the broadcasting station B is equal to the PI code of the broadcast of the broadcasting station A (step 133), the broadcasting station B is kept selected until the next point Pc is reached. 3. If, however, it is found, after the station has been selected as 1. above, that the PI code of the broadcast of the broadcasting station B is different from the PI code of the broadcasting station A (step 133), the PI flag PFLG is set to "0" (step 141) and, then, the original broadcasting station A is selected (step 121). 4. When the original broadcasting station A is selected, since the reception level of its broadcast is below the specified value, the AF list AFLT is referred to again and a broadcasting station relative to the frequency data AFDm may be selected. In this case, however, since the PI flag PFLG of the frequency data AFDm is set to "0" (step 141), the broadcasting station B relative to the frequency data AFDm is not selected (step 112) and the original broadcasting station A is selected (step 121). 5. Thereafter, operations 3. and 4. above are repeated until the point Pc is reached. During the repetition, the broadcasting station A is kept selected and the broadcasting station B is not selected by means of the PI flag PFLG and the check in the step 112. In an RDS receiver according to the present invention, when a broadcasting station whose broadcast is being received is to be switched to the next broadcasting station as an automobile moves forward, if the PI code of the next broadcasting station is different from the PI code of the original broadcasting station, even if the next broadcasting station is that designated by the frequency data of the AF list, the broadcasting station is arranged not to be selected again by the provision of the steps 112 and 141. Accordingly, the program of the original broadcasting station is kept received during the traveling of the automobile, not interrupted by the operations for selecting the next broadcasting station, and the broadcast of the original broadcasting station can be heard continuously, though the condition of reception may be deteriorated. In addition, the above described effect can be achieved only by changing part of the routine 50, and there is no need of changing hardware of the receiver. Hence, cost is prevented from increasing. Although it was arranged in the foregoing that the check in the step 112 is made according to the PI flag PFLG, it may also be applicable to have a list of frequency data with the different PI codes made in the step 141 and to have the list checked in the step 112. Otherwise, the frequency data itself may be eliminated from the AF list AFLT. In an RDS receiver according to the present invention, when a broadcasting station whose broadcast is being received is to be switched to the next broadcasting station as an automobile moves forward, if the PI code of the next broadcasting station is different from the PI code of the original broadcasting station, even if the broadcasting station is that designated by the frequency data of the AF list, the broadcasting station is arranged to be prohibited from being selected by the provision of the steps 112 and 141. Accordingly, such meritorious effects can be obtained that the program of the original broadcasting station is kept received during the traveling of the automobile, not interrupted by the operations for selecting the next broadcasting station, and the broadcast of the original broadcasting station can be heard continuously, though the condition of reception may be deteriorated. In addition, the above described effect can be achieved only by changing part of the routine 50, and there is no need for changing hardware of the receiver. Hence, cost is prevented from increasing.

Claims: A receiver comprising: a tuning circuit (1-6) for selecting a broadcast wave with a predetermined frequency; a detector circuit (21) for detecting the reception level of said broadcast wave; a decoder circuit (26) for extracting an AF list and a PI code of RDS data from the received signal of said broadcast wave; and a memory circuit (33) for storing said AF list, wherein the receiver is adapted when the output of the detector circuit (21) indicates that the current reception level has fallen below a specified value to check the AF list and select a new broadcasting station therefrom, to subsequently check the PI code and, if its program is different, to deselect that station, characterised in that said receiver is further adapted to store data individually associated with each station in the AF list and indicating permission or prohibition of selection of that broadcasting station; and when the detection output of said detector circuit (21) indicates that the reception level of said broadcast wave has fallen below the specified value, to check said permission or prohibition indicative data, then when it is found as the result of the check that said data is permitting selection of a broadcasting station, to perform said selection of the broadcasting station by means of said tuning circuit (1-6), to perform said check said PI code after the selection of said broadcasting station, and when its program is found to be different as the result of the check of said PI code, to set said data into a state prohibiting selection of said broadcasting station and to select another broadcasting station being included in said AF list and not having said data prohibiting selection of this broadcasting station. A receiver according to claim 1, wherein said receiver is adapted, when it is found as the result of the check that said data is prohibiting selection of a broadcasting station, to reselect the broadcasting station of which the reception level fell below a specified value.

Inventors: NAKAMURA TAKAYUKI, NAKAMURA, TAKAYUKI
Applicants: SONY CORP, SONY CORPORATION
Application year: 1992
Main classification: H04H1
IPC codes: H04H60, H04H20, H04B1, H03J7