Receiver

Abstract

 The present invention aims to eliminate the sense of displeasure due to an interruption of sound by making a muting time short at a time of examining reception conditions for an alternative frequency (AF) station of a radio receiver.
[Solving Means] A latch circuit 26 is provided for retaining an N value (frequency division ratio of a frequency dividing circuit 21) data to receive an AF station, which is transmitted from a microcomputer 30. After the N value data is transmitted to the latch circuit 26, a mute signal is transmitted to a mute circuit 18, a zero-cross of an audio signal is detected at the mute circuit, muting is applied, and the N value received from a currently listening broadcasting station is switched to the N value retained in the latch circuit of the AF station and the AF station is received. After examining the reception condition for the AF station, in case the reception condition for the AF station is not excellent, the N value is returned to the N value of the current broadcasting station, muting is cancelled and the currently listening station is received; or in case the reception condition for the AF station is favorable, muting is cancelled and the AF station is received. Thus it is possible to make the muting time short by an N value transmitting duration compared with a conventional system of transmitting the N value data of the AF station to a PLL circuit 20 after applying muting.

Description

[0001] The present invention relates to a receiver having a function of switching to an alternative frequency station broadcasting the same broadcasting content in case the reception condition for a currently receiving broadcasting station deteriorates.

[Background Art]

[0002] For example, a receiver equipped in a car or the like, particularly an RDS (Radio Data System) receiver, when a reception condition deteriorates because the car is driven far from a currently receiving station, has a function of switching to an AF station (alternative frequency station) of another frequency from which the same broadcast content can be favorably received based on an AF (Alternative Frequency) list or an AF reception history. Each broadcasting station is transmitting RDS data that includes, as an AF list, the frequency data of network stations in the vicinity of the periphery of a service area of the relevant station.

[0003] As shown in FIG. 4, a conventional RDS receiver includes a PLL receiving circuit 2 for receiving a broadcast signal input from an antenna 1, a muting circuit 3 connected to the PLL receiving circuit 2, a microcomputer 4, an RDS data demodulating circuit 5 that demodulates an RDS data signal including RDS data from a broadcasting station connected to the PLL receiving circuit 2, a reception sensitivity detecting circuit 6, a memory 7 storing the RDS data signal supplied from the RDS data demodulating circuit 5 and the like.

[0004] The above-mentioned RDS receiver, when examining the reception condition for an AF station, applies muting by the muting circuit 3 that is controlled by the microcomputer 4 so that a squawky noise may not be heard, transmits an N value data for selecting the AF station to a PLL circuit in the PLL receiving circuit 2 and examines the reception condition for the AF station after a tuning frequency of the PLL receiving circuit 2 is switched to a reception frequency of the AF station. When it is found that the degree of the reception condition is more favorable than that for a broadcasting station from which reception is now being carried out, the frequency of the AF station is set to a reception state and, when the reception condition is found to be worse, the N value is changed to receive the frequency of the currently broadcasting station and muting is canceled (refer to FIGS. 5 and 6). (Refer to patent document 1, for example).

[0005] There can be other systems than the RDS receiver for examining another frequency by applying muting for a short period of time while receiving a radio broadcast as mentioned above.
[Patent document 1] Japanese Published Patent Application No. H11-97983

[0006] In an RDS receiver, when muting is applied to examine a reception condition for an AF station, if the muting lasts long, it gives a listener a sense of displeasure because sound is interrupted. Conventionally, since the N value data of the AF station is transmitted to the PLL circuit in the PLL receiving circuit 2 after applying muting, the reception of the AF station is delayed, which gives a listener a sense of displeasure.

[0007] The present invention is implemented in view of the above problem of a conventional RDS receiver, and has an object to provide a receiver in which muting time is shortened when examining a reception condition for the AF station of the receiver, so that a radio broadcast can favorably be received.

[0008] The invention described in Claim 1 is a receiver including an electronically tuning means for changing a tuning frequency by changing an N value of a PLL circuit and a function of receiving an alternative frequency station by applying muting to change the N value while receiving a broadcast of a certain broadcasting station and examining a reception condition for the alternative frequency station; in which latching means is provided prior to the PLL circuit for latching N value data to receive the alternative frequency station and when examining the reception condition for the alternative frequency station, transmission of the N value data to the latching means for receiving the alternative frequency station is carried out before applying the muting, so that a muting time is shortened.

[0009] Further, the invention described in Claim 1 or Claim 2 is an FM receiver or RDS receiver including an electronically tuning means for changing a tuning frequency by changing an N value of a PLL circuit and a function of receiving an alternative frequency station by applying muting to change the N value while receiving a broadcast of a certain broadcasting station and examining a reception condition for the alternative frequency station; in which latching means is provided prior to the PLL circuit for latching N value data to be changed and when examining the reception condition for the alternative frequency station, transmission of the N value data to the latching means for receiving the alternative frequency station is carried out before applying the muting to shorten a muting time, and after canceling the muting, the FM receiver or RDS receiver receives an original frequency or the alternative frequency station based on the result of examining the reception condition.

[0010] According to the invention described in any one of Claims 1 to 3, since the latching means is provided, and the transmission of the N value data to the latching means is carried out for receiving the alternative frequency station before applying the muting, the muting time can be made short by the time for transmitting the N value.

[0011] According to the present invention, since the transmission to the latching means of an alternative frequency station data for changing the N value of the PLL is carried out before applying the muting, the muting time is made short by the time for transmitting the N value data, resulting in the degree to which a listener can not discern the muting. As a result, the listener is capable of listening to a radio broadcast in a favorable reception condition without cease.

[0012] FIG. 1 shows a block diagram of an RDS receiver according to an embodiment of the present invention. In FIG. 1, a tuner 12 is a tuner of an electronically tuning system and receives an FM broadcast signal from a reception signal that an antenna 11 inputs, with a voltage for controlling VCO (voltage control oscillator) 22 output from an LPF (low pass filter) 24 of a PLL circuit 20 as a station selecting voltage. An RF amp 13 amplifies the FM broadcast signal, and a mixer circuit 14 converts the FM broadcast signal to an intermediate frequency signal by having an oscillating frequency signal of the VCO 22 of the PLL circuit 20 as a local oscillating signal. An IF amplifier 15 amplifies this intermediate frequency signal.

[0013] An FM detecting circuit 16 detects the intermediate frequency signal and a stereo-decoder 17 outputs a stereo-audio signal from the detected signal (hereinafter referred to as audio signal). A muting circuit 18 is provided with a zero-cross detecting circuit, detects a zero-cross of an audio signal when receiving a mute-on controlling signal transmitted from a microcomputer 30 and makes a mute ON. Further, in case the result of examining a reception condition for an AF station is favorable, that is described later on, the muting circuit 18 detects the zero-cross and makes a mute OFF when receiving a mute-off controlling signal transmitted from the microcomputer 30.

[0014] The PLL circuit 20 includes a frequency dividing circuit 21 for dividing an oscillating frequency of the VCO 22 whose frequency division ratio N is set by N value data input, a phase comparing circuit 23 for comparing a phase of an output signal of an oscillator 25 with that of the frequency dividing circuit 21, the LPF 24 for inputting an output of the phase comparing circuit 23, and the VCO 22 whose oscillating frequency is controlled by an output voltage of the LPF 24.

[0015] A latch circuit 26 is connected between the microcomputer 30 and the frequency dividing circuit 21, receives an AF search bit and the N value (frequency division value of the PLL circuit 20) data of the AF station which are transmitted from the microcomputer 30, latches the N value and outputs the N value that is controlled and latched by the microcomputer 30 to the frequency dividing circuit 21 after the muting circuit 18 detects the zero-cross of the audio signal. A reference numeral 27 denotes a reception sensitivity detecting circuit, a reference 28 denotes an RDS demodulating circuit, and a memory 29 stores RDS data demodulated by the RDS demodulating circuit, an AF station list and the like.

[0016] The microcomputer 30 controls an AF search operation and the like of an RDS receiver 10 according to a processing routine written in an ROM (not shown).

[0017] Next, the AF search operation of the RDS receiver 10 will be explained with reference to a flowchart shown in FIG. 2 and a timing chart shown in FIGS. 3A and 3B. While receiving a broadcast of a certain broadcasting station (S11), the microcomputer 30 receives a signal from the reception sensitivity detecting circuit 27 and judges whether or not the reception condition for a current broadcasting station deteriorates (S12). For example, in case the reception condition for a currently receiving station deteriorates due to the movement of a car equipped with the RDS receiver 10 and the result of judging if the reception condition for the current broadcasting station deteriorates is YES, the microcomputer 30 transmits the AF search bit of the AF station that is broadcasting the same broadcast as the current broadcasting station and the N value data of the AF station list (or AF reception history) to the latch circuit 26, both the search bit and the AF list being stored in the memory 29 (S13).

[0018] Thereafter, the microcomputer 30 transmits the mute-on control signal to the muting circuit 18, and the muting circuit 18, after receiving the mute-on control signal, detects the zero-cross of the audio signal output from the stereo decoder 17 and makes the mute ON and makes the audio signal in a state of the mute ON (S14). Since the latch circuit 26, at the time of the zero-cross being detected, outputs the N value that is latched of the AF station to the PLL circuit 20 when receiving a signal transmitted from the microcomputer 30, the N value of the currently selected broadcasting station in the frequency dividing circuit 22 switches in an instant to an N value of a selected AF station, and the AF station is received (S15). Then, the microcomputer 30 receives a signal from the reception sensitivity detecting circuit 27 and examines the reception condition for the AF station. (S16).

[0019] In case the result of examining the reception condition for the AF station is worse than that for the current broadcasting station, the microcomputer 30 returns the N value of the AF station to the N value of the current station, tunes in to the frequency of the current broadcasting station, later transmits the mute-off signal to the muting circuit 18 and makes the muting circuit 18 detect the zero-cross of the audio signal. When the zero-cross is detected, the muting circuit 18 makes the mute OFF, and the current broadcast station is received (S18). The muting time from the mute-on to the mute-off in this case is about 6ms (FIG. 3A).

[0020] Further, in case the result of examining the reception condition for the AF station is favorable, the microcomputer 30 transmits the result to the muting circuit 18, and when the muting circuit 18 detects the zero-cross, the mute is made OFF and the AF station is received (S17). The muting time from the mute-on to the mute-off in this case is about 4.5ms (FIG. 3B).

[0021] On the contrary, a conventional RDS receiver (FIG. 4) is not provided with the latch circuit 26 of the FIG. 1. In addition, since the RDS receiver carries out the AF search operation as shown in the flowchart of FIG. 5, in case the result of examining the reception condition for a broadcasting station of S22 is YES, the muting circuit 18 detects the zero-cross of the audio signal, makes the muting ON and, after putting the audio signal of the current broadcasting station in a muted state, the microcomputer 30 transmits the AF search bit and the N value data of the AF station to the PLL circuit 20 (S24 and, S25). As a result, as shown in FIG. 6, time (N value transmitting time) from the mute-on to tuning in to the AF frequency is required.

[0022] Consequently, the muting time becomes about 7ms in case the result of examining the reception condition for the AF station of S26 is worse than that for the current broadcasting station (FIG. 6A), while in case the reception condition for the AF station is more favorable than that for the current broadcasting station, the muting time becomes about 5.5 ms (FIG. 6B).

[0023] According to the present invention, since the N value transmission period of time (time of S24) required to tune in to the AF frequency from the mute-on of the conventional FIG. 6 can be eliminated, the muting time can be made short by about 1ms. As a result, since the muting time can be brought close to about 3ms that is said to be incapable of discerning by the ear of human beings, an RDS receiver that does not make the user feel an interruption of sound at the time of the AF search operation can be obtained.

[0024] In FIG. 1, though the muting circuit 18 is provided in an audio circuit unit, it may be provided in the tuner, and the stereo decoder 17 can be made a monaural decoder. Further, the latch circuit 26 is replaceable with other units as long as the unit includes an equivalent function.

[0025] Further, though the RDS receiver is explained in the above-description, a receiver of an electronically tuning system in which a tuner changes an N value of PLL circuit to be tuned in can be applied if not provided with an RDS function. For example, by making beforehand the memory 29 store the N value list of the AF station, the AF research operation can be carried out as shown in FIG. 2. Further, in the case of an FM multiplex broadcasting, it is possible to obtain an alternative frequency station data by receiving the FM multiplex broadcasting. The present invention is not limited to the RDS receiver and can be applied to the receiver of the electronically tuning system that performs tuning-in by changing the N value of the PLL circuit.

[0026] The invention will be more clearly understood from the following description, given by way of example only, with reference to the accompanying drawings, in which:

[FIG. 1] A block diagram of an RDS receiver according to an embodiment;

[FIG. 2] A flowchart of an AF search operation according to the embodiment;

[FIGS. 3A and 3B] Timing charts of the search operation according to the embodiment;

[FIG. 4] A block diagram of the RDS receiver according to a conventional example;

[FIG. 5] A block diagram of the AF research operation according to a conventional example; and

[FIGS. 6A and 6B] Timing charts of the AF search operation according to a conventional example.

[Description of Reference Numerals]

[0027] 10 ... RDS receiver, 12 ... Tuner, 14 ... Mixer, 16 ... FM detecting circuit, 17 ... Stereo decoder, 18 ... Muting circuit, 20 ... PLL circuit, 26 ... Latch circuit, 27 ... Reception sensitivity detecting circuit, 28 ... RDS data demodulating circuit, 29 ... Memory, 30 ... Microcomputer

Claims

1. In a receiver having electronically tuning means to change a tuning frequency by changing an N value of a PLL circuit and having a function, while receiving a broadcast of a certain broadcasting station, of changing said N value by applying muting to receive an alternative frequency station and of examining the reception condition for the alternative frequency station, a receiver characterized by comprising latching means prior to said PLL circuit for latching N value data to receive said alternative frequency station, and at a time of examining the reception condition for said alternative frequency station, by carrying out transmission of the N value data to said latching means before applying said muting to receive said alternative frequency station and making the muting time short.

2. In an FM receiver having electronically tuning means to change a tuning frequency by changing an N value of a PLL circuit and having a function of obtaining data of an alternative frequency station, while receiving an FM multiplex broadcasting, applying muting to change said N value and receiving the alternative frequency station to examine the reception condition for the alternative frequency station,
   an FM receiver characterized by comprising latching means prior to said PLL circuit to latch said N value to be changed, and
   at a time of examining the reception condition for said alternative frequency station, by carrying out transmission of the N value data to said latching means before applying said muting to receive said alternative frequency station, making a muting time short and, after canceling said muting, by receiving an original frequency or said alternative frequency station based on the result of examining said reception condition.

3. In an RDS receiver having an electronically tuning means to change a tuning frequency by changing an N value of a PLL circuit and having functions of obtaining data of an alternative frequency station, while receiving a broadcast of a broadcasting station transmitting RDS data, applying muting to change said N value to receive the alternative frequency station and examining the reception condition for the alternative frequency station,
   an RDS receiver characterized by comprising latching means prior to said PLL circuit to latch said N value to be changed, and
   at a time of examining the reception condition for said alternative frequency station, by carrying out transmission of the N value data to said latching means before applying said muting to receive said alternative frequency station, making a muting time short and, after canceling said muting, receiving an original frequency or said alternative frequency station based on the result of examining said reception condition.

Drawing