JP2009152874A - Tuner for fm data broadcasting - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the IC chip size and package size of a tuner for FM data broadcasting. <P>SOLUTION: Adjacent disturbance is detected by using an IF counter 74 which is used for a seek search for a broadcasting station, and then the need for an extra circuit for adjacent disturbance detection is eliminated, enabling size reduction. The IF counter 74 counts the frequency of an intermediate signal obtained by frequency-converting a reception signal. A counted value N is input to a control unit 54. Once the adjacent disturbance is received, the counted value N becomes different from a value n<SB>IF</SB>corresponding to an original intermediate frequency f<SB>IF</SB>. The control unit 54 decides that the adjacent disturbance has occurred, when the deviation amount thereof exceeds a predetermined allowable error δn. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an FM data broadcast tuner used for receiving FM data broadcast such as RDS (Radio Data System) and VICS (Vehicle Information and Communication System).

  FM data broadcasting is conducted in Japan in VICS, and in 2008, broadcasting will also begin in China. In Europe, RDS is widespread. In recent years, with the spread of navigation, dedicated FM tuners are required for these data broadcasts. The FM data broadcast tuner is used for navigation and is required to be miniaturized, and the main part thereof is made into an integrated circuit (IC).

  Since FM broadcasting requires a relatively wide frequency band, interference (adjacent interference) is likely to occur from nearby broadcast channels (broadcast frequencies). When adjacent interference is received, the detection output of the tuner is distorted, and the bit error rate (BER) is degraded when data is decoded. In this regard, in data broadcasting, there may be a case where data broadcasting that can be replaced by a broadcasting station other than the currently receiving broadcasting station is performed, and the reception state can be improved by substituting for another station.

  For example, in RDS, a broadcasting station that performs data broadcasting of the same content is provided. Then, an AF search for automatically selecting a broadcast station having the same reception content and having a good reception state is performed. Conventionally, adjacent interference is detected using a circuit such as a signal quality sensor (SQ sensor) and used for AF search.

The SQ sensor detects adjacent interference based on the AC component _{SM -AC} extracted from the intermediate signal by the S meter circuit and the AC component of the FM detection output _SDET . The sensor extracts a high-frequency component corresponding to the adjacent interference by a high-pass filter (HPF) from an AC component such as SM _-AC , and detects and smooths the extracted high-frequency component by a detection circuit. Then, the comparator compares the DC voltage with a predetermined threshold value, and determines that adjacent disturbance has occurred when the threshold value is exceeded. In the SQ sensor, the detection circuit requires a capacitor for smoothing, and the capacitor is an external component of the IC.
Japanese Patent Laid-Open No. 11-239064

  When the SQ sensor is provided, there is a problem that the chip size of the IC is increased and the number of terminals of the IC package is increased because an external capacitor is attached. Furthermore, there is a problem in that an external capacitor hinders miniaturization and increases costs.

  The present invention has been made to solve the above problems, and an object of the present invention is to provide an FM data broadcast tuner that can be further reduced in size.

  The FM data broadcast tuner according to the present invention tunes to the broadcast frequency of the target broadcast station to obtain a received signal, performs frequency conversion that shifts the carrier frequency of the received signal to a predetermined intermediate frequency, and generates an IF signal A frequency conversion unit that performs detection, an IF counter that counts the frequency of the IF signal, an adjacent interference detection unit that detects the occurrence of adjacent interference according to the count value of the IF counter, and the occurrence of the adjacent interference is detected And an automatic channel selection unit that controls the frequency conversion unit to switch the target broadcast station from a current broadcast station to an alternative broadcast station.

  According to the present invention, the presence or absence of adjacent interference is detected using an IF count function that is generally provided for the automatic channel selection function. Therefore, it is basically unnecessary to provide a separate circuit only for detecting adjacent interference, and the FM data broadcast tuner can be reduced in size and cost. Incidentally, the adjacent disturbance detection unit and the automatic channel selection unit use a microcomputer that controls each part of the tuner, and the functions of the adjacent disturbance detection unit and the automatic channel selection unit can be realized by a program executed by the microcomputer. An increase in circuit scale due to the addition of elements and circuits can be suppressed.

  Hereinafter, embodiments of the present invention (hereinafter referred to as embodiments) will be described with reference to the drawings.

FIG. 1 is a schematic block diagram of an FM data broadcast tuner according to the embodiment. The FM data broadcast tuner 50 includes an FM signal processing unit 52, a control unit 54 that controls the operation of the FM signal processing unit 52, and a system bus 56 that enables communication therebetween. Broadcast data is reproduced from the RF signal S _RF0 received by the antenna 58. The main part of the FM signal processing unit 52 is made into an IC. The control unit 54 can be configured by a microcomputer.

  The FM signal processing unit 52 includes an RF circuit 60, a local oscillation unit 62, a mixing circuit 64, an IFBPF 66, a limiter amplifier 68, an FM detection circuit 70, a broadcast data decoder 72, an IF counter 74, an S meter circuit 76, and a station detection circuit 78. It is comprised including.

The RF signal S _RF0 is input from the antenna 58 to the RF circuit 60. The RF circuit 60 performs a tuning process for extracting a relatively narrow band RF signal S _RF including the target broadcast station having the carrier frequency f _R from the RF signal S _RF0 over the reception target band. The tuning frequency in the RF circuit 60 is controlled by the control unit 54 via the system bus 56.

The RF signal S _RF extracted by the RF circuit 60 is input to the mixing circuit 64. The mixing circuit 64 mixes the input RF signal S _RF with the local oscillation signal S _LO input from the local oscillation unit 62 to generate an intermediate signal S _IF . The control unit 54 sets the frequency f _{LO of} S _LO corresponding to the tuning frequency. Frequency _{f LO} of S _{LO is} a predetermined intermediate frequency by the frequency conversion to _{S IF} the carrier frequency _{f R} of the signal of interest broadcast stations included in the _{S RF} is due to the mixing circuit _{64 (Intermediate Frequency: IF) f} IF conversion To be adjusted. The intermediate frequency f _IF is set to 10.7 MHz, for example.

S _IF is input to IFBPF 66. IFBPF66 _is centered frequency _{f IF,} and is a band pass filter the pass bandwidth _{W F} can be variably set.

_{S IF} outputted from IFBPF66 is input to the limiter amplifier 68. The limiter amplifier 68 amplifies the amplitude of the _SIF , which is an FM signal, to form a rectangular wave, and removes noise on the FM signal. S _IF, which is a rectangular wave is amplified by the limiter amplifier 68 is inputted to the FM detection circuit 70. The FM detection circuit 70 performs FM detection on the output signal of the limiter amplifier 68 and outputs a detection output signal. The broadcast data decoder 72 decodes the broadcast data included in the detection output signal and outputs it to the control unit 54.

The IF counter 74 receives the intermediate signal _SIF and counts its frequency. The frequency count value is passed to the control unit 54.

S meter circuit 76, the S _IF and peak detection based on the output signal of each stage of the configured limiter amplifier 68 in a plurality of stages of amplifiers connected in series, the variation component signal S _M-AC included in the S _IF And the fluctuation component is smoothed by the LPF to generate the received electric field strength signal S _M-DC .

The station detection circuit 78 compares the received electric field strength signal S _M-DC with a predetermined reference value to detect the presence / absence of a broadcasting station, and outputs the detection result to the control unit 54.

  The control unit 54 controls the operation of each unit of the FM signal processing unit 52. For example, as already described, the RF circuit 60 and the local oscillator 62 are controlled to select a channel. Further, the control unit 54 automatically selects a station that can be suitably received from among a plurality of broadcasting stations. Hereinafter, this automatic channel selection will be described by taking as an example the case where the FM data broadcast tuner 50 is an RDS tuner. The RDS tuner has a function called AF search. This AF search is, for example, in the case of receiving a broadcast while moving in a car, and if the field intensity of the currently receiving broadcast station is reduced, the other broadcast station performing the same program is searched for and the broadcast station Is a function of automatically selecting a broadcast station when the field strength of the signal is greater than or equal to a predetermined value. The FM data broadcasting tuner 50 selects a broadcasting station that can obtain a suitable reception state in consideration of the presence or absence of adjacent interference in addition to the electric field strength.

The controller 54 determines whether there is adjacent interference based on the count value from the IF counter 74. The count value of the IF counter 74 is, in principle, an intermediate frequency f _IF that is the average frequency of the frequency spectrum of the target receiving station when there is no adjacent interference, but is adjacent to the S _IF when receiving adjacent interference. because it contains the signal component of the interference station, shifts the frequency spectrum to the adjacent interference station, the count value value N also shifted from f _IF obtained corresponding to the mean frequency. Here, since the presence / absence of adjacent interference is determined based on the count value within a relatively short period, the count value N can deviate from the value n _IF corresponding to f _IF even in the absence of adjacent interference. Therefore, an allowable error δn corresponding to the count time for acquiring the count value N is set, and the control unit 54 determines that the measured count value N is within a range of ± δn centering on n _IF without adjacent interference. When the difference between N and n _IF is larger than δn, it is determined that there is an adjacent disturbance.

The control unit 54 monitors the received electric field strength S _M-DC and the count value N, and when the received electric field strength of the currently receiving broadcasting station falls below a predetermined value α _L or when adjacent interference is detected, the control unit 54 Start the search.

The control unit 54 acquires and stores an AF (alternative frequency list) signal and received electric field strength based on the received signal of the current broadcasting station. Thereafter, the control unit 54 changes the tuning frequency of the RF circuit 60 and the local oscillation frequency f _LO of the local oscillation unit 62 to change the reception channel. When a broadcast station (substitution candidate station) exists in the changed reception channel, a station detection signal is obtained from the station detection circuit 78. When the station detection signal for the alternative candidate station is obtained, the control unit 54 detects the received electric field strength of the alternative candidate station from the output signal S _M-DC of the S meter circuit 76 and performs IF for the alternative candidate station. The count value N of the counter 74 is acquired, and the AF signal is acquired.

Control unit 54, received electric field intensity S _M-DC Alternatives station determines whether a proper field strength at or above the predetermined value alpha _H. α _H is set so as to satisfy α _H > α _L , and preferably α _H > α _L + δα in consideration of the allowable fluctuation range δα of the received electric field intensity in the normal reception state. . Further, the control unit 54 determines the presence / absence of adjacent interference with respect to the alternative candidate station based on the count value N. Further, the control unit 54 compares the AF signal acquired from the alternative candidate station with the AF signal stored for the target broadcast station received so far.

  The control unit 54 has received the target broadcast station up to now when all of the conditions that the alternative candidate station is in the appropriate electric field strength state, the condition that there is no adjacent interference, and the condition that the AF signals match are satisfied. Switch from a broadcast station to an alternative candidate station that is currently tuned. That is, the FM data broadcast tuner 50 receives the alternative candidate station as the target broadcast station.

  On the other hand, when the alternative candidate station does not satisfy any of the above conditions for the received electric field strength, adjacent interference, and AF signal, the control unit 54 further changes the reception channel and continues the AF search.

  If none of the reception channels satisfy all the conditions, for example, it is possible to return to the original broadcasting station and continue the reception. In addition, information such as received electric field strength obtained from each AF station searched for AF, the magnitude of the deviation of the count value of the IF counter is stored, and from these, a broadcasting station with a favorable reception state is determined comprehensively, You may make it switch to the said broadcast station.

In general, in an FM tuner, station detection at the time of search is also performed by frequency detection of the intermediate signal _SIF , and an IF counter is provided. If this search IF counter is used, it can be shared with the adjacent interference IF counter, and there is no need to newly provide an IF counter.

  Further, since adjacent interference is detected according to the count value of the IF counter, it is not necessary to separately provide a circuit such as an SQ sensor for detecting adjacent interference in the IC constituting the FM signal processing unit 52. The FM data broadcast tuner 50 can be reduced in size and cost.

  Incidentally, in order to detect adjacent interference with high accuracy, the count period is lengthened to ensure the accuracy of the count value N. For that purpose, the count period needs about 30 milliseconds, for example.

  Here, the operation of the IF counter 74 requires a mute in the tuner that receives the audio broadcast, but if the mute exceeds about 5 milliseconds, it will be heard by the listener as a sound interruption. For this reason, it is difficult for an FM tuner for audio broadcasting to accurately detect adjacent interference using an IF counter. On the other hand, in the FM tuner for data broadcasting, sound interruption does not cause a problem, and therefore, it is possible to accurately detect adjacent interference by setting a long count period.

The control unit 54 performs detection of the occurrence of adjacent interference based on the count value N and AF search corresponding to the occurrence of adjacent interference based on a program stored in a memory provided in the control unit 54 in advance. Therefore, these processes can be flexibly customized simply by rewriting the program without changing the IC that basically constitutes the FM signal processing unit 52. For example, change the size of the signal component of the interference station are superimposed on the intermediate signal S _IF desired according to the strength of the electric field strength of the adjacent interference station station, the amount of shift of the frequency of the S _IF changes. Therefore, the detection sensitivity of the adjacent disturbance can be arbitrarily set by changing the detection range δn in the program.

  In the above embodiment, the RDS AF search has been described as an example. However, the present invention can also be applied to other FM data broadcast tuners such as VICS. For example, when a vehicle or the like is moving in the boundary area between the service areas of each broadcasting station that performs VICS FM multiplex broadcasting, there are situations where reception is possible for a plurality of broadcasting stations. Under such circumstances, when adjacent interference is detected in the current receiving station, it is possible to switch to another broadcasting station. Therefore, even in a VICS-compatible FM data broadcast tuner, the configuration of adjacent interference detection based on the count value of the IF counter is useful, and downsizing and the like can be achieved by employing this configuration.

1 is a schematic block configuration diagram of an FM data broadcast tuner according to an embodiment of the present invention. FIG.

Explanation of symbols

  50 FM data broadcasting tuner, 52 FM signal processing unit, 54 control unit, 56 system bus, 58 antenna, 60 RF circuit, 62 local oscillation unit, 64 mixing circuit, 66 IFBPF, 68 limiter amplifier, 70 FM detection circuit, 72 Broadcast data decoder, 74 IF counter, 76 S meter circuit, 78 station detection circuit.

Claims (3)

An FM data broadcast tuner for receiving FM data broadcast,
A frequency converter that tunes to the broadcast frequency of the target broadcast station to obtain a received signal, performs frequency conversion to shift the carrier frequency of the received signal to a predetermined intermediate frequency, and generates an IF signal;
An IF counter for counting the frequency of the IF signal;
An adjacent interference detection unit that detects the occurrence of adjacent interference according to the count value of the IF counter;
When the occurrence of the adjacent interference is detected, an automatic channel selection unit that controls the frequency conversion unit to switch the target broadcast station from the current broadcast station to an alternative broadcast station;
An FM data broadcast tuner characterized by comprising: The FM data broadcast tuner according to claim 1,
The adjacent disturbance detection unit detects a case where the count value of the IF counter is outside a predetermined target range centered on a count value corresponding to the intermediate frequency as the occurrence of the adjacent disturbance. FM data broadcasting tuner. In the FM data broadcast tuner according to claim 1 or 2,
The automatic channel selection unit preferentially selects a broadcast station having the same content of the FM data broadcast as the current broadcast station as the alternative broadcast station;
FM data broadcast tuner characterized by the above.

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