JP2009152873A - Tuner for fm data broadcasting - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem wherein a tuner for FM data broadcasting which is used frequently on a moving body does not always select a broadcasting station, in a sufficiently superior reception state, as an alternative station, during switching to the alternative station, when there is deterioration in the reception state. <P>SOLUTION: Through reception electric field strength search operation, an S meter circuit 98 detects the reception electric field strengths of respective broadcasting channels within a reception object band to acquire a reception electric field strength list C<SB>I</SB>, representing the reception electric field strength of the respective broadcasting channel. The reception electric field strength list C<SB>I</SB>is stored in a memory 56. The reception electric field strength list C<SB>I</SB>is suitably updated during reception operation. When an alternative station is selected, occurrence of disturbances, such as, intermodulation is estimated based on the reception electric field strength list C<SB>I</SB>, a broadcasting station which is free of disturbances is selected; and AGC sensitivity, the gain of an RF amplifying circuit 72, and the like, are suitably set, according to the kind of disturbances estimated. <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.

  Since FM broadcasting requires a relatively wide frequency band and the frequency range is relatively narrow, problems such as interference from neighboring channels with respect to the reception target channel tend to occur as the number of broadcast channels (broadcast frequencies) increases. .

For example, phenomena such as intermodulation, sensitivity suppression, and adjacent interference are known as interference. Intermodulation is a phenomenon in which a signal having a frequency component that should not be included is output when an amplifier circuit or the like has nonlinear characteristics. For example, if you enter two radio frequencies _f 1, _{f 2} to the amplifier circuit, in addition to the _f 1, _{f 2} at its _{output, n · f 1 ± m ·} f 2 by intermodulation (n, m are integers ) Frequency component is included. For example, transmission waves exist in two channels of frequencies f ₁ and f ₂ adjacent to the reception target channel of frequency f _R (where the channel interval is Δ and f ₁ ≡f _R + Δ and f ₂ ≡f _R + 2Δ). Then, the intermodulation wave of the same frequency as _{f R (2f} 1 -f _R) can occur. Therefore, if the transmission waves of f ₁ and f ₂ are strong, the intermodulation wave may interfere with the reception target channel and cause interference.

This intermodulation interference can be reduced by automatic gain control (AGC) for the RF signal. That is, when reception signals (jamming signals) of neighboring channels such as frequencies f ₁ and f ₂ are strong, AGC operates to reduce the intensity of these jamming signals, thereby reducing intermodulation waves. Can do.

  Even if the intermodulation wave does not interfere with the reception target channel, if there is a strong interference signal in the channel in the broadcast band, the AGC operates, the intensity of the reception signal of the reception target channel is reduced, and the sensitivity is improved. Can be reduced. This is reception interference called sensitivity suppression.

  Further, even if the signal of the neighboring channel is not strong enough to operate the AGC, if it is stronger than the reception signal of the reception target channel, adjacent interference that has a dominant influence on the reception signal may occur.

  When these disturbances are received, the reception characteristics deteriorate. 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.
JP 2003-218711 A Japanese Patent Laid-Open No. 10-285062

  In FM data broadcasting with high usage on a mobile body, the reception state changes according to movement. Correspondingly, the FM data broadcasting tuner switches to an alternative station. Conventionally, the alternative station is selected by basically switching broadcast channels in order, and broadcasting contents based on the received signal. In this aspect, a search is performed to determine whether or not there is a possibility of substitutability and the reception state, and if a broadcast station that satisfies the determination criteria is found, the search is stopped and the broadcast station is used as an alternative station.

  This method has a problem that the reception state realized by the alternative station is not always suitable. For example, there is a possibility that a broadcasting station that is more suitable as an alternative station exists within a range that has not been searched yet. In addition, when the received signal of the alternative station is disturbed by another station, there is not enough consideration for setting the tuner appropriately for the interference. It is difficult to do in a situation where the reception state changes according to movement.

  The present invention has been made to solve the above problems, and an object thereof is to provide an FM data broadcast tuner capable of maintaining a suitable reception state.

  The FM data broadcast tuner according to the present invention includes a reception field strength detection circuit that detects a reception field strength, and a reception field strength detection circuit that determines the reception field strength of a plurality of broadcast channels set within a reception target band. A reception field strength search means for detecting and acquiring a reception field strength list representing the reception field strength in each broadcast channel; a storage unit for storing the reception field strength list; and a predetermined timing after starting reception of the broadcast When the reception field strength list update unit that starts the reception field strength search means repeatedly to update the reception field strength list stored in the storage unit and the reception state of the current reception broadcast station deteriorates And an automatic channel selection unit that selects an alternative broadcast station based on the received electric field strength list.

  According to the present invention, when it is necessary to select an alternative broadcast station, signal strength information (reception field strength list) in each broadcast channel within the reception target band is obtained in advance. This received electric field strength list is repeatedly updated, and for example, it is possible to reflect a change in the radio wave state according to the movement of the FM data broadcast tuner used in the mobile body. Based on this received electric field strength list, for example, the occurrence of reception interference in the channel of interest is inferred. Receiving interference by preferentially selecting a broadcasting station other than the broadcasting station where the occurrence of reception interference is estimated as an alternative broadcasting station, or by controlling the gain of the amplification means according to the type of interference estimated for the alternative broadcasting station Can be reduced. That is, according to the FM data broadcast tuner according to the present invention, it is possible to maintain a suitable reception state.

  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, a memory 56, and a system bus 58 that enables communication therebetween. The broadcast data is reproduced from the RF signal S _RF0 received by the antenna 60. 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 antenna tuning circuit 68, a damping circuit 70, an RF amplification circuit 72, an RF tuning circuit 74, a local oscillation unit 76, a mixing circuit 78, an IFBPF 80, a limiter amplifier 82, an FM detection circuit 84, and a broadcast data decoder 86. A wide band AGC circuit 90, a narrow band AGC circuit 92, an AGC driver circuit 94, a damping control circuit 96, an S meter circuit 98, and a station detection circuit 100.

The RF signal S _RF0 is input from the antenna 60 to the RF amplifier circuit 72 via the antenna tuning circuit 68 and the damping circuit 70.

The damping circuit 70 is a circuit for damping an input signal to the RF amplifier circuit 72 when the received electric field intensity exceeds a predetermined value. When a current flows through the PIN diodes 70a and 70b in the damping circuit 70 by an output signal of a damping control circuit 96 described later, the damping circuit 70 is turned on. The cathode of the PIN diode 70a is grounded, while the anode is connected to the output terminal of the damping control circuit 96 via the PIN diode 70b and received from the antenna tuning circuit 68 to the RF amplifier circuit 72 via the capacitor 70c. Connected to signal line. When a current flows through the PIN diodes 70a and 70b, the resistance value of the PIN diode 70a decreases, and the reception signal line is grounded in an AC manner via the capacitor 70c and the PIN diode 70a. When the damping circuit 70 is turned on, a part of the output RF signal S _RF1 of the antenna tuning circuit 68 flows to the ground, so that the input signal level of the RF amplifier circuit 72 is reduced.

The RF amplifier circuit 72 is configured using a low noise amplifier (LNA), and amplifies the RF signal S _RF1 extracted by the antenna tuning circuit 68. As will be described later, the gain of the RF amplifier circuit 72 is automatically controlled by the AGC driver circuit 94 based on the received electric field strength, and can be controlled by the control unit 54.

RF tuning circuit 74, the RF signal _{S RF1,} performs the tuning process of extracting further narrow band RF signal _{S RF} containing the desired broadcasting station having a carrier frequency _{f R.} The tuning frequency in the RF tuning circuit 74 is controlled by the control unit 54 via the system bus 58.

The RF signal S _RF2 extracted by the RF tuning circuit 74 is input to the mixing circuit 78. The mixing circuit 78 mixes the input RF signal S _RF2 with the local oscillation signal S _LO input from the local oscillation unit 76 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 RF2} is due to the mixing circuit _{78 (Intermediate Frequency: IF) f} IF conversion To be adjusted. The intermediate frequency f _IF is set to 10.7 MHz, for example. The mixing circuit 78 reduces the conversion gain based on the control of the control unit 54 has a function of adjusting the gain of the S _IF.

The S _IF is input to the IFBPF 80. IFBPF80 _is centered frequency _{f IF,} and is a band pass filter the pass bandwidth _{W F} can be variably set. _{S IF} outputted from IFBPF80 is input to the limiter amplifier 82. The limiter amplifier 82 amplifies the amplitude of the _SIF , which is an FM signal, into a rectangular wave, and removes noise on the FM signal. S _IF, which is a rectangular wave is amplified by the limiter amplifier 82 is inputted to the FM detection circuit 84. The FM detection circuit 84 performs FM detection on the output signal of the limiter amplifier 82 and outputs a detection output signal. The broadcast data decoder 86 decodes the broadcast data included in the detection output signal and outputs it to the control unit 54.

The broadband AGC circuit 90 receives the output signal S _RF2 of the RF tuning circuit 74, and the narrow band AGC circuit 92 receives the output signal S _{IF of the} IFBPF 80. Each AGC circuit 90, 92 detects the peak of the input signal and smooths it to generate AGC voltages V _W-AGC and V _N-AGC . Wideband AGC circuit 90, narrow band AGC circuit _92, the signal strength _{S RF2} and _{S IF} exceeds AGC start level, _{V W-AGC} of a magnitude corresponding to the excess _amount, to produce a _{V N-AGC. These} V _W-AGC and V _N-AGC are combined and input to the AGC driver circuit 94. The AGC driver circuit 94 controls the gain of the RF amplifier circuit 72 based on the input AGC voltage. Specifically, the AGC voltage input to the AGC driver circuit 94 is basically the larger voltage value of V _W-AGC and V _N-AGC . The AGC driver circuit 94 generates a control signal V _RF-AGC for the gain of the RF amplifier circuit 72 according to the input AGC voltage, and operates so as to decrease the gain of the RF amplifier circuit 72 as the AGC voltage increases.

Here, V _W-AGC and V _N-AGC have frequency dependency according to the passband characteristics of the RF tuning circuit 74 and IFBPF 80, and generally the frequency of the signal input to the RF tuning circuit 74 and IFBPF 80. As A goes away from the center frequency of the passband, the AGC voltage tends to decrease. Correspondingly, the AGC sensitivity also has frequency dependency. Here, the AGC sensitivity corresponds to the AGC start level. The lower the AGC start level, the higher the AGC sensitivity.

FIG. 2 is a schematic graph showing the frequency dependence of AGC sensitivity (AGC start level), where the horizontal axis represents frequency and the vertical axis represents AGC start level. Frequency _{f R} of the objective broadcasting station with respect to AGC sensitivity characteristic 110 of wideband AGC circuit 90, also an intermediate frequency _{f IF} with respect to AGC sensitivity characteristic 112 of narrowband AGC circuit 92, respectively corresponding to the center frequency _{f 0.} AGC sensitivity 110,112 AGC start level at the center frequency _{f 0} none is minimized (AGC sensitivity maxima). On the other hand, the AGC start level increases as the distance from f ₀ increases, and the AGC sensitivity decreases. This increase in the AGC start level is more rapid in the AGC sensitivity characteristic 112 than in the AGC sensitivity characteristic 110. This corresponds to the difference that the pass band width of the IFBPF 80 is narrower than that of the RF tuning circuit 74.

Here, as shown in FIG. 2, the AGC start level of the narrowband AGC circuit 92 is set lower than that of the wideband AGC circuit 90 within a range of ± Δf with the frequency f ₀ corresponding to the received signal of the target receiving station as the center. On the other hand, the AGC start level of the wideband AGC circuit 90 can be set lower than that of the narrowband AGC circuit 92, on the other hand, outside the range of ± Δf. With this setting, V _W-AGC <V _N-AGC within the range of ± Δf, V _W-AGC > V _N-AGC outside the range, and the input AGC voltage to the AGC driver circuit 94 is It becomes larger within the range than outside the range of ± Δf. Δf can be set so that neighboring channels that can strongly impede the target broadcast station are included in the range of ± Δf. By doing so, the AGC operation can be performed based on V _N-AGC for the disturbing signal existing in the neighboring channel, and the disturbing signal can be greatly attenuated. On the other hand, an AGC operation is performed based on VW _-AGC for a channel away from the target broadcast station, and relatively moderate gain suppression can be achieved.

Next, the damping control circuit 96 receives the output voltage V _RF-AGC of the AGC driver circuit 94. The damping control circuit 96 compares the reference voltage v _REF having a voltage lower than V _RF-AGC when the AGC operation is not started with the input V _RF-AGC, and when V _RF-AGC falls below v _REF. The damping circuit 70 is operated by outputting a current to the PIN diode 70b. v _REF is set so that the damping control circuit 96 operates at the point where the strength of the received signal increases and the AGC operation starts.

S meter circuit 98, the S _IF and peak detection based on the output signal of each stage of the configured limiter amplifier 82 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 received electric field strength signal S _M-DC is input to the control unit 54 and also to the station detection circuit 100.

The station detection circuit 100 compares the 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 tuning is performed by controlling the RF tuning circuit 74 and the local oscillation unit 76. Further, the control unit 54 automatically selects a station that can be suitably received from among a plurality of broadcasting stations. This automatic channel selection will be described later.

Before that, an operation of acquiring the received electric field strength in the FM data broadcast tuner 50 will be described. FIG. 3 is a schematic graph for explaining the characteristics of the received electric field strength signal S _M-DC generated by the S meter circuit 98. In the figure, the vertical axis represents the voltage value of the output _SM-DC of the S meter circuit 98, and the horizontal axis represents the received electric field strength. The characteristic curve 120 represents the original characteristic of the S meter circuit 98. When the received electric field strength is 0 to 60 dBμV, the SM _-DC changes linearly, and at 60 dBμV or more, the SM _-DC is saturated and flat. Characteristics. That is, the S meter circuit 98 itself has a function capable of satisfactorily detecting the received electric field strength up to 60 dBμV. The FM data broadcast tuner 50 includes a damping circuit 70, and the damping amount of the damping circuit 70 is, for example, 40 dB. Therefore, the SM _-DC characteristic curve 122 when the received RF signal is attenuated by the damping circuit 70 is obtained by shifting the characteristic curve 120 to the high electric field strength side by 40 dBμ. The intensity can be detected well up to 40-100 dBμV. That is, by damping the received signal, the received electric field intensity exceeding 60 dBμV can be measured using the S meter circuit 98. Incidentally, the damping circuit 70 is basically set to start in conjunction with the start of the AGC operation as described above and to operate in the vicinity of 60 dBμV. Further, the damping circuit 70 can be forcibly operated by controlling the AGC driver circuit 94 or the damping control circuit 96 from the control unit 54.

The operation of AGC will be described. FIG. 4 is a graph schematically showing gain characteristics of AGC. In the figure, the vertical axis represents the control signal V _{RF-AGC with} respect to the gain of the RF amplifier circuit 72, and the horizontal axis represents the received electric field strength. V _RF-AGC is maintained at v _RF-MAX until the start point P ₁ of the AGC operation, and the gain is maintained at a high value. For example, as normal time shown in a characteristic curve 130, received signal strength _{V RF-AGC} Until 60dBμV corresponding to _{P 1} is _v is maintained at _RF-MAX. When the received electric field strength increases and reaches an area where AGC operation is performed, V _RF-AGC starts to decrease. When V _RF-AGC decreases and falls below v _REF , the damping circuit 70 starts operating (point P ₂ ). V _RF-AGC is basically maintained at the same level in the range of the received electric field strength in which the damping circuit 70 is operating (for example, a width of 40 dBμV). When the received electric field strength at the upper limit of the operating range of the damping circuit 70 (point P ₃ ) is exceeded, the strength of the input RF signal to the RF amplifier circuit 72 starts to increase again, and V _RF-AGC decreases correspondingly. The gain of the RF amplifier circuit 72 is reduced.

  The control unit 54 is configured to be able to adjust the AGC start level (that is, AGC sensitivity). For example, the characteristic curve 132 when the AGC start level is decreased (that is, the AGC sensitivity is increased) is obtained by shifting the characteristic curve 130 to the low electric field strength side. The AGC according to the characteristic curve 132 is more effective than the AGC according to the characteristic curve 130, that is, the attenuation of the strong reception electric field strength with respect to the broadcasting station is increased.

  Next, the automatic channel selection operation of the FM data broadcast tuner 50 will be described. Here, a case where the FM data broadcast tuner 50 is an RDS tuner will be described as an example. 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.

In relation to this automatic channel selection, the control unit 54 performs a seek search for all broadcast channels set within the reception target band, and receives the received electric field strength signal for each channel by the output signal S _M-DC of the S meter circuit 98. detects, it acquires the received field strength list C _I representing the received field strength of each channel, and the received signal strength list C _I a received signal strength search function to be stored in the memory 56.

In the reception field strength search, the control unit 54 controls the local oscillation unit 76 to seek, for example, the reception channel from one of the reception target bands to the other. When the station detection circuit 100 detects a broadcast station in the reception channel, the control unit 54 acquires the received electric field strength in the reception channel based on the output S _M-DC of the S meter circuit 98. Incidentally, the detection sensitivity of the station detection circuit 100 can be set to 20 to 30 dBμV.

Here, it is preferable to accurately obtain the strength of a received signal having a strong electric field. Therefore, the control unit 54 utilizes the fact that the S meter circuit 98 can measure a strong electric field up to, for example, 100 dBμV by performing the above-described damping. Specifically, the control unit 54 switches the measurement of the received electric field strength in the high sensitivity mode (DX mode) and the measurement of the received electric field strength in the low sensitivity mode (LO mode) as necessary. In the high sensitivity mode, the control unit 54 performs control so that the damping circuit 70 is not activated, and acquires the high sensitivity data D _DX by A / D converting the signal _SM-DC in that state. Thereby, for example, measurement up to 60 dBμV is performed. On the other hand, in the low sensitivity mode, the control unit 54 forcibly activates the damping circuit 70 and A / D-converts the signal S _M-DC in that state to acquire the low sensitivity data D _LO . Thereby, for example, the received electric field strength in the range of 40 to 100 dBμV is measured.

For example, the control unit 54 sets the high sensitivity mode in the seek operation, and measures the _{DX in the} high sensitivity mode for the broadcast station detected by the seek operation. When D _DX is a value corresponding to or close to the saturation level of S _M-DC , the mode is switched to the low sensitivity mode and D _LO is measured for the broadcasting station. The control unit 54 stores the frequency for the broadcast station and D _DX , D _LO in the memory 56 in association with each other. When the seek operation is in progress, the high sensitivity mode is set and the seek operation is continued. On the other hand, when the end of the reception target band is reached, the reception field strength search is completed.

FIG. 5 is a schematic flowchart for explaining the reception operation of the FM data broadcast tuner 50. When reception starts, the control unit 54 seeks the target broadcast station (S140). The target broadcast station at the start of reception is selected by the user, for example. When receiving data broadcast from the broadcasting station (“Y” branch of S142), the FM signal processing unit 52 operates the damping or AGC under the set conditions to acquire the received signal, and from the received signal Broadcast data is extracted (S144). On the other hand, when an idle time occurs in the data reception operation (“N” branch of S142), the control unit 54 performs the above-described reception field strength search (S146). The control unit 54 monitors the reception state based on the received electric field strength signal _SM-DC from the S meter circuit 98, a sensor circuit (not shown in FIG. 1), etc. (S148), and while the deterioration is not detected (in S148). "N" branch), the state synchronized with the current broadcasting station is continued, and processing S142, S144, and S146 are performed. On the other hand, when it is detected that the reception state is deteriorated such as a weak electric field state less than the reference value or adjacent interference has occurred ("Y" branch in S148), an AF search is performed (S150).

The AF search of the FM data broadcast tuner 50, an alternative broadcasting station is selected is acquired by the reception field strength search using a received signal strength list C _I stored in the memory 56, further assumptions about the broadcast station The FM signal processing unit 52 is adjusted according to the received state. FIG. 6 is a schematic process flow diagram of the AF search of the FM data broadcast tuner 50. Based on the alternative frequency list (AF list) received from the current broadcast station and stored in the memory 56, the control unit 54 selects another broadcast station with the same broadcast content as an alternative candidate station (S160). Control unit 54 for the selected alternative candidate station, mutual modulation disturbance described above, desensitization, and guess based on the presence or absence of adjacent interference in the received field strength list _{C I (S162, S164, S166} ).

In the estimation process S162 regarding the occurrence of intermodulation interference, other broadcasting stations having frequencies f ₁ and f ₂ satisfying, for example, f ₁ −f _R = f ₂ −f ₁ with respect to the frequency f _R of the alternative candidate station are detected. If they exist and have a strong received electric field strength greater than or equal to a predetermined value, the control unit 54 estimates that intermodulation occurs.

As for the speculation process S166 guess processing S164 and adjacent interference of desensitization, the control unit 54 obtains the reception field intensity of another broadcasting station in the vicinity frequency of the alternative candidate station from the reception electric field strength list C _I, interfere It is possible to infer the presence or absence of occurrence.

  If no interference is estimated for the alternative candidate station, this is selected as an alternative broadcast station, a switching operation is performed so as to receive the broadcast station (S168), and the AF search is terminated. Here, in addition to controlling the local oscillation unit 76 to switch the tuning frequency, the switching operation can perform processing for setting the FM signal processing unit 52 to a state suitable for reception by a broadcasting station without interference. For example, the sensitivity to the target broadcast station can be improved by increasing the AGC start level to suppress the effect of AGC, or by setting the gain of the RF amplifier circuit 72 high.

  When occurrence of any interference is estimated for the alternative candidate station (“Y” branch in each of S162, S164, and S166), if there is a broadcast station that has not yet been selected as an alternative candidate station in the AF list (S170). , S172, S174, “Y” branch), the alternative candidate station is selected again (S160), and the above-described processing is repeated. On the other hand, when the current alternative candidate station is the last broadcast station in the AF list, for example, the current alternative candidate station that is estimated to be disturbed is selected as the alternative broadcast station, and the broadcast station is received. A switching operation is performed (S176, S178, S180), and the AF search is terminated. Here, in addition to switching the tuning frequency by controlling the local oscillation unit 76, the switching operation can perform processing for adjusting the FM signal processing unit 52 so as to reduce the influence of the estimated interference as much as possible.

  For example, as the adjustment process (S176) when the occurrence of intermodulation is estimated, it is possible to increase the AGC sensitivity, that is, to decrease the AGC start level. As a result, the strong received signal of the jamming station is attenuated, and the occurrence of distortion in the mixing circuit 78 can be suppressed. It is also preferable to set the gain of the RF amplifier circuit 72 and the gain of the mixing circuit 78 low.

  Further, as the adjustment processing (S178) when the occurrence of sensitivity suppression is estimated, it is possible to decrease the AGC sensitivity, that is, increase the AGC start level. Sensitivity suppression is a problem that the AGC operates with a strong interference signal and attenuates to the reception signal of the target broadcast station. Therefore, the sensitivity suppression is reduced by lowering the AGC sensitivity and reducing the effectiveness of the AGC. be able to.

  In the alternative broadcast station selection process described above, when there is no alternative candidate station that is not disturbed, the alternative broadcast station is switched to the last alternative candidate station that is disturbed. Is possible. For example, a suitable one may be selected again from all the alternative candidate stations whose interference has been estimated.

  In the above-described embodiment, the configuration in which the reception field strength list is generated by measuring the reception field strength for all the channels in the reception target band has been described. However, the control unit 54 acquires broadcast channel information for a local broadcast station having a broadcast area corresponding to the current reception position from other external devices and the like, and selectively receives a received electric field for the broadcast channel of the local broadcast station. The intensity can also be detected. As a result, the time required for the received field strength search can be shortened. For example, the map information used in the car navigation system stores information indicating broadcast channels of local broadcasting stations in advance, and the system detects the destination of a car or the like using a GPS or the like, and Information on the destination can be read from the storage device and presented to the user at any time. The FM data broadcast tuner 50 may be configured to provide an interface with a car navigation system so as to acquire broadcast channel information from information provided according to a destination and use it for a received electric field strength search. it can.

Received signal strength search, there a way is carried out by using the interval of the reception processing of the broadcast data, but the present invention must necessarily take place in each interval, the received signal strength list C _I is appropriately updated during the reception operation That's fine.

1 is a schematic block configuration diagram of an FM data broadcast tuner according to an embodiment of the present invention. FIG. It is a typical graph which shows the frequency dependence of AGC sensitivity (AGC start level). It is a typical graph explaining the characteristic of the reception electric field strength signal _SM-DC produced | generated by S meter circuit. It is a graph which shows typically the gain characteristic of AGC. It is a general | schematic flowchart explaining the receiving operation of the tuner for FM data broadcasting. FIG. 5 is a schematic process flow diagram of an AF search of an FM data broadcast tuner.

Explanation of symbols

  50 FM data broadcast tuner, 52 FM signal processing unit, 54 control unit, 56 memory, 58 system bus, 60 antenna, 68 antenna tuning circuit, 70 damping circuit, 72 RF amplification circuit, 74 RF tuning circuit, 76 local oscillation unit , 78 mixing circuit, 80 IFBPF, 82 limiter amplifier, 84 FM detection circuit, 86 broadcast data decoder, 90 wide band AGC circuit, 92 narrow band AGC circuit, 94 AGC driver circuit, 96 damping control circuit, 98 S meter circuit, 100 stations Detection circuit.

Claims (10)

An FM data broadcast tuner for receiving FM data broadcast,
A received electric field strength detection circuit for detecting the received electric field strength;
A received electric field intensity list that represents the received electric field intensity in each broadcast channel by detecting the received electric field intensity with respect to a plurality of broadcast channels set in a reception target band. Intensity search means;
A storage unit for storing the received electric field strength list;
A reception field strength list update unit that starts the reception field strength search means repeatedly at a predetermined timing after starting the reception of the broadcast, and updates the reception field strength list stored in the storage unit;
An automatic channel selection unit that selects an alternative broadcast station based on the received electric field strength list when the reception state of the current reception broadcast station deteriorates;
An FM data broadcast tuner characterized by comprising: The FM data broadcast tuner according to claim 1,
The automatic channel selection unit estimates presence / absence of reception interference based on the received field strength list, and preferentially selects a broadcast station estimated to be free of reception interference as the alternative candidate station. FM data broadcasting tuner. The FM data broadcast tuner according to claim 2,
The FM tuner for FM data broadcasting, wherein the automatic channel selection unit estimates whether or not there is intermodulation interference as the reception interference. The FM data broadcast tuner according to claim 2,
The FM tuner for FM data broadcasting, wherein the automatic channel selection section estimates whether or not there is sensitivity suppression interference as the reception interference. The FM data broadcast tuner according to claim 2,
Amplifying means for the received signal from the broadcasting station;
Gain control means for controlling the gain of the amplification means;
Have
The gain control means controls the gain according to the reception interference estimation result for the alternative candidate station by the automatic channel selection unit;
FM data broadcast tuner characterized by the above. The FM data broadcast tuner according to claim 5,
As the amplifying means, a high-frequency amplifier that amplifies the received signal,
When the occurrence of the intermodulation interference is estimated for the alternative candidate station, the gain control means lowers the gain of the high-frequency amplifier compared to when the interference is not estimated when the reception interference is not estimated,
FM data broadcast tuner characterized by the above. The FM data broadcast tuner according to claim 5,
As the amplifying means, a high-frequency amplifier that amplifies the received signal,
As the gain control means, an AGC voltage corresponding to the intensity of the received signal on the output side of the high-frequency amplifier is generated, and the gain of the high-frequency amplifier is reduced according to the amount of the AGC voltage exceeding the AGC start level. Having an AGC circuit,
The AGC circuit sets an AGC sensitivity determined by the AGC start level higher than that in the non-jamming when the occurrence of the intermodulation jamming is estimated for the alternative candidate station;
FM data broadcast tuner characterized by the above. The FM data broadcast tuner according to claim 5,
As the amplifying means, a high-frequency amplifier that amplifies the received signal,
As the gain control means, an AGC voltage corresponding to the intensity of the received signal on the output side of the high-frequency amplifier is generated, and the gain of the high-frequency amplifier is reduced according to the amount of the AGC voltage exceeding the AGC start level. Having an AGC circuit,
The AGC circuit sets the AGC sensitivity determined by the AGC start level to be equal to or less than that at the time of non-jamming when the occurrence of the sensitivity suppression jamming is estimated for the alternative candidate station;
FM data broadcast tuner characterized by the above. The FM data broadcast tuner according to claim 5,
As the amplification means, the reception signal and the local oscillation signal are mixed to convert the reception signal into a predetermined intermediate frequency, and a mixer having an amplification function is provided.
When the occurrence of the intermodulation interference is estimated for the alternative candidate station, the gain control means reduces the mixing gain by reducing the gain of the mixer compared to when the reception interference is not estimated. Expanding the dynamic range of the vessel,
FM data broadcast tuner characterized by the above. The FM data broadcast tuner according to any one of claims 1 to 9,
The reception field strength search means obtains information on the broadcast channel from the outside for a local broadcast station having a broadcast area corresponding to the current reception position, and selectively receives the reception field strength for the broadcast channel of the local broadcast station. Detecting
FM data broadcast tuner characterized by the above.

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