JP2009105729A - Fm radio receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve a bit error rate in an weak electric field state during an AF search of an FM radio receiver having an RDS receiving function. <P>SOLUTION: The bandwidth WF of a band-pass filter which band-limits an intermediate frequency signal is fixed to a wide bandwidth w<SB>W</SB>in a state of no adjacent-channel interference during the AF search without reference to whether receiving electric field intensity is large or small. Namely, the bandwidth is narrowed during normal reception for a weak electric field even in the absence of adjacent-channel interference to remove weak electric field noise, but widened during the AF search. Thus, the bandwidth is widened in the weak electric field state to improve a bit error rate of the AF search, thereby suitably detecting a PI code. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

The present invention is an FM (Frequency) having a function of receiving RDS (Radio Data System) data.
Modulation) Radio receiver.

The FM radio receiver frequency-converts an RF (Radio Frequency) signal received by an antenna into an intermediate signal having a predetermined intermediate frequency (IF) f _IF, and detects the intermediate signal by an FM detection circuit. To play the audio signal. The intermediate signal is input to the FM detection circuit via the IFBPF. IFBPF _the band-pass filter having a center frequency of _{f IF (Band Pass Filter: BPF} ) a and, its bandwidth _{W F} is, for example, a variable configured in a range such about 40kHz~ about 220 kHz.

  Since the FM signal changes the frequency of the carrier wave based on an audio signal or the like, its transmission requires a wider frequency band than, for example, an AM signal. For this reason, in the FM radio receiver, the received signal of the station desired to receive is susceptible to interference (adjacent interference) of the received signal from the adjacent station, which may adversely affect the quality of the detected audio signal. This adjacent interference can be reduced by narrowing the IFBPF band and removing the reception signal of the adjacent station.

For example, the adjacent interference can be detected based on an AC component extracted by the S meter circuit and a high-frequency component included in the detection output output from the FM detection circuit. Bandwidth control circuit for controlling the bandwidth of the IFBPF monitors the output signal of a sensor circuit for detecting such adjacent-channel interference changes the bandwidth W _F.

Also, the bandwidth control circuit, even when the received field intensity is a predetermined weak electric field state is controlled so as to narrow the bandwidth W _F. Thereby, the weak electric field noise component which passes IFBPF can be decreased, and a sensitivity improvement is achieved. An S meter circuit is provided as a sensor circuit for detecting the received electric field strength, and the bandwidth control circuit monitors the DC output of the S meter circuit to determine whether or not a weak electric field state exists.

  The bandwidth control of the IFBPF described above is also performed at the time of receiving RDS data transmitted using a 57 kHz subcarrier, thereby making the bit error rate of RDS data reception suitable and the RDS data at the time of adjacent interference. Improvement of accuracy is achieved.

The RDS can realize a function of performing an AF search for searching for an alternative candidate station and automatically switching to an alternative station when the reception state deteriorates. In the control, when the reception state deteriorates, the mute state is set, the reception frequency is set to the frequency of the alternative candidate station obtained from the RDS data, and the presence / absence of the alternative candidate station having the reference electric field strength or higher is determined. If it is determined that there is an alternative candidate station, the program identification (PI) code determination is performed after performing IFBPF band automatic variable based on the sensor output of adjacent interference, and the PI code is in a good reception state. Are the same, the alternative candidate station is determined as an alternative station, the reception state is maintained, the AF search is stopped, and switching to the alternative station is performed. On the other hand, if a good alternative station is not found, the original receiving station is restored.
JP 2004-312077 A

  The conventional configuration described above has a problem that the bit error rate can be unnecessarily lowered when receiving RDS data in a state where there is no adjacent interference and a weak electric field. In particular, the AF search has a problem that a bit error rate necessary for ensuring the sensitivity of PI code detection cannot be obtained.

  The present invention has been made to solve the above-described problems, and an object thereof is to provide an FM radio receiver capable of improving the PI code detection sensitivity in an AF search in a weak electric field state.

  The FM radio receiver according to the present invention has an RDS data reception function, and searches for an alternative reception station having the same program identification code included in the RDS data when the reception state of the current reception target station deteriorates. An AF search, which performs frequency conversion on the FM reception signal to shift the carrier frequency of the reception target station to a predetermined intermediate frequency, and generates an intermediate signal; and a pass bandwidth A band-pass filter that passes through the intermediate signal of the reception target station, an adjacent disturbance detection unit that detects adjacent disturbance to the reception target station, and a reception electric field intensity of the reception target station is a predetermined weak electric field An electric field strength discriminating unit for discriminating whether or not the current state is present, and whether or not the adjacent interference is present, whether or not the weak electric field state is present, and whether or not the AF search is performed. A bandwidth controller configured to reduce the pass bandwidth from a predetermined reference bandwidth in the presence of the adjacent interference and in the weak electric field state, while performing the AF search. If there is no adjacent interference, the pass bandwidth is set to the reference bandwidth even in the weak electric field state.

According to the present invention, when AF search, if there is adjacent interference, but narrowing the bandwidth W _F of the IFBPF, if there is no adjacent interference, W _F even in a weak electric field state is set to the reference bandwidth, I can't narrow it. By not narrow the W _F is no adjacent-channel interference state, RDS data in a weak electric field state is easily passed through the IFBPF, it improves the detection sensitivity of the PI code in the AF search with weak electric field 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 radio receiver according to the embodiment. The FM radio receiver 50 is formed on a common circuit board while making its main part into an IC.

  The FM radio receiver 50 has an RDS data reception function, and is incorporated as, for example, an in-vehicle audio device of an automobile. The FM radio receiver 50 has a function of using an RDS and automatically switching to an alternative station by performing an AF search when the reception state of a currently receiving broadcasting station deteriorates as a vehicle moves. is doing.

The RF signal S _RF received by the antenna 54 is received in the FM radio receiver 50 by an FM-RF tuning amplification circuit 56, a first local oscillation unit 58, a first mixing circuit 60, a band pass filter (BPF) 62. , 66, buffer amplifiers 64, 72, second local oscillator 68, second mixing circuit 70, IFBPF (Intermediate Frequency BPF) 74, limiter amplifier 76, FM detection circuit 78, noise canceller 80, and matrix circuit (MPX circuit) 82 And an output signal S _OUT corresponding to the audio signal of the desired station is generated.

  In addition to the components described above, the FM radio receiver 50 includes an RDS decoder 90, an S meter circuit 92, a bandwidth control circuit 94, a quality sensor circuit 96, an adjacent interference noise extraction circuit 98, a modulation degree signal generation circuit 100, and an SD circuit. 102 is comprised. The FM radio receiver 50 operates under the control of the microcomputer 104.

The RF signal S _RF is input to the FM-RF tuning amplifier circuit 56. FM-RF tuned amplifier circuit 56, of the RF signal _{S RF,} it attenuates the components out of the band corresponding to the carrier frequency _{f R} of the FM signal from the desired station. As a result, the FM-RF tuning amplification circuit 56 passes the RF signal S _{RF in the} band including the frequency f _{R of the} desired reception station, and the output signal of the FM-RF tuning amplification circuit 56 is input to the first mixing circuit 60. Is done.

The first local oscillator 58 generates a first local oscillation signal S _LO1 and outputs it to the first mixing circuit 60.

The first mixing circuit 60 mixes the RF signal S _RF and the first local oscillation signal S _LO1 to generate a first intermediate signal S _IF1 . Frequency of S _{LO1 f LO1,} as the signal of the desired station frequency _{f R} included in the _{S RF} is converted to a first intermediate frequency _{f IF1} predetermined by the frequency conversion to _{S IF1} by the first mixing circuit 60 Adjusted. The first intermediate frequency _{f IF1} is set to, for example, 10.7 MHz.

S _IF1 is input to the second mixing circuit 70 via the BPF 62, the buffer amplifier 64, and the BPF 66. For example, the BPFs 62 and 66 can be configured using ceramic filters.

The second local oscillation unit 68 generates a second local oscillation signal S _LO2 and outputs it to the second mixing circuit 70.

The second mixing circuit 70 mixes the first intermediate signal S _IF1 input from the BPF 66 with the second local oscillation signal S _LO2 input from the second local oscillation unit 68 to generate the second intermediate frequency f _IF2 . 2 Intermediate signal S _IF2 is generated. The frequency f _{LO2 of} S _LO2 is set to (f _IF1 −f _IF2 ), and the target reception signal of the frequency f _IF1 included in S _IF1 is converted into the frequency f _IF2 in the second mixing circuit 70. The second intermediate frequency f _IF2 is set to 450 kHz, for example.

S _IF2 is input to the IFBPF 74 via the buffer amplifier 72. IFBPF74 _is centered frequency _{f IF2,} and a band-pass filter the pass bandwidth _{W F} can be variably set. Bandwidth _{W F} passing IFBPF74 is controlled by the bandwidth control circuit 94 as will be described later.

The S _IF2 output from the IFBPF 74 is input to the FM detection circuit 78 via the limiter amplifier 76. The FM detection circuit 78 is composed of, for example, a quadrature detection circuit. The FM detection circuit 78 performs FM detection on the S _IF2 input from the limiter amplifier 76, and outputs a detection output signal _SDET .

The noise canceller 80 removes pulse noise from the detection output signal _SDET . For example, in an in-vehicle FM tuner, pulsed noise with a short time width and a large amplitude can be superimposed on a received signal due to the operation of a vehicle engine, an electric mirror, a wiper, or the like. The noise canceller 80 suppresses sound quality deterioration due to such pulse noise. S _DET removed pulse noise is input to a matrix circuit 82.

The matrix circuit 82 cancels the pilot signal from _SDET using the pilot signal input from the pilot signal extraction circuit (not shown) during stereo broadcasting, and extracts the (L + R) signal and the (LR) signal, respectively. can do. Then, the L signal and the R signal can be separated and output from the (L + R) signal and the (LR) signal by a matrix method.

  The RDS decoder 90 demodulates the RDS data transmitted by modulating the 57 kHz subcarrier. For example, a PI code is sent as RDS data at a predetermined transmission timing. The RDS decoder 90 has a function of correcting an error in the demodulated RDS data based on an error correction code added to the data.

S meter circuit 92, for example, on the basis of the _{S IF1} inputted from the BPF _66, and generates a fluctuation component signal _{S M-AC} included in the _{S IF1,} the variation component low pass filter (Low Pass Filter: LPF ) To generate a reception electric field strength signal S _M-DC . The S _M-DC is input to the bandwidth control circuit 94 and the SD circuit 102. On the other hand, _SM-AC is input to the quality sensor circuit 96.

The quality sensor circuit 96 is a circuit that detects the presence or absence of adjacent interference or multipath interference based on _SM-AC , and includes a high-pass filter (HPF) 130, a detection circuit 132, and a comparator 134. Composed.

The HPF 130 can switch the cut-off frequency f _C depending on whether the frequency band component corresponding to the adjacent interference or the frequency band component corresponding to the multipath interference is extracted from the SM _-AC . Regarding the adjacent interference, if the difference in RF frequency between the broadcasting station that gives adjacent interference and the desired station is Δf, a high frequency component having a frequency corresponding to Δf appears in SM _-AC when the adjacent interference occurs. For example, since the FM broadcast channel step in Japan is 100 kHz, the cut-off frequency f _C of the HPF 130 when extracting the component corresponding to the adjacent interference from the SM _-AC can be set to about 100 kHz, for example. . In general, high frequency components caused by multipath interference are not as high in frequency as adjacent interference components, so that f _C when extracting components corresponding to multipath interference from SM _-AC is set to about 50 kHz. be able to.

The detection circuit 132 rectifies and detects high-frequency components that have passed through the HPF 130 to generate a DC signal V _SQ having a voltage level corresponding to the adjacent interference noise component amount or multipath noise amount in the received signal. _{Here, V SQ} is at the bandwidth control circuit 94 as will be described later, is used for automatic variable control of the passband width _{W F} of the IFBPF 74.

The comparator 134 compares the output level V _SQ of the detection circuit 132 with the reference voltage V _ref1 set to a predetermined threshold. For example, if V _SQ > V _ref1 , adjacent interference or multipath interference occurs. H level is output as the SQ sensor signal S _SQ indicating the determination result of S _SQ . On the other hand, if V _SQ ≦ V _ref1 , S _SQ indicating the determination result that no adjacent interference or multipath interference has occurred. L level is output as This S _SQ is input to the microcomputer 104. The microcomputer 104 uses S _SQ in AF search, for example.

An adjacent interference noise extraction circuit 98 is provided as another circuit for detecting adjacent interference. The adjacent interference noise extraction circuit 98 extracts an adjacent interference noise component included in the output signal _SDET of the FM detection circuit 78. The _SDET at the time of occurrence of adjacent interference has a high frequency component having a frequency corresponding to the RF frequency difference Δf between the desired station and the disturbing station, superimposed on the signal component of the voice band corresponding to the desired station. The adjacent interference noise extraction circuit 98 includes an HPF 138 and a detection circuit 140, and outputs a DC signal S _AI having a voltage level corresponding to the strength of a high frequency component that may be caused by adjacent interference. For example, the cutoff frequency f _C of the HPF 138 can be set to about 100 kHz as in the HPF 130. S _AI is input to the bandwidth control circuit 94, for example.

The modulation degree signal generation circuit 100 generates a DC signal _SMD having a voltage level corresponding to the modulation degree of the received signal based on _SDET . Modulation degree signal generation circuit 100, LPF 142, and a detection circuit 144, removes the high-frequency component caused by adjacent interference or the like, and outputs a DC signal S _MD having a voltage level that corresponds to the modulation degree. The _SMD is used in the bandwidth control circuit 94, for example.

SD (Station Detection) circuit 102 outputs an SD signal S _SD that shows whether the receiving station has been detected by the set tuning frequency. The _SSD is input to the microcomputer 104 and used for AF search. The SD circuit 102 determines whether or not the received electric field strength signal S _M-DC from the S meter circuit 10 exceeds a predetermined threshold value. Further, SD circuit 102, based on the f-V conversion characteristic referred to as S curve between the frequency f of the intermediate signal _{S IF2} and the voltage V of the detection output _{S OUT,} band band of the reception station's target (SD band ) Is determined. The SD circuit 102 determines that a receiving station has been detected when a received signal having a predetermined strength is obtained within the SD band.

The bandwidth control circuit 94 includes an S _M-DC generated by the S meter circuit 92, a V _SQ generated in the quality sensor circuit 96, an S _AI generated by the adjacent interference noise extraction circuit 98, and a modulation degree signal generation circuit. based on the _{S MD} from 100, automatically variably controls the bandwidth _{W F} of the IFBPF 74.

First, bandwidth control of the bandwidth control circuit 94 during normal reception for performing audio reproduction based on the received signal will be described. Figure 2 is an explanatory view illustrating a basic control operation of W _F during normal reception. This figure shows the wide and narrow of the W _F in each combination of the intensity of received field strength and presence or absence of adjacent interference (or medium electric field more or weak electric field).

Based on V _SQ and S _AI , the bandwidth control circuit 94 determines whether the state of “adjacent interference exists” in which the strength of adjacent interference exceeds a predetermined threshold or “no adjacent interference” below the threshold. in the state without adjacent-channel interference, it sets the W _F to the reference bandwidth w _W rather wide so as not to cause audio distortion. On the other hand, if any of the V _SQ and S _AI, or both exceeds the threshold value, the bandwidth control circuit 94, it is determined that there is adjacent interference, sets the W _F to the reference bandwidth narrower value w _N Thus, the adjacent interference wave can be removed by the IFBPF 74.

In addition, the bandwidth control circuit 94, for example, when it is detected that the received electric field strength is in a predetermined weak electric field state based on the _SM-DC even when there is no adjacent interference, the bandwidth control circuit 94 W _F to be set to a narrow value _{w N} than the reference bandwidth. As a result, high-frequency component noise that increases in a weak electric field state is removed by IFBPF 74, and the sensitivity is improved.

Incidentally, the bandwidth control circuit 94, in consideration of the output S _MD of the modulation degree signal generation circuit may be configured to vary the W _F.

Next, bandwidth control of the bandwidth control circuit 94 during AF search will be described. The microcomputer 104, based on the output _{S SD} of the output _{S SQ} and SD circuits 102 Quality sensor circuit 96, when it is determined that the current reception state is not good, starts an AF search. With the start of AF search, the microcomputer 104 sends a control signal _{S AF} to the bandwidth control circuit 94, shifted in operation during AF search. Figure 3 is an explanatory view illustrating a basic control operation of W _F during AF search. FIG Similarly in Figure 2, showing the wide and narrow of the W _F in each combination of the intensity of received field strength and presence or absence of adjacent interference.

Bandwidth control circuit 94 at the time of AF search, if there is adjacent interference, sets the bandwidth W _F to a narrow value w _N than the reference bandwidth. Thereby, loss of RDS data due to adjacent interference can be suppressed, and RDS data can be easily demodulated. On the other hand, when there is no adjacent interference, regardless of the strength of the received signal strength, bandwidth W _F is set to a reference bandwidth w _W. As a result, the sensitivity to the signal transmitting the RDS data can be improved, the bit error rate can be reduced, and the PI code detection can be quickly performed particularly in the AF search.

Speaking in accordance with the procedure of AF search, the microcomputer 104 is strongly subjected to adjacent interference, weak electric field, and multipath based on sensor output such as S _SQ and S _SD during normal reception. When it is detected that the reception state has deteriorated such as the state, the AF search is started. The microcomputer 104 controls the FM-RF tuning amplifier circuit 56 to change the tuning channel to one of the alternative candidate stations. The bandwidth control circuit 94 switched to the operation mode at the time of AF search performs the same control as the automatic bandwidth automatic change operation at the time of normal reception when there is an adjacent disturbance in the movement destination channel. In the state, the RDS decoder 90 acquires the PI code. On the other hand, when there is no adjacent interference, without performing the operation of automatically changing the bandwidth according to the received electric field strength as in normal reception, for example, the bandwidth is fixed to a wider reference bandwidth w _W and is in that state. The RDS decoder 90 acquires the PI code. Here, w _W may simply be the maximum bandwidth of IFBPF 74, but the necessary and sufficient value of w _W is basically a value corresponding to twice the 57 kHz that is the subcarrier of RDS, by setting the w _W, the passband of the IFBPF 74 is set to _{f IF2} ± 57kHz, RDS signal component included in the received signal can satisfactorily pass the IFBPF 74.

Note that the bandwidth control at the time of AF search is compared with the normal bandwidth control at the time of reception, the point of setting a wide bandwidth W _F at a weak electric field state and adjacent-channel interference is not state at the time of AF search Different from normal reception. In general, since there are more channels without adjacent interference than channels with adjacent interference, it is expected that performing bandwidth control that operates differently from normal reception in the above-described case for AF search will have great effectiveness. it can.

Since the control described above to simplify the description, according to the bandwidth W _F is set to switching of the two values of w _N and w _W, for example, in the state of there adjacent interference, the intensity of the adjacent-channel interference is strong W _F can be a controlled narrowing in multiple steps or continuously.

1 is a schematic block diagram of an FM radio receiver according to an embodiment of the present invention. It is explanatory drawing explaining the bandwidth control operation | movement of IFBPF at the time of normal reception. It is explanatory drawing explaining the bandwidth control operation | movement of IFBPF at the time of AF search.

Explanation of symbols

  50 FM radio receiver, 54 antenna, 56 FM-RF tuning amplifier circuit, 58 first local oscillation unit, 60 first mixing circuit, 62, 66 BPF, 64, 72 buffer amplifier, 68 second local oscillation unit, 70 first 2 mixing circuit, 74 IFBPF, 76 limiter amplifier, 78 FM detection circuit, 80 noise canceller, 82 matrix circuit, 90 RDS decoder, 92 S meter circuit, 94 bandwidth control circuit, 96 quality sensor circuit, 98 adjacent interference noise extraction circuit, 100 modulation degree signal generation circuit, 102 SD circuit, 104 microcomputer, 130, 138 HPF, 132, 140, 144 detection circuit, 134 comparator, 142 LPF.

Claims (2)

This FM radio receiver has an RDS data reception function and performs an AF search for searching for an alternative receiving station having the same program identification code included in the RDS data when the reception state of the current reception target station deteriorates. And
An intermediate signal generation circuit that performs frequency conversion for shifting the carrier frequency of the reception target station to a predetermined intermediate frequency with respect to the FM reception signal, and generates an intermediate signal;
A bandpass filter that can variably set a passband width and passes the intermediate signal of the reception target station;
An adjacent interference detector for detecting adjacent interference to the reception target station;
An electric field strength determination unit for determining whether or not the received electric field strength of the reception target station is a predetermined weak electric field state;
A bandwidth control unit that controls the pass bandwidth according to whether there is the adjacent interference, whether the weak electric field state, and whether the AF search,
Have
The bandwidth control unit narrows the pass bandwidth below a predetermined reference bandwidth in the presence of the adjacent disturbance and in the weak electric field state, while in the weak electric field state if the adjacent disturbance is absent during the AF search. Setting the pass bandwidth to the reference bandwidth even if
FM radio receiver. The FM radio receiver according to claim 1.
The reference bandwidth is set according to a frequency of a subcarrier transmitting the RDS data;
FM radio receiver.

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