JPH11239064A - Fm radio receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely eliminate adjacent interference even when it is small by optionally setting detection sensitivity with a simple configuration. SOLUTION: In this FM radio receiver, an IF signal is applied to an IF counter 15 and the frequency of the IF signal is counted. A count value is inputted to a control circuit 17 and adjacent interference is decided according to whether or not the count value deviates from the center frequency of the IF signal of a desired station. When it is decided that adjacent interference occurs, an output signal of a narrowband filter 4 is selected and an interfering station is eliminated by the filter 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radio receiver which takes measures against adjacent interference.

[0002]

2. Description of the Related Art Generally, in a FM radio receiver, when a strong electric field jamming station exists adjacent to a desired station, the radio wave of the jamming station jumps into the FM radio receiving system and the desired station is jammed by the jamming station. May occur. As a countermeasure to prevent this, two filters of a wide band and a narrow band are prepared as IF filters, and when adjacent interference occurs, the band of the FMIF signal is limited to a narrower band to remove an interfering station. An FM radio receiver that takes such measures against adjacent interference is configured as shown in FIG.

In FIG. 4, an FM RF signal is FM-R
After being tuned and amplified by the F-tuned amplification circuit 1, the mixing circuit 2
The center frequency is 1 according to the local oscillation signal of the local oscillation circuit 3.
The frequency is converted to an IF signal of 0.7 MHz. After the IF signal is band-limited by the IF filter 4I, the selection circuit 5
Through the wideband filter 4W and the narrowband filter 4N
And the IF signal is band-limited by the respective pass bandwidths. The output signal of the wide band filter 4W or the narrow band filter 4N is selected by the selection circuit 6, and one of the output signals is amplified by the limiter amplifier 7, and then FM detected by the FM detection circuit 8. At the time of normal reception, an output signal of the wideband filter 4W (hereinafter, referred to as a wide IF signal) is selected, and the wide IF signal is subjected to FM detection.

[0004] It is assumed that an interference station Fud is generated adjacent to the desired station Fd during FM reception. This interfering station Fud is within the pass band of the wide band filter 4W and outside the pass band of the narrow band filter 4N as shown in FIG. However, the passbands of the wideband and narrowband filters 4W and 4N have the relationship shown in FIG. In the adjacent interference detection circuit 9, the connection is made as shown by a signal line a to check the level relationship between the output levels of the wideband and narrow band filters 4 and 5, and the connection is made as shown by a signal line b, and the detection output of the FM detection circuit 8 is detected. The adjacent interference is detected by looking at the smoothing level of. Then, the detection signal
The DET occurs, and the control circuit 10 determines that the adjacent interference has occurred based on the DET, and the output signal of the narrow band filter 4N (hereinafter, referred to as a narrow IF signal) is selected by the selection signal SL. In the narrow-band filter 4N, the interfering station Fud is out of the pass band, so that the interfering station Fud is removed by the narrow-band filter 4N, so that adjacent interference can be removed, and the reception state is improved.

[0005]

As described above, it is possible to remove the adjacent interference by removing the interfering station by the narrow band filter 4N. However, the circuit for detecting the adjacent interference was complicated and could not be reliably detected, so that the circuit for removing the adjacent interference was also complicated and insensitive. That is, the conventional adjacent interference is a wideband and narrowband filter 4W.
4N and the smoothed output level of the FM detection circuit 8 are detected. In the conventional detection that looks at the level relationship between the wide IF signal and the narrow IF signal, the output signals of the wideband and narrowband filters 4W and 4N are respectively smoothed, and both smoothed levels are compared with each other. The selection circuit was being switched. However, an external capacitor for smoothing and an external pin to which these are connected are required for IC conversion, and two smoothed signals are further extracted and compared.
The circuit becomes complicated and is not suitable for use as an IC.

In the detection of the output signal of the FM detection circuit 8, the smoothing level of the detection output is set to I by the interfering station Fud.
Adjacent interference is detected by deviating from the level corresponding to the center frequency of the F signal. However, if the level of the disturbing station Fud is higher than the desired station Fd and the disturbing is not disturbed, the smoothing level does not clearly shift unless the disturbing effect is small. Was difficult. For this reason, it was not possible to reliably remove the interfering station when the adverse effect of the interfering station was small.

Accordingly, the present invention simplifies the circuit configuration,
FM that can reliably remove adjacent interference even in situations where interference is small
It is intended to provide a radio receiver.

[0008]

SUMMARY OF THE INVENTION The present invention is an FM radio receiver having a wide band and a narrow band filter for band limiting an IF signal.
An F counter, first detection means for detecting occurrence of adjacent interference in accordance with a count value of the IF counter,
A control circuit comprising first selection means for selecting one of the output signals of the wide band filter or the narrow band filter according to the detection result of the detection means.

Further, the first detection means detects that adjacent interference has occurred when the count value of the IF counter is out of a predetermined detection range. Especially,
The detection range is set within a pass band of a narrow band filter. Still further, the first selecting means includes:
An output signal of the narrow band filter is selected when adjacent interference occurs, and an output signal of the wide band filter is selected when adjacent interference does not occur.

Further, the control circuit selects an output signal of the broadband filter when adjacent interference does not occur, and detects the received electric field strength of a desired station when adjacent interference occurs. First comparing means for comparing the received electric field strength of the desired station with a first level, and second selecting means for selecting an output signal of the wide band filter or the narrow band filter according to a result of the comparison by the first comparing means. It is characterized by having.

In particular, the second selecting means selects the output signal of the narrow band filter when the reception electric field strength of the desired station is higher than the first level, and the reception electric field strength of the desired station is at the first level. If lower, the output signal of the broadband filter is selected. Furthermore, the control circuit causes the output signal of the narrow band filter to be selected when the reception electric field strength is higher than the first level, and sets the reception frequency of the desired station when the reception electric field strength is lower than the first level. Shifting means for shifting to the vicinity, third detecting means for detecting the electric field strength when the reception frequency is shifted, second comparing means for comparing the electric field strength detected by the third detecting means with the second level, and A third selection means for selecting an output signal of the wide band filter or the narrow band filter according to a comparison result of the two comparison means is provided.

[0012] In particular, the third selecting means selects the output signal of the narrow band filter when the detected electric field strength of the third detecting means is higher than the second level, and the detected electric field strength is higher than the second level. When the signal is low, the output signal of the broadband filter is selected. Also, in particular,
The shift means shifts the reception frequency to a frequency separated from the desired station by a predetermined frequency back and forth, and the third detection means detects the electric field strength of each shifted reception frequency,
Further, the third selecting means selects the output signal of the narrow band filter only when at least one of the detected electric field intensities of the third detecting means is larger than the second level. Further, the predetermined frequency is one channel step of the FM reception band.

According to the present invention, when the interfering station is received by the FM radio receiver together with the desired station, the count value of the IF counter deviates from the center frequency of the IF signal. By this detection, the output signal of the narrow band filter is selected to remove adjacent interference.

[0014]

FIG. 1 is a diagram showing an embodiment of the present invention. Reference numeral 11 denotes a primary coil from which an FM IF signal from a mixing circuit 2 is derived, and reference numerals 12 and 13 denote primary coils. Corresponding first and second secondary coils, 14 is a filter forming an IF filter with the wide band filter 4W or the narrow band filter 4N, 15 is an IF counter for counting the frequency of the output signal of the filter 14, and 16 is the output of the filter 14. An electric field intensity detection circuit 17 detects the received electric field intensity according to the signal. A control circuit 17 controls the selection circuit 6 and the local oscillation circuit 3 according to the count value of the IF counter 15 and the received electric field intensity. In FIG. 1, the same circuits as those in FIG. 2 are denoted by the same reference numerals as those in FIG.

First, referring to FIG.
The F signal is led out to a primary coil 11 serving as a common output circuit. Then, the same IF signals are respectively derived to the secondary coils 12 and 13, and the respective IF signals are applied to the wideband and narrowband filters 4W and 4N. The wideband and narrowband filters 4W and 4N each have filter characteristics as shown in FIG. After that, one of the wide and narrow IF signals is selected and applied to the filter 14. By applying a signal whose frequency is selected by the wideband or narrowband filter 4W or 4N to the filter 14, necessary IF filter characteristics can be obtained. The output signal of the filter 14 is amplified by the limiter amplifier 7 and then subjected to FM detection by the FM detection circuit 8.

Next, referring to the flowchart of FIG.
The operation of the FM radio receiver in FIG. 1 will be described. The FM radio receiver is in the normal reception state, the wide IF signal of the wideband filter 4W is selected, and the wide IF signal is FM-detected (S1). During normal reception, the control circuit 17 starts an operation of detecting whether or not adjacent interference has occurred. I
The F counter 15 counts the frequency of the wide IF signal from the filter 14. The count value of the IF counter 15 is output to the control circuit 17 as needed. When the adjacent interference detection operation is started, the control circuit 17 fetches the count value, and detects whether or not adjacent interference is received according to the count value (S2). Then, the control circuit 17 detects whether or not the count value is out of the predetermined frequency range (S
3). As shown in FIG. 3A, for example, 0.1M from the desired station Fd.
If the interference station Fud exists at a frequency of Hz and the electric field strength of the interference station Fud is stronger than the desired station Fd, the IF signal of the interference station is superimposed on the IF signal of the desired station, and the IF signal level of the interference station is changed to the IF signal of the desired station. Higher than the signal level, so that the center frequency of the IF signal is pulled towards the jammer. Therefore, wide I
The center frequency of the F signal is the center frequency 10.7 of the desired station Fd.
The frequency is shifted from MHz. As a result, at the time of FM detection, the desired station Fd is disturbed by the disturbing station Fud, and the reception state deteriorates. Therefore, if the count value of the IF counter 15 is 1
Since it deviates from the value corresponding to 0.7 MHz (desired station), the control circuit 17 can determine whether or not adjacent interference has occurred by looking at the count value.

When the count value of the IF counter 15 is detected to be within the predetermined detection range Δf, the control circuit 17
Determines that no adjacent interference has occurred, and generates the first state switching signal SL. The wide IF signal is selected by the switching signal SL. That is, the normal reception state of the FM radio receiver is continued (S4). Thereafter, the control circuit 17 enters a standby state (S5), and after a predetermined time (for example, about 10 seconds) elapses, returns to step S1 and starts detecting the adjacent interference again.

In step S3, adjacent interference can be detected.
The F frequency may be shifted. Therefore, when it is detected that the count value of the IF counter 15 is outside the predetermined detection range Δf, the control circuit 17 proceeds to the next step of detecting whether or not the interference is really due to the adjacent interference. By the way, the output signal of the limiter amplifier 7 is applied to the electric field strength detection circuit 1.
6, and the received signal strength is detected by smoothing the output signal. The output signal of the electric field strength detection circuit 16 is taken into the control circuit 17, and the received electric field strength is measured (S
6). Next, the control circuit 17 selects the wide IF signal.
Determines whether the detected reception electric field strength is equal to or higher than a predetermined level (S7). If the received electric field strength is above a predetermined level,
It is recognized that a disturbing station with a strong electric field disturbs the desired station and shifts the IF frequency, or that a strong disturbing station with a strong electric field strength shifts the IF frequency even if the desired station has a strong electric field strength. It is determined that it has occurred. If the level is equal to or lower than the predetermined level, it is determined that there is a possibility that the desired station itself is small and the other station may be affected.

If the received electric field strength is equal to or higher than the predetermined level, the control circuit 17 determines that adjacent interference actually occurs,
A second state switching signal SL is generated. According to the switching signal SL, a narrow IF signal of the narrow band filter 4N is selected,
The narrow IF signal is FM detected. If this interfering station Fud is within the pass band of the wide band filter 4W and outside the pass band of the narrow band filter 4N as shown in FIG. 3A, the interfering station Fud is outside the pass band of the narrow band filter 4N. , The jamming station Fud is removed by the narrow band filter 4N. Therefore, adjacent interference can be removed, and the reception state of the FM radio receiver is improved (S8). Thereafter, the control circuit 17 enters a standby state (S9), and when a predetermined time (for example, about 10 seconds) elapses, the switching signal SL becomes the first state and the wide IF signal is selected, so that the FM radio receiver normally receives the signal. After switching to the state (S10), the process returns to step S1 to start detecting adjacent interference again.

In step S7, the control circuit 17
When it is determined that the electric field strength of the desired station itself is small and there is a possibility that other interference is being caused, noise or the like that interferes with the desired station is detected in detail. If the electric field strength of the desired station itself is small, it is also disturbed by noise or the like. First, the control circuit 17 shifts the local oscillation control signal LO, shifts the local oscillation frequency of the local oscillation circuit 3, and shifts the frequency of the RF signal at which the center frequency of the IF signal becomes 10.7 MHz. The control circuit 17 shifts by one channel step unit of the FM reception band, and specifically shifts the RF frequency Fd of the desired station to the RF frequency FdL in the lower frequency direction as shown in FIG. RF frequency F in high frequency direction
Shift dH and finally return the RF frequency to the desired station.
During the shift, the control circuit 17 detects the electric field strength of the RF frequency FdH, stores the value in an internal memory (not shown) of the control circuit 17, and detects the electric field strength of the RF frequency FdL and stores the value in the internal memory. It is stored (S11). By detecting the electric field strength by shifting the RF frequency, the magnitude and amount of other interference signals generated near the desired station are detected. Thereafter, it is detected whether both the received electric field strengths of the RF frequencies FdL and FdH are smaller than the predetermined level V2 (S12). If both the received electric field strengths of the RF frequencies FdL and FdH are smaller than the predetermined level V2, it is determined that the desired station itself has a weak electric field strength and the reception state has been deteriorated due to the insufficient electric field strength. If at least one of the received electric field strengths of the RF frequencies FdL and FdH is higher than the predetermined level V2, it is determined that the desired station itself has a weak electric field strength and has been disturbed by another disturbing signal near the desired station.

In step 12, the RF frequency FdL
If both the received electric field strengths of FdH and FdH are smaller than the predetermined level V2, the control circuit 17 determines that there is no interference, and proceeds to step S4 to continue the normal reception in the weak electric field state by the wide IF signal for a predetermined time. , Adjacent interference is detected again. If at least one of the received electric field strengths of the RF frequencies FdL and FdH is higher than the predetermined level V2, the process proceeds to S8, and the noise near the desired station can be removed by selecting the narrow IF signal. Is improved. After a lapse of a predetermined time, FM
After the standby state, the radio receiver switches to the normal reception state and starts to detect the adjacent interference again.

Note that the wide band and narrow band filters 4W and 4
If the passband N and the detection range Δf of the IF frequency are set as shown in FIG. 3A, adjacent interference can be reliably removed. Although the IF frequency is counted only once in step S2, the process may proceed to step S3 when counting is performed a plurality of times and the count value matches the same value. As a result, it is possible to detect whether a temporary disturbance or an adjacent disturbance is always occurring. Further, step S
The electric field intensity may be measured a plurality of times in step 6. Particularly in a car tuner, the received electric field intensity changes due to movement, so that the adjacent interference can be reliably detected by using the average value of the detected electric field intensity. .

Generally, the FM radio receiver detects a station at the time of search by detecting the frequency of an IF signal, and is provided with an IF counter. This search IF
If a counter is used, it can be shared with an IF counter for adjacent interference, and there is no need to provide a new IF counter. Also, the magnitude of the IF signal of the interfering station that is superimposed on the IF signal of the desired station changes according to the strength of the electric field strength of the adjacent interfering station. Therefore, depending on the strength of the jamming station, I
The amount of deviation of the frequency of the F signal changes and the IF counter 15
The count value changes. Therefore, the detection sensitivity of the adjacent interference can be arbitrarily set by arbitrarily changing the detection range Δf. In step S11, the shift of the RF frequency is shifted from the desired station Fd to the RF frequency FdL as shown in FIG.
After shifting from d to the RF frequency FdH, it may return to the desired station Fd. This shift operation is effective for the case where the local oscillation frequency of the local oscillation circuit 3 moves slowly, and the time when the local oscillation frequency actually moves can be shortened by shifting the short moving distance a plurality of times.
Sound breaks can be prevented.

[0024]

According to the present invention, the adjacent interference is detected in accordance with the count value of the IF counter, and the adjacent interference is removed based on the detection result. Therefore, the adjacent interference can be removed with a simple circuit. In addition, no external element is required separately.
A radio receiver suitable for C conversion can be provided.

Further, when it is detected that adjacent interference has occurred, the received electric field strength of the desired station is detected, so that it is possible to more reliably determine whether adjacent interference has occurred or other interference has occurred. When the interference is received, the electric field strength near the desired station is detected, so that it is possible to determine whether the electric field strength of the desired station is low or the interference of the surrounding noise is present. Therefore, by approximately accurately selecting the output signal of the wideband or narrowband filter in the above situation,
The reception state of the M radio receiver can be reliably improved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a flowchart for explaining the operation of FIG. 1;

FIG. 3 is a frequency characteristic diagram for explaining the operation of FIGS. 1 and 2;

FIG. 4 is a block diagram showing a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 RF amplifier circuit 2 Mixing circuit 3 Local oscillation circuit 4W Wide band filter 4N Narrow band filter 4I IF filter 5, 6 Selection circuit 7 Limiter amplifier 8 FM detection circuit 9 Interference detection circuit 14 Filter 15 IF counter 16 Electric field intensity detection circuit 10, 17 Control circuit

Claims (10)

[Claims] 1. An FM radio receiver comprising a wide band filter and a narrow band filter for band limiting an IF signal, an IF counter for counting the frequency of the IF signal, and detecting occurrence of adjacent interference according to the count value of the IF counter. And a control circuit comprising first selection means for selecting one of the output signals of the wide band filter or the narrow band filter according to the detection result of the first detection means. Radio receiver. 2. The FM radio receiver according to claim 1, wherein said first detection means detects that adjacent interference has occurred when the count value of said IF counter is out of a predetermined detection range. 3. The FM radio receiver according to claim 2, wherein said detection range is set within a pass band of a narrow band filter. 4. The first selection means selects an output signal of the narrow band filter when adjacent interference occurs,
3. An output signal of the wideband filter is selected when no adjacent interference occurs.
An FM radio receiver as described. 5. The control circuit selects an output signal of the wideband filter when adjacent interference does not occur, and detects a received electric field strength of a desired station when adjacent interference occurs. First comparing means for comparing the received electric field strength of the desired station with a first level, and second selecting means for selecting an output signal of the wide band filter or the narrow band filter according to a result of the comparison by the first comparing means. The FM radio receiver according to claim 1 or 2, further comprising: 6. The second selection means selects an output signal of the narrow band filter when the reception electric field strength of the desired station is higher than the first level, and the reception electric field strength of the desired station is at the first level. 6. The FM radio receiver according to claim 5, wherein an output signal of the broadband filter is selected when the frequency is lower. 7. The control circuit selects an output signal of the narrow band filter when the received electric field intensity is higher than the first level, and selects a reception frequency when the received electric field intensity is lower than the first level. Shifting means for shifting to the vicinity of the station, third detecting means for detecting electric field strength when the reception frequency is shifted, second comparing means for comparing the electric field strength detected by the third detecting means with a second level, The second
6. The FM radio receiver according to claim 5, further comprising third selection means for selecting an output signal of the wide band filter or the narrow band filter according to a comparison result of the comparison means. 8. The third selection means selects the output signal of the narrow band filter when the detected electric field strength of the third detecting means is higher than the second level, and the detected electric field strength is higher than the second level. The F signal according to claim 7, wherein when the signal is low, the output signal of the wide band filter is selected.
M radio receiver. 9. The shift means shifts a reception frequency to a frequency which is separated from a desired station by a predetermined frequency back and forth, and the third detection means detects an electric field strength of each shifted reception frequency. 8. The FM radio receiver according to claim 7, wherein the third selection means selects the output signal of the narrow band filter only when at least one of the electric field strengths detected by the third detection means is higher than the second level. 10. The predetermined frequency is one of FM reception bands.
10. A channel step amount.
An FM radio receiver as described.