JPH0787412B2 - FM radio receiver - Google Patents

Description

TECHNICAL FIELD The present invention relates to an FM radio receiver, and in particular, a diversity type FM radio that performs reception using two antennas that are arranged apart from each other. Regarding the receiver.

(B) Conventional technology In an on-vehicle FM radio receiver that receives FM broadcasts while moving, noise that occurs with changes in electric field strength, so-called skip noise, and interference due to multiple propagation paths of radio waves Reception interference is caused by noise generated as a result, so-called multipath distortion and the like. The reception interference is described in JP-A-59-
As disclosed in Japanese Patent No. 190746, the high frequency noise component included in the output signal of the FM detection circuit is detected, and the high frequency component in the output signal of the FM detection circuit is attenuated by using the detection output and removed. I can.

Further, as shown in "Multipath-preventing Antenna System" described in the magazine JAS JOURNAL November 1981, pages 3 to 9, high frequency noise components included in the output signal of the FM detection circuit are detected, There is also proposed a method of removing reception interference by selecting an antenna having a good reception state from two types of antennas according to the detection output and performing reception (so-called diversity reception).

(C) Problems to be Solved by the Invention However, the method of attenuating the high frequency component disclosed in Japanese Patent Laid-Open No. 59-190746 has a problem in that the high frequency information in the detection output signal is lost, resulting in deterioration of sound quality. However, JAS JOURNAL's diversity reception system responds to the ignition noise generated from the engine of the car, so there is a problem that an antenna with a poor radio wave condition is selected due to a malfunction. By the way, in the case of the diversity reception system, a time constant circuit or the like can be provided to prevent a malfunction due to the ignition noise. However, the provision of the time constant circuit causes a new defect that the sensitivity and the speed are lowered when the normal detection for the skip noise and the multipath distortion is performed, which is a problem.

(D) Means for Solving the Problems The present invention has been made in view of the above-mentioned points, and generates a pulse according to noise included in the signals received by the first and second antennas. According to the output control signals of the first and second pulse generation circuits, the pulse number comparison circuit for comparing the output pulse numbers of the first and second pulse generation circuits to generate a control signal, and the output control signal of the pulse number comparison circuit, And a switching circuit for switching and outputting a signal received by one of the first and second antennas.

(E) Function According to the present invention, it is possible to select and receive a signal with less noise from the signals received by the two antennas, and thus suppress reception interference caused by skip noise or multipath distortion. You can do it. Further, when the ignition noise that similarly affects two antennas is generated, the number of output pulses of the first and second pulse generation circuits becomes equal, so that the control signal is not generated from the count value comparison circuit,
The received signal is not switched. Therefore, according to the present invention, it is possible to obtain an FM radio receiver capable of distinguishing between skip noise or multipath distortion and ignition noise, and switching reception only when necessary.

(F) Embodiment FIG. 1 is a circuit diagram showing an embodiment of the present invention, in which (1) is a first antenna arranged in a front portion of a vehicle,
( 2 ) comprises an RF (radio frequency) amplification stage (3), a mixing stage (4), a local oscillation stage (5), an IF (intermediate frequency) amplification stage (6) and a detection stage (7), First to obtain FM detection output signal from the signal received by antenna (1)
A tuner section, (8) is a second antenna arranged, for example, in the rear part of the automobile, and ( 9 ) is the first tuner section ( 2 ).
A second tuner section having the same configuration as the above, for obtaining an FM detection output signal from the signal received by the second antenna (8),
(10) is a first high-pass filter that passes high-frequency noise included in the detected output signal, (11) is a first amplifier circuit that amplifies the output signal of the first high-pass filter (10), (12)
Is a first pulse generation circuit for generating a pulse corresponding to noise of a predetermined level or higher contained in the output signal of the first amplification circuit (11), (13) is a second high-pass filter, and (14) is a second
Amplifier circuit, (15) is the second pulse generation circuit, (16) is the first
And an OR gate that takes the logical sum of the output signals of the second amplifier circuits (11) and (14), and (17) generates a pulse corresponding to the output signal of a predetermined level or higher obtained at the output end of the OR gate (16). A third pulse generation circuit, (18) is a monostable multivibrator to which the output signal of the third pulse generation circuit (17) is applied, and (19) and (20) are output signals of the monostable multivibrator (18). First and second counters for counting the output pulses of the first and second pulse generation circuits (12) and (15), respectively, during the generation period, and (21) for the first and second counters.
A subtraction circuit for subtracting the count values of the counters (19) and (20), (22) is an RS flip-flop which is set according to the first output of the subtraction circuit (21) and reset according to the second output. (23) is the RS flip-flop (22)
Switching circuit that is switched by the output control signal of
4) is a stereo multiplex circuit for separating the output signal of the switching circuit (23) into left and right stereo signals.

Now, assuming that the switching circuit (23) is switched to the illustrated state, the signal received by the first antenna (1) is the first
The signal is processed by the tuner section ( 2 ) and applied to the stereo multiplex circuit (24) via the switching circuit (23). Therefore, left and right stereo signals are generated at the first and second output terminals (25) and (26), respectively. At that time, the signal received by the second antenna (8) is processed by the second tuner section ( 9 ), but since the switching circuit (23) is in the state shown in the figure, the signal is sent to the stereo multiplex circuit (24). Not applied. Detection stage (7) of the first and second tuner sections ( 2 ) and ( 9 )
The high frequency noise (Fig. 2 (a)) contained in the FM detection output signal obtained at the output terminals of (7 ') and (7') passes through the first and second high pass filters (10) and (13), respectively. , First
And amplified by the second amplifier circuits (11) and (14). Then, an output pulse (FIG. 2 (b)) is generated from the first pulse generation circuit (12) in response to a signal of a predetermined level (V ₁ ) or higher among the output signals of the first amplification circuit (11), An output pulse is generated from the second pulse generation circuit (15) in response to a signal having a predetermined level or higher among the output signals of the second amplification circuit (14).
On the other hand, the output signals of the first and second amplifier circuits (11) and (14) are applied to the OR gate (16). Then, an output pulse is generated from the third pulse generating circuit (17) in response to a signal having a predetermined level or higher among the output signals of the OR gate (16). Further, the output pulse of the third pulse generation circuit (17) is expanded by the monostable multivibrator (18) and formed into a pulse having a predetermined width (FIG. 3C). The output signals of the monostable multivibrator (18) are the first and second
It is applied as an operation signal to the counters (19) and (20). Therefore, the first and second counters (19) during which the output signal of the monostable multivibrator (18) is "H"
Output pulses of the first and second pulse generation circuits (12) and (15) are counted at (20) and (20). The count values of the first and second counters (19) and (20) are subtracted by a subtraction circuit (21). The subtraction circuit (21) adds the count value of the first counter (19) and the complement of the count value of the second counter (20) and generates an output signal when the difference is more than a predetermined value (for example, 3). To do. Therefore, when the count value of the first counter (19) becomes 3 or more larger than the count value of the second counter (20), the subtraction circuit (21) causes the RS flip-flop (2
When the set signal is applied to the set terminal (S) of 2),
When the count value of the counter (20) exceeds the count value of the first counter (19) by 3 or more, a reset signal is applied from the subtraction circuit (21) to the reset terminal (R) of the RS flip-flop (22). To be done. The RS flip-flop (22) is
When a set signal is applied, an "H" signal is generated at the Q terminal, the switching circuit (23) is switched to the opposite state to that shown in the figure, and when a reset signal is applied, an "L" signal is generated at the Q terminal, and the switching circuit (2
3) Switch to the state shown.

In the reception state using the first antenna (1), multipath distortion or the like occurs, and the count value of the first counter (19) becomes the second value.
If the count value of the counter (20) becomes 3 or more, R-
The S flip-flop (22) is set, and the switching circuit (2
3) is switched to the state opposite to that shown. Therefore, the signal received by the second antenna (8) and having a higher quality than the received signal of the first antenna (1) is processed by the second tuner section ( 9 ) and passed through the switching circuit (23). It is applied to the plex circuit (24). Also, in that state, the reception state using the second antenna (8) deteriorates, and the second counter (2
When the count value of 0) becomes larger than the count value of the first counter (19) by 3 or more, R-
The S flip-flop (22) is reset, and the switching circuit (23) returns to the illustrated state again. Therefore, good reception is performed again using the first antenna (1).

As described above, when skip noise or multipath distortion that adversely affects only one of the first and second antennas (1) and (8) occurs, the noise determination circuit of FIG. 1 detects it and automatically Since the reception is switched to, it is possible to always maintain a good reception state. On the other hand, when ignition noise that adversely affects the first and second antennas (1) and (8) equally occurs, the first and second counters (1
Since the count values of 9) and (20) change equally and the difference does not open, the switching circuit (23) is not switched. Therefore, the skip noise, the multipath distortion, and the ignition noise are automatically distinguished.

The first and second counters (19) and (20), the OR gate (16), the third pulse generating circuit (17), the monostable multivibrator (18), the subtracting circuit (21), and the R -S
The flip-flop (22) constitutes a pulse number comparison circuit, and the pulse number comparison circuit is formed integrally with the first and second pulse generation circuits on a single IC substrate.

(G) Effect of the Invention As described above, according to the present invention, when the skip noise or the multipath distortion occurs, the antenna used can be changed and a good reception state can be maintained. Also, ignition noise can be distinguished from skip noise and multipath distortion.
In particular, since the output pulse generated according to the noise contained in the received signal is counted and the number of pulses is compared and the switching circuit is switch-controlled, the reception switching can be surely performed without malfunction.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing one embodiment of the present invention, and FIGS. 2A to 2C are characteristic diagrams for explaining the present invention. (1) (8) …… antenna, (11) (14) …… amplifier circuit, (12) (15) (17) …… pulse generator circuit, (19)
(20) …… Counter, (21) …… Subtraction circuit, (23) ……
Switching circuit.

Claims (1)

[Claims] 1. A first and second pulse generating pulse according to noise contained in a signal received by a first antenna and a second antenna.
A pulse generation circuit, a pulse number comparison circuit for comparing the output pulse numbers of the first and second pulse generation circuits to generate a control signal, and an output control signal of the pulse number comparison circuit,
An FM radio receiver comprising a switching circuit for switching and outputting a signal received by one of the first and second antennas.