JP2895858B2 - FM stereo receiver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Industrial application field The present invention relates to an improvement of an FM stereo receiver.
In particular, the present invention relates to an FM stereo receiver capable of controlling an output signal level of a stereo multiplex circuit to improve an apparent separation between channels.

(B) Conventional technology When receiving an FM stereo broadcast signal, usually, the broadcast signal is FM detected using an FM detection circuit, and the detection output signal is converted into a left and right stereo signal (L) and (L) using a stereo multiplex circuit. R), amplified by a low frequency amplifier circuit, and then applied to left and right speakers. Also, a three-channel system using a center speaker to which a stereo sum signal (L + R) included in the FM detection output signal or a stereo sum signal (L + R) formed by adding the separated left and right stereo signals is applied together with the left and right speakers. And a rear speaker to which a stereo difference signal (LR) included in the FM detection output signal or a stereo difference signal (LR) formed by subtracting the separated left and right stereo signals together with the center speaker is applied. Conventionally, a four-channel system or the like has been proposed. When such channel expansion is performed, the localization and spread of the sound can be improved.

(C) Problems to be Solved by the Invention However, simply performing channel expansion as described above is still insufficient, and a system for further increasing the stereo effect has been desired.

(D) Means for Solving the Problems The present invention has been made in view of the above points, and has a first comparison circuit for generating a first control signal in accordance with a ratio between left and right stereo signals, and a first control circuit. A first separating circuit for separating the signal into a left dominant signal and a right dominant signal, and a second comparing circuit for generating a second control signal according to a ratio between the stereo sum signal (L + R) and the stereo difference signal (LR) A second separating circuit for separating the second control signal into a sum dominant signal and a difference dominant signal; and a second separating circuit for controlling an output signal level of a stereo multiplex circuit using the left and right dominant signals and the sum and difference dominant signal. A one-level control circuit, a noise detection circuit for detecting noise included in a received signal, and an output signal of the noise detection circuit.
A second level control circuit that controls at least the level of the difference dominance signal.

(E) Function According to the present invention, which of the left and right stereo signals and the stereo sum difference signal is dominant using the first and second control signals obtained from the first and second comparison circuits. Can be determined. Then, since the level control of the output signal of the stereo multiplex circuit is performed based on the result of the determination, it is possible to apply a signal whose directionality is emphasized to the left and right speakers, the center speaker, and the rear speaker. Further, since noise included in the received signal is detected and at least the level of the difference dominant signal is controlled, it is possible to prevent erroneous directional emphasis caused by the noise.

(F) Embodiment FIG. 1 is a circuit diagram showing one embodiment of the present invention.
Is an antenna for receiving FM stereo broadcast signals, (2)
Is an RF amplifier circuit for amplifying the RF signal received by the antenna (1), and (3) is a mixing circuit for mixing the amplified RF signal and the output signal of the local oscillator circuit (4) to generate an IF signal. , (5) an IF amplifier circuit for amplifying the IF signal, (6)
Is an FM detection circuit for detecting the amplified IF signal, and (7) is the FM detection circuit.
A stereo multiplex circuit for separating left and right stereo signals (L) and (R) from a stereo sum signal (L + R) and a stereo difference signal (LR) contained in an output signal of the FM detection circuit (6), (8) (11) are first to fourth rectifier circuits for rectifying the output signal of the stereo multiplex circuit (7), respectively, and (12) is the ratio of the first and second rectifier circuits (8) and (9). The first comparison circuit to be taken, (13)
Is a second comparison circuit that takes the ratio of the third and fourth rectifier circuits (10) and (11), and (14) and (15) are the first and second rectifier circuits.
First and second time constant circuits connected to the output terminals of the comparison circuits (12) and (13), and (16) the first time constant circuit (14)
A first signal that separates the output signal of
A separation circuit, (17) a second separation circuit for separating the output signal of the second time constant circuit (15) into a sum dominant signal and a difference dominant signal, and (18) a first and second separation circuit (16) And (1
7) a direction control circuit for generating first to fourth output signals in accordance with the output signal, and (19) to (22) stereo signals in response to the first to fourth output signals of the direction control circuit (18). First to fourth attenuating circuits for attenuating the output signal of the multiplex circuit (7), (23) a high-pass filter for passing high-frequency noise included in the detection output signal, and (24) for detecting the high-frequency noise. Noise detection circuit, and (25)
Is a second level control circuit for controlling the level of the output difference dominant signal of the second separation circuit (17) according to the output signal of the nozzle detection circuit (24). Note that the direction control circuit (18) and the first to fourth attenuation circuits (19) to (22) constitute a first level control circuit.

The FM stereo signal received by the antenna (1) is RF-amplified, converted to an IF signal, and FM-detected, similarly to a conventional FM stereo receiver. Then, in the stereo multiplex circuit (7), the left and right stereo signals (L) and (R) are obtained from the stereo sum signal (L + R) and the stereo difference signal (LR) contained in the output signal of the FM detection circuit (6). ) Are separated. Therefore, left and right stereo signals (L), (R),
Stereo sum signal (L + R) and stereo difference signal (L-
R) can be generated. Each signal obtained at the output terminal of the stereo multiplex circuit (7) is rectified by first to fourth rectifier circuits (8) to (11), and is respectively rectified by first and second comparator circuits (12) and (13). ). An output signal corresponding to the level ratio between the left and right stereo signals (L) and (R) is generated from the first comparison circuit (12), and a stereo sum difference signal (L) is output from the second comparison circuit (13).
An output signal corresponding to the level ratio between (+ R) and (LR) is generated. The details of the first and second comparison circuits (12) and (13) are omitted since they are described in detail in Japanese Patent Application No. 63-180516.

The first and second control signals generated from the first and second comparison circuits (12) and (13) are respectively transmitted through the first and second time constant circuits (14) and (15). Applied to the separation circuits (16) and (17). The first separation circuit (1
6) separates the first control signal into a left dominant signal and a right dominant signal, and the second separating circuit (17) separates the second control signal into a sum dominant signal and a difference dominant signal. Fig. 2 (a)
Indicates the first control signal, (b) indicates the left dominant signal,
(C) is the right dominant signal, (d) is the sum dominant signal, (e)
Indicates a difference dominant signal, respectively. Output signals of the first and second separation circuits (16) and (17) are applied to a direction control circuit (18), and the direction control circuit (18) outputs one of the output signals of the stereo multiplex circuit (7). First to fourth output signals for emphasizing the three signals are generated, and the first to fourth attenuating circuits (19) to (22) are driven to attenuate the remaining three signals. For example, if only the left dominant signal is generated among the output signals of the first and second separation circuits (16) and (17), according to the second and third output signals of the direction control circuit (18), Right stereo signal (R), stereo sum signal (L +
R) and the stereo difference signal (LR) are attenuated by a predetermined amount,
The left stereo signal (L) is emphasized.

Noise in the received signal is small, and the noise detection circuit (22)
If no more than a predetermined level of noise is detected, an "L" level output signal is generated from the buffer amplifier (23). In this case, the second level control circuit (25) to which the "L" level output signal is applied becomes equivalent to an amplifier having a gain of 1, and the output difference dominant signal of the second separation circuit (17) remains large. This is applied to the direction control circuit (18).

On the other hand, if the noise in the received signal increases due to multipath interference or the like, the noise included in the output signal of the FM detection circuit (6) also increases, and the noise is detected by the noise detection circuit (22), and the buffer amplifier The output signal of (23) has a level corresponding to the detected noise. When the output signal of the buffer amplifier (23) is applied to the second level control circuit (25), the level of the difference dominant signal decreases.
On the spectrum of the FM stereo signal, the stereo difference signal (LR) is in a relatively high band, and is easily affected by noise generated by multipath interference or the like. Therefore, when the noise increases, the second separation circuit (17)
The output difference dominant signal becomes abnormally large, making it impossible to perform correct directionality enhancement according to the state of the FM stereo signal. Therefore, in the present application, a second level control circuit (25) is provided in the difference dominant signal path to prevent the difference dominant signal caused by noise from being applied to the direction control circuit (18). In that case, the second level control circuit (25) may be changed linearly in accordance with the output signal level of the buffer amplifier (26), or a predetermined threshold level may be provided and the buffer amplifier (26) may be provided. The difference dominant signal may be cut off when the output signal of (2) exceeds the threshold level. If the difference dominant signal is changed, for example, as shown by a one-dot chain line or a two-dot chain line in FIG.

Note that the noise generated at the time of multipath interference has a large effect on the stereo difference signal (L-R), but the left and right stereo signals (L) and (R) and the stereo sum signal (L + R).
Also has an effect on Therefore, level control circuits are inserted into all of the output signal paths of the first and second separation circuits (16) and (17), and all the level control circuits are connected by using the output signal of the noise detection circuit (24). It may be controlled.

(G) Effect of the Invention As described above, according to the present invention, the directionality can be enhanced according to the state of the received signal, so that the apparent separation can be improved and the sense of presence can be enhanced. I can do it. In particular, since the noise included in the received signal is detected and the level of the difference dominant signal is controlled at least by using the second level control circuit when the noise increases, an erroneous direction caused by the noise is detected. Sex emphasis can be prevented, and accurate direction emphasis can be performed.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIGS. 2A to 2F are characteristic diagrams for explaining the present invention. (6) FM detection circuit, (7) Stereo multiplex circuit, (12), (13) Comparison circuit, (16),
(17) Separation circuit (18) Direction control circuit (1
7), (18), (19), (20) ... Attenuation circuit, (24) ...
... noise detection circuit, (25) ... level control circuit.

Claims (4)

(57) [Claims] 1. An FM stereo receiver for receiving an FM stereo broadcast signal, comprising: a first control signal generating a first control signal corresponding to a ratio of a left stereo signal (L) to a right stereo signal (R). A comparison circuit; a first separation circuit for separating the first control signal into a left dominant signal and a right dominant signal; a stereo sum signal (L + R) and a stereo difference signal (LR)
A second comparison circuit that generates a second control signal according to the ratio of the second control signal, a second separation circuit that separates the second control signal into a sum dominant signal and a difference dominant signal, and a left and right dominant signal and a sum difference dominant signal. To control the output signal level of the stereo multiplex circuit using
A level control circuit; a detection circuit for detecting noise included in a received signal; and a second level control circuit for controlling at least the level of the difference dominant signal according to an output signal of the nozzle detection circuit. FM stereo receiver characterized by the following. 2. The apparatus according to claim 1, wherein said second level control circuit simultaneously controls the levels of said left and right dominant signal and said sum and dominant signal according to an output signal of said noise detecting circuit. FM stereo receiver. 3. The circuit according to claim 2, wherein said second level control circuit includes variable resistance means, and a resistance value of said variable resistance means changes according to an output signal level of said noise detection circuit. The FM stereo receiver according to claim 1. 4. The second level control circuit includes a switch, controls the switch according to an output signal of the noise detection circuit having a predetermined level or more, and stops transmission of a dominant signal. Item 3. The FM stereo receiver according to item 1.