JP2895857B2 - 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) formed by subtracting the left and right stereo signals separated from the stereo difference signal (LR) included in the FM detection output signal together with the center speaker is applied. Conventionally, a four-channel system or the like has been proposed. Thus, by expanding such a channel, 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 corresponding to a ratio between left and right stereo signals, and a stereo sum difference signal. A second control signal for generating a second control signal corresponding to the ratio of the first and second control signals, a level control circuit for controlling an output signal level of the stereo multiplex circuit using the first and second control signals, And a means for changing at least the dynamic range of the second comparison circuit in accordance with the output signal of the noise detection circuit.

(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 dynamic range of the second comparison circuit is changed, it is possible to prevent erroneous emphasis on directionality 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 create 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) included in an output signal of an 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) according to output signals of the first and second time constant circuits (14) and (15). A direction control circuit for generating first to fourth output signals, and (17) to (20) are provided in accordance with the first to fourth output signals of the direction control circuit (16).
First to fourth attenuating circuits for attenuating the output signal of the stereo multiplex circuit (7); (21) a high-pass filter for passing high-frequency noise included in the detection output signal;
And (22) a noise detection circuit for detecting the high frequency noise and generating a control signal for controlling the dynamic range of the second comparison circuit (13). The direction control circuit (16) and the first to fourth damping circuits (17) to (20) are
It constitutes a 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),
Left and right stereo signals (L) and (R) are separated from the stereo sum signal (L + R) and the stereo difference signal (LR) contained in the output signal of the FM detection circuit (6). Therefore, left and right stereo signals (L) and (R) and a stereo sum signal (L +
R) and a stereo difference signal (LR), respectively. 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 the second comparison circuit (1
From 3), the stereo sum difference signal (L + R) and (LR)
An output signal corresponding to the level ratio 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 output control signals of the first and second comparison circuits (12) and (13) are supplied to the direction control circuit (16) via the first and second time constant circuits (14) and (15), respectively. Is applied to The direction control circuit (16) generates first to fourth output signals in order to emphasize one signal in the output signal of the stereo multiplex circuit (7).
To the fourth attenuating circuits (17) to (20) to drive the remaining three
Attenuation of two signals. For example, if the first and second output control signals of the first and second comparison circuits (12) and (13) indicate that the left stereo signal (L) is dominant, the direction control circuit (16) ), The right stereo signal (R) and the stereo sum signal (L +
R) and the stereo difference signal (LR) are attenuated by a predetermined amount,
The left stereo signal (L) is emphasized. The output signals of the first and second comparison circuits (12) and (13) are, as shown in FIGS. 3A and 3B, a level ratio of the left and right stereo signals (L) and (R) or a stereo signal. Sum-difference signal (L
It changes linearly according to the level ratio between (+ R) and (LR).

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 output signal at the “L” level does not affect the second comparison circuit (13) at all, and the second comparison circuit (13) operates normally. 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). The output signal of (23) has a level corresponding to the detected noise. Thus, when the output signal of the buffer amplifier (23) is applied to the second comparison circuit (13), the dynamic range of the second comparison circuit (13) is limited. When the noise in the detection output signal increases, the noise in the output signal of the stereo multiplex circuit (7) naturally increases, and the output signal is rectified and applied to the second comparison circuit (13). Correct directionality emphasis according to only the signal cannot be performed. On the other hand, when the noise increases, the second comparison circuit (13) uses the output signal of the buffer amplifier (23).
Is changed, the noise can be out of the dynamic range, and the adverse effect of the noise at the time of emphasizing the direction can be prevented. On the spectrum of the FM stereo signal, the stereo difference signal (L-
Since R) is in a relatively high range, it is easily affected by noise generated by multipath interference or the like. For this reason, in the embodiment of FIG. 1, the dynamic range of the second comparison circuit (13) relating to the stereo difference signal (LR) is changed, but the output signal of the buffer amplifier (23) is changed. May be used to simultaneously change the dynamic range of the first comparison circuit (12).

FIG. 2 shows a specific circuit example of the second comparison circuit (13). The output signal of the third rectifier circuit (10) is supplied to the first input terminal (24) and the second input terminal (25) is supplied to the second input terminal (25). 4 The output signal of the rectifier circuit (11) is applied to each, and the stereo sum difference signal (L +
An output signal corresponding to the level ratio between (R) and (LR) is generated. In this case, the collectors of the third and fourth transistors (30) and (31) constituting the current mirror circuit are connected to the collectors of the differentially connected first and second transistors (28) and (29). And the collector current of the third and fourth transistors (30) and (31) is a current source (32)
It depends on the current flowing through When the current flowing through the current source (32) is set to a predetermined value, generation of an undesired output signal when there is no input can be prevented, and a sufficiently wide dynamic range can be secured.

When the noise in the output signal of the FM detection circuit (6) is small, the output of the buffer amplifier (23) becomes "L" and the control signal is not applied to the control terminal (33).
The current flowing in 2) is kept at a relatively low predetermined value. When the noise in the output signal of the FM detection circuit (6) increases, the output signal level of the buffer amplifier (23) applied to the control terminal (33) increases accordingly, and the current flowing to the current source (32) also increases. Increase. As a result, the collector currents of the third and fourth transistors (30) and (31) also increase, the dynamic range of the circuit of FIG. 2 decreases, and malfunction due to noise is prevented.

In the embodiment shown in FIG. 1, the stereo sum signal (L
+ R) and a stereo difference signal (LR) included in the output signal of the FM detection circuit (6) are used.
The separated left and right stereo signals (L) and (R) may be added and subtracted to create a stereo sum signal (L + R) and a stereo difference signal (LR). Further, in the above-described embodiment, the level control circuit which generates four output signals from the stereo multiplex circuit (7) and inserts an attenuation circuit into each of them to perform level control is used. A control circuit and a level control method are conceivable. For example, the left and right stereo signals (L) and (R) are subjected to level control in advance, and then the stereo sum is obtained by using the level controlled left and right stereo signals (L) and (R). The difference signals (L + R) and (LR) may be created.

(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 noise included in the received signal is detected and the dynamic range of the second comparison circuit is changed by increasing the noise, particularly at least the erroneous directionality caused by the noise can be prevented. Accurate direction emphasis can be performed.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing one embodiment of the present invention, FIG. 2 is a circuit diagram showing a specific circuit example of the second comparison circuit, and FIGS. 3 (a) and 3 (b) are views for explaining the present invention. It is a characteristic diagram for providing. (6) FM detection circuit, (7) Stereo multiplex circuit, (12), (13) Comparison circuit, (16)
Steering circuit, (17), (18), (19), (20) ...
... Attenuation circuit, (22) ... Noise detection circuit.

Claims (4)

(57) [Claims] 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). Comparison circuit, stereo sum signal (L + R) and stereo difference signal (LR)
A second comparison circuit that generates a second control signal according to the ratio of the first and second control signals, a level control circuit that controls the output signal level of the stereo multiplex circuit using the first and second control signals, An FM stereo receiver comprising: a noise detection circuit that detects noise included therein; and means for changing at least a dynamic range of the second comparison circuit in accordance with an output signal of the noise detection circuit. 2. The level control circuit according to claim 1, further comprising a left stereo signal (L), a right stereo signal (R), a stereo sum signal (L + R), and a stereo difference signal (LR) obtained from a stereo multiplex circuit. 2. The FM stereo receiver according to claim 1, wherein the level of another signal is reduced so that the level of one signal determined according to the states of the first and second control signals is emphasized. Machine. 3. The second comparison circuit according to claim 1, wherein the second comparison circuit includes a first differentially connected first comparison circuit.
And a second transistor; a current source for supplying collector currents of the first and second transistors;
The first and second collector output signals of the transistor are
2. An FM stereo according to claim 1, further comprising a feedback circuit for feeding back to one base of the transistor, wherein said current source is controlled by an output signal of said level control circuit to change a dynamic range. Receiving machine. 4. Using the output signal of the level control circuit,
2. The FM stereo receiver according to claim 1, wherein the dynamic ranges of the first and second comparison circuits are changed simultaneously.