JPS63285034A - Fmx stereoscopic broadcast receiver - Google Patents

Abstract

PURPOSE:To reduce the influence of multi-path noise by switching a receiver into the FM stereoscopic broadcast reception state in response to an output signal of a detection circuit of multi-path noise. CONSTITUTION:When multi-path disturbance takes place, a multi-path noise is detected by a noise detection circuit 18, a control signal is generated at its output terminal and fed to a switching signal generating circuit 19. The switching signal generating circuit 19 generates a 1st output signal L in response to the control signal to switch the selection circuit 16 and the selection circuit 16 selects an output signal S of the synchronizing detection circuit 14 to apply the signal to a matrix circuit 20. In the matrix circuit 20, the stereoscopic sum signal m and the stereoscopic difference signal S are given thereto and the reception state the same as that of a normal FM stereoscopic broadcast is attained. Thus, the influence of the multi-path disturbance is reduced.

Description

Detailed Description of the Invention (a) Field of Industrial Application The present invention relates to an FMX stereo broadcast receiver that can switch and receive FM stereo broadcasts and FMX stereo broadcasts, and in particular takes measures against multipath noise. FM
This invention relates to an X stereo broadcast receiver.

(b) Conventional technology FMX stereo broadcasting has been proposed as a way to improve the S/H of FM stereo broadcasting and expand the service area. The broadcast signal of the FMX stereo broadcast is one that simultaneously transmits a compressed stereo difference signal (L-R) in addition to the conventional FM stereo broadcast transmission signal,
The transmitted signal is expressed as follows. As is clear from the above equation (1), the compressed stereo difference signal (L-R)' is the stereo difference signal (L-
The spectrum of the FMX stereo broadcasting signal is shown in FIG.

Furthermore, the relationship between the stereo difference signal (L-R) and the compressed stereo difference signal (L-R)', that is, the compression characteristics, is
It will look like Figure 3. In Figure 3, when the level of the input signal is low, the signal (L-R)' becomes 20 dB larger than the stereo difference signal (L-R), the input/output characteristics become linear, and the compression ratio is 1:1. When the level of the input signal becomes medium (approximately -30 dB), the compression ratio becomes ω:1, and the input/output characteristics become flat over a range of approximately 10 dB. When the level of the input signal becomes high, the signal (LR)' is rapidly attenuated. Therefore, compared to the stereo difference signal (L-R) (solid line (A)), the compressed stereo difference signal (L-R)' becomes as shown in the solid line (B), and the signal (L-R) and the The sum signal of the signal (LR)' is as shown by the dotted line (C).

The transmission signal of the FMX stereo broadcast as described above is the 4th rM.
The signal is received by a receiver as shown in FIG. In Figure 4,
The transmission signal of the FMX stereo broadcast received by the antenna (1) is received by the receiving circuit (2), which has the same configuration as a conventional FM stereo receiver, and is converted into a stereo sum signal (L+R
) (hereinafter referred to as M), stereo difference signal (LR) (
(hereinafter referred to as S), fully compressed stereo difference signal (L-R)
' (hereinafter referred to as S') are respectively demodulated. If the received signal is detected using the FM detection circuit included in the receiving circuit, the stereo sum signal M is demodulated, and the PL in the receiving circuit is
If the stereo composite signal is synchronously detected using the 38 KHz subcarrier signal obtained from L, the stereo difference signal S will be demodulated, and if quadrature detection is performed, the compressed stereo difference signal S' will be demodulated.

The stereo difference signal S obtained from the receiving circuit (2) and the compressed stereo difference signal S' are amended by the addition circuit (3) and then sent to a VCA (voltage controlled amplifier) that operates as an attenuator.
(4) can be applied completely. Stereo difference signal S and V CA
(4) When the output signal (SO5') is above a predetermined level (knee point), the first
and the second level detection circuits (5) and (6) operate, and the level of the stereo difference signal S and the level of the output signal <SO5' of the V CA (4) are detected by the first and second level detection circuits ( 5) and (6), and compared in a comparison circuit (7). Then, a signal corresponding to the level difference obtained from the comparator circuit (7) is rectified and smoothed by the rectifier circuit (8) and then applied to the VCA (4) as a control signal. The output signal (srs') of V CA (4) is controlled to be equal to the level of the stereo difference signal S. On the other hand, the output signal (srs') of V CA (4) is controlled to be equal to the level of the stereo difference signal S.
(7) When the output signal (SO5') is below the knee point, the first and second level detection circuits (5) and (6) do not operate, and the attenuation amount in the VCA (4) is fixed at approximately 20 dB. Ru.

The stereo sum signal M obtained from the receiving circuit (2) is directly applied to the matrix circuit (9), and the stereo difference signal S and the output signal (SO5') of the VCA (4) are applied to the matrix circuit via the switch (10). Applied to the circuit (9>).

Although omitted in the previous explanation, the transmission signal of the FMX stereo broadcast includes a 10H2 ID signal, and the
The D signal distinguishes FMX stereo broadcasting from conventional FM stereo broadcasting. And in the receiving circuit (2),
Since a detection circuit for detecting the ID signal is built-in, it is possible to determine whether or not it is an FMX stereo broadcast based on the output signal of the detection circuit. The switch (10) is controlled by the ID signal. If an ID signal is present, said switch (10) is switched to the state shown. Therefore, in the matrix circuit (9), the stereo sum signal M and the level-controlled output signal (545') of the VCA (4) are matrixed, and the left and right output terminals (1
Left and right stereo signals and R are generated at 1) and (12). Also, if there is no ID signal, switch (
10) switches to the opposite state as shown, and the matrix circuit (
In 9), the stereo sum signal M and the stereo difference signal S are matrixed.

As mentioned above, FMX stereo broadcasting uses the stereo difference signal S
Since transmission and reception are performed by compressing and decompressing the data, it is possible to significantly improve S/H and expand the service area to the same extent as conventional FM monaural broadcasting.

Note that the transmission signal of the FMX stereo broadcast can be accurately received by a conventional FM stereo receiver. In this case, the compressed stereo difference signal S' is orthogonally modulated with respect to the stereo difference signal S, so that it does not adversely affect reception.

For FMX stereo broadcasting, JAS JOURNA
L September 1986 issue, page 11 to September issue no. 11.

(C) Problems to be Solved by the Invention However, if multipath interference occurs while receiving FMX stereo broadcasting using the FMX broadcasting receiver, and multipath noise is mixed into the received signal, the reception condition will be significantly degraded. The problem is that it gets worse. Even when receiving normal FM broadcasts, there is an effect of multipath noise, but the effect is particularly significant when receiving FMX broadcasts. That is, when receiving FMX stereo broadcasting, the sum signal (SO5') of the stereo difference signal S and the compressed stereo difference signal S' must be expanded as described above, so the multi-path The adverse effects of noise increase and the reception condition worsens.

(d) Means for Solving the Problems The present invention has been made in view of the above points, and includes a noise detection circuit for detecting multipath noise, and multipath noise is detected in a 2MX stereo broadcast reception state. When it was done,
The present invention is characterized in that the FMX stereo broadcast receiver is switched to an FM stereo broadcast reception state.

(*) Effect According to the present invention, the stereo difference signal S or the sum signal (SO5) of the stereo difference signal S and the compressed stereo difference signal S'
') can be forcibly switched to select the stereo difference signal S when multipath noise is detected, thereby creating an FM stereo reception state.

(f) Embodiment FIG. 1 is a circuit diagram showing an embodiment of the present invention, (13)
is an FM detection circuit, (14) is a synchronous detection circuit that synchronously detects the stereo difference signal S included in the output signal (composite signal) of the FM detection circuit (13), and (15) is included in the composite signal. A quadrature synchronous detection circuit (16) for synchronously detecting the compressed stereo difference signal S' generates a level-controlled signal (SO5') using the stereo difference signal S and the compressed stereo difference signal S'. At the same time, the stereo difference signal S or the signal (SO5'
), a selection circuit (17) selects and outputs one of the 10H2 signals included in the output signal of the orthogonal synchronous detection circuit (15).
(18) is a noise detection circuit that detects multipath noise included in the composite signal; (19) is a low-pass filter that detects the ID signal of (18);
(20) is a switching signal generation circuit that generates a switching signal for the selection circuit (16) according to the output signal of the noise detection circuit (17) and the output signal of the noise detection circuit (18);
) and the stereo sum signal M obtained at the output end of the selection circuit (
16) Stereo difference signal S or signal (
S+S') and output terminals (21) and (
22) is a matrix circuit that generates left and right stereo signals and R, and (23) is a time constant circuit inserted between the noise detection circuit (18) and the switching signal generation circuit (19).

If an FM stereo broadcast is now received, a stereo sum signal M and a stereo difference signal S are included in the composite signal obtained from the FM detection circuit (13). The stereo difference signal S is synchronously detected by a synchronous detection circuit (14) and applied to a selection circuit (16). At that time, since there is no ID signal, no output is generated from the low-pass filter 17), and a first output signal (for example, "L") is generated from the switching signal generation circuit (19). Therefore, the selection circuit (1
6) is switched to select the output signal of the synchronous detection circuit (14), and the stereo sum signal M in the composite signal and the stereo difference signal S from the selection circuit (16) are matrixed in the matrix circuit (20). Ru.

Next, assume that an FMX stereo broadcast is received.

In that case, stereo sum signal M1 stereo difference signal S1 is included in the composite signal obtained from the FM detection circuit (13).
A compressed stereo difference signal S' and an ID signal are included. The stereo difference signal S is detected by a synchronous detection circuit (14), and the compressed stereo difference signal S' is detected by an orthogonal synchronous detection circuit (15) and applied to a selection circuit (16). Further, the ID signal included in the output signal of the quadrature synchronous detection circuit (15) passes through a low-pass filter (17) and is applied to the switching signal generation circuit (19). For that reason,
A second output signal (for example, "H") is generated from the switching signal generation circuit (19), and the selection circuit (16) switches to select the output signal of the orthogonal synchronous detection circuit (15), and the selection circuit (16) switches to select the output signal of the quadrature synchronous detection circuit (15). stereo sum signal M and selection circuit (16)
(SO5') is matrixed by the matrix circuit (20).

By the way, when there is no multipath interference, the FM
Multipath noise is not included in the output signal of the detection circuit (13). Therefore, the noise detection circuit (18) does not generate an output signal, and the noise detection circuit <18) does not generate an output signal from the switching signal generation circuit (18).
19). When multipath interference occurs, multipath noise is generated at the output of the FM detection circuit (13), and the multipath noise is detected by the noise detection circuit (18). Therefore, a control signal is generated at the output end of the noise detection circuit (18), and this control signal is transmitted to the switching signal generation circuit (19).
is applied to Since the switching signal generation circuit (19) is configured to generate the first output signal (L) in response to the control signal, switching of the selection circuit (16) is performed, and the selection circuit (16) ) selects the output signal S of the synchronous detection circuit (14) and applies it to the matrix circuit (20). Therefore, in the matrix circuit (20), the stereo sum signal M and the stereo difference signal S are matrixed, resulting in a reception state similar to that of normal FM stereo broadcasting. Therefore, the influence of multipath interference can be reduced compared to the FMX stereo broadcast reception state.

When multipath noise occurs, V CA (4) in FIG. 4 is controlled by a control signal generated in response to the stereo difference signal S disturbed by the multipath noise, so that the addition signal (545') The influence of multipath noise on Moreover,! ! Because of the presence of the flow path (8), the effect of multipath noise becomes longer depending on the time constant of the rectifier circuit (8). Therefore, the noise detection circuit (18)
The noise detection circuit (18) and the switching signal generation circuit (
19), a time constant circuit (23) is inserted between the two.

When a predetermined period of time has elapsed since the multipath interference disappeared and the output control signal of the noise detection circuit (18) was no longer generated, the output switching signal of the switching signal generation circuit (19) returned to the second state (H), The receiver returns to the FMX stereo broadcast reception state again.

In addition, a noise detection circuit (18
), various circuits conventionally used for detecting multipath noise can be used.

(G) Effects of the Invention As described above, according to the present invention, when multipath noise occurs during FMX stereo broadcast reception, the receiver is immediately switched to the FM stereo broadcast reception state, so that the multipath noise is reduced. It is possible to reduce the impact of Furthermore, if a time constant circuit is provided at the output end of the noise detection circuit as in the embodiment, the influence of multipath noise can be further reduced, and the audibility can be improved.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG. 2 is a circuit diagram showing an embodiment of the present invention.
FIG. 3 is a characteristic diagram showing the spectrum of an MX stereo broadcast signal, FIG. 3 is a characteristic diagram showing the relationship between a stereo difference signal and a compressed stereo difference signal, and FIG. 4 is a circuit diagram showing a conventional FMX stereo broadcast receiver. be. (14)...Synchronous detection circuit, (15)...Quadrature synchronous detection circuit, (16)...Selection circuit, (18)...
・・Noise detection circuit, <19) ・・Switching signal generation circuit,
(23)...Time constant circuit.

Claims (1)

[Claims] (1) In an FMX stereo broadcast receiver that can switch and receive FM stereo broadcasts and FMX stereo broadcasts, a noise detection circuit that detects multipath noise included in the received signal is provided, and according to the output signal of the noise detection circuit, and turn the receiver
An FMX stereo broadcast receiver characterized in that it is configured to switch to an M stereo broadcast reception state.