JPH036138A - Fm stereo receiver - Google Patents

Abstract

PURPOSE:To decrease a multi-path noise and to eliminate a sense of incongruity on the auditory sense at the time of switching by allowing a switching operation mutually between stereo reception and monaural reception to have a hysteresis characteristic. CONSTITUTION:Between an output terminals S of an FM intermediate frequency circuit 1 and an input terminal A of a separation control circuit 2, resistances R1, R2 and a capacity C are provided as usual, and on the positive side of an operational amplifier OP, an R3 is provided, an intermediate connecting point of series resistances R7, R8 between a reverence power source VREF and a ground through the negative side of the OP and an R6 and a TR, a base is connected to the terminal A through an R5 and an R4, and the intermediate connecting point is connected to an output side of the OP. According to this constitution, by a reception converting operation to stereo monaural, and monaural stereo, a hysteresis characteristic running along curves 12, 11 can be permitted. Accordingly, a sense of incongruity on the auditory sense can be eliminated surely without impairing the effect for reducing a multi-path noise at the time of receiving a stereo broadcast.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to an FM stereo receiver,
In particular, it is possible to receive stereo broadcasts by providing a predetermined hysteresis characteristic between the conversion operation from stereo reception to monaural reception and the conversion operation from monaural reception to stereo reception without significantly increasing the number of parts. The present invention relates to an FM stereo receiver having a function of eliminating audible discomfort when multipath noise is reduced.

[Prior Art] Second, FM broadcast waves are highly susceptible to the influence of topography, etc., and the electric field strength changes significantly. Therefore, especially in vehicle-mounted FM receivers, skip noise may occur or be affected by multipath noise, resulting in a significant drop in S/N especially in environments with weak electric fields. Therefore, in order to overcome this kind of drawback, various efforts have been made in the past. For example, as a noise reduction measure when the received electric field decreases, noise is reduced based on separation reduction (so-called SRC response). ), but although this method had the effect of reducing noise, it was not possible to avoid the aural discomfort due to the frequent repetition of stereo reception and monaural reception.

Therefore, in order to maintain the effect of reducing noise and also to reduce the audible discomfort, we proposed a method that would speed up the SRC response when the electric field decreases and slow down its recovery. It has been done.

FIG. 2 is an explanatory diagram of a conventional FM stereo receiver of this type. In this FIG. 2, FIG. 2(A) is a schematic configuration diagram showing the main part of the conventional example, and FIG. 2(B)
is a graph diagram for explaining the operation of this conventional example.

First, in FIG. 2(A), (1) is an FM intermediate frequency circuit (FM-IF) that converts a received signal from a receiving antenna (not shown) into a corresponding intermediate frequency (IF) signal. It is. Further, (2) is a separation control circuit (spc) from which left and right channel signals as appropriately separated stereo signals can be obtained. And FM intermediate frequency circuit (
A control circuit (Co) provided between the FM intermediate frequency circuit (1) and the separation control circuit (2) is connected to the output terminal (S) of the FM intermediate frequency circuit (1) and the separation control circuit (2).
A first resistor (R1) connected between the input terminal (A) of the control circuit (2), and this first resistor (R1
) is connected in parallel between the output side of the resistor (
R2) and a capacitor (C).

Next, in the graph of FIG. 2(B), the horizontal axis shows the strength of the received electric field, and the vertical axis shows the degree of separation (in dB) corresponding to the strength of the predetermined received electric field. It shows. Note that OdB indicates 0 degree of separation (that is, a perfect monaural state), and 30 dB (this is just an example) indicates a saturated degree of separation (that is, a perfect stereo R).

In such a conventional example, as can be seen from the graph in FIG. 2(B), there is no hysteresis characteristic in the switching operation curve between stereo reception and monaural reception.
For this reason, when the receiving electric field decreases and switching between stereo reception and monaural reception is repeated, the generation of noise itself is considerably suppressed, but the sound quality deteriorates when switching between stereo reception and monaural reception. is so pronounced that it is still impossible to eliminate the audible discomfort.

[Problems to be Solved by the Invention] As mentioned above, conventional FM stereo receivers have been devised to avoid the negative effects of multipath noise; however, when switching between stereo reception and monaural reception, There was a problem in that the deterioration of the sound quality was significant and it was impossible to eliminate the sense of discomfort caused by the sound quality.

This invention was made to solve the above-mentioned problems, and by providing a hysteresis characteristic to the switching operation between stereo reception and monaural reception, multipath noise can be reliably reduced. To provide an FM stereo receiver capable of eliminating audible discomfort when switching between stereo reception and monaural reception.

[Means for Solving the Problems] An FM stereo receiver according to the present invention includes: an FM intermediate frequency circuit; a separation control circuit; and a control provided between the FM intermediate frequency circuit and the separation control circuit. The control circuit includes at least a circuit, and the control circuit is equipped with a Schmitt trigger function.

[Function] In this invention, by providing hysteresis characteristics to the switching operation between stereo reception and monaural reception, multipath noise is reliably reduced, and the switching operation between stereo reception and monaural reception is improved. This is done to eliminate the sense of discomfort in the auditory sense.

[Example] Hereinafter, an example of the present invention will be described with reference to the drawings. 1st
The figure is an explanatory diagram of an FM stereo receiver that is an embodiment of the present invention. In this FIG. 1, FIG. 1(A) is a schematic configuration diagram showing the main parts of the embodiment, and FIG.
) is a graph diagram for explaining the operation of this embodiment.

First, in FIG. 1(A), (1) is an FM intermediate frequency circuit (FM-IF) that converts a received signal from a receiving antenna (not shown) into a corresponding intermediate frequency (IF) signal. It is. Further, (2) is a separation control circuit (spc) from which left and right channel signals as appropriately separated stereo signals can be obtained. And FM intermediate frequency circuit (
A control circuit (C01) as described below is provided between the separation control circuit 1 (1) and the separation control circuit 1 (2).

First, the output terminal (S) of the FM intermediate frequency circuit (1) and the input terminal (A) of the separation control circuit (2)
Regarding the first resistor (R1) connected between the first resistor (R1), and the second resistor (R2) and capacitor (C) connected in parallel between the output side of this first resistor (R1) and the ground, , which is the same as in the conventional example described above.

Furthermore, the output terminal (S) of the FM intermediate frequency circuit (1) and the input terminal (A) of the separation control circuit (2)
A Schmitt trigger circuit centered around an operational amplifier (OP) is connected between the two as shown below.

That is, it is connected between the field strength indication output terminal <S) of the FM intermediate frequency circuit (1) and the ground, and its output terminal (
A third resistor (R3) whose S) side is connected to the (+) side of the operational amplifier (OP) is connected in series between the reference power supply (V REF) and ground, and the intermediate connection is connected to the operational amplifier (OP). The seventh resistor (R) connected to the (-) side of the amplifier (OP)
7) and an eighth resistor (R8), one terminal of which is connected to the output terminal side of the operational amplifier (OP), and the other terminal of which is connected to the base terminal of a transistor (TR) described later. 5 resistor (R5), the 6th resistor (R6) and transistor (TR) connected in series between the (-) side of the operational amplifier (OP) and ground, and the output terminal of the operational amplifier (0P). A fourth resistor (R4) is connected between the side and the input terminal (A) of the separation control circuit (2).

Next, in the graph of FIG. 1(B), the horizontal axis shows the strength of the received electric field, and the vertical axis shows the degree of separation (in dB) corresponding to the strength of the predetermined received electric field. It shows. Note that OdB indicates the degree of separation (ie, a perfect monaural state), and 30 dB (this is just an example) indicates the degree of saturation separation (ie, a perfect stereo state). In addition, in this Figure 1 (B), the operating curve when switching from monaural reception to stereo reception is shown by (11), whereas the operating curve when switching from stereo reception to monaural reception is shown in (11). is shown in (12).

That is, in the embodiment described above, when switching from monaural reception to stereo reception, the operating curve (11
), the degree of separation increases.

Then, the received electric field for a certain degree of separation (β) is E
Suppose that it was l. On the other hand, when switching from stereo reception to monaural reception, the operating curve (12
), the degree of separation decreases along

Then, the received electric field for the predetermined degree of separation (β) is R
2 (<El).

As described above, according to the embodiment described above, a predetermined hysteresis characteristic is provided between the conversion operation from stereo reception to monaural reception and the conversion operation from monaural reception to stereo reception, For this reason, it is possible to reliably eliminate the audible discomfort without impairing the effect of reducing multipath noise when receiving stereo broadcasts.

[Effects of the Invention] As explained above, the FM stereo receiver according to the present invention includes: an FM intermediate frequency circuit; a separation control circuit; and an FM intermediate frequency circuit provided between the FM intermediate frequency circuit and the separation control circuit. at least a control circuit configured to include a Schmitt trigger function section, the control circuit being configured to include a Schmitt trigger function section, which performs a conversion operation from stereo reception to monaural reception; A predetermined hysteresis characteristic is provided between the conversion operation from monaural reception to stereo reception, and for this reason, the multipath noise reduction function when receiving stereo broadcasts is not impaired. This has the effect of reliably eliminating the sense of discomfort in the auditory sense.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of an FM stereo receiver that is an embodiment of the present invention, and FIG. 2 is an explanatory diagram of a conventional FM stereo receiver of this type. (1) is an FM intermediate frequency circuit, (2) is a separation control circuit, (COI
) is the control circuit, (○P) is the operational amplifier, (11) and (12) are the conversion operation curves. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Claims] (1) An FM stereo receiver including at least an FM intermediate frequency circuit: a separation control circuit; and a control circuit provided between the FM intermediate frequency circuit and the separation control circuit; The control circuit is equipped with a Schmitt trigger function, and there is a predetermined hysteresis between the separation operation when converting from monaural reception to stereo reception and the separation operation when converting from stereo reception to monaural reception. An FM stereo receiver characterized by the existence of a characteristic.