JPH01255331A - Fm stereo receiver - Google Patents

Abstract

PURPOSE:To execute a satisfactory reception regardless of an area by changing a separation characteristic, a high-cut characteristic, etc., according to a noise level. CONSTITUTION:Based on whether the level of at least one side of multipass noise and electrically-charged noise detected by a noise detecting part 21 is above or below a set level, a characteristic change deciding part 22 controls a characteristic changing part 23 and changes the separation characteristic and high-cut characteristic in a stereo demodulating circuit 17. Simultaneously, a soft mute characteristic is changed through an electronic volume 15. Thus, the satisfactory reception can be executed regardless of the area in which the noise is large or small.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to an FM stereo receiver, and particularly to an FM stereo receiver that changes separation characteristics and high-cut characteristics according to the level of electrical equipment noise and multipath noise.

<Prior Art> It is known that in an FM stereo receiver, the S/N ratio in a weak electric field can be improved by switching from stereo to monaural in a weak electric field where noise becomes large.

Also, if the broadband level is attenuated in a weak electric field, the effective S
It is also known that the /N ratio can be improved.

For this reason, conventionally the received electric field strength (antenna input level)
is monitored, and when the received electric field strength falls below a predetermined first level E in a weak electric field, the degree of separation is continuously weakened according to the received electric field strength, and when the received electric field strength is lowered to a second level.
When the level E2 (<E, l JJt) is lowered, the degree of high-cut is increased according to the received electric field strength, and furthermore, the received electric field strength reaches the third level E.

When the signal falls below, a soft mute is applied to increase the attenuation of the volume according to the received field strength.

FIG. 3 [Jl] shows such a conventional separation characteristic and high-cut characteristic diagram, and FIG. 4 (solid line) shows a conventional soft mute characteristic diagram.

<Problem to be solved by the invention> In a vehicle-mounted FM stereo receiver, the separation fan characteristic, high cut characteristic, and soft mute characteristic are generally set assuming a region where it will be used where there is a lot of multipath noise and electrical equipment noise. .

For this reason, a first level E1 begins to weaken the degree of separation 1, and a second level E2 begins to strengthen the degree of high cut.
, the third level E3 for starting soft mute is set relatively high.

However, if each characteristic is set for such a subcommittee, good stereo listening will not be possible in areas where there is little noise, for example in areas such as wilderness areas where there are no obstructions such as pills. This is because, although no noise occurs in those areas, the received electric field strength is weak and often falls below the first, second, and third levels, and as a result, the degree of separation is weakened and the sound tends to be monaural. , Moreover, the sound quality deteriorates as the high cut begins, and the volume also decreases, making it difficult to listen.

Therefore, Fig. 3 (E, /, E2/ in bl and E in Fig. 4)
If the first, second, and third levels are made small as shown in , /, it is convenient because good stereo reception can be achieved in areas where there is little noise but the received electric field strength is low. However, with this setting, in a noisy area such as a subcommittee, if the previous month
/N ratio deteriorates, loud noise is output from the speaker, and good listening cannot be achieved.

From the above, an object of the present invention is to provide an FM stereo receiver that can change separation characteristics, high-cut characteristics, etc. in accordance with the noise level, and can perform good reception regardless of the area.

Means for Solving the Problems> FIG. 1 is a block diagram of an FM stereo receiver according to the present invention.

12 is a front end, 15 is an electronic volume, 17 is a stereo demodulation circuit (MPX), 2 is a Net level meter circuit, 21 is a noise detection section, 22 is a characteristic change determination section, and 23 is a characteristic change section.

Based on whether the level of multipath noise and electrical equipment noise detected by the noise detection unit 21 is above or below the set level, the characteristic change judgment unit 22 determines whether the characteristic change unit 2
3 to change the separation characteristic and high cut characteristic in the stereo demodulation circuit 17, and at the same time, control the electronic volume 15 to change the soft mute characteristic.

<Embodiment> FIG. 1 is a block diagram of a vehicle-mounted FM stereo receiver according to the present invention, and FIG. 2 is an explanatory diagram of main parts.

In the figure, 11 is an antenna, 12 is a float end (F/E
), 13 is an intermediate frequency amplifier, 14 is an FM detector, 15
inputs the FM detection output, and when the received electric field strength (antenna input level) is small, the electronic polyphony 5 and 16 which attenuates the volume wt according to the received electric field strength are pulsed noises (ignition noise) included in the electronic volume output. A noise canceling circuit (NK) 17 is input with the stereo signal Se□2 outputted from the noise canceling circuit, and a stereo uiL tuning circuit which outputs the stereo signals SL and S of both R channels, respectively. This circuit includes a separation control ml7a (m2[[) and a cut control section 17b for controlling the degree of stereo separation.

18.19 is a low frequency amplifier, 20 is an intermediate frequency amplification @13
This is a level meter circuit that is connected to the level meter terminal of , and outputs a level meter signal v6 having a value according to the received electric field strength E.

21 is a noise detection section, and electrical equipment noise detection circuit l152
1a and a multipath noise detection circuit 21b. Electrical equipment noise detection circuit Q 21 a is intermediate frequency amplifier 13
Detects electrical noise such as ignition noise contained in the output of the The multipath noise detection circuit 21b is connected to the level meter terminal of the intermediate frequency amplifier 13 to detect multipath noise. That is, since the DC component appearing at the level meter terminal contains an AM component proportional to multipath noise, the AM component is used to detect multipath noise.

Reference numeral 22 denotes a characteristic change determination unit that changes the separation characteristic, high-cut characteristic, and soft mute characteristic according to the noise level, and a comparison circuit 22a.

22c, a time constant circuit 22b1 and a judgment circuit 22d. The comparison circuit 22a detects the detected electrical equipment noise level Lo.
+ and a set level LSI, and the time constant circuit 22b has a multipath noise level L. . The comparison circuit 22c is used to compare the multipath noise level output from the time constant circuit with the set level LSM, and the comparison circuit 22c is used to compare the multipath noise level output from the time constant circuit with the set level LSM. $22d is level meter output■
5, and outputs a characteristic change enable signal CCE according to the electrical equipment noise and multipath noise level.

Reference numeral 23 denotes a characteristic changing section that changes the separate ring characteristic and high-cut characteristic based on the characteristic change enable signal CCE, and includes a turning point change diagram 923a and a high-cut/separate characteristic change circuit 23b. The turning point change circuit 23a includes a switch S
1, S2, and two diodes connected in series.
The second voltage shift circuit VS2 includes a voltage shift circuit VSI and a second voltage shift circuit VS2 formed of one diode.

Note that when the noise becomes large, the first voltage shift circuit VSI
is selected, and when the noise is small, the second voltage shift circuit is selected.

As shown in FIG. 2, the high cut/separation characteristic f change 923b is the separation voltage V applied to the stereo noise terminal SNC of the stereo demodulation diagram 'R517.
,. a separation voltage changing circuit SvC that controls the high-cut voltage vH0 applied to the high-cut terminal HCC of the stereo demodulation circuit 17 based on the characteristic change enable signal CCE; have.

That is, separation voltage change diagram @ S V C1
11 Variable resistance VR based on characteristic enable signal CCE
The high-cut voltage changing circuit HvC changes the capacitance value of the variable capacitor VC.

Note that the variable resistor VR and variable capacitor VC may be constructed by inserting/removing a resistor and a capacitor in parallel to the fixed resistor and fixed capacitor using transistors that are turned on and off by the enable signal CCE, respectively.

The overall operation of FIG. 1 will be explained below.

In advance, each circuit constant of the turning point change circuit 23a and the high-cut/separation characteristic change circuit 23b is determined. fi) If the noise is large, the separation characteristic,
High-cut characteristics and soft mute characteristics are each third.
It is set so that it changes according to the solid line in Figure fal and Figure 4, and (11) when the noise is small, it is set so that it changes according to the dotted line in Figure 3 (bl and Figure 4).

Now, at the initial stage, the characteristics are selected so as to have the characteristics shown in FIG. 3 (al) and the solid line in FIG. The voltage shift amount is set to a large value, and in the high-cut/separation characteristic changing circuit 23b, the variable capacitor VC and the variable resistor VR
is set to an appropriate value so that the characteristics change relatively slowly.

In such a state, if the level meter signal value output from the level meter circuit R120 is equal to or higher than a predetermined level, in other words, if the received electric field strength is equal to or higher than a predetermined level E0 (>E,), the characteristic change determination unit 22 maintains the currently selected characteristics regardless of the level of electrical equipment noise and multipath noise, and does not change the characteristics. In other words, when the received electric field strength is large, the degree of separation is maximized for each characteristic to create a stereo state, the degree of high cut is reduced to zero, and the amount of attenuation in the electronic volume is reduced to zero, so the characteristics are changed. do not have to.

However, when the received electric field strength falls below a predetermined level E0,
The characteristic change determination unit 22 determines the electrical equipment noise or multipath noise level L. The characteristics are changed depending on the magnitude of l#LOM and the respective setting levels LSI and LsM.

That is, the electrical equipment noise level L detected by the noise detection unit 21. I and multipath noise level L. ,,
The level L s + p set for each
If it is larger than L S M, the judgment circuit 22d does not change the characteristics and changes the initial characteristics (Fig.
1). As a result, when the received electric field strength decreases and becomes below the first level E, the degree of separation begins to weaken, when it falls below the second level E2, high cut starts, and when it falls below the third level E3, soft mute starts. starts.

However, if any of the noise levels LD, LD becomes equal to or lower than the respective set level Ls+pLsr+, the determination circuit 22d causes the turning point change circuit 23a of the characteristic change unit 23 to select the second voltage shift circuit VS2. (Set the voltage shift amount to be small) and change the values of the variable capacitor c and variable resistor VR in the high-cut/separation characteristic changing circuit 23b to change the separation characteristic and high-cut characteristic as shown in FIG. 3 (bl). At the same time, the characteristics of the electronic volume 15 are set as shown by the dotted line in Fig. 4.As a result, when the received electric field strength decreases to below the first level E,'(<E,), the degree of separation becomes weaker. Beginning, second level E2
'(<E,) or below, high cut will start,
Soft muting starts when the level falls below the third level E,'(<E,).

As a result, in areas with little noise, the starting point for changing the degree of separation, the starting point for high cut, and the starting point for soft muting are extended to a weaker electric field than in areas where noise is louder.

Note that the above is a case where the noise changes from large to small, but when the noise changes from small to large, the selected characteristics are simply reversed. Furthermore, since the time constant 122b exists, the fall of the multipath noise level is delayed by a time determined by a predetermined time constant, and therefore the multipath noise level oscillates around the set level Lsn at time intervals shorter than the time constant. However, no changes are made to the characteristics.

Further, although the above description is a case in which both electrical equipment noise and multipath noise are taken into consideration, a case in which only one of them is taken into consideration may be used.

<Effects of the Invention> According to the present invention, the separation characteristics, high-cut characteristics, etc. of the stereo demodulation circuit are changed based on the level of at least one of multipath noise and electrical equipment noise. , good reception is now possible regardless of the small area.

According to the present invention, since the soft mute characteristic is also changed, the above effect can be made even more remarkable.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of the FM stereo receiver according to the present invention, Fig. 2 is an explanatory diagram of the main part circuit, Fig. 3 (al is a characteristic diagram of a region with large noise, Fig. 3 (
bl is a characteristic diagram of a region with low noise, and FIG. 4 is a soft mute characteristic diagram. 12...Front end, 15...Electronic volume, 17...Stereo demodulation # (MPX), 20...Level meter circuit, 21...Noise detection section, 22...Characteristics change determination section, 23...Characteristics change Department Patent Applicant Alpine Co., Ltd. Agent Patent Attorney

Claims (2)

[Claims] (1) In an FM stereo receiver that changes the degree of separation and high-cut according to the strength of the received electric field, it includes a detection section that detects the level of at least one of multipath noise and electrical noise, and changes the separation characteristics and high-cut characteristics. An FM stereo receiver comprising: a characteristic changing section for changing separation characteristics and a high-cut characteristic by causing the characteristic changing section to change separation characteristics and high-cut characteristics based on a noise level. (2) FM stereo reception according to claim 1, characterized in that an electronic volume is provided to control the volume according to the received electric field strength, and the volume attenuation characteristic of the electronic volume is changed based on the noise level. Machine.