JPH104369A - Fm receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the sensitivity of the small sized FM receiver. SOLUTION: The receiver is provided with a reception circuit 60 to extract audio signals L, R from received FM signals SL, SR and a headphone 7 receiving the audio signals L, R. An antenna tuning circuit 81 is made up of a coil 81L and a capacitor 81C in the reception circuit 60. The coil 81L is used to configure a loop antenna receiving the FM signals SL, SR. A cord 71 of the headphone 7 is connected to a ground line through bypass capacitors 82L, 82R and 82G.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an FM receiver.

[0002]

2. Description of the Related Art A headphone stereo cassette player, that is, a so-called headphone stereo in which a wireless system is used between the cassette player and headphones has been considered.

FIG. 5 is a perspective view showing an external appearance of an example of such a wireless cassette player. Reference numeral 1 denotes a cassette player, and reference numeral 6 denotes a dedicated receiver for headphones.

At the time of reproduction, the cassette player 1 reproduces left and right channel stereo audio signals L and R from a tape cassette (not shown), and these signals L and R are converted into FM signals SL having a predetermined carrier frequency. ,
The signals SL and SR are transmitted to the receiver 6.

In the receiver 6, when the FM signals SL and SR from the cassette player 1 are received, the audio signals L and R are demodulated from the signals SL and SR, and the signals L and R are supplied to the headphones Headphones 7 through cord 71
Are supplied to the left and right sound units 7L and 7R, respectively.

In this case, the distance at which the receiver 6 can be used away from the cassette player 1 is about 1.5 m in consideration of the Radio Law and the like.

FIGS. 6 and 7 show an example of the signal system of the wireless cassette player 1 and the receiver 6 described above. During playback, the player 1 reproduces left and right channel audio signals L and R from the tape 2 by the reproducing heads 11L and 11R. The reproduced signals L and R are reproduced by the reproduction equalizer amplifiers 12L and 12R and the pre-emphasis circuit. FM through 13L, 13R
The FM signals SLT and S are supplied to the modulation circuits 14L and 14R.
Converted to RT.

In this case, the carrier frequencies fLT and fRT of the FM signals SLT and SRT are, for example, fLT = 11.29 MHz fRT = 11.75 MHz.

The FM signals SLT and SRT are supplied to mixer circuits 15L and 15R, and the oscillation circuit 16 forms an oscillation signal S16 having a stable predetermined frequency f16, for example, f16 = 249.75 MHz. This signal S16 is supplied to the mixer circuits 15L and 15R.

Thus, the FM signals SLT and SRT supplied to the mixer circuits 15L and 15R have the carrier frequencies fL and fR of the FM signals fL = f16-fLT = 238.46 MHz fR = f16-fRT = 238.0 MHz by the signal S16. The signal is frequency-converted into signals SL and SR.

The FM signals SL and SR are supplied to bandpass filters 17L and 17R and a power amplifier 18 respectively.
L, 18R to the antenna 19,
Sent to

On the other hand, in the receiver 6, reference numeral 60 denotes FM.
1 shows a receiving circuit for signals SL and SR. The acoustic units 7L and 7R of the headphones 7 are of an electromagnetic type having a configuration similar to that of a small speaker.

Then, F transmitted from the player 1
The M signal SL, SR is the headphone cord 7 of the headphone 7.
1, the received signals SL and SR are supplied to a mixer circuit 63 through a band-pass filter 61 and a high-frequency amplifier 62, and the local oscillation circuit 6
4 supplies a local oscillation signal S64 to the mixer circuit 63.

In this case, the frequency f64 of the signal S64
Is, for example, f64 = 248.7 MHz.

In this manner, the FM signals SL and SR are converted into the frequencies fLI and fRI in the mixer circuit 63 by the signal S64.
Is frequency-converted into intermediate frequency signals SLI and SRI of, for example, fLI = fL-f64 = 10.24 MHz and fRI = fR-f64 = 10.7 MHz.

The intermediate frequency signals SLI and SRI are:
An FM demodulation circuit 66L through an intermediate frequency circuit 65L, 65R having a ceramic filter and a limiter amplifier,
66R, and the audio signals L and R are demodulated.
These signals L and R are supplied to de-emphasis circuits 67L and 67L, respectively.
It is supplied to output amplifiers 68L and 68R through R. Further, a dummy amplifier 68G is provided, and its input terminal is AC grounded through a capacitor 68C.

In this case, the output amplifiers 68L to 68G
For example, as shown in FIG. 8, the DC bias voltage VBB is supplied while being constituted by operational amplifiers 681 to 681.

The output terminals of the amplifiers 68L and 68R are connected to the hot-side input terminals of the sound units 7L and 7R through the high-frequency choke coils 69L and 69R, and the output terminal of the amplifier 68G is connected to the sound unit through the high-frequency choke coil 69G. 7L and 7R are connected to cold-side input terminals.

Therefore, an audio signal L is output between the output terminal of the amplifier 68L and the output terminal of the amplifier 68G, and this signal L is supplied to the sound unit 7L. An audio signal R is output between the output terminal of the amplifier 68R and the output terminal of the amplifier 68G, and the signal R is supplied to the audio unit 7R.

Therefore, the audio signals L and R reproduced by the player 1 can be heard by the headphones 7. In that case, the size of the receiver 6 can be reduced to half or less of the business card. When listening to the cassette, the cassette player 1 can be put in a bag or a bag and the receiver 6 can be put in a breast pocket of a jacket or the like, so that it can be used, for example, on a train on the way to work or When the user listens to the cassette while walking, the cord 71 of the headphones 7 does not interfere.

The carrier frequencies fL and fR of the FM signals SL and SR transmitted from the cassette player 1 to the receiver 6
However, for example, fL = 238.46 MHz, fR = 238.0 MHz, which is a frequency band of 76 MHz used in general FM broadcasting and television broadcasting.
Because it is higher than 222 MHz, it is less susceptible to broadcast waves and interference from cities.

Further, when a DC cut capacitor is connected between the amplifiers 68L and 68R and the sound units 7L and 7R, the impedance of the sound units 7L and 7R is generally low. Requires a large capacity, which hinders downsizing of the receiver 6. However, in the receiver 6 of FIG. 7, the amplifier 68G makes the DC potential of the cold-side input terminals of the acoustic units 7L and 7R equal to the DC potential of the hot-side input terminals of the acoustic units 7L and 7R. Therefore, there is no need to connect a DC cut capacitor between the amplifiers 68L, 68R and the sound units 7L, 7R.
Therefore, the size of the receiver 6 can be reduced.

[0023]

However, since the above-mentioned receiver 6 is miniaturized, it is not possible to secure a sufficient area of a portion that becomes a ground potential, and the radiation sensitivity deteriorates.

The headphone cord 71 is connected to the FM signal S
Although they are used as L and SR receiving antennas, when the receiver 6 is used, the headphone cord 71 comes close to or close to the user's body and is equivalently grounded, so that the sensitivity as an antenna is considerably reduced. I will. In particular, the FM signal SL,
When the SR frequency is high as described above, the antenna sensitivity is further reduced.

The present invention aims to solve the above problems.

[0026]

Therefore, according to the present invention, there is provided a receiving circuit for extracting an audio signal from a received FM signal, and a headphone to which the audio signal is supplied. An antenna tuning circuit configured by a capacitor, an antenna configured to receive the FM signal by the coil;
The cord of the headphone is an FM receiver connected to a ground line through a bypass capacitor.

As a result, the reception sensitivity is improved by the coil of the antenna tuning circuit and the headphone cord.

[0028]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG.
And the coil 81L are connected in parallel to form an antenna tuning circuit 81 that uses the FM signals SL and SR as a tuning band. One end of the tuning circuit 81 is connected to the ground line 6G, and an intermediate tap of the coil 81L is connected to the bandpass filter 61.

In this case, the coil 81L constitutes a loop antenna, and is therefore configured as shown in FIG. 2, for example. Note that, in FIG.
In this case, L is constituted by a printed wiring board.

That is, a printed pattern 812 is formed in a rectangular shape as a whole with respect to, for example, a flexible insulating substrate 811 having a plate shape, and one vertex of the printed pattern 812 is cut. It has been. Thus, the pattern 812 forms the coil 81L and the one-turn loop antenna.

The size of the rectangle formed by the print pattern 812 is, for example, about 15 mm × about 45 mm.

Further, a capacitor 81C is connected between the land 813 and the land 814 to form the antenna tuning circuit 81.

Then, of the lands 813 and 814, the land 81 formed on the long side of the print pattern 812
3 is connected to a printed pattern 816 for a lead line, and the end is connected to the ground line 6G. In the print pattern 812, a print pattern 815 for a lead wire is connected to a predetermined position on the long side where the land 813 is formed, and the end of the print pattern 815 is connected to the bandpass filter 61.

Further, in the receiver 6, the output amplifier 6
The output terminals of the audio amplifiers 8L and 68R are connected to the hot-side input terminals of the sound units 7L and 7R through the headphone cord 71, and the output terminals of the output amplifier 68G are connected to the headphone cord 7
1 are connected to the cold-side input terminals of the acoustic units 7L and 7R.

The output terminals of the output amplifiers 68L to 68G are connected to the ground line 6G through the bypass capacitors 82L to 82G, and are grounded at a high frequency. The amplifiers 68L to 68G can be configured by operational amplifiers 681 to 681, as shown in FIG. The other signal system of the receiving circuit 60 is configured as described with reference to FIG.

According to such a configuration, the FM signals SL and SR from the cassette player 1 are transmitted to the loop antenna 81L.
And supplied from the tuning circuit 81 to the band-pass filter 61.

Accordingly, the audio signals L and R are output from the amplifiers 68L and 68R, and the signals L and R are supplied to the audio units 7L and 7R. 7 can be heard.

In this case, the ground line 6G of the receiver 6 is connected to the headphone cord 71 through the capacitors 82L to 82G, and as shown in FIG. C
Grounded to the user's body through S. At this time, since a considerable portion of the headphone cord 71 comes close to or adheres to the user's body, the stray capacitance CS has a large value, and the impedance to the FM signals SL and SR is sufficiently small. Therefore, the ground line 6G is sufficiently grounded, or the area of the receiver 6 at the ground potential is increased, and the radiation sensitivity is improved.

Further, since the antenna tuning circuit 81 is provided and the coil 81L is used as a loop antenna to receive the FM signals SL and SR, the sensitivity of the receiver 6 is also improved from this point.

According to the experiment, in the case of the above numerical example, the receiving sensitivity could be improved by 8 to 10 dB.

Thus, according to the FM receiver 6, the receiving sensitivity can be greatly improved. Moreover, the antenna tuning circuit 81 and the bypass capacitors 82L to 82L
G can be provided, and the high-frequency choke coils 69L to 69G in FIG. 7 are not required, which is simple and can contribute to cost reduction.

FIG. 3 shows an example of an arrangement state of the loop antenna 81L (coil 81L) in the receiver 6. The receiver 6 is formed as a flat rectangular parallelepiped as a whole, and a main circuit is mounted therein. Printed wiring board 611
Is arranged. In addition, a rechargeable battery for power supply, a so-called gum type battery 612, which is a flat rectangular parallelepiped as a whole, is arranged alongside the substrate 611.

The printed circuit board 8 on which the antenna tuning circuit 81 shown in FIG.
11 are arranged. In this case, according to the experiment, no decrease in the sensitivity of the loop antenna 81L was measured when the printed board 811 was separated from the other conductive parts by several mm or more.

In the above description, the antenna tuning circuit 81 is constituted by a parallel circuit of a capacitor 81C and a coil 81L, and the coil 81L is a loop antenna.
In addition to forming a series circuit of L and the capacitor 81C, the coil 81L may be a helical antenna.

[0045]

According to the present invention, the receiving sensitivity can be greatly improved with a simple configuration.

[Brief description of the drawings]

FIG. 1 is a connection diagram illustrating one embodiment of the present invention.

FIG. 2 is a plan view showing a part of one embodiment of the present invention.

FIG. 3 is a cross-sectional view for explaining the present invention.

FIG. 4 is an equivalent circuit diagram for explaining the present invention.

FIG. 5 is a perspective view for explaining the present invention.

FIG. 6 is a system diagram for explaining the present invention.

FIG. 7 is a system diagram for explaining the present invention.

FIG. 8 is a connection diagram for explaining the present invention.

[Explanation of symbols]

1 = cassette player, 6 = receiver, 7 = headphone,
7L and 7R = sound unit, 61 = bandpass filter, 62 = high frequency amplifier, 63 = mixer circuit, 64 =
Local oscillator circuit, 65L and 65R = intermediate frequency circuit, 6
6L and 66R = FM demodulation circuit, 67L and 67R
= De-emphasis circuit, 68L, 68R and 68G
= Output amplifier, 71 = headphone cord, 81 = antenna tuning circuit, 81 L = loop antenna (coil), 82
L, 82R and 82G = bypass capacitors

Claims (4)

[Claims] A receiving circuit for extracting an audio signal from a received FM signal; and a headphone to which the audio signal is supplied. The receiving circuit has an antenna tuning circuit including a coil and a capacitor. An FM receiver in which an antenna for receiving the FM signal is configured by the coil, and a cord of the headphone is connected to a ground line through a bypass capacitor. 2. The FM receiver according to claim 1, wherein the antenna tuning circuit is configured by connecting the coil and the capacitor in parallel, and the coil forms a loop antenna. . 3. The FM receiver according to claim 2, wherein said coil is a one-turn coil formed on a printed circuit board. 4. The FM receiver according to claim 3, wherein the receiving circuit has an output amplifier for supplying the audio signal to the headphones, and a dummy amplifier configured similarly to the output amplifier. The headphone is connected between the output terminal of the output amplifier and the output terminal of the dummy amplifier, and the bypass capacitor is connected to the output terminal of the output amplifier and the output terminal of the dummy amplifier; An FM receiver adapted to be connected to a ground line.