JPS5918773Y2 - AM-FM stereo receiver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an AM-FM stereo receiver.

In an AM-FM stereo receiver, if a PLL circuit is used in the FM stereo demodulation circuit, beat interference occurs during AM reception.

To prevent this, it is necessary to stop the voltage controlled oscillator (hereinafter referred to as VCO) of the PLL circuit during AM reception.

For this reason, conventionally, as shown in FIG. 1, a changeover switch has been used, one circuit each for switching the input to the FM stereo demodulation circuit and for controlling the ON/OFF of the vCO.

In Figure 1, 1 is an FM RF converter circuit, 2 is an AM converter circuit, 3 is an AM/FM intermediate frequency amplification circuit, 4 is an AM detection circuit, 5 is an FM detection circuit, and 6 is a PLL circuit, including an FM stereo IC that constitutes the demodulation circuit (e.g. LA336
1 etc)7. 8.15.16.17.18.21゜23, 26.27.28 are resistors, 9.10.11.1
2.19゜ 20 is a capacitor, 13 and 14 are low-pass filters (filters for 19KHz and 38KHz cut), 22 is a band selection switch (connected to the AM side in the figure), and 24 is a low frequency and output amplifier. .

25 is a band changeover switch that works in conjunction with 22.

30 is an LED (FM stereo indicator), and 29 is a diode.

However, in order to miniaturize devices, the number of switch circuits has recently been limited.

Therefore, the present invention allows switching of the input to the FM stereo demodulation circuit and ON/OFF control of vCO to be performed with a single circuit switch, and also allows the AM detection output to be easily divided equally into left and right channels when receiving AM. An embodiment of the present invention will be described below with reference to FIG.

Note that in FIG. 2, the same parts as in FIG. 1 are designated by the same numbers as in FIG. 1.

In the circuit shown in FIG. 2, a first resistor 17 and a second resistor 18 are connected in series between the left and right stereo signal output terminals R, and the connection point and the output terminal 31 of the AM detection circuit 4 are connected in series. Connected.

In addition, the connection point of resistors 17 and 18 and the band selection switch 2
A capacitor 19 and a diode 29 are connected in series between the FM side terminal of No. 2, and a connection point between the capacitor and the diode is connected to the ground E via a third resistor 28.

The diode 29 is connected so that its anode is on the switch 22 side.

The output terminal 32 of the FM detection circuit 5 is connected to the ■ pin which is the input terminal of the IC 6, and the FM side terminal of the band selection switch 220 is connected to the ■ pin which is the 10B input terminal of the IC 6, and one of the LED 30 and the resistor 27. The AM side terminal is an idle terminal.

The rest of the circuit configuration is the same as that in FIG. 1, so a description thereof will be omitted.

The operation of the AM-FM stereo receiver configured in this manner will now be described.

When the band selection switch 22 is on the AM side (as shown in the figure), the output of the AM detection circuit 4 is
Therefore, it passes through the capacitor 19 and the resistor 28 and falls to the ground E, and also passes through the resistors 17 and 18 and comes out to the output terminal R.

At this time, the resistors 15 and 16 and the low-pass filter 13
．． Even if it passes through 14, a part of the signal falls to ground.

Also, the magnitude of the output of the AM detection circuit 4 is about 20 dB larger than the level of the FM terminal R, but the output appearing at the output terminal R during AM reception is the same as that of the resistor 17.1.
It can be adjusted to the same level as the FM output with 8°15 and 16.28.

Furthermore, first and second resistors 17 are connected between the output terminal 31 of the AM detection circuit 4 and the left and right stereo signal output terminals R, respectively.
．． 18, the AM detection output can be easily divided equally into the left and right channels by simply making the resistance values of the first and second resistors 17 and 18 equal. .

In addition, since the power to both the ■ pin of IC6 and the LED 30 is turned off by the switch 22, IC6 does not operate, and the operation of the vCO in the IC has stopped, so no beat disturbance occurs, and due to a malfunction, the LED (stereo for indicator)
AM broadcasting can be received without the 30 being lit.

Furthermore, since the AM low frequency signal does not pass through the stereo demodulation circuit 6, the low pass filters 13 and 14, and the high emphasis circuit, it does not cause deterioration of distortion rate or frequency characteristics, and improves the AM characteristics. I can do it.

Next, when the switch 22 is switched to the FM side, 10B → resistor 21 → common terminal of band changeover switch 22 → F
A current flows from the M side terminal to the diode 29 to the resistor 28 to the ground E, and the diode 29 is turned on.

Therefore, the connection point of resistors 17 and 18 is grounded via capacitor 19→diode 29→switch 22→capacitor 20.

At this time, 10B → resistor 21 → switch 22 → LED 30
And 10B is applied to IC6 in connection with pin 2 of IC6, and IC6 operates.

Therefore, the FM stereo signal is separated into stereo signals (however, in the case of monaural broadcasting, it is output as a monaural signal to both channels).

) Output comes out to the L and R output terminals.

At this time, resistors 17 and 18 drop part of the signal to ground, but serve as output level adjustment resistors.

Also, since the connection point of 17.18 is grounded, L
, no deterioration of the R channel separation occurs.

FM stereo broadcasting can be received as described above.

As mentioned above, the conventional circuit required two circuits, one circuit to switch between AM and FM, and one circuit to turn off vCO, but with the present invention, only one circuit is required.
It is possible to switch between AM and FM and turn off vCO at the same time, and the number of circuits for band changeover switches can be reduced.

Furthermore, since the power to the stereo demodulation circuit is turned off during AM reception, malfunctions will never occur during AM reception.

Furthermore, during AM reception, there is no deterioration of frequency characteristics due to the influence of an FM low-pass filter or a de-emphasis circuit, and the AM characteristics can be improved.

Moreover, when receiving AM, the AM detection output can be easily divided equally into left and right channels.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a conventional AM-FM stereo receiver, and FIG. 2 is a circuit diagram showing an AM-FM stereo receiver according to the present invention.

Claims (1)

[Scope of utility model registration request] The output terminal of the AM detection circuit and the left and right stereo signal output terminals are directly connected via first and second resistors, respectively, and the first
The connection point of the second resistor is connected to ground via a capacitor and a third resistor, and a semiconductor switching element and a single circuit band changeover switch are connected between the connection point of the capacitor and the third resistor and the power supply. The band selector switch conducts the semiconductor switching element during FM reception, connects the connection point of the first and second resistors to ground in an alternating current manner through the semiconductor switching element, and performs FM stereo demodulation. An AM-FM stereo receiver which supplies power to a circuit, cuts off power to the FM stereo demodulation circuit during AM reception, and puts the semiconductor switching element into a non-conductive state.