JPH1168687A - Simultaneous am/fm reception equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the noise of an AM audio signal by displaying the multiplex character data of an FM multiplex signal, selecting any one of audio signals demodulated from the FM multiplex signal and AM signal, acoustically outputting it and stopping demodulating the acoustic signal from the FM signal when selecting the acoustic signal demodulated from the AM signal. SOLUTION: The AM/FM received signal from an antenna 1 is amplified by a high frequency amplifier circuit 2 and respectively demodulated by an AM circuit 5 and an FM demodulation circuit 3. When the FM reception signals are FM multiplex character data, the contents are displayed on a display 9. According to the select signal (AM/FM) of AM/FM, a control circuit 4 controls a switch circuit 6 and selects any one of demodulated AM and FM audio signals. When selecting the AM audio signal, the operation of an oscillator 15 or a stereo demodulation circuit 14 is stopped. Thus, the S/N of the AM reception signal can be prevented from being degraded.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an AM / FM receiving apparatus, and more particularly to an AM / FM receiving apparatus capable of simultaneously receiving AM broadcast audio and FM multiplex broadcast data.

[0002]

2. Description of the Related Art An AM / FM receiver selects and receives only one of an AM audio broadcast and an FM audio broadcast. Therefore, there has been no request for simultaneous reception of AM / FM broadcast.

However, in recent years, FM multiplex broadcasting has become widespread, and there is an increasing demand for displaying character data by FM multiplex broadcasting on a display of an AM / FM receiving apparatus while receiving AM audio broadcasting.

[0004]

By the way, in an FM receiving circuit using an oscillation element of 456 kHz or 912 kHz for demodulating an FM stereo signal, the oscillation frequency is divided by 12 or 24 to obtain a subcarrier of FM broadcasting. A certain 38 KHz has been obtained.

In this case, in order to enable simultaneous reception of the AM broadcast and the FM multiplex broadcast, if both the AM receiving circuit and the FM receiving circuit are turned on at the same time, the 4
There is a problem that the oscillation frequency component of 56 kHz or 912 kHz is mixed as noise into the signal band of the AM receiving circuit. As an example, in the AM broadcasting band of 600 kHz to 1500 kHz, especially 912 kHz and 1368
There has been a problem that the signal-to-noise ratio (S / N) at the time of AM broadcast reception in the vicinity of kHz (456 kHz × 3) is greatly deteriorated.

Accordingly, an object of the present invention is to stop the operation of the FM stereo demodulation circuit or its oscillating element at the time of AM / FM simultaneous reception from the viewpoint that an FM stereo demodulation circuit is not required when character data is received by FM multiplex broadcasting. AM / F that prevents deterioration of the S / N ratio of AM broadcast audio
An object of the present invention is to provide an M simultaneous receiving device.

That is, according to the present invention, there is provided a radio receiver capable of simultaneous AM / FM reception (AM broadcast audio reception and FM multiplex broadcast character data reception) with reduced AM audio signal noise.

[0008]

According to the present invention, an FM multiplexing circuit for receiving an FM multiplexed signal and providing the multiplexed character data to a display device, an AM circuit for receiving an AM signal, the FM multiplexing circuit, A switch circuit that selects one of the audio signals demodulated by the AM circuit and supplies the selected audio signal to the audio output device; and controls the selection of the audio signal in the switch circuit and operates the FM audio demodulation unit in the FM multiplexing circuit. AM / FM composed of a control unit for controlling stop
A simultaneous receiving device is provided.

In the control of stopping the operation of the FM sound demodulation unit by the control unit, the operation of the oscillator for generating the FM subcarrier frequency in the FM multiplexing circuit is stopped when the AM circuit receives the AM signal. The operation of the oscillator is stopped by a bypass switch circuit that bypass-controls an output signal of the oscillator to ground or a power supply.

[0010] The bypass switch circuit bypasses an output signal of the oscillator to ground or a power supply when power is supplied to the AM circuit, or a predetermined AM / F
According to the M selection signal, when the AM circuit selects the AM side indicating the reception of the AM signal in the AM circuit, the output signal of the oscillator is bypassed to the ground or the power supply.

Further, according to the present invention, F
In the control for stopping the operation of the M audio demodulation unit, the FM multiplexer in the FM multiplexing circuit receives the AM signal in the AM circuit.
Stop the operation of the stereo demodulation unit. The operation of the FM stereo demodulation unit is stopped by a power switch circuit that controls power supply to the FM stereo demodulation unit.

The power switch circuit stops the power supply to the FM stereo demodulation unit when the power is supplied to the AM circuit, or in accordance with a predetermined AM / FM selection signal, and the power is supplied to the AM circuit in the AM circuit. When the AM side indicating signal reception is selected, power supply to the FM stereo demodulation unit is stopped.

[0013]

FIG. 1 shows an AM / FM according to the present invention.
2 shows an example of a basic configuration of a simultaneous receiving device. In the present invention, simultaneous reception of AM / FM refers to simultaneous reception of FM multiplex broadcast data while listening to AM audio and display of the data on a display device.

In FIG. 1, an AM / FM broadcast signal received by an antenna (ANT) 1 is amplified by a high frequency amplifier 2. The AM reception signal is demodulated by an AM circuit 5, and the FM reception signal is demodulated by an FM multiplexing circuit 3.

The switch circuit 6 selects one of the demodulated AM audio signal and the FM audio signal. The control circuit 4 controls the switch circuit 6 according to an AM / FM selection instruction signal (AM / FM) or the like. The detailed operation of the control circuit 4 will be described in the following embodiments of the present invention.

The audio signal from the AM circuit 5 or the FM multiplex circuit 3 selected by the switch circuit 6 is power-amplified by an amplifier 7 and then output from a speaker 8. When the FM reception signal is FM multiplexed character data, the content is displayed on the display 9.

Next, in connection with the present invention, the FM multiplexing circuit 3
The main block configuration of will be briefly described. Note that a general AM receiving circuit is used for the AM circuit 5, and a description thereof will not be given here.

First, regarding demodulation of an FM audio signal, a predetermined FM channel signal amplified by the high-frequency amplifier 2 is temporarily converted to an intermediate frequency of 10.7 MHz by a mixer (MIX) 10 using a local frequency from a local oscillation circuit 11. Is converted to The detector 12 converts a frequency change of the FM channel signal into an amplitude change, and removes the carrier to extract a low-frequency channel signal of a 75 kHz band.

In the stereo demodulation circuit, the oscillation frequency of 456 kHz or 912 kHz from the crystal oscillator 15 is frequency-divided by 12 or 24 to generate a 38 kHz subcarrier for FM broadcasting, which is received by the built-in PLL circuit.
Phase-synchronized with the pilot signal.

[0020] Then, from the low frequency channel signal, 15
The (L + R) signal is extracted by a low-pass filter in a KHz band, and the sub-carrier 38 KHz is converted to a high-frequency (LR) signal.
(LR) signal is obtained by AM detection in addition to the signal. Finally, the stereo audio signals of the L signal and the R signal are demodulated by adding and subtracting them by a matrix circuit.

On the other hand, since the demodulation of the stereo sound is not required in the reception of the character data of the FM multiplex broadcast, the signal from the detection circuit 12 is directly supplied to the FM multiplex decoder circuit 13. The FM multiplex decoder circuit 13 receives 16 Kbps character data having a center frequency of 76 KHz, which is called a DARC system using an empty band of an FM channel signal, and displays it on the display 9.

Thus, when receiving only FM multiplexed data, the stereo demodulation circuit 14 becomes unnecessary. Therefore, the operation of the oscillating element 15 or the stereo demodulation circuit 14 can be stopped when the AM audio and the data of the FM multiplex broadcast are simultaneously received, and as a result, the deterioration of the S / N of the AM reception signal can be prevented. The present invention has been made by paying attention to this point, and each embodiment of the present invention will be described in detail below.

FIG. 2 shows a first embodiment of the present invention. In FIG. 2, at the time of AM / FM simultaneous reception, the output terminal of the oscillation element 15 is bypassed to the ground by the bypass capacitor 41 and the switch 42 provided inside the control circuit 4, thereby stopping the operation of the oscillator 11. Let it.

FIG. 3 shows another basic second embodiment of the present invention. In FIG. 3, a power switch 4 provided inside the control circuit 4 at the time of AM / FM simultaneous reception.
3, the operation of the stereo demodulation circuit 14 is stopped.

FIGS. 4 to 7 show more specific examples of the above two basic embodiments of the present invention. FIG.
Shows a third embodiment which is a specific example of FIG. In FIG. 4, similarly to FIG. 2, at the time of simultaneous AM / FM reception, the oscillation capacitor 15 is controlled by a bypass capacitor 41 provided inside the control circuit 4 and an electric switch 44 including active elements such as FETs and transistors. The output end is bypassed to ground, thereby stopping the operation of the oscillator 11.

In this example, the power supply (AMVc) to the AM circuit 5
c) The switch 44 is turned on with the start of supply as a trigger signal, and the output terminal of the oscillation element 15 is bypassed to ground. Therefore, in this example, the AM audio signal automatically takes precedence over the FM audio signal.

FIG. 5 shows a fourth embodiment which is a specific example of FIG. In FIG. 5, similarly to FIG. 3, at the time of simultaneous AM / FM reception, the power switch 45 provided inside the control circuit 4 is turned off, thereby stopping the operation of the stereo demodulation circuit 14.

The power switch 45 of this embodiment is also formed of an electric switch composed of active elements such as FETs and transistors, as in FIG. 4, and supplies a power supply (AMVc) to the AM circuit 5.
c) The start of supply is turned off as a trigger signal, and power supply to the stereo demodulation circuit 14 is stopped. Therefore, also in this example, the AM audio signal automatically takes precedence over the FM audio signal.

FIG. 6 shows a fifth embodiment which is a modification of FIG. FIG. 7 shows a sixth embodiment which is a modification of FIG. 6 and 7 respectively correspond to FIGS. 4 and 5 described above. In each case, the start of power supply (AMVcc) to the AM circuit 5 is not used as a trigger signal, but an externally supplied AM / FM selection. The difference is that the corresponding switches 41 and 45 are turned on / off based on the signal.

The AM / FM selection signal may be provided by a manual operation from outside the apparatus, or an AM sound detection signal from the AM circuit 5 may be used.

FIG. 8 shows an example of measured data at the time of AM / FM simultaneous reception. FIG. 8 shows measured S / N values when FM multiplex character data and AM918 kHz broadcast are simultaneously received in a receiver using the 912 kHz oscillator 15 in the FM stereo demodulation circuit 14.

FIG. 8 shows that when simultaneously receiving the FM multiplexed character data and the AM broadcast near the oscillation frequency of the oscillator 15 according to the present invention, the S / N ratio at a weak input (35 dBuV) is 16 dB, and the residual noise ratio is 16 dB. It can be seen that a degree of improvement of 13 dB is achieved with the above.

[0033]

As described above, according to the present invention, the AM
A significant improvement in the S / N ratio at the time of AM signal reception during simultaneous / FM reception is achieved. Especially 912kHz and 1386kHz
The effect is significant when simultaneously receiving AM broadcasts in the vicinity of Hz.

As a result, according to the present invention, there is provided a radio receiver capable of simultaneous AM / FM reception (sound reception of AM broadcast and character data reception of FM multiplex broadcast) with reduced noise of the AM audio signal.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of a basic configuration of an AM / FM simultaneous receiving apparatus according to the present invention.

FIG. 2 is a diagram showing a first embodiment as a basis of the present invention.

FIG. 3 is a diagram showing another basic second embodiment of the present invention.

FIG. 4 is a view showing a third embodiment which is a specific example of FIG. 2;

FIG. 5 is a diagram showing a fourth embodiment which is a specific example of FIG. 3;

FIG. 6 is a diagram showing a fifth embodiment which is a modification of FIG.

FIG. 7 is a diagram showing a sixth embodiment which is a modification of FIG. 5;

FIG. 8 is a diagram showing an example of actual measurement data at the time of AM / FM simultaneous reception.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 3 ... FM multiplexing circuit 4 ... Control circuit 5 ... AM circuit 6 ... Switching circuit 8 ... Speaker 9 ... Display 13 ... FM multiplexing decoder 14 ... Stereo demodulation circuit 15 ... Oscillator 41 ... Bypass capacitor 42,43,44,45 ... Switch circuit

Claims (9)

[Claims] 1. An FM multiplexing circuit for receiving an FM multiplexed signal and applying the multiplexed character data to a display device, an AM circuit for receiving an AM signal, and an audio signal demodulated by the FM multiplexing circuit and the AM circuit. A switch circuit for selecting one of the switches and supplying the selected sound signal to the sound output device; and a control unit for performing selection control of an audio signal in the switch circuit and controlling stop of operation of an FM audio demodulation unit in the FM multiplexing circuit. AM / FM simultaneous receiving apparatus. 2. The method according to claim 1, wherein the control of stopping the operation of the FM audio demodulation unit by the control unit stops the operation of the oscillator that generates the FM subcarrier frequency in the FM multiplexing circuit when the AM circuit receives the AM signal. An apparatus according to claim 1. 3. The device according to claim 2, wherein the operation of the oscillator is stopped by a bypass switch circuit that bypass-controls an output signal of the oscillator to ground or a power supply. 4. The AM circuit according to claim 1, wherein
4. The device according to claim 3, wherein an output signal of the oscillator is bypassed to a ground or a power supply when power is supplied to the circuit. 5. The circuit of claim 1, wherein the bypass switch circuit has a predetermined A
4. The device according to claim 3, wherein an output signal of said oscillator is bypassed to ground or a power supply according to an M / FM selection signal and when it selects an AM side indicating reception of an AM signal in said AM circuit. 6. The apparatus according to claim 1, wherein the control of stopping the operation of the FM audio demodulation unit by the control unit stops the operation of the FM stereo demodulation unit in the FM multiplexing circuit when the AM circuit receives an AM signal. 7. The operation of the FM stereo demodulator is stopped.
7. The apparatus according to claim 6, wherein the power is supplied to the FM stereo demodulation unit by a power switch circuit that controls power supply. 8. The apparatus according to claim 7, wherein said power switch circuit stops power supply to said FM stereo demodulation unit when power is supplied to said AM circuit. 9. The power supply switch circuit according to claim 1, wherein a predetermined AM /
According to the FM selection signal, it is determined that the AM
The apparatus according to claim 7, wherein power supply to the FM stereo demodulation unit is stopped when an AM side indicating signal reception is selected.