JPS6052121A - Amplitude modulation receiver - Google Patents

Abstract

PURPOSE:To attain amplitude modulation reception with high fidelity by transmitting an IF signal to a limiter via a broadcast band filter, phase-detecting its output and amplifying differentially an output signal so as to mask a disturbing signal. CONSTITUTION:A desired broadcast signal is selected from a reception signal subject to high frequency tuning 72 and the frequency is given to a mixing circuit 37, where the received signal is converted into an IF and given to the broadcast filter 76, and after the result is amplified (77), the amplitude component is suppressed by a limiter circuit 79. Then the output of the circuit 79 is phase-detected by a phase detection circuit 82, the level is matched by a differential amplifier 81, and the signal is subtracted from a signal subject to amplitude modulation by a differential amplifier 80 so as to attain the masking of the disturbing signal. Thus, a sound signal of a desired broadcast station is transmitted from the amplifier 80.

Description

[Detailed Description of the Invention] Technical Field The present invention receives an audio signal sent by amplitude modulation,
The present invention relates to an AM receiver that reproduces audio.

BACKGROUND ART Conventionally, AM wave modulation has existed up to 9 KHz in one country, and if all of this was extracted, it would be possible to create a high-fidelity sound source. However, when the broadcasting frequencies of stations are adjacent to each other, such as at night, interference occurs for the broadcasting station that the user wants to receive (by the carrier frequency signal of the adjacent broadcasting station), resulting in poor sound quality.

For this reason, the intermediate frequency band is narrowed to about 15 kHz.

The audio band by synchronous detection is 9KH using a high-order filter.
Ingredients above z were removed. In the former case, the signal can be received without any problems, but the sound quality deteriorates significantly, and in the latter case, there is a problem in that beats due to modulation components of the interference waves are mixed in.

the purpose The object of the present invention is to solve the above-mentioned technical problems.

While keeping the intermediate frequency band and audio band wide, only the beat components caused by interference waves are removed.

The objective is to provide a high-fidelity AM receiver.

Embodiment FIG. 1 is a block diagram showing the basic configuration of an embodiment of the present invention. The high frequency tuning circuit 2 is connected to the antenna 1 via line 11 and the mixing circuit 3 via line l2.
connected to. Mixing circuit 3 is connected to oscillator 4 via line 13 and connected to line I! 4 to an intermediate frequency tuning circuit 5. The intermediate frequency tuning circuit 5 is connected to the line 15.
It is connected to the amplitude modulation detection circuit 6 and the limiter circuit 7 via. Amplitude modulation detection circuit 6 is connected via line 16 to a non-inverting input of operational amplifier 8 .

7 limiter circuits, phase detection circuit 9 via line 17
connected to. Phase detection circuit 9 is connected to phase shift circuit 10 via line /8.

Phase shift circuit 10 is connected to the inverting input terminal of operational amplifier 8 via variable resistor 11 .

FIG. 2 shows the spectrum of the intermediate frequency signal. Line 22Lri indicates the carrier frequency from the broadcast station you wish to listen to. Line 21 shows the upper modulation frequency, line 23
indicates the lower modulation frequency. Line 25Fi, the carrier frequency from the adjacent broadcast station. Line 24 shows the upper modulation frequency.

Line 26 shows the lower modulation frequency.

FIG. 3 shows a spectrum of amplitude modulation detection. A line 32 indicates a modulation frequency from a broadcast station to be listened to. Line 31 indicates the interfering carrier frequency; line 33
is the modulated frequency that causes interference.

FIG. 4 shows the spectrum of one-phase detection. line 41
indicates the carrier frequency of the jammer, and line 42 indicates the modulation frequency of the jammer.

The non-inverting input terminal of operational amplifier 8 shown in FIG.

A signal with a frequency corresponding to lines 31-33' in FIG. 3 is provided. Further, a fourth
A signal with a frequency corresponding to lines 41 and 42 in the figure is provided. Therefore, in the operational amplifier 8, subtraction is performed, and the signals at the frequencies shown on lines 31 and 33 in FIG.
A signal with a frequency corresponding to c is transmitted.

Furthermore, the reason why the phase detection circuit 9 can extract interference waves will be supplemented. First, in a normal amplitude-modulated wave, only an amplitude change occurs and no phase change occurs, as shown in FIG.

Next, when there is an interference wave, a phase change of angle ψ occurs as shown in FIG. The composite wave in this case is.

It is determined by the following first equation.

Composite wave (1) Here, if b sin B in the first equation is small to some extent, the amplitude b cos(A − B ) =131. Due to the change in phase ψ, one phase detection circuit F? ! r9 can extract interference waves.

FIG. 7 is a block diagram showing the electrical configuration of one embodiment of the present invention. The high frequency tuning circuit 72 is connected to an antenna 711C rL via a line Z71' and to a mixing circuit 73 via a line 172.

The output of amplifier 75 provides automatic gain control of high frequency tuning circuit 72 via line 173. Mixing circuit 73 is connected to oscillator 74 via line 174 and line l!
It is connected to terminal a of the broadband filter 76 via 75'. The terminal bu of the broadband filter 76 is connected to the input of the amplifier 77, and its terminal C is grounded. The output of amplifier 77 is connected via line 177 to amplitude modulation detection circuit 78 and limiter circuit 79Vc. Amplitude modulation detection circuit 7
8 is line I! 78 and the input of amplifier 75 via resistor R1'r. Further, the input of the amplifier 75 is grounded via a capacitor C1. Further, the amplitude modulation detection circuit 78 is connected to a non-inverting input terminal of a differential amplifier 80 via a resistor R2. A non-inverting input terminal of differential amplifier 80 is grounded via resistor R3. The inverting input terminal of differential amplifier 80 is connected to the output terminal of differential amplifier 80 via resistor R4, and to the collector of transistor Q1 via m resistor R5e. The connofter of the transistor Ql is
It is connected to the output terminal vc of the differential amplifier 81 via a resistor R6. The inverting input terminal of the differential amplifier 81 is.

It is connected to its output terminal via a resistor R7. Further, the inverting input terminal of the differential amplifier 81 is grounded via a variable resistor R8.

The output of limiter circuit 79 is connected to the input of phase detection circuit 82 via line 179'ft. Further, the output of the limiter circuit 79 is connected to the input of the limiter off detection circuit 83 via a line 179.

The output of the phase detection circuit 82 is connected to a non-inverting input terminal of the differential amplifier 81. Resistor R7 at the output of limiter off detection? It is connected to the base of transistor Ql through the transistor Ql.

The entire operation of this circuit will be explained below. A desired broadcasting frequency is selected by the high frequency tuning circuit 72 which receives all the high frequency signals, and is applied to the mixing circuit 73. The mixing circuit 73 converts the high frequency signal into an intermediate frequency signal.

The intermediate frequency signal is applied to a wide band filter 76Vc.

The amplitude component of the intermediate frequency signal amplified by the amplifier 77 is suppressed by the limiter circuit 79, and only the phase change due to interference is suppressed. Since the intermediate frequency signal has a modulation degree of 100% due to desired wave modulation, it is difficult to apply a limiter at this time. However, when the modulation degree is high or when the input is weak,
It is considered that there is no need to cancel the interfering components. When the modulation degree is high, the interfering signal is masked by the volume of the desired signal.

Since interference signals are masked by white noise during weak input, the limiter ability is set to a modulation degree of about 90%. When the limiter comes off, the limiter comes off, all limiters come off, and it is detected by the detection circuit 83, and the transistor Q1
cant the interference canceling signal.

Next, the limiter output from the limiter circuit 79 is phase-detected by the phase detection circuit 82, but as described in FIG. The levels are matched by a differential amplifier 81, and the signal is subtracted from the amplitude modulated and detected signal by a differential amplifier 8o, thereby masking the interference signal.

Therefore, the audio signal of the desired broadcasting station is sent out from the output of the differential amplifier 80.

Effects As described above, according to the present invention, even if the intermediate frequency signal and the audio frequency band are wide-band, they are not affected by adjacent interference and high-fidelity reception is possible. Further, since the general amplitude modulation stereo receiver VC is equipped with a limiter and a phase detection, the configuration of one circuit becomes simple.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the basic configuration of the present invention. Figure 2 is a diagram of the spectrum of intermediate frequency, Figure 3 is 1
is a diagram showing the spectrum of amplitude modulation detection, Figure 4 is a diagram showing the spectrum of phase detection, Figures 5 and 6 l1
-1' A diagram for explaining the principle by which interference waves can be extracted by the circuit of FIG. 1. FIG. 7 is a block diagram showing the electrical configuration of an embodiment of the present invention. 2.72...High frequency tuning circuit, 3.73...Mixing circuit, 6.78...Amplitude modulation detection circuit, 7.79...,
Limiter circuit, 9.82... Phase detection circuit, 8.80
...Differential amplifier agent Patent attorney Kei Nishi part = Spectrum - = Swatram = 5th Ward bsinB 8g style? ISG Cause = Be Kutle 2 Procedural Amendment (Method) 1. Indication of the case Patent application 1987-1'61264 2. Title of the invention 11171 "1'& investigation I old ryo 3. Case of the person making the amendment Relationships Applicant name: Fujitsu Ten Ltd. 4, agent address: Shinkosan Building, 1-13-38 Nishihonmachi, Nishi-ku, Osaka January 31, 1980 (shipment date) 6. Subject of amendment: 5inB

Claims (1)

[Claims] A high-frequency tuning circuit that selects and sends out all desired high-frequency signals, a mixing circuit that converts the high-frequency signal from the high-frequency tuning circuit into an intermediate frequency signal, an amplitude modulation detection circuit that detects the output of the mixing circuit, and a mixing circuit that selects and sends out all desired high-frequency signals. a limiter circuit that limits the total output amplitude; a phase detection circuit that detects the phase of the output of the limiter circuit; a phase shift circuit that shifts the phase of the output of the single-phase detection circuit; and the output of the amplitude modulation detection circuit and the output of the phase shift circuit. and a differential amplifier circuit that subtracts the amplitude modulation receiver.