JP2605631Y2 - Receiving machine - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a receiver having an oscillator for obtaining a frequency signal required for a demodulation operation in a demodulation circuit, such as an AM stereo radio receiver.

[0002]

2. Description of the Related Art FIG. 3 shows a conventional A having an automatic tuning function.
It is a block diagram which shows the structure of an example of an M stereo radio receiver.

In FIG. 1, a high-frequency signal, which is a broadcast signal received by an antenna 1, is amplified by a high-frequency amplifier circuit 2 and supplied to a mixing circuit 3. The mixing circuit 3 includes a PLL circuit 4
The local oscillation signal is supplied and mixed with the above-described high-frequency signal to form an intermediate-frequency signal SIF. PLL circuit 4
The frequency of the local oscillation signal output from the controller is controlled by the controller 5 composed of a microcomputer, and the channel is selected.

The intermediate frequency signal S output from the mixing circuit 3
The IF is supplied to an input terminal 7i of the AM stereo demodulation circuit 7 after being amplified by the intermediate frequency amplification circuit 6. When the selected station is for stereo broadcasting, a left audio signal L and a right audio signal R are obtained at the output terminals 7oL and 7oR of the demodulation circuit 7, respectively. If they are the same, a monaural audio signal is obtained on both sides. The audio signals obtained at the output terminals 7oL and 7oR of the demodulation circuit 7 are supplied to the speakers 10L and 10R via the muting circuit 8 and the low frequency amplification circuits 9L and 9R.

[0005] Further, the station detector 1
The intermediate frequency signal SIF amplified to 1 is supplied. Station detector 11 the level of the intermediate frequency signal is detected that there station when greater than a predetermined value. From the station detector 11, the station Yes
Ri when not detected at a high level "H", the station Yes
Ri is the station detection signal SD becomes a low level "L" when the detected output. This station detection signal SD is supplied to the controller 5. A display (indicator) 12 is connected to the controller 5, and the display 12 displays whether or not there is a station based on the station detection signal SD.

[0006] A stereo detection signal ST is supplied from the demodulation circuit 7 to the controller 5, and the station selected on the display 12 based on the stereo detection signal ST is either a stereo broadcast or a monaural broadcast. Is displayed.

Reference numeral 13 denotes a key panel on which various operation keys connected to the controller 5 are arranged. When the automatic tuning is instructed by the key panel 13, the controller 5
, The frequency of the local oscillation signal output from the PLL circuit 4 is sequentially changed. And the station detector 1
1 becomes low level "L", and the station detection signal SD from
There are detected Rutoki is the change in frequency stop of the local oscillation signal, thereby automatically tuning is performed.

FIG. 4 shows an example of a specific configuration of the AM stereo demodulation circuit 7, which corresponds to the well-known C-QUAM system. In the figure, an intermediate frequency signal SIF supplied to an input terminal 7i is supplied to an envelope detector 71, and an output signal of the envelope detector 71 is supplied to a matrix circuit 72.

The intermediate frequency signal SIF supplied to the input terminal 7i is supplied to an in-phase synchronous detector 74 and a quadrature synchronous detector 75 via a gain control amplifier 73. Reference numeral 76 denotes a voltage controlled oscillator (VCO) having a center frequency of an intermediate frequency (450 KHz).
The phase signal is supplied to the synchronous detector 74, and the 90 ° frequency signal output from the oscillator 76 is supplied to the synchronous detector 75. In this case, the voltage controlled oscillator 76
Is supplied with the output signal of the synchronous detector 75 as a control signal, and constitutes a PLL synchronous detection circuit.

The output signal of the synchronous detector 74 and the output signal of the envelope detector 71 are supplied to an error amplifier 77, and the output signal of the error amplifier 77 is supplied to a gain control amplifier 73 as a control signal. The output signal of the synchronous detector 75 is supplied to the matrix circuit 72.

If the intermediate frequency signal SIF is for stereo broadcasting, the envelope detector 71 outputs a sum signal (L + R).
Is output. Also, from the synchronous detector 74, (L + R)
The signal of cos θ is output. cos θ is a correction value on the transmission side. The signal of cos θ is output from the error amplifier 77, the gain of the gain control amplifier 73 is feedback-controlled by the signal, and the cos θ component is removed from the intermediate frequency signal SIF. As a result, the difference signal (LR) is output from the synchronous detector 75, and the left audio signal L and the right audio signal R are separated by the matrix circuit 72.
A left audio signal L and a right audio signal R are obtained at oL and 7oR, respectively.

When the intermediate frequency signal SIF is for monaural broadcasting, a monaural audio signal is output from the envelope detector 71, and the difference signal (L−L) is output from the synchronous detector 75.
R) is not output, and a monaural audio signal is obtained at both the output terminals 7oL and 7oR.

The output signal of the synchronous detector 75 is supplied to a pilot signal detection circuit 78. This detection circuit 78
In the transmission side, the pilot signal of 25 Hz added to the difference signal LR is detected on the transmission side. When the intermediate frequency signal SIF is for stereo broadcasting, the difference signal (LR) is output from the synchronous detection circuit 75, and the detection circuit 78 detects a pilot signal. H "is output. On the other hand, when the intermediate frequency signal SIF is for monaural broadcasting, the difference signal (LR) is not output from the synchronous detection circuit 75, and the pilot signal is not detected by the detection circuit 78. A signal of level "L" is output.

[0014]

By the way, in an AM stereo radio receiver as shown in FIG. 3, for example, at the time of automatic channel selection in which the frequency of the local oscillation signal is sequentially changed, the intermediate frequency signal SIF and the voltage of the demodulation circuit 7 are changed. There was a problem that beat sounds were generated from the speakers 10L and 10R due to interference with the output signal of the control oscillator 76.

Since the beat sound is generated for a predetermined period of time, for example, 1 second or more after the time t1 when the station detector 11 detects the presence of a station, the predetermined period during which the beat sound is generated in the example of FIG. The muting circuit 8 is operated to mute the sound until time t2 after the lapse. FIG. 5B shows a muting control signal MU supplied from the controller 5 to the muting circuit 8. The muting operation is performed when the control signal MU is at a high level “H”, and when the control signal MU is at a low level “L”. Does not perform the muting operation.

FIG. 5A shows a station detection signal SD outputted from the station detector 11, and FIG. 5C shows a stereo detection signal ST outputted from a pilot signal detection circuit 78 of the demodulation circuit 7.
FIG. 3D shows audio output from the speakers 10L and 10R.

However, as described above, when the sound is muted until time t2 after the elapse of the predetermined period in which the beat sound is generated, at the time t1 when the presence of the station is detected, the display 12 is displayed based on the station detection signal SD. Since the silent state continues for one second or more after the display of the presence of the station is displayed, there has been a problem that it becomes unnatural.

Accordingly, an object of the present invention is to provide a receiver capable of shortening a silent state after detecting the presence of a station without generating a beat sound.

[0019]

According to the present invention, a mixer for obtaining an intermediate frequency signal by mixing a received high frequency signal and a local oscillation signal from a first oscillator, and a frequency of a substantially intermediate frequency required for a demodulation operation are provided. a second oscillator to obtain a signal, a demodulation circuit for demodulating an audio signal from the intermediate frequency signal obtained in the mixer, and a station detecting means for detecting the presence station the state that the intermediate frequency signal is output from the mixer, the From one oscillator
Tuning by sequentially changing the frequency of the local oscillation signal
And a control means for stopping the operation of the second oscillator of the demodulation circuit at least until the presence of a station is detected by the station detection means at the time of tuning .

[0020]

In this invention, the frequency of the local oscillation signal is
When tuning to perform channel selection by going is sequentially changed, than to stop the operation of the second oscillator of the demodulation circuit until there station in the station detecting means is detected frequency signal and a second oscillator between middle The output signal does not interfere with the output signal and no beat sound is generated, and the muting period of the sound after the presence of the station is detected can be shortened. Thereby, the silent state after the presence of the station is detected can be shortened, and the unnaturalness in relation to the display of the presence of the station can be eliminated.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG. This example is an example applied to an AM stereo radio receiver. In FIG. 1, portions corresponding to those in FIG. 3 are denoted by the same reference numerals, and detailed description thereof will be omitted.

In this example, the controller 5
The forced monaural control signal MN is supplied to the voltage control oscillator 76 of the stereo demodulation circuit 7 (see the broken line in FIG. 4), and the time immediately after the time t1 when the station detector 11 detects the station (for example, the time within 100 msec from the time t1) ) Until t3, the operation of the voltage controlled oscillator 76 is stopped and a forced monaural state is set. In this forced monaural state, the difference signal (LR) is not output from the synchronous detector 75 even if the selected station is a stereo broadcast, and the matrix circuit 72 outputs both the output terminals 7oL and 7oR. Respectively have a sum signal (L +
R) is output.

FIG. 2B shows the forced monaural control signal MN, wherein the voltage controlled oscillator 76 operates when the control signal MN is at a low level "L", while the voltage controlled oscillator 76 is operated when the control signal MN is at a high level "H". The operation is controlled to stop.

In the present embodiment, the muting circuit 8 operates at a time immediately after the time t3 (for example, 25 times after the time t1).
Muting of the sound is performed until t4 (at the time of 0 msec). FIG. 2C shows the muting control signal MU. In the muting circuit 8, the muting operation is performed when the control signal MU is at the high level “H”, and the muting operation is performed when the control signal MU is at the low level “L”. Not done. The broken line in FIG. 2C indicates the muting control signal MU in the conventional example.

FIG. 2A shows a station detection signal SD output from the station detector 11, and FIG. 2D shows a stereo detection signal ST output from a pilot signal detection circuit 78 of the demodulation circuit 7.
FIG. 5E shows audio output from the speakers 10L and 10R.

The present embodiment is configured as described above, and the rest is configured similarly to the example of FIG.

In the present embodiment, since the stops the operation of the voltage controlled oscillator 76 of the demodulator circuit 7 to the time point t3 immediately after the time point t1 where there station in the station detector 11 is detected, for example, P
At the time of automatic channel selection in which the frequency of a local oscillation signal from a voltage controlled oscillator (not shown) of the LL circuit 4 is sequentially changed to automatically select a channel, the intermediate frequency signal SIF and the output signal of the voltage controlled oscillator 76 are output. No beat sound is generated due to interference. Therefore, as compared with the conventional, it can be shortened muting period Ruoto voice put the muting circuit 8 after detection valid station can be shortened silence after detecting there station, indicator 1
2 can eliminate the unnaturalness due to the longer period from when the station presence detection display is performed to when the sound is output.

In this embodiment, the muting circuit 8 is turned on at time t4 after time t3 when the forced monaural state is released.
Since the muting of the sound at the time of is canceled, the noise generated when the operation of the voltage controlled oscillator 76 starts at the time point t3, that is, the so-called pop sound output from the speakers 10L and 10R can be prevented.

In the above embodiment, the station detector 1
At 1, the presence of a station is detected based on the level of the intermediate frequency signal SIF. However, the station detection means is not limited to this, and may have another configuration.

In the above embodiment, the present invention is applied to an AM stereo radio receiver. However, the present invention is directed to another receiver having an oscillator for obtaining a frequency signal of a substantially intermediate frequency necessary for a demodulation operation in a demodulation circuit. Needless to say, the present invention can be similarly applied.

[0031]

According to the invention, the frequency of the local oscillation signal
When tuning to perform channel selection by going by sequentially changing the number, than is available stations in the station detecting means stops the operation of the second oscillator of the demodulator circuit to be detected, frequency signal between the middle and the second The output signal of the oscillator does not interfere with the generation of a beat sound, and the muting period of the sound after the presence of the station is detected can be shortened.
Unnaturalness can be eliminated.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a receiver according to the present invention.

FIG. 2 is a time chart for explaining the operation of the embodiment.

FIG. 3 is a block diagram showing an example of a conventional AM stereo radio receiver.

FIG. 4 is a block diagram illustrating an example of an AM stereo demodulation circuit.

FIG. 5 is a time chart for explaining the operation of the conventional example.

[Explanation of symbols]

 Reference Signs List 3 mixing circuit 4 PLL circuit 5 controller 6 intermediate frequency amplification circuit 7 AM stereo demodulation circuit 8 muting circuit 10L, 10R speaker 11 station detector 12 display

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) H04H 5/00 H04B 1/10 H04B 1/16

Claims (2)

(57) [Scope of request for utility model registration] 1. A mixer for obtaining an intermediate frequency signal by mixing a received high-frequency signal and a local oscillation signal from a first oscillator, and a second mixer for obtaining a frequency signal of a substantially intermediate frequency necessary for demodulation operation.
Has a oscillator, a demodulation circuit for demodulating an audio signal from the intermediate frequency signal obtained by the mixer, a station detecting means for detecting the presence station a state in which the intermediate frequency signal from the mixer is output, said first Sequentially changes the frequency of the local oscillation signal from the first oscillator.
Channel selection means for performing channel selection by making the channel change, and control means for stopping the operation of the second oscillator of the demodulation circuit at least until the presence of a station is detected by the station detection means during the channel selection. A receiver comprising: 2. An automatic tuning means for sequentially changing the frequency of a local oscillation signal from the first oscillator and stopping a change in the frequency of the local oscillation signal when the presence of a station is detected by the station detecting means. The receiver according to claim 1, further comprising: