JPH0730447A - Radio receiver - Google Patents

Abstract

PURPOSE:To simplify circuit constitution for muting and to attain stable muting control. CONSTITUTION:An IF signal is fetched from the post stage of an amplifier 14a in an IF amplification part 14 and rectified and detected by a level detection part 21 to generate a DC signal I proportional to the level of the IF signal. The DC signal is sent to a muting control part 23. The control part 23 operates so as to turn on a muting switch 24 when the DC signal I is lower than a prescribed level, so that an audio output is short-circuit by earth and interrupted. Since the level of a noise component is low when the whole signal level in an IF band is high or the noise level is high when the signal level is low, muting is controlled by utilizing the above characteristics.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a receiver or a radio receiver for receiving an AM or FM data signal, and more particularly to a receiver having a simplified circuit configuration for muting.

[0002]

2. Description of the Related Art FIG. 6 is a circuit diagram showing a part of a conventional FM radio receiving apparatus, and FIG. 7 is a block diagram showing a circuit configuration for muting in FIG. Reference numeral 1 in FIG. 6 is an IC package provided in the FM radio device. The audio output signal from the terminal 1a of the IC package 1 is passed through a bandpass filter and a diode D.
Is inputted to the mute trigger circuit 6, which is then rectified and detected to be a DC signal, and further a level-adjusted DC signal (DC voltage) is supplied to the mute trigger circuit 6. The mute trigger circuit 6 switches the mute switch 7.

The operation of this circuit is such that the audio output signal output from the terminal 1a and branched at the point (a) passes through the bandpass filter 2 to generate a noise component in a frequency band higher than the audio frequency band, that is, as shown in FIG. As shown in FIG. 5, only noise components in the frequency range higher than about 10 KHz are separated and extracted. Further, this is detected by the detection unit 4 and becomes a DC signal. In the mute trigger circuit 6, when the direct current output from the detection unit 4 is higher than a predetermined level, the mute switch 7 is turned on, the audio output is short-circuited to the ground, and the reception output is cut off, and the mute state is set. That is, it is controlled so as to be in the mute state when the level of the high band noise component shown in FIG. 8 is high.

[0004]

In the conventional receiver shown in FIG. 6, a bandpass filter 2 and a detector 4 for extracting a noise component in a high frequency band from an audio output signal.
Since a large number of resistors and capacitors and amplifiers 3 and diodes are used in both circuits,
The number of parts is large and the manufacturing cost is high. Further, since the audio output signal is branched at the point (a) in FIG. 6 to generate the output for muting control, the control operation of the mute trigger circuit 6 and the change in the noise level of the audio output signal are There was a drawback that adversely affected the output impedance and sound quality.

The present invention is intended to solve the above-mentioned conventional problems, and provides a receiving apparatus which can configure a circuit for muting with a minimum number of parts and which does not adversely affect output impedance and sound quality. It is intended to be provided.

[0006]

A receiving apparatus according to the present invention comprises a frequency conversion section for converting a high frequency input signal into an intermediate frequency signal, a signal output section for obtaining a DC signal proportional to the level of the intermediate frequency signal, and this signal. A mute control unit is provided for switching the reception output to a mute state when the output from the output unit is lower than a predetermined level.

As the signal output section, it is possible to use a level detection section for driving a signal meter.

[0008]

In the above means, the high frequency input signal is converted into the intermediate frequency signal, and then the direct current signal proportional to the level of the intermediate frequency signal is generated, whereby the mute control is performed. Regarding the S / N ratio of the signal level of the intermediate frequency, the ratio of the noise level is high when the overall signal level is low, and the ratio of the noise level is low when the overall signal level is high. Therefore, muting is performed by generating a direct current signal proportional to the level of the intermediate frequency signal and cutting off the audio output path when the level of the direct current signal is below a predetermined level.

[0009]

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a circuit block diagram showing a data receiving apparatus for receiving and demodulating a digital signal as a first embodiment of the present invention, and FIG. 2 is a block diagram showing a circuit configuration of a portion for performing the muting. In the data receiving apparatus 10 shown in FIG. 1, an IC package for a reception tuner shown by reference numeral 11 is provided. The reception output received from the antenna input unit 25 is frequency-selected by the first-stage tuning unit 26, is high-frequency amplified by the field-effect transistor (FET) 27, and is further frequency-selected by the second-stage tuning unit 28 for coupling. It enters the IC package 11 via the capacitor C1.

Frequency converter 12 in IC package 11
Then, the local oscillating frequency from the local oscillating unit 12b and the frequency of the received high-frequency signal input through the coupling capacitance C1 are mixed by the frequency mixer 12a, and 455 KHz.
Becomes an intermediate frequency (IF) signal. This IF
The signal passes through the IF filter 13 and the noise component of the adjacent frequency is removed. Further, after being amplified by the IF amplifier 14, it is detected by the detector 15 to remove the carrier component. The detected signal is compared with a predetermined threshold voltage by the waveform shaping circuit 16 and becomes a rectangular wave demodulation signal. This demodulated signal is output from the data output unit 17.

Next, a circuit configuration for muting in the data receiving apparatus 10 will be described. The signal for mute control is taken out from the IF amplifier 14. As shown in FIG. 2, the IF amplifier 14 includes an amplifier amplifier 14a.
And a limiter amplifier 14b in the subsequent stage.
In this embodiment, an intermediate frequency signal is taken out from the output section of the amplification amplifier 14a and rectified and detected by the level detection section 21 as a signal output section to obtain a DC signal I proportional to the level of the intermediate frequency signal. FIG. 5 shows the level of the intermediate frequency signal that has passed through the amplification amplifier 14a.
The intermediate frequency signal has a bandwidth centered on 455 KHz, but the level detection section 21 obtains a DC signal (DC current) I proportional to the maximum value of the level change shown in FIG. .

The DC signal I is level-adjusted (voltage-adjusted) by the level adjuster 22, and then the mute controller 23.
Sent to. In the mute controller 23, a threshold value S having a constant voltage level is set, and when the voltage level of the DC signal I becomes lower than the threshold value S, a switching signal is issued, and the switching signal mutes. The switch 24 is turned on. When the mute switch 24 is turned on, the data output path from the waveform shaping circuit 16 is short-circuited to ground, and the data output is cut off. When the voltage level of the DC signal I is higher than the threshold value S, the mute switch 24 remains OFF, and the waveform shaping circuit 16 outputs the received data.

That is, when the transmission signal is normally received, the signal level in the band shown in FIG. 5 becomes high as a whole in the IF stage, and the noise component in the S / N ratio is lower than the overall signal level. Become. Therefore, in this case, it is not necessary to set the mute state, and the mute switch 24
When is OFF, received data can be obtained. Conversely, when normal reception is not possible, the signal level at the IF stage is generally low and the noise component ratio is high. Therefore, in this case, the mute switch 24 is turned on to cut off the reception output. Level adjustment of the DC signal I by the level adjuster 22 (voltage adjustment)
By properly setting the threshold value S in the mute control unit 23, the reception output can be cut off when the transmission signal is not normally received, which causes an error in the subsequent digital signal processing unit. It becomes possible to prevent malfunction due to reception. In particular, the signal of the IF stage has a very low noise level, and since the signal with a low noise level is used for mute control, and the IF stage has a high impedance, the level setting of the mute control, for example, the level adjuster 22 is optimal. Easy to set level.

Next, FIG. 3 shows an example of an FM or AM radio receiving apparatus using a circuit for muting similar to the above as a second embodiment of the present invention. Reference numeral 31 in FIG. 3 is an IC package. In the radio receiving apparatus, a front end is provided in front of the apparatus shown in FIG. 3, and a transmission signal from a ground station, a satellite station, etc. is received by an antenna, tuned, and amplified in a high frequency amplification stage. Then, this reception frequency is frequency-mixed with the local oscillation frequency to become an IF band signal. This intermediate frequency signal passes through the IF filter 13, and the amplification amplifier 14a and the limiter amplifier 14b at the subsequent stage pass through the IF amplification section 14.
Is amplified within a certain level by and this is the detector 15
Is detected by and is output from the terminal 31a of the IC package 31 as an audio signal.

Also in this radio receiving apparatus, the IF signal is taken out from the latter stage of the amplification amplifier 14a of the IF amplification unit 14, detected by the level detection unit 21 as a signal output unit, and the IF signal is output from the terminal 31b of the IC package 31. A DC signal I proportional to the level is obtained. This DC signal I
Is set to a voltage by the level adjuster 22 and sent to the mute control circuit 23. And, like the first embodiment,
When the voltage level of the DC signal I is lower than the threshold value S, the mute switch 24 is turned on, the audio output is short-circuited to the ground and cut off, and the mute state is set. In this embodiment, since the audio output from the terminal 31a is not used for mute control, the mute control does not adversely affect the sound quality characteristics of the audio output.

Further, in the first embodiment shown in FIG. 1 and the second embodiment shown in FIG. 3, a detection circuit for driving a signal meter, which is built in the IC package 11 or 31 for a general receiver as the level detection unit 21, is provided. Can be used as is. By using the detection circuit for driving the signal meter as the signal output section (level detection section 21), the number of components can be extremely reduced. For example, comparing the embodiment of FIG. 3 with the conventional example of FIG. 6, it can be seen that the number of components mounted outside the IC package is extremely small.

FIG. 4 shows a third embodiment of the present invention.
In this embodiment, a waveform shaping circuit 33 is provided before or after the level adjuster 22 in the path of the DC signal I detected by the level detector 21, and the waveform shaping circuit 33 is provided.
The stable voltage obtained by the above is sent to the mute controller 23. That is, when the analog DC signal I detected by the level detection unit 21 is directly applied to the mute control unit 23 as in the first or second embodiment, the DC current is passed through the path outside the IC package 11 or 31. External noise is likely to be superimposed on the signal I. When the direct current I superimposed with external noise is input, the mute control unit 23 may turn on the mute switch 24 when it is not necessary, which causes a problem that the reception output is interrupted. Therefore, if the DC signal I obtained by the level detection unit 21 is compared with a predetermined threshold value in the waveform shaping circuit 33 and is output as a constant current or voltage, the mute control unit 23 does not malfunction due to external noise. , Stable reception output can be obtained.

[0018]

As described above, according to the invention of claim 1,
Since the signal converted to the intermediate frequency is used for the mute control, the bandpass filter as in the prior art is unnecessary, and the signal can be obtained from the latter stage of the amplifier in the IF amplifier as in the above embodiment. In this case, the conventional amplifier for generating the mute signal is unnecessary, and the circuit configuration can be simplified. In addition, the stability of mute control is also high.

According to the second aspect of the present invention, the number of circuit components can be further reduced by using a detection circuit for driving a signal meter provided in an IC package for a general receiver as the level detection section.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a data receiving device as a first embodiment of the present invention.

FIG. 2 is a block diagram showing a circuit portion for muting in FIG.

FIG. 3 is a circuit diagram showing a part of a radio receiving apparatus as a second embodiment of the present invention.

FIG. 4 is a circuit block diagram showing a third embodiment in which a waveform shaping circuit is provided in the next stage of the level detector 21.

FIG. 5 is a diagram illustrating a signal level of an IF stage.

FIG. 6 is a circuit diagram showing a part of a conventional radio receiver.

7 is a block diagram showing a circuit configuration for muting in the receiving apparatus of FIG.

FIG. 8 is a diagram illustrating a conventional mute control.

[Explanation of symbols]

 10 receiver 11 IC package 12 frequency converter 13 IF filter 14 IF amplifier 14a amplification amplifier 14b limiter amplifier 15 detector 21 level detector (signal output unit) 22 level adjuster 23 mute controller 24 mute switch

Claims (2)

[Claims] 1. A frequency conversion unit for converting a high frequency input signal into an intermediate frequency signal, a signal output unit for obtaining a DC signal proportional to the level of the intermediate frequency signal, and an output from this signal output unit is lower than a predetermined level. A receiving device, comprising: a mute controller for switching a reception output to a mute state. 2. The receiving device according to claim 1, wherein the signal output unit is a level detection unit for driving a signal meter.