JPH0253979B2 - - Google Patents

Description

[Detailed Description of the Invention] "Industrial Application Field" The present invention is applicable to satellite broadcast television receivers and FM
In broadcast receivers, the present invention relates to a filter switching circuit of an intermediate frequency amplification circuit that automatically switches the filter circuit according to a normal narrowband frequency shift (modulation) and a wideband frequency shift (modulation). , once the switch is made to the broadband filter circuit, it is maintained as is to prevent unnecessary switching.

"Prior Art" First, an outline of a satellite broadcast television receiver will be explained. Currently, in the United States, the interval is 2 to 5 degrees.
More than 20 private broadcasting geostationary satellites have been launched, each receiving signals using a television receiver equipped with an antenna position control device as shown in Figure 3. In this figure, 1 is a reflector of a parabolic antenna, an antenna 2 is installed at the focal point of this reflector 1, and a low noise amplifier and down converter 3 coupled to this antenna 2 are connected to a receiver via a waveguide. 4 is combined. A monitor TV 5, an audio device 6, and an antenna positioner 7 are connected to the receiver 4, and the audio device 6 is connected to left and right speakers 9, 1 via an audio amplifier 8.
0 is connected. Further, the antenna positioner 7 is coupled with an actuator 12 for pointing to the position of the geostationary satellite 11 and the antenna 2.

In the above configuration, when a certain satellite 11 is selected by the antenna positioner 7, the actuator 12 directs the parabolic antenna reflector 1 to the target satellite. At the same time, the angle of the metal rod inside the antenna 2 is set depending on whether the wave is vertically polarized or horizontally polarized. Further, since each satellite has 24 channels, the antenna positioner 7 selects one of the channels.

The 3.7~4.2GHz signal from the satellite 11 is reflected by the reflector 1, received by the antenna 2, and converted to 430~930MHz by the low noise amplifier and down converter 3.
and sent to receiver 4. The antenna positioner 7 sends to the receiver 4 a control code signal indicating which video channel is selected. The input signal from the antenna 2 is further lowered to 90MHz by the receiver 4, and then the video signal is separated into audio signals.
sent to. The audio signal separated by the receiver 4 is carried by a subcarrier signal of 5 to 8 MHz and sent to the audio device 6. At this time, a control code signal is sent to the audio device 6 from the antenna positioner 7 to indicate which satellite and which channel the audio is from. That is, information such as the distinction between discrete stereo, matrix stereo, multiplex stereo, and monaural, and the frequency of the subcarrier is sent to the audio device 6. Furthermore, this audio device 6 amplifies the audio intermediate frequency.
FM detection is performed, which is further amplified by an audio amplifier 8, and audio is output from left and right speakers 9 and 10.

However, conventionally, there have been few satellite broadcasts, and therefore there have been few broadcasts with large frequency shifts, so the switch 20 of the intermediate frequency amplification circuit in the audio device 6 is normally set to a narrow band, as shown in FIG. It was connected to the contact 22 on the filter 21 side. Even if a satellite broadcasting signal with a large frequency shift is input, the signal is first filtered through the narrowband filter 2.
1 is modulated and becomes an external output, which is output from the speaker via an audio amplifier.By sensing the audio distortion at that time, the user directly switches the selector switch 20 manually to the contact 24 on the broadband filter 23 side. I was switching. In addition, in Figure 2, 2
5 is an input terminal, 26 is a preamplifier circuit, 27, 28
is a chiyoke coil for electronic switching, 29,2
9, 30, 30 are electronic switching diodes, 31, 31, 32, 32 are electronic switching circuit resistors, 23 is a broadband filter circuit, 21
33 is a narrowband filter circuit, 33 is a rear stage amplifier circuit,
34 is a detector, 35 is an output terminal, and +E is a power supply terminal.

``Problems to be Solved by the Invention'' As mentioned above, in the past, there were very few broadcasts with large frequency shifts, and it was sufficient to simply change the changeover switch manually. However, in recent satellite broadcasting, the number of broadcasts with large frequency deviations has increased dramatically, and it has become cumbersome to manually operate the changeover switch. Currently, more than ten private broadcasting geostationary satellites have been launched in the United States, and the receiver's parabolic antenna is equipped with an antenna positioner to direct it to the target geostationary satellite. There has been a problem in that it is becoming increasingly impractical to manually switch filters in intermediate frequency amplification circuits, as switching speeds have become faster. Therefore, in order to solve this problem, the present applicant has proposed a circuit that automatically switches between a narrowband filter circuit and a wideband filter circuit in response to the magnitude of frequency shift. However, in broadcasting with a large frequency deviation and a signal with a wide range of strength such as music broadcasting, if the bandwidth changes each time, switching nozzles may occur or the characteristics may change due to switching. There were problems in that the auditory sensation changed and audio distortion occurred at the rising edge of switching.

"Means for Solving the Problems" The present invention has been made to solve the above-mentioned problems, and after amplifying the audio intermediate frequency signal with a preamplifier circuit, a narrowband filter circuit and a wideband filter circuit are used. In a circuit that obtains an audio output through either one of the filter circuits for use in the filter circuit, and then through a subsequent stage amplifier circuit and a detector, the circuit is coupled to the output side of the detector, and is connected to the output side of the detector to determine the average level of the detected output. an average level detection circuit for detecting; a rectifier coupled to the average level detection circuit for rectifying the average level output signal; and a rectifier coupled to the rectifier and opened or closed depending on whether the average level is greater than a set value level. A switching element, a hold circuit that holds the switching element with a first open/close signal of the switching element, shuts off the narrow band filter circuit with this hold signal, and activates the wide band filter circuit, and a hold circuit for resetting the hold circuit. It is equipped with a reset circuit.

``Operation'' The input audio intermediate frequency signal is amplified by the preamplifier circuit and then sent to the filter circuit, but regardless of the magnitude of the frequency deviation, it first passes through the narrowband filter circuit and then is sent to the post-amplifier circuit. , passes through a wave detector, and is sent to an audio amplifier and speaker.
Here, the average level of the output of the wave detector is detected by an average level detection circuit, and the signal is further rectified and sent to a switching circuit. If the average level of the detector is lower than the set value, the frequency deviation is small, so the switching element does not switch and the hold circuit
Turn on the narrowband filter circuit and turn off the wideband filter circuit. When a broadcast with a large frequency shift is received, the switching element switches, and the hold circuit turns on the wideband filter circuit and turns off the narrowband filter circuit. After that, even if the frequency deviation changes and the switching element repeats opening and closing, the hold circuit holds only the first switching signal and does not switch with the second switching signal or lower, so it is necessary to switch to the broadband filter circuit. Hold on. When the reset circuit is activated by opening and closing the power switch, switching modes, switching channels, etc., the hold circuit is returned to its original state.

“Example” An example of the present invention will be described below with reference to FIG. Note that in FIG. 1, the same parts as in FIG. 2 are given the same reference numerals.

An average level detection circuit 36 consisting of a variable resistor for detecting the average level of the detection output is coupled to the output side of the detector 34, and the average level detection circuit 36 includes a low frequency amplifier circuit 37, a rectifier 38, A switching element 44 is coupled through a low-pass filter circuit 42 consisting of a resistor 39 and capacitors 40 and 41. The collector of this switching element 44 is coupled to the power supply terminal +E via a resistor 46 and to the hold circuit 5 via a resistor 50.
1 and its emitter is grounded. This hold circuit 51 includes two NOR gates 52 and 53.
One input side of the first NOR gate 52 is connected to a resistor 54,
55 to the power supply terminal +E, and is coupled to the reset circuit 57 via a resistor 56.
One input side of the second NOR gate 53 has a resistor 50
It is coupled to the collector of the switching element 44 via the switching element 44. The output side of the first NOR gate 52 is coupled to the other input side of the second NOR gate 53, and is connected to the switching diodes 29, 29 of the narrowband filter circuit 21 and the resistors 31, 3.
1, and the output side of the second NOR gate 53 is coupled to the other input side of the first NOR gate 52.
2 and 32. The reset circuit 57 includes a transistor 58, resistors 59, 60,
It consists of a capacitor 61, and the transistor 58
The collector of is coupled to the input side of the first NOR gate 52 via resistors 56 and 54, and the input terminal 62 receives a positive signal in response to opening/closing of the power switch, mode switching, channel switching of the antenna positioner, etc. is now being entered.

In the above configuration, the audio signal input to the input terminal 25 is amplified by the preamplifier circuit 26. Here, while there is no output from the detector 34,
Since the switching element 44 is off and the output appears on the output side of the first NOR gate 52 of the hold circuit 51, the narrowband switching diodes 29, 29 are on. In addition,
At this time, there is no output on the output side of the second NOR gate 53. Therefore, the signal amplified by the preamplifier circuit 26 is sent to the narrowband filter circuit 2 for the time being.
1, the signal is sent to the subsequent amplifier circuit 33, where it is amplified, and further detected by a detector 34 to produce an audio output.

The output of the wave detector 34 is detected by an average level detection circuit 36, amplified by a low frequency amplifier circuit 37, rectified by a rectifier 38, smoothed by a low pass filter circuit 42, and supplied to the base of a switching element 44.

Now, when the frequency deviation of the signal input to the input terminal 25 is small, the output of the detector 34 is small;
Because it is below the set value in the average level detection circuit 36,
This is below the threshold level of the switching element 44, the switching element 44 is turned off, and the narrowband filter circuit 21 continues to operate.

When the frequency deviation of the input signal is large,
Since it exceeds the set value of the average level detection circuit 36,
Switching element 44 is turned on. Then, the signal on the other input side of the second NOR gate 53 of the hold circuit 51 disappears, and this second NOR gate 5
The output appears in 3. Therefore, the switching diodes 29, 29 on the narrow band side are turned off, and the switching diodes 30, 29 on the wide band side are turned off instead.
30 turns on. Therefore, the input signal passes through the broadband filter circuit 23 and is then sent to the subsequent amplifier circuit 33.
sent to.

Next, once an output appears in the second NOR gate 53 of the hold circuit 51 with the first open/close signal of the switching element 44, no signal enters one input side of the second NOR gate 53, so the switching element Even if 44 repeatedly sends the second and subsequent open/close signals, it will not switch,
The hold circuit 51 is a broadband filter circuit 23
The switching diodes 30, 30 are kept on. In other words, even if an audio signal with a small frequency shift is subsequently input, the state remains switched to the broadband filter circuit 23 side.

Here, when a positive signal is input to the input terminal 62 due to the opening/closing of the power supply, mode switching, channel switching, etc., the transistor 58 of the reset circuit 57 is turned on, and the first NOR gate 5 of the hold circuit 51 is turned on.
Since one input side of NOR gate 2 is grounded, an output appears from this first NOR gate 52, and no output from the second NOR gate 53. Therefore, it is switched to the narrowband filter circuit 21 side.

"Effects of the Invention" Since the present invention is configured as described above, in satellite broadcasting or FM broadcasting, when a received signal has a large frequency shift, the narrowband filter circuit is automatically switched to the wideband filter circuit. Once switched to the broadband filter circuit,
Even if the frequency deviation changes, it does not switch each time. Therefore, the generation of noise at the time of switching is eliminated, the audible discomfort caused by the switching of the filter circuit is eliminated, and furthermore, the occurrence of audio distortion due to the rising signal at the time of switching can be prevented.

[Brief explanation of drawings]

FIG. 1 is an electric circuit diagram showing an embodiment of the filter switching circuit according to the present invention, FIG. 2 is a conventional circuit diagram,
FIG. 3 is an overall block diagram of a satellite broadcasting television receiver. 1...Reflector, 2...Antenna, 3...Low noise amplifier and down converter, 4...Receiver, 5...Monitor TV, 6...Audio device, 7...Antenna positioner, 8...Audio amplifier, 9, 10...Speaker, 11
...Satellite, 12...Actuator, 20...Selector switch, 21...Narrowband filter circuit, 22...Contact, 23...Broadband filter circuit, 24...Contact,
25...Input terminal, 26...Preamplifier circuit, 27,2
8...Chiyoke coil for electronic switching, 29,
30...Switching diode, 31, 32...
Resistor, 33... Post-stage amplifier circuit, 34... Detector, 35
...Output terminal, 36...Average level detection circuit, 37...
Low frequency amplifier circuit, 38... Rectifier, 39... Resistor, 4
0, 41... Capacitor, 42... Low pass filter circuit, 44... Switching element, 46, 50, 5
4, 55, 56, 59, 60...Resistor, 51...Hold circuit, 52, 53...NOR gate, 57...Reset circuit, 58...Transistor, 61...Capacitor.

Claims (1)

[Claims] 1. After the audio intermediate frequency signal is amplified by a preamplifier circuit, it is passed through either a narrowband filter circuit or a wideband filter circuit, and then a subsequent stage amplifier circuit and a detector. an average level detection circuit coupled to the output side of the detector to detect the average level of the detected output; and an average level detection circuit coupled to the average level detection circuit to detect the average level output signal. a rectifier that rectifies; a switching element that is coupled to the rectifier and opens and closes depending on whether the average level is greater than a set value level; A filter switching circuit for an intermediate frequency amplifier circuit, comprising a hold circuit for cutting off a narrow band filter circuit and activating a wide band filter circuit, and a reset circuit for resetting the hold circuit. 2. The hold circuit consists of a flip-flop circuit using two NOR gates.
A filter switching circuit for the intermediate frequency amplification circuit described in . 3. The intermediate frequency amplification circuit according to claim 1, wherein the switching element is a transistor that turns on when the average level of the detected output is equal to or higher than a set value, and inverts the output of the hold circuit with the turned-on first signal. filter switching circuit. 4. A filter switching circuit for an intermediate frequency amplification circuit according to claim 1, wherein the average level detection circuit comprises a variable resistor.