JPH0257379B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a satellite television receiver.

“Prior Art” Generally, satellite television receivers in the United States are
As shown in the figure, when a parabolic antenna 1 receives a signal of 3.7 to 4.2 GHz from a satellite, this signal is amplified by a low noise amplifier 2, and converted into an intermediate frequency signal (IF) of 430 to 930 MHz by a down converter 3. Furthermore, tuner 4 has a center frequency of 70MHz.
get the signal. IF amplifier 5, limiter 6,
The signal is sent to the video amplifier 8 via the FM demodulation circuit 7. The video signal further passes through a de-emphasis circuit 9, a clamp circuit 10, and a video amplifier 11, and is sent from a video output terminal 12 to a monitor TV. 5~8.5MHz
The audio signal is passed through the subcarrier filter 13,
The signal is sent from the audio output terminal 18 to the speaker via the mixer 14, bandpass filter 15, demodulation circuit 16, and audio amplifier 17. other TV
RF output terminal 2 from modulator 19 to receiver
Sent through 0.

Further, from the IF amplifier 5 to the AGC circuit 21,
The AGC signal is sent to tuner 1 via AGC amplifier 22.
Sent to 4. The output of the FM demodulation circuit 7 is the AGC
The signal is sent to the CPU 24 via the comparison circuit 23. this
The CPU 24 includes a selector 25 for horizontal polarization (H) and vertical polarization (V) on the operation panel, and a selector 25 for each satellite.
Since there are 24 channels, the selector 26 and the drive circuit 27 of the light emitting element circuit are connected, and the CPU 2
4 is connected to a pulse generation circuit 28 and a SKEW controller 29, and the CPU 24 is further connected to the tuner 4 via a prescaler 30, and antenna control, channel switching, etc. are performed by operating various selectors 25 and 26.

However, the conventional tuner circuit has the following problems.

(1) It was equipped with one stage of bandpass filter, and an additional bandpass filter was inserted after the tuner circuit.

However, for satellite TV, the center frequency of the intermediate frequency is 70MHz, and the frequencies on both sides are around ±20MHz.
Since the bandwidth is extremely wide compared to general television broadcasting, in order to prevent overlap with adjacent channels,
It is necessary to widen the flat part of the filter circuit and make the skirt part sharp. Therefore, conventionally, a double-tuned bandpass filter circuit consisting of a coil, a capacitor, and a resistor was required between an amplifier circuit mainly composed of transistors.

(2) The output waveform of the 70MHz second frequency signal has an intermediate frequency of 70MHz and a frequency bandwidth of at least ±10MHz on both sides.

(3) When displaying the magnitude of a signal level with a level meter, the AGC voltage was extracted from an intermediate frequency amplifier circuit, amplified, and caused to swing the meter.

(4) There are multiple audio signal channels that do not include video signals between each video signal channel, but when receiving these audio signals,
Frequently used audio signal channels are preset, and other audio signal channels are selectively tuned using variable resistors. However, conventionally, circuits for this purpose have a preset circuit consisting of a semi-fixed resistor and a fixed resistor, and an arbitrary channel selection circuit consisting of a variable resistor and a fixed resistor between the power supply terminal (+B) and the ground. These semi-fixed resistors and variable resistors were connected in parallel, and a changeover switch was interposed between them, and the output terminal was coupled to a variable capacitance diode of a local oscillation circuit of the tuner circuit.

(5) In local oscillation circuits, the relationship between oscillation frequency (channel) and tuning voltage is not linear; as the number of channels increases, the change in frequency (Δf) relative to the change in tuning voltage (ΔV) becomes smaller. . When made to correspond to the resistance volume for channel selection, especially when the variable range is wide as in satellite broadcast television, the spacing is wide at the top of the channel and narrow at the bottom. In order to make this constant, a method is used to correct this by applying an AFT voltage to the tuning circuit, but conventionally, when a 430 to 930 MHz signal is input to the tuner circuit, an intermediate frequency amplifier circuit changes the center frequency to 70 MHz. Obtain a signal, use a limiter circuit to keep the amplitude constant, and then
It is demodulated by the FM detection circuit and sent to the video output terminal and audio output terminal via the video amplification circuit. Also,
The S-curve of the FM detection circuit is an integral circuit,
It is sent to the variable capacitance diode of the local oscillation circuit of the tuner circuit via the AFT circuit and the amplifier circuit, but at the same time, the tuning voltage varied by the variable resistor of the channel selection circuit is also sent to the tuner circuit via the amplifier circuit. If the intermediate frequency shifts at this time, the output from the AFT circuit changes the local oscillation frequency of the tuner circuit to return the center frequency to the center.

"Problems to be Solved by the Invention" (1) First Problem When a filter circuit is formed outside the tuner circuit as in the past, interference waves are mixed in by the coil of this filter circuit, and the frequency characteristics If the filter circuit changes and the filter circuit is inserted at a remote location, there are problems such as difficulty in adjustment.

(2) Second problem There is an area where microwave signals (M ₁ ) (M ₂ ) of 60 MHz and 80 MHz exist just ±10 MHz away from 70 MHz, and this microwave signal (M ₁ ) ( There was a problem that _M2 ) became noise and mixed into the TV signal.

(3) Third problem In tuner circuits using FETs (field effect transistors), the AGC voltage and gain reduction characteristics initially have a steep slope, but gradually become gentler. When this is caused to swing with a level meter, there is a problem in that there is a large difference between the change in signal level and the change in the swing of the level meter.

(4) Fourth problem In such a conventional circuit configuration, the preset voltage is output by connecting the changeover switch 9 to one terminal 11, and the preset voltage is output by connecting the changeover switch 9 to the other contact 12. By connecting the variable resistor 5 and varying the variable resistor 5, the tuning voltage of all channels can be output. Therefore, the switch 9 must be used to switch to either contact 11 or 12 each time, and the semi-fixed resistor 1, variable resistor 5, and switch 9 must be constructed as independent components. There was a problem.

(5) Fifth problem In the conventional circuit, the constant output of the AFT circuit was directly applied to the tuner circuit as the AFT superimposition amount, so the AFT sensitivity was determined by the frequency (channel).
There was a problem that as the value increased, the value decreased.
Therefore, in a channel selection circuit with a wide variable range, there was a problem in that the AFT output became poor in the upper channels with high frequencies.

In addition, the AFT circuit side is low impedance,
Since the channel selection circuit side is high impedance, a buffer amplifier circuit must be interposed in the middle, making the circuit complicated.

"Means for Solving the Problems" The present invention has been made to solve all of the various problems mentioned above. In a tuner circuit that converts the frequency of a signal into a signal and further obtains a predetermined bandwidth using a filter circuit, the filter circuit further includes a second intermediate frequency bandpass filter circuit in addition to the first intermediate frequency bandpass filter circuit. A filter circuit is provided, and these bandpass filter circuits are housed together with the tuner circuit in a sheet metal tuner case, and the microwave signal within a certain band is removed from the intermediate frequency signal at a stage subsequent to the intermediate frequency amplifier. A trap circuit is provided on the output side of the AGC amplifier circuit for
A transistor for polarity reversal is connected, a high resistance for base current limiting is inserted into the base circuit of this transistor, a level meter is connected to the collector circuit of this transistor, and a specific channel is connected to a variable capacitance diode for tuning. A high-impedance preset circuit for selecting an arbitrary channel is directly connected, and a low-impedance arbitrary channel selection circuit for selecting an arbitrary channel is connected via a switch. A channel selection circuit mainly consisting of a variable resistor is directly inserted between the AFT circuit and the local oscillation circuit so as to provide a characteristic that increases the frequency.

“Example” An example of the present invention will be described below based on the drawings.

Figure 2 is for solving the first problem, 31a is a 430~930MHz signal input terminal, 31
3 is a high frequency amplifier circuit, 32 is a filter circuit, 33 is a local oscillation circuit, 34 is a mixing circuit, and 5 is an IF amplifier.

The present invention is characterized in that a second intermediate frequency band pass filter circuit 37 is inserted next to the IF amplifier 5 via a first intermediate frequency band pass filter circuit 35 and an amplifier circuit 36, and an emitter follower circuit 37 is inserted next to the IF amplifier 5. output terminal 3 via the amplifier circuit 38 of
It is combined with 9. In addition, Chuyuna 4
All parts are housed in a sheet metal case.

With this configuration, the first and second bandpass filter circuits 35 and 37 can provide a wider and sharper frequency characteristic in the skirt portion.

Figure 3 shows a diagram for solving the second problem, where 40 is the input terminal for the first intermediate frequency signal of 430 to 930 MHz, 4 is the tuner, 5 is the IF amplifier, 41 is the coupling capacitor, and 42 is the micro A wave trap circuit, 7 an FM demodulation circuit, and 43 an output terminal.

The trap circuit 42 consists of a lower microwave removal trap circuit 44 that removes 60MHz microwaves and an upper microwave removal trap circuit 45 that removes 80MHz microwaves.
4 and 45 each constitute a so-called bridged T type with a coil, a capacitor, and a resistor. Furthermore, switching diodes are connected in parallel to the trap circuits 44 and 45, and
A power supply (+B) is coupled to the anode side of one diode through a resistor, a capacitor, and a switch, and a reverse bias power supply (+B) is coupled to the cathode side of the other diode through a resistor.

In the above configuration, the satellite broadcast television signal of 3.7 to 4.2 GHz received by the antenna is converted into a first intermediate frequency signal of 430 to 930 MHz by the down converter, which is inputted to the tuner 4 via the input terminal 40, and then transmitted to the intermediate frequency signal. A second intermediate frequency signal with a frequency of 70 MHz is obtained. This second intermediate frequency signal is amplified by the IF amplifier 5 and input to the trap circuit 42.

Here, if 60MHz and 80MHz microwaves are not present, turn on the switch. Then, the potential on the anode side of one diode (V ₁ )
becomes higher than the potential (V ₂ ) on the other catode side, and the two trap circuits 44 and 45 are both short-circuited by the two diodes. Therefore, the output of the IF amplifier 5 passes through the trap circuit 42 as it is and is sent to the FM demodulation circuit 7.

When 60MHz and 80MHz microwaves are present, when the switch is turned off, a reverse bias is applied to the two diodes, turning them off.
Therefore, the 60 MHz and 80 MHz portions of the output of the IF amplifier 5 are trapped by these trap circuits 44 and 45, the 60 MHz and 80 MHz microwaves are removed, and this output is sent to the next stage.

Figure 4 is for solving the third problem, 40 is a signal input terminal of 430 to 930MHz from a communication satellite, and this input terminal 40 is connected to tuner 4, IF
It is coupled to an FM demodulation circuit 7 and an output terminal 43 via an amplifier 5. Further, an AGC (automatic gain control) circuit 21 is coupled to the output side of the IF amplifier 5. The output side of this AGC circuit 21 is coupled to the tuner 4 via an AGC amplifier 22.

The AGC amplifier 22 is composed of an NPN transistor and a resistor, and the collector of this transistor is formed with a PNP transistor for polarity reversal, a voltage dividing resistor, a high resistor for correcting the rise characteristic, a collector resistor, and an emitter resistor. A drive circuit 47 for driving the level meter is coupled thereto.

In the above circuit configuration, the input terminal 40
tuner 4 when a signal of 430~930MHz is input.
Then, it is converted into a first intermediate frequency signal of 70 MHz, and this is amplified by the IF amplifier 5. Based on this amplified intermediate frequency signal, the AGC circuit 21
The AGC signal is detected by the AGC amplifier 22, and is fed back to the tuner 4, where the gain is automatically controlled. Since the AGC signal in the loop of the AGC amplifier 22 has non-linear characteristics, the polarity of this signal is reversed by the transistor. Although this inverted signal does not have linear characteristics, a high resistance is inserted into the base of the transistor, so that the rise is made gentler, and the overall characteristics are corrected to linear. The starting point of the level meter 46 is set by the dividing ratio of the voltage dividing resistor.
The linear characteristics obtained in this way are supplied to the level meter 46, so that the level meter 4
6 will display a value proportional to the signal level.

In the embodiments described above, level meter 46 may include both analog and digital displays.

Figure 5 is for solving the fourth problem.A high impedance semi-fixed resistor 48 and fixed resistors 49 and 50 are connected between the power supply terminal (+B) and the ground.
A preset circuit 51 is connected in series with a low impedance variable resistor 52.
An arbitrary channel selection circuit 55 is connected thereto, in which a fixed resistor 53 and 54 are connected in series.

The movable piece 56 of the semi-fixed resistor 48 includes a variable capacitance diode 57, a coil 58, a capacitor 59,
It is directly coupled to a local oscillation circuit 61 consisting of a resistor 60 and the like. Further, the variable resistor 52 is coupled to the local oscillation circuit 61 via a switch 63 integrated with the movable piece 62 thereof.

In such a configuration, when the switch 63 is off, the high impedance preset circuit 5
1 is always connected to the local oscillation circuit 61, the voltage determined by the preset circuit 51 is applied to the variable capacitance diode 57, and a preset, for example, frequently used specific channel is selected.

When the switch 63 is turned on, the low impedance arbitrary channel selection circuit 55 is connected, so the voltage determined by the variable resistor 52 and fixed resistors 53 and 54 is almost unaffected by the high impedance preset circuit 51. It is applied to the local oscillation circuit 61. Therefore, this variable resistor 5
By varying 2, any channel can be selected.

Figure 6 was made to solve the fifth problem, where 40 is an input terminal, 4 is a tuner, and 5 is a
IF amplifier, 6 is limiter, 7 is FM demodulation circuit, 8
is a video amplifier, 64 is a video output terminal, and 65 is an audio output terminal.

The feature of the present invention is that the FM demodulation circuit 7
and the tuner 4 local oscillation circuit.
Channel selection circuit 6 in series with AFT circuit 66
7 is inserted. For more details,
The AFT circuit 66 includes a variable resistor 69 for adjusting the voltage at the output point 68 to reach a predetermined value, a smoothing circuit 70 consisting of a low-pass filter,
It consists of an amplifier circuit 71 and the like, and an output point 68 of this amplifier circuit 71 is directly coupled to a channel selection circuit 67 consisting of a variable resistor, a fixed resistor, etc.

In the above configuration, the output voltage of the FM demodulation circuit 7 is supplied to the AFT circuit 66, and the output voltage of the AFT circuit 66 is varied by the variable resistor of the channel selection circuit 67 to obtain an appropriate tuning voltage and to adjust the frequency. As the value increases, an output voltage that gradually increases the amount of AFT superimposition is obtained at the midpoint of the variable resistor, and is applied as a reverse voltage to the variable capacitance diode of the local oscillation circuit of the tuner 4. As a result, AFT sensitivity remains flat.

"Effects of the Invention" Since the present invention is configured as described above, it has the following effects.

(1) Since the first and second bandpass filter circuits are integrated inside the tuner circuit, adjustment can be done in one place.

Since the coil of the filter circuit is housed in a sheet metal case, there is no noise or other contamination, and the characteristics do not change.

Since the flat part of the frequency characteristic can be widened and the skirt part that overlaps with the adjacent part can be sharpened, it is ideal for satellite broadcast television with a wide frequency band.

There is no need to insert a filter circuit that creates frequency characteristics after the tuner circuit.

(2) When microwaves are present within the band of the second intermediate frequency signal in satellite broadcast television, they can be removed by a trap circuit to prevent noise from entering. In addition, if the trap circuit is short-circuited using a switch when no microwave is present, the bandwidth can be sufficiently widened and the image quality can be improved.
Sound quality can be improved.

(3) The AGC voltage is corrected to have linear characteristics, so the level meter can correctly display changes in signal level.

(4) The changeover switch for switching between the preset circuit and the arbitrary channel selection circuit can be integrated with the variable resistor of the arbitrary channel selection circuit instead of being independent, improving operability and reducing the number of parts. can be provided at low cost.

(5) Even in a tuner circuit with a wide variable frequency range, the AFT response remains flat over the entire range. Also, AFT
Since the channel selection variable resistor is inserted directly into the circuit, there is no need for a conventional buffer amplifier circuit, simplifying the circuit configuration.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of a satellite broadcast television receiver according to the present invention, FIG. 2 is a block diagram of a tuner, and FIG. 3 is an electric circuit diagram showing a trap circuit of a satellite broadcast television receiver according to the present invention. , 4th
FIG. 5 is an electric circuit diagram showing an embodiment of the level meter driving circuit according to the present invention, FIG. 5 is an electric circuit diagram showing an embodiment of the tuning voltage control circuit according to the present invention, and FIG. FIG. 2 is a block diagram showing one embodiment of the circuit. 4... tuner, 35... first band pass filter circuit, 37... second band pass filter circuit, 5... IF amplifier, 42... trap circuit,
7...FM demodulation circuit, 44...Lower microwave removal trap circuit, 45...Upper microwave removal trap circuit, 21...
AGC circuit, 22...AGC amplifier, 46...Level meter, 48...Semi-fixed resistor, 51...Preset circuit, 55...Arbitrary channel selection circuit, 5
7... Variable capacitance diode, 67... Channel selection circuit, 66... AFT circuit, 68... Output point.

Claims (1)

[Claims] 1. In a tuner circuit that amplifies a satellite broadcast television signal inputted from an input terminal, converts the frequency of the signal into an intermediate frequency signal, and further obtains a predetermined bandwidth with a filter circuit, the filter circuit is a first In addition to the band-pass filter circuit for intermediate frequency, a second band-pass filter circuit for intermediate frequency is further provided, and these band-pass filter circuits are housed together with the tuner circuit in a sheet metal tuner case, and the band-pass filter circuit for intermediate frequency is A trap circuit is installed after the amplifier to remove microwave signals within a certain band from the intermediate frequency signal.
A transistor for polarity reversal is connected to the output side of the AGC amplifier circuit, a high resistor for base current limitation is inserted in the base circuit of this transistor, a level meter is connected to the collector circuit of this transistor, and a level meter is connected to the collector circuit of this transistor for tuning. A high impedance preset circuit for selecting a specific channel is directly connected to the variable capacitance diode, and a low impedance arbitrary channel selection circuit for selecting an arbitrary channel is coupled via a switch.
The AFT circuit has this characteristic that the amount of AFT superimposition gradually increases as the frequency increases.
A satellite broadcast television receiver characterized in that a channel selection circuit mainly consisting of a variable resistor is directly inserted between an AFT circuit and a local oscillation circuit.