JPH11266407A - Tuner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress disturbance of a peaking circuit in a reception circuit block not in operation onto a reception circuit block in operation in the case of receiving a program while dividing a frequency band into a plurality of reception circuit blocks. SOLUTION: The tuner 31 uses a band changeover switched 35 to select an output of a power supply 34 thereby selectively activating a UHF band block 32 or a VHF band block 33. A loss correction circuit 44 (45) is a parallel resonance circuit consisting of a coil 46 (56) and a capacitor 47 (57) and acts like a peaking circuit to correct a loss within a reception frequency band. When the VHF band block 33 is in operation, the loss correction circuit 45 in the UHF band block 32 does not act like a peaking circuit because a switching circuit 48 is open so as to control extraction of a resonance frequency component with a resonance frequency causing image disturbance to the reception channel of the VHF band block 33.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tuner for extracting a signal of a desired frequency component from radio waves in a wide frequency band.

[0002]

2. Description of the Related Art Conventionally, a general television broadcast receiver has a tuner 1 as shown in FIG. The tuner 1 includes two blocks, a UHF band block 2 and a VHF band block 3. In the UHF and VHF frequency bands, predetermined frequencies are respectively assigned as channels, and television broadcasting is performed. In the tuner 1 having a two-block configuration, the entire reception channel is divided into two parts, and the high band is divided into blocks 2 for the VHF band,
The low band is selected by the VHF band block 3, respectively. UHF band block 2 and V
The HF band blocks 3 do not operate at the same time, and only one of them is supplied with operating power from the power supply 4 via the band changeover switch 5. Broadcast radio waves are input from the antenna to the UHF band block 2 and the VHF band block 3 via the antenna terminal 6. UH
Block 2 for F band and Block 3 for VHF band
Within, the received signal is converted to a common intermediate frequency,
After being further amplified by the intermediate frequency amplifier 7, it is output to an intermediate frequency output terminal 9 via a low-pass filter 8 (hereinafter sometimes abbreviated as “LPF”). From the intermediate frequency output signal from the intermediate frequency output terminal 9, a video signal, an audio signal, various synchronization signals, and the like are extracted, and a television broadcast is received.

A signal input from the antenna terminal 6 to the UHF band block 2 and the VHF band block 3 first includes a band-pass filter (hereinafter referred to as a "band-pass filter") including a variable capacitance diode and having a variable center frequency in a pass frequency band. A signal of a desired channel is selected by the variable band-pass filters 10 and 20 which may be abbreviated as “BPF”, amplified by high frequency amplifiers (hereinafter sometimes abbreviated as “RF AMP”) 11 and 21 and re-amplified. The signals are selected by the variable band-pass filters 12 and 22 and input to mixer circuits (hereinafter sometimes abbreviated as “MIX”) 13 and 23, respectively. Mixer circuit 1
Signals from local oscillators (hereinafter sometimes abbreviated as “OSC”) 14 and 24 are also input to 3, 23, and mixed with the received signals and converted to an intermediate frequency by a superheterodyne method.

The variable band-pass filters 10 and 2 of the UHF band block 2 and the VHF band block 3
0; 12, 22 are configured to be able to tune to a wide range of frequencies, but it is a well-known fact that the loss in the low band of each band increases. The loss correction circuits 15 and 25 lift the low-frequency part of the frequency characteristic of the gain of each band indicated by the broken line, as indicated by the solid line in FIG.
Correct the loss. The loss correction circuits 15 and 25 in FIG.
A frequency is a fixed resonance circuit in which the coils 16 and 26 and the capacitors 17 and 27 are connected in parallel. By inserting such a peaking circuit into each block,
Loss correction can be performed by raising the low-frequency part of the reception frequency band of the block.

The prior art regarding the loss correction circuits 15 and 25 is disclosed, for example, in Japanese Patent Application Laid-Open No. 7-303056. In this prior art, an inductor that forms a resonance circuit with the output capacitance of the high-frequency amplifier circuit is inserted at the output side of the high-frequency amplifier circuit, and the gain sensor in the band is corrected by the peaking action to perform loss correction. I have.

[0006] In a tuner 1 as shown in FIG.
Operating power BU, BV via the band changeover switch 5
Is supplied, one of the UHF band block 2 or the VHF band block 3 is operated, and the other is not operated. In the inactive band block, the high-frequency amplifiers 11 and 21, the mixer circuits 13 and 23, and the local oscillators 14 and 24 are inactive. Since the UHF band block 2 and the VHF band block 3 perform frequency conversion by the superheterodyne method, the oscillation frequencies of the local oscillators 14 and 24 are selected by the variable band-pass filters 10 and 20; ,
It is separated from the reception frequency amplified at 21 by the intermediate frequency. In the superheterodyne method, for example, when the local oscillation frequency is set to be higher than the reception frequency by the intermediate frequency, a signal having a frequency higher than the local oscillation frequency by the intermediate frequency is also converted to the intermediate frequency. is there. Variable bandpass filter 1
0, 20; 12, 22 are adjusted so as to greatly attenuate the image frequency signal in order to suppress image disturbance. However, the loss correction circuit 15,
25, the resonance frequency of the peaking circuit inserted in the UHF band block 2 and the VHF band block 3 may have a frequency relationship that causes image interference in a certain channel in the reception band of each band block.

FIG. 8 shows a circuit in which a band changeover switch 29 is inserted at a portion branched from the antenna terminal 6 to the UHF band block 2 and the VHF band block 3 so that a signal is not inputted to a non-operating circuit block. 2 shows a configuration of a tuner 30 that shuts off the noise. The tuner 30 is basically the same as the tuner 1 in FIG. 6 except for the band changeover switch 29. The band switch 29 connects the antenna terminal 6 to the input side of the variable bandpass filter 10 of the UHF band block 2 when receiving UHF, and connects the antenna terminal 6 to the variable bandpass filter of the VHF band block 3 when receiving VHF. 20 to be connected to the input side. The band changeover switch 29
In conjunction with the band changeover switch 5 for switching the power supply 4,
At the time of UHF operation, the VHF band block 3 stores VHF
During operation, no signal is input to the UHF band block 2. The band changeover switch 29 is
From the non-operation side circuit block to the operation side circuit block,
Prevents sneak of interference frequency components via input signal patterns.

[0008]

When the resonance frequencies of the above-described loss correction circuits 15 and 25 have an interference frequency relationship with image interference in a reception frequency band in another operation band, the loss correction circuit 15 or 25 has a problem. , 25 are not operated, the resonance frequency components are taken out by the resonance circuits of the loss correction circuits 15, 25, and the frequency components are extracted in the printed wiring board on which the tuners 1, 30 are mounted. This causes the signal to wrap around the operating circuit block, causing a significant deterioration in interference characteristics such as image interference cost.
The interference frequency component does not necessarily pass through a regular circuit in the pattern layout on the printed wiring board, but flows from a power supply line, a ground pattern, or the like, and flows from a non-operating circuit block to an operating circuit block. For this reason, as shown in FIG. 8, even if the band changeover switch 29 is inserted on the input side, the deterioration of the image interference characteristic is inevitable due to the sneak from the power supply line or the ground pattern.

In recent years, the tuners 1 and 30 have been downsized, and the components and printed wiring board patterns have become very dense. For this reason, the component layout and pattern layout pattern are also considerably restricted, and it is difficult for power lines and grounds, which should be low impedance, to reduce the impedance at high frequencies, and the high impedance is floating. It is the current situation. Therefore, even if the circuit is cut off using the band changeover switch 29 shown in FIG. 8, it is more and more impossible to completely shut off due to the sneaking from the power supply line or the ground pattern. On the other hand, as the number of channels increases rapidly, it is required to further improve the interference characteristics.

An object of the present invention is to provide a tuner for receiving a reception frequency band by dividing the reception frequency band into a plurality of blocks, and to suppress a peaking circuit in a non-operating circuit block from obstructing reception of an operating circuit block. It is to provide a tuner that can perform.

[0011]

According to the present invention, there is provided a tuner which divides an entire receiving frequency band into a plurality of partial frequency bands and has a dedicated receiving circuit block for each partial frequency band. And a selection circuit for supplying operating power only to the selected reception circuit block, and a selection circuit provided for each reception circuit block to correct a loss of the reception circuit block in a partial reception frequency band. The peaking circuit is inserted into a peaking circuit and a peaking circuit for each receiving circuit block, and the peaking circuit operates when receiving power is not supplied from the selecting circuit so that the peaking circuit can operate when receiving power is supplied from the selecting circuit. A tuner characterized by including a switching circuit that switches each of them so as to be impossible.

According to the present invention, the entire receiving frequency band of the tuner is divided into a plurality of partial frequency bands, and a dedicated receiving circuit block is provided for each partial frequency band. The selecting circuit selects one of the plurality of receiving circuit blocks,
The operating power is supplied only to the selected receiving circuit block. Each receiving circuit block is not supplied with the operating power so that the peaking circuit can operate when the operating power is supplied from the peaking circuit for correcting the loss in the partial receiving frequency band and the selecting circuit. Sometimes a switching circuit for switching each is included so that the peaking circuit is inoperable. Since the peaking circuit becomes operable only when the receiving circuit block is operated by receiving the supply of the operating power, the peaking circuit provided in the receiving circuit block to which the operating power is not supplied from the selection circuit becomes inoperable. In addition, it is possible to prevent the circuit block that is in operation from causing a disturbance.

In the present invention, the peaking circuit includes a resonance circuit, and the switching circuit performs the switching by conducting or blocking at least a part of the resonance circuit.

According to the present invention, the peaking circuit includes a resonance circuit and corrects a loss near the resonance frequency. Since the switching circuit conducts or cuts off at least a part of the resonance circuit and turns on or cut off at least a part of the resonance circuit of the peaking circuit, the switching circuit is turned on when the switching circuit is connected in series to the resonance circuit. In this case, the operation as a peaking circuit becomes possible, and when the circuit is cut off, the operation as the peaking circuit becomes impossible.

Further, in the present invention, each of the receiving circuit blocks includes:
A band-pass filter that selectively filters a partial frequency band received by the receiving circuit block; and a high-frequency amplifier circuit that amplifies a reception frequency signal that is selectively filtered by the band-pass filter, wherein the resonance circuit includes the high-frequency amplifier circuit. And is formed by utilizing the input capacitance of the high-frequency amplifier circuit as a resonance capacitance.

According to the present invention, the resonance circuit forming the peaking circuit is connected between the band-pass filter for filtering a partial frequency band of the receiving circuit block and the input side of the high-frequency amplifier circuit. The input capacitance is used as the resonance capacitance. The number of components constituting the peaking circuit for loss correction can be reduced, and the cost can be reduced.

[0017]

FIG. 1 shows a schematic configuration of a tuner 31 according to an embodiment of the present invention. The tuner 31 of the present embodiment also has a tuner 1 as shown in FIGS.
Similarly to 30, it can receive UHF and VHF band television broadcasts, and has a UHF band block 32 and a VHF band block 33. The operation of the UHF band block 32 and the operation of the VHF band block 33 are switched by switching the operating power BU, BV from the power supply 34 with the band switch 35 and supplying only one of them. The radio wave of the television broadcast to be received is input from an antenna to an antenna terminal 36, and is converted into a superheterodyne-type intermediate frequency by a UHF band block 32 and a VHF band block 33, respectively. Filter 38
Through the intermediate frequency output terminal 39.

In the UHF band block 32, a variable band-pass filter 40 on the input side, a high-frequency amplifier 41,
Output side variable bandpass filter 42, mixer circuit 4
3, a local oscillator 44 and a loss correction circuit 45 are included. The loss correction circuit 45 includes a parallel resonance circuit including a coil 46 and a capacitor 47, and a switching circuit 48.

A band switch 49 is provided between the antenna terminal 36 and the input side of the UHF band block 32 and the VHF band block 33. The band changeover switch 49 operates in conjunction with the band changeover switch 35 on the power supply 34 side, and operates the UHF band block 32.
When the operating power BU is supplied to the antenna terminal 3
6 and the UHF band block 32 are connected, and the connection between the antenna terminal 36 and the VHF band block 33 is cut off. When the band changeover switch 35 supplies the operating power BV to the VHF band block 33, the band changeover switch 49 connects between the antenna terminal 36 and the VHF band block 33, and connects the antenna terminal 36 to the UH band.
The connection with the F-band block 32 is cut off.

In the VHF band block 33, a variable band-pass filter 50, a high-frequency amplifier 51, a variable band-pass filter 52, a mixer circuit 53, a local oscillator 5
4, a loss correction circuit 55 is included, and the loss correction circuit 55 includes a coil 56, a capacitor 57, and a switching circuit 5.
8 is included. The components inside the VHF band block 33 are the components of the UHF band block 32, and the first digit of the reference numeral is basically equivalent to the same component.

The loss correction circuits 45 and 55 of the present embodiment
The parallel resonance circuit of the coils 46 and 56 and the capacitors 47 and 57 is inserted between the variable band-pass filters 40 and 50 on the input side and the high-frequency amplifiers 41 and 51 by the switching circuits 48 and 58 or is not inserted. Switch. When a parallel resonance circuit including the coils 46 and 56 and the capacitors 47 and 57 is inserted, the impedance near the resonance frequency increases, and the level of the signal input to the high-frequency amplifiers 41 and 51 is increased.
50; 42, 52 can be compensated for.
The switching circuits 48 and 58 operate in conjunction with the band changeover switch 35 on the power supply 34 side, and operate powers BU and B
Only when V is supplied, the operating power BU, B
It shuts off when V is not supplied.

FIG. 2 shows a more detailed configuration of the loss correction circuits 45 and 55 of FIG. Switching operations of the switching circuits 48 and 58 are performed by switching diodes 60 and 70, respectively. Switching diode 6
The anode sides of 0 and 70 are connected to the parallel resonance circuit formed by the coils 46 and 56 and the capacitors 47 and 57, and the positive voltage BU of the operating power supplied from the band switch 35 via the resistors 61 and 71. , BV side. Switching diode 60,7
The cathode side of 0 is connected to operating powers BU and BV supplied from the band changeover switch 35 via resistors 62 and 72, respectively. Switching diode 6
The cathode sides of 0 and 70 are AC grounded to ground via capacitors 63 and 73 for cutting direct current (DC).

When the band changeover switch 35 supplies a positive power supply voltage to one of the positive voltage BU of the operating power and the positive voltage BV of the operating power, it sequentially turns to one of the switching diodes 60 and 70. A bias voltage in the direction is applied, and the device becomes conductive. The other switching diodes 60 and 70 are biased in the reverse direction and become non-conductive. Therefore, the coils 46 and 56 and the capacitor 4
One of the parallel resonance circuits formed by 7 and 57 is grounded and the other floats from the ground. Loss correction circuits 45, 5 in which a parallel resonance circuit is installed on the ground
5 is capable of operating as a peaking circuit, and a loss correction circuit 45, in which the parallel resonance circuit is floating from the ground.
Reference numeral 55 indicates a state in which operation as a peaking circuit is disabled.

FIG. 3 shows the concept of suppressing image disturbance according to the present embodiment. For example, it is assumed that the VHF band block 33 in FIG. 1 can receive the partial frequency band from the frequency f1 to f2, and the UHF band block 32 can receive the partial frequency band from the frequency f2 to f3. When the VHF band block 33 for receiving the VHF band, which is the lower partial frequency band, is operating, the desired reception channel frequency is set to fa. The variable bandpass filters 50 and 52 in FIG. 1 are tuned to the frequency of fa. The local oscillator 54 oscillates at the frequency fb, and the difference between the frequencies fa and fb is the intermediate frequency. At this time, if a signal having a frequency fc higher than the oscillation frequency fb of the local oscillator 54 by an intermediate frequency is received, image disturbance occurs. The signal of the frequency fc input from the antenna terminal 36 is supplied to the variable bandpass filters 50 and 5.
2, the characteristics of the variable band-pass filters 50 and 52 are set so that the image is not disturbed. However, if the resonance frequency of the resonance circuit formed by the coil 46 and the capacitor 47 of the loss correction circuit 45 in the non-operating UHF band block 32 is fc, the relationship between the image reception frequency and the reception channel of the frequency fa depends on the reception frequency. Become. As indicated by the broken line in FIG. 3, the resonance frequency component selected by the loss correction circuit 45 is supplied to the VHF band block 3 via a power supply line or a ground pattern.
3 may cause image disturbance. In this embodiment, the conduction between the parallel resonance circuit of the coil 46 and the capacitor 57 and the ground is cut off by the switching circuit 48, so that the resonance circuit of the coil 46 and the capacitor 47 generates a resonance frequency component that may cause image disturbance. The level of a signal that may cause image disturbance is reduced as shown by a solid line in FIG.

Table 1 below shows, for UHF and VHF receiving channels for receiving television broadcasting in the United States (USA), the frequency as shown in FIG. 3 by the embodiment and the conventional circuit as shown in FIG. 6 shows characteristic comparison data of image disturbing costs in relations. From Table 1, it can be seen that the tuner 31 of the present embodiment has a significantly improved image interference ratio compared to the conventional tuner 30.

[0026]

[Table 1]

FIG. 4 shows a schematic configuration of a tuner 81 according to another embodiment of the present invention. Tuner 8 of the present embodiment
1 is substantially equivalent to the tuner 31 of the embodiment in FIG. 1, and corresponding portions are denoted by the same reference numerals and redundant description is omitted. Tuner 81 is also UH of tuner 31
UHF band block 82 and VHF equivalent to F band block 32 and VHF band block 33
The reception frequency band is divided by the band block 83. In the present embodiment, the UHF band block 82 and the VH
Loss correction circuits 85 and 95 inserted between the input sides of the high-frequency amplifiers 84 and 94 in the F-band block 83 and the variable band-pass filters 40 and 50 include coils 86 and 96.
Also, input capacitors 87 and 97 of high-frequency amplifiers 84 and 94 are used as capacitors forming a resonance circuit. The switching circuits 48 and 58 include input capacitances 87 and
The coils 86 and 96 connected in parallel to the circuit 97 and the ground are cut off or conducted. Switching circuit 48,
When 58 is turned on and conducting, the coil 8
A parallel resonance circuit is formed between the input capacitors 6, 96 and the input capacitors 87, 97, and operates as a peaking circuit. When the switching circuits 48 and 58 are shut off, the coil 8
6, 96 are not connected in parallel with the input capacitors 87, 97,
It does not operate as a peaking circuit.

FIG. 5 shows a configuration related to the loss correction circuits 85 and 95. Input capacitance 8 of high frequency amplifiers 84 and 94
7, 97 has a capacitance value of about several pF to several tens pF. Therefore, for frequencies in the VHF and UHF bands of several tens to several hundreds of MHz, a resonance circuit can be formed together with the coils 86 and 96 having appropriate inductance values. A switching diode 60 connected between one end of each of the coils 86 and 96 and the ground;
Although the bias circuit for 70 is omitted,
As in the case of FIG. 2, a bias voltage is applied to switch the conduction or cutoff switching state in accordance with the switching of the band changeover switch 35 of the power supply 34.

In the embodiment shown in FIGS. 1 and 4, both the UHF band blocks 32 and 82 and the VHF band blocks 33 and 83 have loss correction circuits 45, 55;
Although the local oscillation frequency fb is shifted to a higher side than the frequency fa desired to receive as shown in FIG.
The switching circuit 48 is provided only in the loss correction circuits 45 and 85 in the VHF bands 2 and 82, and the VHF band blocks 33 and 83 are provided.
In the loss correction circuits 55 and 95, the switching circuit 58
Can also be omitted. Switching circuit 4
8, 58 are connected between the loss correction circuits 45 and 55 and the ground or in series within the loss correction circuits 85 and 95, but are connected in parallel with the parallel resonance circuit serving as the peaking circuit to make them conductive. A configuration in which the operation of the peaking circuit is disabled and cut off to enable the operation of the peaking circuit is also conceivable. The tuners 31 and 81 set the entire reception frequency band for television broadcasting to UHF and VHF.
Although the frequency band is divided into the two partial frequency bands, it is also possible to divide the frequency band into a larger number of receiving circuit blocks. It is also conceivable to provide a receiving circuit block for satellite broadcasting of a frequency higher than the UHF band. Furthermore, the present invention is applicable not only to television broadcasting but also to a case where a frequency band such as a medium wave (MW) or a short wave (HF) is divided into a plurality of receiving circuit blocks and received for receiving a radio broadcast. The invention can be applied.

Further, the tuner 3 shown in FIGS.
1 and 81, the antenna terminal 36 is shared by the UHF band blocks 32 and 82 and the VHF band blocks 33 and 83, and the intermediate frequency amplifier 37, the low-pass filter 38,
Although the intermediate frequency output terminal 39 is shared, it can be provided independently for each of these receiving blocks.

[0031]

As described above, according to the present invention, a tuner that divides an entire receiving frequency band by a plurality of receiving circuit blocks and receives the signals is used, and a peaking circuit in an inactive receiving circuit block cannot be operated by a switching circuit. Therefore, the frequency component selected by the peaking circuit can be prevented from sneaking around the power supply line, the ground pattern, etc., and entering the receiving circuit block that is operating, thereby improving the interference characteristics. .

According to the present invention, since at least a part of the resonance circuit included in the peaking circuit is switched by the switching circuit so as to be turned on or off, the resonance circuit forming the peaking circuit when the receiving circuit block is not operating is also provided. It is possible to reliably switch to the inoperable state.

Further, according to the present invention, since the resonance circuit of the peaking circuit is formed by using the input capacitance of the high-frequency amplifier circuit, the number of components required for the peaking circuit for compensating the loss can be reduced, and the cost can be reduced. The size of the tuner can be reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic electrical configuration of a tuner 31 according to an embodiment of the present invention.

FIG. 2 is an electric circuit diagram showing a more detailed configuration of the loss correction circuits 45 and 55 of FIG.

FIG. 3 is a diagram illustrating a concept of image interference removal in the embodiment of FIG. 1;

FIG. 4 is a block diagram showing a schematic electrical configuration of a tuner 81 according to another embodiment of the present invention.

FIG. 5 is a partial electric circuit diagram showing a configuration of the loss correction circuits 85 and 95 of the embodiment of FIG.

FIG. 6 is a block diagram showing a schematic electrical configuration of a conventional tuner 1.

7 is a graph showing the operation of the loss correction circuits 15 and 25 of FIG.

8 is a block diagram showing a schematic configuration of a tuner 30 provided with a band changeover switch 29 on the input side in FIG.

[Explanation of symbols]

 31, 81 Tuner 32, 82 Block for UHF band 33, 83 Block for VHF band 34 Power supply 35, 49 Band selector switch 36 Antenna terminal 37 Intermediate frequency amplifier 39 Intermediate frequency output terminal 40, 42, 50, 52 Variable band pass filter 41 , 51, 84, 94 High-frequency amplifiers 43, 53 Mixer circuits 44, 54 Local oscillators 45, 55, 85, 95 Loss correction circuits 46, 56, 86, 96 Coils 47, 57 Capacitors 48, 58 Switching circuits 60, 70 Switching diodes 87,97 input capacity

Claims (3)

[Claims] 1. A tuner which divides an entire receiving frequency band into a plurality of partial frequency bands and includes a dedicated receiving circuit block for each partial frequency band, selects one of the plurality of receiving circuit blocks, and selects A selection circuit that supplies operating power only to the selected reception circuit block; a peaking circuit that is provided for each reception circuit block and corrects a loss in the partial reception frequency band of the reception circuit block; A switching circuit which is inserted into each peaking circuit and switches so that the peaking circuit is operable when receiving power is supplied from the selection circuit, and the peaking circuit is inoperable when no operating power is supplied. A tuner characterized by including a circuit. 2. The tuner according to claim 1, wherein the peaking circuit includes a resonance circuit, and the switching circuit performs the switching by conducting or blocking at least a part of the resonance circuit. 3. Each of the receiving circuit blocks includes a band-pass filter that selectively filters a partial frequency band received by the receiving circuit block, and a high-frequency amplifier circuit that amplifies a reception frequency signal that is selectively filtered by the band-pass filter. The tuner according to claim 2, wherein the resonance circuit is connected to an input side of the high-frequency amplification circuit, and is formed by using an input capacitance of the high-frequency amplification circuit as a resonance capacitance.