JP3459728B2 - Tuner - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tuner used in a television receiver or the like.

[0002]

2. Description of the Related Art Conventionally, in assigning frequencies to be used for broadcasting, it has been general that adjacent frequencies are not set in consideration of interference between frequencies, but in recent years, with the development of CATV broadcasting, adjacent frequencies have not been set. It is not uncommon to use frequencies. Therefore, for example, in a television receiver, in order to reduce interference due to adjacent frequencies, selection of a SAW (surface acoustic wave) filter connected to a subsequent stage of an intermediate frequency signal amplifier circuit that amplifies the intermediate frequency signal supplied from the tuner. Need to be steep. However, since this alone cannot sufficiently reduce the interference due to the adjacent frequency,
In general, a trap circuit is provided in front of the intermediate frequency signal amplification circuit to resonate with a signal of a predetermined frequency to remove or sufficiently reduce the signal (hereinafter, referred to as trapping a signal of a predetermined frequency). .

By the way, there is a problem in designing a television receiver corresponding to the television broadcasting system of each country of the world after adopting the above-mentioned configuration. PAL / G system,
PAL / D system, PAL / K system, NTSC / M system,
There are multiple systems such as NTSC / N system and SECAM / L system, and the SECAM / L system among them is adopted in France, but it is special compared with other broadcasting systems. It can be mentioned that it has become a thing.

More specifically, among the French broadcasting channels, A, which is treated as a VHF low band,
In the four channels B, C and C1, the frequency relationship between the video signal carrier and the audio signal carrier is such that the VHF low band other channel, the VHF high band channel, and the U
It is characterized in that it is inverted as compared with that on the HF channel (hereinafter, the broadcasting system on the four channels A, B, C and C1 is expressed as SECAM / L 'system).

Here, the intermediate frequencies of the video signal carrier, the color signal carrier, and the audio signal carrier of the receiving channel and the intermediate frequency of the audio signal carrier of the lower adjacent channel (SECAM / L 'system) in each of the above broadcasting systems. Then, a general example of the intermediate frequency of the audio signal carrier of the upper adjacent channel is shown in FIG.

As a result, the PAL / B system and the PAL / G system
System, PAL / D system, PAL / K system, NTSC / M
Method, NTSC / N method, SECAM / L method (hereinafter,
These are collectively referred to as a method other than SECAM / L '), and a resonance frequency of 40.4M is required to receive broadcasts.
Hz trap circuit is required, and the resonance frequency is 32.4MHz to receive SECAM / L 'system broadcasting.
A trap circuit is required, and the resonance frequencies are 40.4 MHz and 3
It can be seen that two trap circuits of 2.4 MHz are needed.

The intermediate frequency of the video signal carrier of the upper adjacent channel (the intermediate frequency of the video signal carrier of the lower adjacent channel in the SECAM / L 'method) is not taken into consideration, but the interference by these signals is SA.
This can be sufficiently improved by making the selectivity of the W filter steep.

However, if the two trap circuits are simply provided, the intermediate frequency of the voice signal carrier of the receiving channel is 40.4 in the SECAM / L 'system.
MHz, and in systems other than SECAM / L ', the intermediate frequency of the audio signal carrier of the receiving channel is 3
Since it is at or near 2.4 MHz, audio cannot be played.

FIG. 7 shows a block diagram of a tuner 20 and a circuit connected to the subsequent stage thereof in a conventional television receiver compatible with television broadcasting systems in various countries around the world, which is designed based on the above contents. In the figure, the antenna 1
From the high frequency signals received from the first band pass filter 21, the signal of the desired channel band is selected,
It is amplified by the first amplifier circuit 22. The amplified signal is output from the second bandpass filter 2 to remove unnecessary signals.
After being selected again by 3, the signal is mixed with the local oscillation signal supplied from the local oscillation circuit 25 in the mixing circuit 24 and amplified by the second amplification circuit 26. Then, among the signals output from the second amplifier circuit 26, a signal having a frequency that is the difference between the frequency of the local oscillation signal and the band frequency of the desired signal, that is, 32.4 MHz to 40.4 MHz (see FIG. 6).
The intermediate frequency signal for which the band is secured is selected by the third band pass filter 27 and output from the IF terminal 28. The above is the description of the signal processing in the tuner 20, but in summary, the tuner 20 selects a signal in the desired channel band and converts its frequency to an intermediate frequency.

The intermediate frequency signal output from the IF terminal 28 of the tuner 20 is supplied to the first trap circuit 3 and the second trap circuit 3.
After passing through the trap circuit 4, the signal is amplified by the intermediate frequency signal amplifier circuit 5 and supplied to the SAW filter 6.

Here, the first trap circuit 3 is a bridge T-type trap circuit having a resonance frequency of 40.4 MHz, which is composed of a capacitor C1, a capacitor C2, a resistor R1 and a coil L1. The cathode of the switching diode D1 is connected to the connection point of L1, and the ground side of the coil L1 and the anode of the switching diode D1 are connected via a capacitor C3. A resistor R2 is connected to the anode of the switching diode D1, and a voltage can be applied from the anode side to the switching diode D1 from the terminal T1 via the resistor R2.

Therefore, in this first trap circuit,
When the voltage is not applied from the terminal T1, the bridge T-type trap circuit operates and resonates with the signal of 40.4 MHz, but when the predetermined voltage is applied from the terminal T1, the switching diode D1 is turned on and the DC Since it is grounded at a high frequency via the blocking capacitor C3, that is, the coil L1 is equivalently short-circuited, and no longer constitutes a bridge T-type trap circuit.
The signal of 40.4 MHz does not resonate with the signal of 40.4 MHz and is guided to the circuit in the subsequent stage.

The second trap circuit 4 is composed of a capacitor C4, a capacitor C5, a resistor R3 and a coil L2 and has a resonance frequency of 32.4 MHz.
In the type trap circuit, a switching diode D is provided at the connection point of the capacitors C4, C5 and the coil L2.
The cathode of No. 1 is connected, and the ground side of the coil L2 and the anode of the switching diode D1 are connected via a capacitor C6. A resistor R4 is connected to the anode of the switching diode D1, and a voltage can be applied from the anode side to the switching diode D1 from the terminal T2 via the resistor R4.

Therefore, in this second trap circuit,
When the voltage is not applied from the terminal T2, the bridge T-type trap circuit operates and resonates with the signal of 32.4 MHz. However, when the predetermined voltage is applied from the terminal T2, the switching diode D1 is turned on, and the DC Since it is grounded at a high frequency via the blocking capacitor C6, that is, the coil L2 is equivalently short-circuited, and no longer constitutes a bridge T-type trap circuit.
The signal of 32.4 MHz does not resonate with the signal of 32.4 MHz and is guided to the circuit in the subsequent stage.

With the above structure, if a predetermined voltage is applied to the first trap circuit from the terminal T1 and a voltage is applied to the second trap circuit from the terminal T2, 32.4M is obtained.
Since the Hz signal is trapped and the 40.4 MHz signal is guided to the circuit in the subsequent stage, SECAM / L 'system broadcasting is received without reducing the interference due to adjacent channels and without losing the audio signal. be able to.

On the contrary, if a voltage is not applied to the first trap circuit from the terminal T1 and a predetermined voltage is applied to the second trap circuit from the terminal T2, a signal of 40.4 MHz is trapped, and a signal of 32.4 MHz is trapped. Since the signal is guided to the circuit in the subsequent stage, it is possible to receive the broadcasting of the system other than SECAM / L 'without reducing the interference by the adjacent channel and without losing the audio signal.

[0017]

By the way, since a transformer is used for the coil which constitutes the trap circuit, for example, in a television receiver, interference with a transformer which constitutes a video signal and audio signal processing circuit in the subsequent stage and In order to avoid the influence of external signals, it is necessary to cover the coil (transformer) in the trap circuit with a shield case. As a result, the occupied area of the trap circuit becomes large, which leads to an increase in the size of the entire receiving circuit, and the physical distance from the IF terminal (output) of the tuner to the circuit at the subsequent stage, for example, the intermediate frequency signal amplification circuit. Since it becomes long, the electrical performance is deteriorated, and in addition, there is a problem in that the shield case is required, the number of parts is increased, and the cost is increased. Further, as shown in the above-mentioned prior art, since the receiving circuit corresponding to various broadcasting systems needs two trap circuits, these problems become more serious.

Therefore, the present invention reduces the interference of adjacent channels in a television receiver or the like, or in addition to supporting various broadcasting systems in various countries in the world, downsizing the entire receiving circuit and electrical Reduction of property deterioration, and
An object is to provide a tuner that can realize cost reduction.

[0019]

In order to achieve the above object, the tuner according to claim 1 includes a circuit for extracting a signal of a desired frequency from an input signal and a signal output from the circuit. In a tuner having a circuit for converting to a predetermined frequency, a trap circuit is built in the same chassis, and this trap circuit has a variable capacitance diode, and the voltage applied to the variable capacitance diode from the outside The resonance frequency changes accordingly and this resonance
Voltage is applied to the varactor diode to change the frequency.
The applied terminal also serves as the output terminal of the tuner .

By the way, since the tuner is usually completely shielded by metal in order to prevent the leakage of the signal from the local oscillation circuit, the coil (transformer) of the trap circuit is constructed by configuring the tuner as described above. Will be shielded from the outside without being shielded as in the past.

[0021]

[0022]

[0023]

[0024]

[0025]

Further, in the tuner of the second aspect , the trap circuit includes a first resistor inserted in a signal path, a first capacitor having one end connected to an input side of the first resistor, and a first resistor. A second capacitor having one end connected to the output side of the resistor, the variable capacitance diode connected between the other ends of the first and second capacitors, and a coil connected between the other end of the first capacitor and the ground. , A second resistor connected across the second capacitor, and a voltage is applied to the variable capacitance diode through the second resistor.

[0027]

With this structure, it is not necessary to separately provide a terminal for applying a voltage to the trap circuit.

[0029]

FIG. 1 is a block diagram of a tuner 2 as a first reference example , and an intermediate frequency signal amplifier circuit 5 and a SAW filter 6 are connected to the subsequent stage. The tuner 2 includes a first trap circuit 3 having a resonance frequency of 40.4 MHz in front of the IF terminal 28 of the conventional tuner 20.
And a second trap circuit having a resonance frequency of 32.4 MHz. Since each trap circuit is the same as that shown in the prior art, description thereof will be omitted.

When this tuner is adopted in a television receiver, if a predetermined voltage is applied to the first trap circuit from the terminal T1 and no voltage is applied to the second trap circuit from the terminal T2, the SECAM / L 'system is used. Can be received without reducing the interference due to the adjacent channel and without losing the audio signal, and conversely, the voltage can not be applied to the first trap circuit from the terminal T1 and the second trap circuit can be received. If a predetermined voltage is applied from terminal T2, SECAM / L '
It is possible to receive broadcasts of systems other than the above without reducing interference due to adjacent channels and without losing the audio signal.

By the way, the tuner is usually completely shielded by metal in order to prevent the leakage of the signal from the local oscillation circuit. Therefore, by configuring the tuner as described above, the coil (transformer) of the trap circuit is formed. Is shielded from the outside without being shielded by itself as in the conventional art. For example, in a television receiver, interference with a transformer or the like which constitutes a video signal and audio signal processing circuit in the subsequent stage, It is possible to avoid the influence of extraneous signals.

Therefore, although the tuner may be enlarged by incorporating the trap circuit, it is not necessary to shield the coil itself of the trap circuit, so that the trap circuit occupies a small area and is connected to the subsequent stage. The size of the receiving circuit as a whole including this circuit is reduced. Further, since it is not necessary to provide a trap circuit between the IF terminal (output) of the tuner and a circuit in the subsequent stage, for example, the intermediate frequency signal amplifier circuit, the physical distance between the two becomes short. Further, the shield case is not needed, and the number of parts is reduced.

In the first reference example , the tuner is provided with two trap circuits having different resonance frequencies. However, more trap circuits are provided to adapt to other special broadcasting systems. Good, or, although the broadcast system that can be received is limited, only one trap circuit may be provided.

FIG. 2 is a block diagram of a tuner 2'which is a second reference example , and an intermediate frequency signal amplifier circuit 5 is provided at the subsequent stage.
And the SAW filter 6 are connected. This tuner 2 ′ is provided in front of the IF terminal 28 of the conventional tuner 20,
The trap circuit 7 is provided in which the resonance frequency can be switched to two types depending on whether the voltage is supplied or not.

In this reference example , the trap circuit 7 includes a capacitor C1, a capacitor C2, a resistor R1, and a coil L1.
In the bridge T-type trap circuit having a resonance frequency of 40.4 MHz, the cathode of the switching diode D1 is connected to the connection point of the capacitor C1, the capacitor C2, and the coil L1, and the resistor R
1. The connection point of the capacitor C2 and the anode of the switching diode D1 are connected via the capacitor C7. The resistor R2 is connected to the anode of the switching diode D1, and the resistor R2 is connected from the terminal T3.
A voltage can be applied to the switching diode D1 from the anode side via the.

As a result, in the trap circuit 7, the terminal T
When the voltage is not applied from 3, the bridge T-type trap circuit operates and resonates with the signal of 40.4 MHz,
When a predetermined voltage is applied from the terminal T3, the switching diode D1 is turned on, the capacitors C2 and C7 are connected in parallel, and the resonance frequency changes. Specifically, the resonance frequency f in this case
₀ is the inductance of the coil L1, T _L1 , the capacitance of the capacitor C2 is T _C2 , and the capacitance of the capacitor C7 is T
_C7 is expressed as f ₀ = 1 / {2π (T _L1 × T _C2 × T _C7 ) ^1/2 }, so that the resonance frequency f ₀ can be 32.4 MHz by appropriately selecting the electric capacitance of C 7. I am trying to become.

Therefore, considering the case where this tuner 2'is adopted in a television receiver, the trap circuit 7
When a predetermined voltage is applied to the terminal T3, the resonance frequency of the trap circuit 7 becomes 32.4 MHz.
It is possible to receive the M / L ′ system broadcast without reducing the interference by the adjacent channel and without losing the audio signal.

On the contrary, if no voltage is applied to the trap circuit from the terminal T1, the resonance frequency of the trap circuit 7 is 40.
Since the frequency is 4 MHz, it is possible to receive the broadcasting of the system other than SECAM / L 'without reducing the interference due to the adjacent channel and without losing the audio signal.

Further, by configuring the tuner as described above, it is not necessary to shield the coil itself of the trap circuit as in the case of the first reference example described above, so that the size of the entire receiving circuit is reduced and the output of the tuner is reduced. From the above, not only the physical distance from the circuit to the subsequent stage can be shortened and the number of parts can be reduced, but also the trap circuit itself is one, so that the whole receiving circuit can be further downsized. is there.

Although the voltage for switching the resonance frequency of the trap circuit 7 is applied from the terminal T3, the IF terminal 28 serving as an output terminal may also be used instead (see FIG. 3). reference). By doing so, it is not necessary to separately provide the terminal T3 in the tuner 2 '.

FIG. 4 is a block diagram of a tuner 2 "of the basic configuration of the present invention , and an intermediate frequency signal amplifier circuit 5 and a SAW filter 6 are connected to the subsequent stage. This tuner 2" is a conventional tuner. The trap circuit 8 whose resonance frequency changes in accordance with the supplied voltage is provided in front of the IF terminal 28 of 20.

This trap circuit 8 has the following basic configuration .
Capacitor C8, Capacitor C9, Resistor R5, Coil L
In the bridge T-type trap circuit constituted by 3, the variable capacitance diode D2 is connected between the connection point of the capacitor C8 and the coil L3 and the capacitor C9, and its anode is connected to the connection point of the capacitor C8 and the coil L3. , Provided. Then, the variable capacitance diode D2
A resistor R6 is connected to the cathode of the terminal, and a voltage can be applied from the cathode side to the variable capacitance diode D2 from the terminal T4 via the resistor R6.

Therefore, from the terminal T4 to the trap circuit 8
Since the capacitance of the variable-capacitance diode D2 changes in accordance with the voltage applied to, and the resonance frequency of the trap circuit 8 is determined, when this tuner 2 "is adopted in a television receiver, the terminal T4 changes from the terminal T4 to the trap circuit 8. By setting multiple types of applied voltage and switching them,
Not only the broadcasting of the SECAM / L 'system and other systems but also any broadcasting system can be received without reducing the interference due to the adjacent channel and without losing the audio signal.

Further, by configuring the tuner as described above, it is not necessary to shield the coil itself of the trap circuit as in the case of the first reference example described above, so that the size of the entire receiving circuit is reduced and the output of the tuner is reduced. From the above, not only the physical distance from the circuit to the subsequent stage can be shortened and the number of parts can be reduced, but also the trap circuit itself is one, so that the whole receiving circuit can be further downsized. is there.

FIG . 5 shows a tuner which is an embodiment of the present invention.
2 is a block diagram of 2 ", and in the above-described basic configuration, a voltage for switching the resonance frequency of the trap circuit 8 is applied from the terminal T4, but instead of this, the IF terminal 28 which is an output terminal is also used. By doing so, it is not necessary to separately provide the terminal T4 in the tuner 2 ″.

Further, the resonance frequency of the trap circuit shown in the above embodiment and each reference example is merely an example, and the present invention is not limited to these.
The same applies to the configuration of the trap circuit.

[0047]

As described above, according to the tuner of the first aspect, the coil (transformer) of the trap circuit is formed.
Without being shielded itself as in the past
Since it is cut off from the outside, it is not necessary to shield the coil of the trap circuit itself, and therefore the occupied area of the trap circuit is small, and the receiving circuit as a whole including the circuit connected in the subsequent stage is small in size. Will be realized. Further, since it is not necessary to provide a trap circuit between the IF terminal (output) of the tuner and a circuit in the subsequent stage, for example, an intermediate frequency signal amplification circuit, the physical distance between the two becomes short, and deterioration of electrical properties is reduced. be able to. Further, the shield case is unnecessary, the number of parts is reduced, and the cost can be reduced. Also,
Multiple broadcasts depending on the voltage applied to the variable capacitance diode
It becomes possible to correspond to the system, and as a trap circuit
Since it has only one, the overall size of the receiving circuit is small
Can be further promoted.

[0048]

[0049]

[0050]

Further, according to the tuner of the first aspect , it is not necessary to separately provide a terminal for applying a voltage to the trap circuit, so that the above effect can be obtained without wasteful cost increase. .

[Brief description of drawings]

FIG. 1 is a block diagram of a tuner that is a first reference example .

FIG. 2 is a block diagram of a tuner that is a second reference example .

FIG. 3 is a block diagram of a tuner in which the tuner of the second reference example is partially improved.

FIG. 4 is a block diagram of a tuner that is a basic configuration of the present invention.

FIG. 5 is a block diagram of a tuner that is an embodiment of the present invention .

FIG. 6 is an intermediate frequency of each of a video signal carrier, a color signal carrier, and an audio signal carrier of a receiving channel in each broadcasting system, and an intermediate frequency of an audio signal carrier of a lower adjacent channel (upper adjacent in SECAM / L ′ system). The figure which shows the general example of the intermediate frequency of the audio | voice signal carrier wave of a channel.

FIG. 7 is a block diagram of a conventional tuner.

[Explanation of symbols]

1 Antenna 2, 2 ', 2 "Tuner 3 1st trap circuit (resonance frequency 40.4 MHz) 4 2nd trap circuit (resonance frequency 32.4 MHz) 5 Intermediate frequency signal amplifier circuit 6 SAW filter 7 Trap circuit (resonance frequency 32) .4 / 40.4 MH
z) 8 trap circuit (variable resonance frequency) 21 first bandpass filter 22 first amplification circuit 23 second bandpass filter 24 mixing circuit 25 local oscillation circuit 26 second amplification circuit 27 third bandpass filter 28 IF terminal R1, R2, R3, R4, R5, R6 resistors C1, C2, C3, C4, C5, C6, C7, C8, C
9 Capacitors L1, L2, L3 Coil D1 Switching diode D2 Variable capacitance diodes T1, T2, T3, T4 Voltage application terminal for trap circuit

─────────────────────────────────────────────────── ─── Continuation of front page (56) Reference JP 62-231525 (JP, A) JP 5-48989 (JP, A) JP 4-284078 (JP, A) JP 5- 191303 (JP, A) Actual Kaihei 1-115394 (JP, U) (58) Fields investigated (Int.Cl. ⁷ , DB name) H03J 3/20

Claims (2)

(57) [Claims] 1. A tuner having a circuit for extracting a signal of a desired frequency from an input signal and a circuit for converting a signal output from the circuit to a predetermined frequency, wherein a trap circuit is built in the same chassis. Along with
The trap circuit has a variable capacitance diode, the resonant frequency changes depending on the voltage applied from the outside to the variable capacitance diode, the change of the resonance frequency
Terminal that applies voltage to the varactor diode to activate
, Which also serves as the output terminal of the tuner. 2. The trap circuit has a first resistor inserted in a signal path, a first capacitor having one end connected to an input side of the first resistor, and one end connected to an output side of the first resistor. A second capacitor, the variable capacitance diode connected between the other ends of the first and second capacitors, a coil connected between the other end of the first capacitor and the ground, and between both ends of the second capacitor And a second resistor that is
The tuner according to claim 1, wherein a voltage is applied to the variable capacitance diode through a resistor.