JP3031077B2 - Electronic tuner - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic tuner used for a television receiver or a home VTR.

[0002]

2. Description of the Related Art In recent years, TV screens have become larger, and household VTRs have become larger.
As the use of high-band has increased the image quality, the number of channels used by end users has increased due to the spread of CATV. For this reason, an electronic tuner (hereinafter, referred to as a tuner) used for a television receiver, a home VTR, or the like is required to have a high interference rejection capability in a wide frequency band.

Conventionally, this type of tuner has a circuit configuration as shown in FIG. 6 (for example, Japanese Patent Laid-Open No. 3-160815).
issue). Hereinafter, a conventional technique will be described with reference to the drawings. FIG.
1, an input terminal 1 has an input circuit 2 to which an input signal is supplied, and a high-frequency amplifier circuit 3 (hereinafter referred to as R) to which an output signal of the input circuit 2 is supplied.
It is called an F amplifier circuit. ), A mixing circuit 4 for supplying the output signal of the RF amplifier circuit 3 to one input, a local oscillation circuit 5 for supplying a local oscillation signal to the other input of the mixing circuit 4, An IF amplifier circuit 6 (hereinafter, referred to as an IF amplifier circuit) to which an output signal is supplied, and an output terminal 7 to which an output signal of the IF amplifier circuit 6 is supplied.

The input circuit 2 includes a first inductance element 9 having one end connected to the input side 8 thereof, and a first varactor having one end connected to the other end of the first inductance element 9. And a diode 10. Then, a second inductance element 12 and a second varactor diode 13 are connected in parallel between a connection point between the first inductance element 9 and the first varactor diode 10 and the ground. Further, the second capacitor 1 is connected in parallel with the first inductance element 9.
4 was connected.

The operation of the tuner constructed as described above will be described below. A television signal (hereinafter, referred to as an RF signal) output from an antenna or the like is
After being input to the input terminal 1 of the tuner, it is input to one end of an anti-resonance circuit 15 composed of the input coupling inductance element 9 and the second capacitor 14. The RF signal output from the other end of the anti-resonance circuit 15 is input to a tuning circuit including the tuning inductance element 12 and the tuning second varactor diode 13, and the RF signal of the receiving channel is selected. Then, the first varactor diode 10 for coupling the RF amplifier circuit 3
And amplified by the RF amplifier circuit 3. Then, the signal is mixed by the local oscillation circuit 5 and the mixing circuit 4 of the reception channel frequency and converted into an intermediate frequency, and the output is
The configuration is such that the signal is amplified by the F amplifier circuit 6 and output from the output terminal 7.

Next, the operation of the anti-resonance circuit 15 constituted by the first inductance element 9 for input coupling and the capacitor 14 for input coupling will be described in more detail with reference to FIG. FIG. 7 shows impedance characteristics at both ends of the anti-resonance circuit 15. In FIG. 7, 16 is a reception channel frequency band, and 17 is a resonance frequency of the anti-resonance circuit 15.

First, the operation in the reception channel frequency band 16 and a frequency band lower than the reception channel frequency band 16 will be described. Since the resonance frequency 17 of the anti-resonance circuit 15 is set to a higher frequency than the reception channel frequency band 16, the impedance characteristic at both ends of the anti-resonance circuit 15 becomes an inductance component as shown in the reception channel frequency band 16 of FIG. . Therefore, the anti-resonance circuit 15 is connected to the input terminal 1 having a low impedance in the reception channel frequency band 16 and the frequency band lower than the reception channel frequency band 16, and to the tuning second frequency band.
Has a function of impedance matching for connection with a tuning circuit having a high impedance constituted by the inductance element 12 and the second varactor diode 13 for tuning.

Next, an operation in a frequency band higher than the reception channel frequency band 16 will be described. As shown in FIG. 7, the impedance characteristic at both ends of the anti-resonance circuit 15 increases in the vicinity of the resonance frequency 17. Since this anti-resonance is connected between the input channel 1 and the reception channel tuning circuit composed of the tuning inductance element 12 and the tuning varactor diode 13, the passage of the RF signal near the resonance frequency 17 is prevented. Operate.

[0009]

However, in such a conventional configuration, in order to improve the selectivity characteristics without causing transmission loss in the receiving channel frequency band 16, the setting of the resonance frequency 17 must be performed in the receiving channel frequency band. The frequency must be set higher than at least the highest frequency of the sixteen. For this reason, usually, the resonance frequency 17 is set to a frequency higher by (2 × the number of local oscillation waves) of the high-frequency reception channel frequency to improve the selectivity characteristics of the image interference frequency. In this case, the selectivity characteristic of the image disturbing frequency becomes only the Q of the tuning circuit, and it is difficult to improve the selectivity characteristic of the image disturbing frequency in the entire receiving channel frequency band because it is worse than the high frequency receiving frequency. I was

An object of the present invention is to solve the above-mentioned conventional problems, and an object of the present invention is to provide a tuner having excellent selectivity characteristics of an image interference frequency in all reception channel frequency bands.

[0011]

In order to achieve this object, an input circuit of a tuner according to the present invention comprises a first inductance element having one end connected to its input side, and another end connected to the first inductance element. a and a first varactor diode having one end connected, the first inductance between said first connection point and grayed <br/> lands between the inductance element and the first varactor diode Equivalent to element
A second inductance element having a high inductance value and a second varactor diode are connected in parallel, and a first capacitor is connected between the input side of the first inductance element and the output side of the first varactor diode. Connected.

[0012]

According to this configuration, the resonance frequency can be made to follow the reception channel by the function of the first varactor diode. That is, when the reception frequency is low, the resonance frequency also decreases, and when the reception frequency increases, the resonance frequency also increases. By setting this resonance frequency to the image interference frequency, almost constant image interference frequency selectivity characteristics are obtained. Will be done. As a result,
The interference rejection capability of all reception channel frequency bands can be improved.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIG. In FIG. 1, reference numeral 1 denotes an input terminal. The input terminal 1 has an input circuit 2 to which an input signal is supplied, and an R to which an output signal of the input circuit 2 is supplied.
An F amplifier circuit 3, a mixing circuit 4 to which an output signal of the RF amplifier circuit 3 is supplied to one input, a local oscillation circuit 5 to supply a local oscillation signal to the other input of the mixing circuit 4,
IF amplifier circuit 6 to which the output signal of the mixing circuit 4 is supplied
And an output terminal 7 to which an output signal of the IF amplifier circuit 6 is supplied.

The input circuit 2 has a first inductance element 9 having one end connected to the input side 8 thereof, and a first varactor having one end connected to the other end of the first inductance element 9. And a diode 10. Then, a second inductance element 12 and a second varactor diode 13 are connected in parallel between a connection point between the first inductance element 9 and the first varactor diode 10 and the ground, and the second A first resistor 20 is connected to a connection point between the first varactor diode 10 and the second varactor diode 13, and a voltage application terminal 21 is connected to the other end of the first resistor 20. A second resistor 22 is connected between the connection point between the output 10 and the output side 11 and the ground. Further, the first capacitor 1 is connected between one end of the first inductance element 9 and the other end of the first varactor diode 10.
4 are connected.

Further, a second capacitor 19 is connected in parallel with the first varactor diode 10.

In this embodiment, when the reception channel frequency input to the input terminal 1 is 50 MHz to 170 MHz, a good result can be obtained by using the following constants for the elements of the input circuit 2. It has gained. That is, the first inductance element 9 used for input coupling is an air-core coil made of polyurethane copper wire and has a frequency of about 340 nH. The second inductance element 12 used for tuning is made of the same material as the input-coupling inductance element 9 and is about 400 nH. The second varactor diode 13 is used for tuning at about 45 pF at 2 V and about 3 pF at 25 V. The first capacitor 14 is approximately 1 pF and serves as an input coupling capacitor. The first varactor diode 10 is set to about 13 pF at 2 V and about 2 pF at 25 V, and serves as a varactor diode for RF amplifier circuit coupling.

The operation of the tuner configured as described above will be described below. An RF signal of a tuner output from an antenna or the like is input to an input terminal 1, and thereafter, a first inductance element 9 for input coupling, a first capacitor 14 for input coupling, and a first capacitor for coupling an RF amplifier circuit are provided. Is input to one end of a variable anti-resonance circuit 18 constituted by the varactor diode 10 of FIG. This variable anti-resonance circuit 1
The RF signal output from the other end of 8 is input to a tuning circuit including a second inductance element 12 for tuning and a second varactor diode 13 for tuning, and an RF signal of a receiving channel is selected. . Then, the first varactor diode 10 for coupling to the RF amplifier circuit is coupled to the RF amplifier circuit 3 and amplified by the RF amplifier circuit 3. Then, the signal is mixed by the local oscillation circuit 5 and the mixing circuit 4 of the frequency for the reception channel and converted into an intermediate frequency, and the output is amplified by the IF amplifier circuit 6 and output from the output terminal 7.

Next, the reception channel of the variable anti-resonance circuit 18 constituted by the first inductance element 9 for input coupling, the first capacitor 14 for input coupling, and the first varactor diode 10 for coupling the RF amplifier circuit. The operation in the vicinity of 170 MHz where the frequency is high will be described in more detail with reference to FIG. FIG. 2 shows that the reception channel frequency is 1
It is an impedance characteristic of both ends of the variable anti-resonance circuit 18 near 70 MHz. In FIG. 2, reference numeral 23 denotes a high-band reception channel frequency, and 24 denotes a high-band resonance frequency of the variable anti-resonance circuit 18.

First, the operation in the high-band receiving channel frequency 23 and the frequency band lower than the high-band receiving channel frequency 23 will be described. Since the high-band resonance frequency 24 of the variable anti-resonance circuit 18 is set to a frequency higher than the high-band reception channel frequency 23, the impedance characteristics at both ends of the variable anti-resonance circuit 18 are set to the high-band reception channel frequency 23 in FIG. As shown, it becomes an inductance component. Therefore, the variable anti-resonance circuit 18 has the input terminal 1 having a low impedance in the high-band reception channel frequency 23 and the frequency band lower than the high-band reception channel frequency 23.
And has a function of impedance matching for connecting to a tuning circuit having a high impedance constituted by the tuning inductance element 12 and the tuning varactor diode 13.

Next, the operation in a frequency band higher than the high band reception channel frequency 23 will be described. As shown in FIG. 2, the impedance characteristics at both ends of the variable anti-resonance circuit 18 increase in the vicinity of the high-band resonance frequency 24. This anti-resonance is caused by the tuning inductance element 1
2. Since the high frequency resonance frequency 24 is higher than the high frequency reception channel frequency 23 by (2 × the number of local oscillation waves) because it is connected between the reception channel tuning circuit composed of the tuning varactor diode 13 and the input terminal 1. , And the selectivity characteristic of the high-frequency image interference frequency is improved similarly to the prior art.

Next, the operation of the variable anti-resonance circuit 18 when the receiving channel frequency is in the low band around 50 MHz will be described in detail with reference to FIG. FIG. 3 shows impedance characteristics at both ends of the variable anti-resonance circuit 18 in the vicinity of 50 MHz where the receiving channel frequency is low. In FIG. 3, reference numeral 25 denotes a low-band reception channel frequency, and 26 denotes a low-band resonance frequency of the variable anti-resonance circuit 18. At the time of reception in the low-frequency channel, the capacitance of the varactor diode 10 for coupling the RF amplification circuit becomes large, so that the anti-resonance frequency of the variable anti-resonance circuit 18 becomes high as shown in FIG. It becomes lower than the band resonance frequency 24. Therefore, the variable anti-resonance circuit 18
Has an impedance matching function in the low-band receiving channel frequency 25 and in a frequency band lower than the low-band receiving channel frequency 25. By setting the low-band resonance frequency 26 to the image interference frequency of the low-band reception channel frequency 25, the selectivity characteristics of the image interference frequency at the low-band reception channel frequency 25 are improved.

FIGS. 4 and 5 show the selectivity characteristics in this embodiment. FIG. 4 shows the selectivity characteristics at the time of the high frequency reception channel,
FIG. 5 shows the selectivity characteristics at the time of a low-band reception channel. 4 and 5 are selectivity characteristics in the present embodiment,
28 is a selectivity characteristic in the conventional circuit. As is clear from FIGS. 4 and 5, the selectivity characteristic 27 in the present embodiment is different from the selectivity characteristic 28 in the conventional circuit in that the high-frequency image interference selectivity at the time of the high-frequency reception channel in FIG. Although the characteristic 29 is the same, the low-frequency image interference selectivity characteristic 30 is a superior selectivity characteristic at the time of the low-frequency reception channel in FIG. I understand. Further, it is needless to say that the selectivity of the image interference frequency in the mid-range reception channel frequency around 100 MHz can be improved by optimizing the constant of the variable anti-resonance circuit 18.

As described above, the first inductance element 9 having one end connected to the input side 8 and the first varactor diode 10 having one end connected to the other end of the first inductance element 9 are provided. Then, a second inductance element 12 and a second varactor diode 13 are connected in parallel between a connection point between the first inductance element 9 and the first varactor diode 10 and a ground, and the second By connecting the first capacitor 14 between the input side of the first inductance element 9 and the output side of the first varactor diode 10, the anti-resonance of the variable resonance circuit 18 is reduced to the image interference frequency of the reception channel frequency. It is a television receiver that can be set optimally and has excellent selectivity characteristics of image interference frequency in all reception channel frequency bands. It is possible to realize a tuner for use.

Further, in FIG.
Is a high-frequency reception correction capacitor of about 1 pF. By optimally setting the constant of the second capacitor 19 for high-frequency correction, the frequency variable range of the tuning circuit of the RF signal formed by the tuning inductance element 12 and the tuning varactor diode 13 can be set to some extent arbitrarily. At the same time, the coupling characteristics with the RF amplifier circuit 3 at the time of receiving the high band reception channel are improved. As a result, it is possible to reduce the transmission loss of the circuit and to provide a tuner having excellent NF.

[0025]

As described above, in the input circuit of the tuner of the present invention, the first inductance element having one end connected to the input side, and one end connected to the other end of the first inductance element. A first varactor diode, wherein the first varactor diode is connected between a ground and a connection point between the first inductance element and the first varactor diode .
Has an inductance value approximately equal to the inductance element
That the second connecting the inductance element and a second varactor diode, the configuration of connecting the first capacitor between the output side of the first input side to the first varactor diode of the inductance element, The variable anti-resonance circuit of the input circuit can follow the reception channel. That is, when the reception frequency is low, the resonance frequency also decreases, and when the reception frequency increases, the resonance frequency also increases. By setting this resonance frequency to the image interference frequency, almost constant image interference frequency selectivity characteristics are obtained. Will be done. As a result, it is possible to improve the ability to eliminate interference in the entire reception channel frequency band.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of an electronic tuner according to an embodiment of the present invention.

FIG. 2 is an impedance characteristic diagram at both ends of a variable anti-resonance circuit at the time of a high-frequency reception channel according to an embodiment of the present invention.

FIG. 3 is an impedance characteristic diagram at both ends of a variable anti-resonance circuit at the time of a low-frequency reception channel according to an embodiment of the present invention.

FIG. 4 is a diagram showing selectivity characteristics of an embodiment of the present invention and a conventional circuit according to an embodiment of the present invention and a conventional circuit at the time of a high-frequency reception channel.

FIG. 5 is a diagram showing selectivity characteristics of a circuit according to an embodiment of the present invention and a conventional circuit according to an embodiment of the present invention and a conventional circuit at the time of a low-frequency reception channel;

FIG. 6 is a circuit diagram of a conventional electronic tuner.

FIG. 7 is a diagram showing impedance characteristics at both ends of a conventional anti-resonance circuit.

[Explanation of symbols]

 Reference Signs List 1 input terminal 2 input circuit 4 mixing circuit 5 local oscillation circuit 7 output terminal 9 first inductance element 10 first varactor diode 11 output side 12 second inductance element 13 second varactor diode

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-3-160815 (JP, A) JP-A-61-228843 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) H04B 1/18 H03J 3/08 H03J 5/24

Claims (1)

(57) [Claims] An input terminal, an input circuit to which a signal input to the input terminal is supplied, a mixing circuit to which an output signal of the input circuit is supplied to one input, and the other input of the mixing circuit. And an output terminal to which an output signal of the mixing circuit is supplied. The input circuit includes a first inductance element having one end connected to an input side thereof, A first varactor diode having one end connected to the other end of the first inductance element and the other end connected to the output circuit side of the input circuit; the first inductance element and the first varactor; The first point between the connection point with the diode and the ground ;
Has an inductance value approximately equal to the inductance element
That a second inductance element and a second varactor diode connected in parallel, the electronic tuner of connecting the first capacitor between the output side of the first input side to the first varactor diode inductance element .