JPH07303031A - Electronic tuner - Google Patents

Abstract

PURPOSE:To provide an electronic tuner provided with an input circuit of wide band. CONSTITUTION:The input circuit 21 of this electronic tuner is constituted in such a way that a first inductance element 9 whose one terminal is connected to an input side 8 between the input side 8 and the ground is connected in series to a second inductance element 12 whose one terminal is connected to the ground. A first varactor diode 10 whose one terminal is connected to the connecting point of those inductance elements is connected in series to a second varactor diode 20 whose one terminal is connected to the ground, and the connecting point of them is connected to an output side 13. Consequently, the second inductance element 12 can be formed with an air-core coil enabled to be adjusted while securing a frequency change ratio>2.22, which enables a reception circuit of wide band such as a CATV correspondence tuner for U.S.A to be provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic tuner (hereinafter referred to as a tuner) used in a television receiver, a home VTR, or the like.

[0002]

[Prior art]

(Prior Art 1) A conventional tuner has a circuit configuration as shown in FIG. Hereinafter, the conventional technique 1 will be described with reference to the drawings. In FIG. 4, reference numeral 1a denotes an input terminal, and an input circuit 2 to which a signal input from the input terminal 1a is supplied.
a, a high frequency amplifier circuit 3a to which the output signal of the input circuit 2a is supplied, a mixing circuit 4a to which the output signal of the high frequency amplifier circuit 3a is supplied to one input, and the other input of the mixing circuit 4a. Oscillation circuit 5 for supplying local oscillation signal
a, an intermediate frequency amplifier circuit 6a to which the output signal of the mixing circuit 4a is supplied, and an output terminal 7a to which the output signal of the intermediate frequency amplifier circuit 6a is supplied.

Further, the input circuit 2a has the following configuration. That is, the first inductance element 9a having one end connected to the input side 8a of the input circuit 2a, the first varactor diode 10a having the anode side connected to the other end of the first inductance element 9a, and the first inductance element 9a. 11a connected between the cathode side of the varactor diode 10a and the ground, the second inductance element 12a connected between the anode side of the first varactor diode 10a and the ground, and the first varactor. The cathode side of the diode 10a and the input circuit 2
The third inductance element 14a is connected to the output side 13a of a, and the resistor 16a is connected to the cathode side of the first varactor diode 10a and the voltage application terminal 15a.

The operation of the tuner configured as described above will be described below. A television signal (hereinafter referred to as an RF signal) input from an antenna or the like is input to the input terminal 1a of the tuner and then to one end of the first inductance element 9a. The RF signal impedance-matched and output from the other end of the first inductance element 9a is input to a tuning circuit configured by the second inductance element 12a, the first varactor diode 10a, and the like. This tuning circuit has a voltage application terminal 1
The capacitance value of the first varactor diode 10a is controlled by the voltage value of 5a, and the RF signal of the reception channel is selected. Then, the third inductance element 14a is coupled to the high frequency amplifier circuit 3a and is amplified by the high frequency amplifier circuit 3a. The RF signal output from the high frequency amplifier circuit 3a is the local oscillation circuit 5a of the frequency for the receiving channel.
Are mixed in the mixing circuit 4a and converted to an intermediate frequency. Then, this output is amplified by the intermediate frequency amplifier circuit 6a and output from the output terminal 7a.

Next, the reception frequency range when the input circuit 2a is used as the UHF band for Japan will be described in more detail with reference to FIG. Reference numeral 17 in FIG. 4 is an equivalent circuit of a main part of the input circuit 2a, and a circuit portion of the equivalent circuit 17 of the main part is shown in FIG. In the equivalent circuit 17 of the main part of FIG. 5, the third inductance element 14a of FIG.
It is not shown because it is a small inductance element that can be ignored up to frequencies higher than the band. Further, 18a is an input capacitance of the high frequency amplifier circuit 3a, and 19a is a stray capacitance due to an arrangement at the time of mounting. The capacitance of the normally used first varactor diode 10a is the capacitance (C when the voltage applied to the cathode side of the first varactor diode 10a is 1V).
1 _L ) 20 pF, capacitance at applied voltage 24 V (C1 _H )
It is about 2.5 pF, and the capacitance (C _P ) of the capacitor 11a is about 10 pF. In addition to this, the input capacitance 18a (C _L1 ) 2 of the high-frequency amplifier circuit 3a, which becomes the load of the tuning circuit
About pF is connected in parallel with the capacitor 11a, and about 0.2 pF of stray capacitance 19a (C _L2 ) is connected in parallel with the tuning circuit. Therefore, the capacitance change ratio (hereinafter referred to as the capacitance change ratio) when the applied voltage is 1 V to 24 V is 3.3 according to (Equation 1).
When the applied voltage is 1 V to 24 V, the frequency change ratio (hereinafter referred to as the frequency change ratio) is 1.84 according to the general formula (Equation 2), which is 1.84, and 470 to 470 to 770 MHz which is the UHF band for Japan. The frequency can be changed by about 866 MHz.

[0006]

[Equation 1]

[0007]

[Equation 2]

However, in the configuration of the conventional technique 1 as described above, the frequency change ratio of the UHF band is 1.8.
It was very difficult to make it larger than 4. For example, in the case of the CATV channel for the United States, the reception frequency range is about 55 MHz to 800 MHz, and in order to receive this, in order to set the reception frequency range as wide as possible in the VHF band, for example, a varactor diode for a tuner is selected. Therefore, even if an attempt is made to increase the frequency change ratio, a varactor diode with a large capacitance change ratio tends to have a large capacitance at a low applied voltage. Therefore, the tuning circuit and a load with a high impedance coupled to it (such as a high frequency amplifier circuit) ) And the loss increases.
Even if the VHF band is divided into two bands and a varactor diode having a large capacitance change range is used as the Hi band and the Lo band, the VHF band has a limit in reception in the range of 55 MHz to 360 MHz in view of the total electrical characteristics. It is possible to divide the VHF band into three bands to further broaden the VHF band. However, downsizing and cost reduction become difficult as the number of parts increases. Therefore, in the input circuit 2a shown in FIG. 5, the frequency change range of the UHF band needs to be 360 MHz to 800 MHz. That is, the frequency change ratio is 2.22 or more. Capacitor 11a of FIG.
The larger the value of, the larger the frequency change range, but
Similar to the case described in the HF band, there is a problem that mismatch with the high frequency amplifier circuit 3a occurs, loss increases, and NF of the tuner deteriorates. In order to solve this problem, a conventional technique 2 in which two varactor diodes are used in the input circuit 2a
The method of can be considered. Prior art 2 will be described below with reference to the drawings.

(Prior Art 2) FIG. 6 is an equivalent circuit diagram of a main part of the prior art 2. 10a, 12a, 18a, 19a
Since the components are the same as those of the conventional technique 1 described above, the description thereof will be omitted. A second varactor diode 20a for coupling is connected between the tuning circuit and the high frequency amplifier circuit 3a. The capacitance change ratio of the second varactor diode 20a is the same as that of the first varactor diode 10a, and
Voltage applied to the cathode side of the varactor diode 20a of a capacitor (C2 _L) 20 pF approximately at 1V, the capacitance (C2 _H) 2.5 pF about when the applied voltage 24V.
With this configuration, the input capacitance 18a is equivalently smaller than that of the tuning circuit. Therefore, the capacitance change ratio according to Conventional Technique 2 is 5.78 according to (Equation 3), and the frequency change ratio is 2.
40. In other words, the frequency change range is 360 MHz to 86
It is up to 5MHz, and it is sufficient to include variations in parts.

[0010]

[Equation 3]

For example, in order to tune 360 MHz with an applied voltage of 1 V, the equivalent capacitance of FIG.
Therefore, the inductance value obtained by the general formula of (Equation 2) is about 9 nH. The first inductance element 12a, which is used for tuning the tuner, needs to be able to adjust the variation in parts, and an adjustable brass inductance line or polyurethane copper wire air core coil has been used.

[0012]

[Equation 4]

[0013]

However, in the structure of the prior art 2, since the adjustable brass inductance line is high in cost, the air core coil made of polyurethane copper wire is usually mainly used. In order to adjust this air-core coil, the number of turns is 2 or more in view of the elastic recovery characteristic of the coil, the wire diameter is about 0.3 mm, and the inner diameter of the air-core coil is 1.8 mm or more. Therefore, there is a problem that the inductance value of the air-core coil satisfying this condition is about twice as large as about 9 nH required in the conventional technique 2 and is difficult to realize.

The present invention solves the problems of the conventional technique 1 and the conventional technique 2 described above. An inductance element for tuning is provided by an air-core coil while ensuring a frequency change ratio of 2.22 or more in the UHF band. The object is to provide a tuner that can be formed.

[0015]

To achieve this object, a tuner input circuit according to the present invention has a first inductance element having one end connected to the input side, and the other end of the first inductance element. A second inductance element connected between the second inductance element and the ground, a first varactor diode whose anode side is connected to a connection point between the second inductance element and the first inductance element, and the first varactor. A second varactor diode in which both the cathode side of the diode is connected to the cathode side and the anode side is connected to the ground and a connection point between the first varactor diode and the second varactor diode are supplied with voltage from the voltage applying terminal. The connection point is connected to the input side of the high frequency amplifier circuit connected to the next stage.

[0016]

According to this structure, since the high frequency amplifier circuit is connected in parallel to the connection point of the first varactor diode and the second varactor diode, the input capacitance of the high frequency amplifier circuit connected to the input circuit is equivalent. Becomes smaller and at the same time the first
Since the varactor diode and the second varactor diode are connected in series, the capacitance of the entire input circuit also becomes small.
As a result, a frequency change ratio of 2.22 or more can be secured.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG. In FIG. 1, reference numeral 1 denotes an input terminal, an input circuit 21 to which a signal input from the input terminal 1 is supplied, a high frequency amplifier circuit 3 to which an output signal of the input circuit 21 is supplied, and the high frequency amplifier circuit. A mixing circuit 4 whose output signal is supplied to one input, and an oscillating circuit 5 which supplies a local oscillation signal to the other input of the mixing circuit 4.
And an intermediate frequency amplifier circuit 6 to which the output signal of the mixing circuit 4 is supplied, and an output terminal 7 to which the output signal of the intermediate frequency amplifier circuit 6 is supplied.

The input circuit 21 has the following structure. That is, the first inductance element 9 whose one end is connected to the input side 8 of the input circuit 21 and the first inductance element 9
Second inductance element 12 connected between the other end of the inductance element 9 and the ground, a first varactor diode 10 whose anode side is connected to the other end of the first inductance element 9, and The second varactor diode 20 whose cathode side is connected to the cathode side of the first varactor diode 10 and the anode side of this second varactor diode 20 are connected to the ground, and the first varactor diode 10 and the second varactor diode 10 are connected. The connection point of the varactor diode 20 is connected to the input side of the high-frequency amplifier circuit 3, and is composed of a resistor 16 connected between the cathode side of the first varactor diode 10 and the voltage application terminal 15.

The operation of the tuner configured as described above will be described below. R input from an antenna
The F signal is input to the input terminal 1 of the tuner and then to one end of the first inductance element 9. The RF signal impedance-matched and output from the other end of the first inductance element 9 is input to a tuning circuit including the second inductance element 12 and the first varactor diode 10, and the voltage application terminal 15 The capacitance value of the first varactor diode 10 and the second varactor diode 20 is controlled by the voltage value of
The F signal is selected by this tuning circuit. The RF signal output from the connection point between the first varactor diode 10 and the second varactor diode 20 is input to the high frequency amplifier circuit 3 and amplified. Then, the RF signal output from the high frequency amplifier circuit 3 is mixed with the local oscillation circuit 5 having a reception channel frequency in the mixing circuit 4 and converted into an intermediate frequency. Then, this output is amplified by the intermediate frequency amplifier circuit 6 and output from the output terminal 7.

Next, the reception frequency range of the input circuit 21 will be described in more detail with reference to FIG. 2 shows an equivalent circuit 22 of the main part of the input circuit 21 shown in FIG. In the essential part equivalent circuit 22, reference numeral 18 is an input capacitance of the high frequency amplifier circuit 3, and 19 is a stray capacitance due to the arrangement at the time of mounting. For example, in the case of a tuner compatible with CATV channels for the United States, the tuning frequency of the input circuit 21 has a frequency change range of 360 MHz to 800 MHz as a UHF band, and a frequency change ratio of 2.22 or more is required as described in Related Art 1 above. Becomes The capacitance of the first varactor diode 10 is about 20 pF when the applied voltage to the cathode side of the first varactor diode 10 is 1 V (C1 _L ), and the capacitance when the applied voltage is 24 V (C1 _H ) is 2.5 pF.
It is a degree. The capacitance of the second varactor diode 20 is about 20 pF when the voltage applied to the cathode side of the second varactor diode 20 is 1 V (C2 _L ).
The capacitance (C2 _H ) at an applied voltage of 24 V is about 2.5 pF. The input capacitance 18 (C _L1 ) of the high frequency amplifier circuit 3
Is about 2 pF and the stray capacitance 19 (C _L2 ) is 0.2 p
It is about F. Therefore, the capacitance change ratio is 5.91 according to (Equation 5), and the frequency change ratio is 2.43 according to the general formula of (Equation 2). That is, the frequency change range is 36
The range is from 0 MHz to 875 MHz, and it is sufficient to include variations in parts.

[0021]

[Equation 5]

In order to tune, for example, 360 MHz with an applied voltage of 1 V, the capacitance of FIG. 2 has the first varactor diode 10 and the second varactor diode 20 connected in series, so that the capacitance of the entire tuning circuit is small. Become. That is, since it is about 10.7 pF according to (Equation 6), (Equation 2)
The inductance value obtained by the general formula is about 18 nH, and the second inductance element 12 has two turns.
It can be realized with an adjustable air core coil with a wire diameter of about 0.3 mm and an inner diameter of 2.6 mm.

[0023]

[Equation 6]

Next, the input circuit 21 with less loss will be described with reference to FIG. In FIG. 3, a capacitor 23 and a resistor 24 are connected in parallel between the anode side of the second varactor diode 20 of FIG. 2 and the ground. In FIG. 3, the capacitor 23 is a laminated ceramic chip capacitor of about 47 pF, and the resistor 24 is about 100 KΩ, which is a carbon film chip resistor for DC grounding of the second varactor diode 20. At this time, the tuning circuit has a capacitance change ratio of 5.08 and a frequency change ratio of 2.25.
The frequency can be changed from 360MHz to 810MHz. The capacitance of the second varactor diode 20 at 360 MHz is about 9 pF, and the required inductance value is about 20 nH. Therefore, the second inductance element 12 can be realized by an air-core coil having two turns, a wire diameter of about 0.3 mm, and an inner diameter of about 2.8 mm, and variations in parts can be adjusted. Further, since the capacitance value of the input circuit 21 viewed from the high frequency amplifier circuit 3 becomes small, the matching with the high frequency amplifier circuit 3 having high impedance becomes good. That is, the frequency change range can be corrected by setting the capacitance value of the capacitor 23, and at the same time, the input circuit 21 has a circuit configuration with less loss. Further, the stray capacitance 19 can be made small by arranging the connection point between the anode side of the first varactor diode 10 and the second inductance element 12 as far as possible from the ground. Since the frequency variable range of the tuning circuit can be widened by this, if the capacitor 23 is made smaller than the capacitance value previously determined and selected in the necessary frequency variable range, the matching with the high frequency amplifier circuit 3 becomes good and the input with less loss is input. The circuit 21 can be realized.

As described above, according to the present invention, since the high frequency amplifier circuit 3 is connected to the connection point of the first varactor diode 10 and the second varactor diode 20, the high frequency amplifier circuit connected to the input circuit 21. The input capacitance of 3 becomes equivalently small. At the same time, since the first varactor diode 10 and the second varactor diode 20 are connected in series, the capacity of the input circuit 21 as a whole also becomes small. As a result, the second inductance element 12 can be formed by an adjustable air-core coil while ensuring a frequency change ratio of 2.22 or more.

[0026]

As described above, in the input circuit of the electronic tuner of the present invention, between the first inductance element whose one end is connected to the input side and the other end of the first inductance element and the ground. A second inductance element connected to the first inductance element, and a first node whose anode side is connected to a connection point between the second inductance element and the first inductance element.
Varactor diode, a second varactor diode in which both the cathode side of the first varactor diode is connected to the cathode side, and the anode side is connected to the ground, and the first varactor diode and the second varactor diode are connected. The first varactor diode and the second varactor diode are provided with a configuration in which a voltage is supplied from a voltage application terminal to the point and the connection point is connected to the input side of the high frequency amplifier circuit.
Since the high-frequency amplifier circuit is connected to the connection point of the varactor diode of, the input capacitance of the high-frequency amplifier circuit connected to the input circuit is equivalently reduced, and a wide-band variable tuning circuit is possible, and at the same time, the first varactor. Since the diode and the second varactor diode are connected in series, the capacitance of the entire input circuit is reduced, so that the second inductance element can be formed by an inexpensive air-core coil. Therefore, a broadband receiving circuit such as a CATV tuner for the United States can be realized at low cost.

[Brief description of drawings]

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

FIG. 2 is an equivalent circuit diagram of a main part of an input circuit of a tuner according to an embodiment of the present invention.

FIG. 3 is an equivalent circuit diagram of a main part of an input circuit of a tuner with improved loss according to another embodiment of the present invention.

FIG. 4 is a circuit diagram of a tuner according to the related art 1.

FIG. 5 is an equivalent circuit diagram of a main part of a tuner input circuit according to prior art 1.

FIG. 6 is an equivalent circuit diagram of a main part of an input circuit of a tuner according to Conventional Technique 2.

[Explanation of symbols]

 1 Input Terminal 3 High Frequency Amplifier Circuit 4 Mixing Circuit 5 Local Oscillation Circuit 6 Intermediate Frequency Amplifier Circuit 7 Output Terminal 8 Input Side 9 First Inductor Element 10 First Varactor Diode 12 Second Inductor Element 15 Voltage Applying Terminal 20 Second Varactor diode 21 input circuit

Claims (2)

[Claims] 1. An input terminal, an input circuit to which a signal input to the input terminal is supplied, a high frequency amplifier circuit to which an output signal of the input circuit is supplied, and an output signal of the high frequency amplifier circuit is one of The input circuit is provided with a mixing circuit supplied to an input, an oscillation circuit supplying a local oscillation signal to the other input of the mixing circuit, and an output terminal supplied with an output signal of the mixing circuit. A first inductance element whose one end is connected to the side, a second inductance element connected between the other end of the first inductance element and the ground, the second inductance element and the first inductance element. The first varactor diode whose anode side is connected to the connection point of the inductance element and the cathode side of this first varactor diode are both connected to the cathode side and the anode side is A second varactor diode connected to the ground, the first varactor diode and the second varactor diode.
An electronic tuner in which a voltage is supplied from a voltage application terminal to the connection point of the varactor diode of (1) and the connection point is connected to the input side of the high frequency amplifier circuit. 2. The electronic tuner according to claim 1, wherein a capacitor and a resistor are connected in parallel between the anode side of the second varactor diode and the ground.