JP2928248B2 - TV tuner input filter - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a television tuner device used in the field of video equipment.

2. Description of the Related Art In recent years, television tuner devices have been required to have improved interference rejection capability due to the increase in channels due to the development of CATV and the like.

Hereinafter, an example of the above-described conventional television tuner device will be described with reference to the drawings.

FIG. 2 shows an input filter of a conventional television tuner device. In FIG. 2, 2A is an input terminal, 2B is an output terminal, 2C is a first switching potential application terminal, 2D is a second switching potential application terminal, 2E is a tuning potential application terminal, 21, 22, 2
3, 24, 213, 218 are tuning coils, 25, 210, 214 are coupling capacitances,
26, 28 and 29 are switch diodes, 215, 216 and 217 are variable capacitance diodes, and 27, 211, 212 and 219 are bias resistors.

The operation of the television tuner device configured as described above will be described below.

First, the input signal (VHF) is input from terminal 2A,
They are divided into three bands, each with terminals 2C, 2D
The reception band can be set by setting the potential applied to the power supply as shown in Table 1 below.

First, when receiving 90 MHz to 150 MHz, the switch diodes 26, 28, and 29 all become non-conductive. For this reason, the signal is transmitted to the tuning coils 21, 22, 23, 24 and the variable capacitance diodes 215, 21.
The tuning frequency of the circuit is determined by the tuning capacitance constituted by 6,217. The tuning capacitance is determined by the reverse bias potential applied to the variable capacitance diodes 215, 216, 217 from the terminal 2E. The tuned frequency is supplied from a terminal 2B to the next high-frequency amplifier circuit. When receiving 150MHz to 220MHz,
Only the switch diode 26 conducts, and the input signal is supplied to the next stage from the terminal 2B at the reception frequency corresponding to the resonance frequency determined by the tuning coils 21, 22, 23, and 24 and the resonance capacitance. In this band, the resonance frequency becomes higher as the number of tuning coils decreases.

When receiving from 220 MHz to 460 MHz, all the switching diodes 26, 28, 29 conduct, so the tuning coils 21, 22,
23 and 24 are bypassed, only the tuning coil 213 participates in tuning, and the tuning frequency further increases.

Problems to be Solved by the Invention However, in the above configuration, 150 MHz to 220 M
At the time of receiving a Hz signal, interference in which the second-order distortion occurs in the 300 MHz to 440 MHz band occurred, and the commercialization level was sometimes not reached.

The present invention has been made in view of the above problems, and provides a television tuner device that attenuates the passage of a second harmonic of 150 MHz to 220 MHz at an input stage of the television tuner device, thereby improving the elimination of second-order distortion. It is the purpose.

Means for Solving the Problems In order to solve the above problems, the television tuner device of the present invention, after passing an input signal through an impedance conversion circuit by a parallel resonance circuit and a coil, the parallel resonance circuit and the tuning coil The tuning circuit includes a tuning circuit composed of a tuning coil component inserted in series and a reverse bias capacitance of a variable capacitance diode.

Effect of the Invention According to the present invention, since the parallel resonance circuit functions as a trap in a band of, for example, 300 MHz to 440 MHz with the above-described configuration, it is possible to improve the second-order distortion when a signal of, for example, 150 MHz to 300 MHz is received.

Embodiment Hereinafter, a television tuner device according to an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows an input filter section of a television tuner circuit of the present invention. In FIG. 1, 1A is an input terminal, 1B is an output terminal, 1C is a first switching terminal, and 1D is a second switching terminal.
A switching terminal, 11 is a first coil, 12 is a second coil, 13 is a third coil, 14 is a fourth coil, 113 is a sixth coil, 118 is a fifth coil, and 15 is a first coil. Coupling capacitance, 110 is a second coupling capacitance, 114 is a third coupling capacitance, 16 is a first switch diode, 18 is a second switch diode, 19 is a third switch diode, 115 is a first variable capacitance Diode, 116 is a second variable capacitance diode, 117 is a third variable capacitance diode, 17, 111, 112 are bias resistors, 11
Reference numerals 9 and 120 denote trapping capacitors connected in parallel to the first coil 11 and the fourth coil 14, respectively.

The operation of the input filter device of the television tuner device configured as described above will be described below with reference to FIG.

The input signal is input from terminal 1A. The parts other than the trap capacitors 119 and 120 in FIG. 1 are the same as those in the conventional configuration in FIG. 2 and the operation is also the same, so that the description of the parts will be omitted to avoid duplication.

Each of the trap capacitors 119 and 120 is a capacitor for parallel resonance. These capacitors 119 and 120 are inserted in parallel with the first coil 11 and the fourth coil 14 for tuning as described above,
The 300MHz to 440MHz band is attenuated. 150 MHz for this
It is possible to reduce the secondary distortion at the time of reception of up to 220 MHz.

As described above, the present invention can attenuate, for example, a signal component in a 300 MHz to 440 MHz band by installing a resonance capacitor in parallel with a tuning coil used for 150 MHz to 220 MHz reception. A television tuner device having a high ability to eliminate distortion interference can be provided.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a television tuner device according to an embodiment of the present invention, and FIG. 2 is a circuit diagram showing a conventional television tuner device. 11,12,13,14,113,118 …… Tuning coil, 15,110,114…
... Coupling capacitance, 16, 18, 19 ... Switch diode, 115, 11
6,117… Variable capacitance diode, 119,120… Capacity for trap.

Claims (1)

(57) [Claims] A first coil connected to an input terminal and a second coil connected to an input terminal, and a third coil connected to the input terminal;
A fourth coil, a first variable capacitance diode, and a second variable capacitance diode are coupled in this order and grounded, and a fifth variable capacitance diode is crossed from an intersection of the first variable capacitance diode and the second variable capacitance diode. An output terminal is provided through a coil, a first path grounded from a point between the fifth coil and the output terminal through a third variable capacitance diode, the first coil connected to an input terminal, and the first path connected to an input terminal. Grounded through two coils, a first coupling capacitance and a first switch diode are coupled in this order at the intersection of the first coil and the second coil, and further, the third coil and the fourth coil And the fourth coil, the first variable capacitance diode, and the second variable capacitance diode are coupled in this order and then grounded, and the first variable capacitance diode and the An output terminal is provided from the intersection of the second variable capacitance diode through a fifth coil, and a second path grounded from a point between the fifth coil and the output terminal through a third variable capacitance diode; The second coupling capacitance, the sixth coil, and the third coupling capacitance are coupled in this order through a second switch diode connected to a terminal, and then grounded, and the second coupling capacitance and the sixth coil are connected to each other. The third switching diode is coupled from the intersection to the intersection of the fourth coil and the first variable capacitance diode, and further grounded through the first variable capacitance diode and the second variable capacitance diode. An output terminal is provided from the intersection of the variable capacitance diode and the second variable capacitance diode through a fifth coil, and from the point between the fifth coil and the output terminal. A third path grounded through a third variable capacitance diode, the input filter of a television tuner being capable of selecting one of the three paths by switching a switch diode; An input filter for a television tuner, wherein a capacitor is connected in parallel to the fourth coil.