JP2911136B2 - Input tuning filter - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an input tuning filter used in a television receiver or the like.

2. Description of the Related Art In recent years, input tuning filters have been required to have higher performance than ever before with the development of new media.

Hereinafter, an example of a conventional input tuning filter will be described with reference to the drawings.

 FIG. 3 is a circuit diagram of a conventional input tuning filter.

The input tuning filter includes a tuning circuit A and an amplifier circuit B. The input tuning filter tunes and amplifies an input signal a in the VHF band input from the input terminal 1 and outputs the signal from the output terminal 2 to, for example, a mixing circuit.

The tuning circuit A includes tuning coils 3, 4, 5, 6 connected in parallel to the input terminal 1, two variable capacitance diodes 8 connected to the tuning potential terminal 7, and a resistor connected to the switch voltage terminal 9.
A switch diode 11 whose anode is connected via 10 and whose cathode is connected to the connection point of the tuning coils 3 and 4;
Amplifying circuit B has a first gate connected to the output of tuning circuit A, a second gate connected to gain control terminal 15, Drain is power terminal via choke coil 16
A field-effect transistor (FET) 20 connected to a source 17 and grounded via resistors 18 and 19, a resistor 21 and a capacitor inserted between the drain and the first gate of the FET 20
22; a resistor 23 inserted between the connection point of the resistors 18 and 19 and the first gate of the FET 20;
It is composed of five.

 The operation of the above configuration will be described.

First, an input signal (VHF band) a is input from an input terminal 1. Input signal a is a VHF low channel (90 to 150 MHz)
z), the switch voltage terminal 9 is set to a negative potential,
The switch diode 11 is turned off. Then, the input signal a is boosted by the ratio between the tuning coils 3 and 4 and the tuning coils 5 and 6 and supplied to the variable capacitance diode 8 via the coupling capacitor 13. A reverse bias potential is applied to the variable capacitance diode 8 from the tuning potential terminal 7, and tuning is performed by the reverse bias capacitance of the variable capacitance diode 8 and the tuning coils 3, 4, 5, 6 so as to receive a low channel. When the switch voltage terminal 9 is at a high potential (12 V), the switch diode 11 becomes conductive, and the reverse bias capacitance of the tuning coils 3, 6 and the variable capacitance diode 8 causes the VHF high band 150 to 220M.
Tune to receive Hz. The signal b filtered in this way is connected to the FET2 of the amplifier circuit B via the coupling capacitor 14.
0 is engaged with the first gate, and is amplified to a high gain by the FET 20,
Output from the output terminal 2 via the coupling capacitor 25.

However, in the above-described conventional configuration, when a signal from channel 1 (91.25 MHz) to channel 3 (103.25 MHz) is received, there is an interference signal having a frequency twice as high as the reception frequency. That is, if there is a signal from channel 6 (181.25 MHz) to channel 11 (211.25 MHz), a second-order distortion interference in which the frequency of the difference between the interference signal and the desired signal matches the frequency of the desired signal will occur. Further, when a signal of channel 11 is received from channel 6 and there is an interference signal of half the reception frequency, that is, if there is a signal of channel 1 to channel 3, the frequency of the interference signal is twice as high. A second-order distortion that coincides with the frequency of the desired signal is generated, and a beat is generated on the screen particularly in an area where the level of the interfering signal is larger than the desired signal by 20 dB or more. There was a problem.

The present invention solves the above-described problem. When receiving the channel 1 to the channel 3, the interference of the signal of the channel 6 to the channel 11 is reduced, and when the channel 11 is received from the channel 6, the reception of the channel 1 is performed. It is an object of the present invention to provide an input tuning filter for reducing interference of a signal of channel 3.

Means for Solving the Problems To solve the above problems, an input tuning filter of the present invention comprises a first filter interposed between a high-frequency signal input terminal and a ground.
A series resonant circuit composed of a switch diode, a tuning capacitor, and a first tuning coil, and a variable capacitance diode, a coupling capacitor, and a second switch diode interposed between the high frequency signal input terminal and the output terminal. And a parallel resonance circuit formed of a series circuit and a second tuning coil, wherein a first mode in which only the second switch diode conducts and a first mode in which only the first switch diode conducts, and the variable capacitance A second mode in which a reverse bias tuning potential is applied to the diode is selectable.

Operation According to the above configuration, when the VHF low channel is received, the first mode is selected, and the second switch diode is turned on. Channel 11 high channel frequency signal is attenuated,
When receiving a VHF high channel and a low channel station is located in the same area, the second
Is selected, and the first switch diode is turned on, so that the series resonance circuit attenuates half the channel frequency of the reception frequency, for example, the frequency of channel 1 to channel 3, and thus the secondary frequency generated during reception. The distortion is suppressed below the detection limit.

Embodiment Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of a video detector using an input tuning filter according to an embodiment of the present invention.

In the video detector, VH input from input terminal 31
The F-band input signal d is tuned and amplified by the input tuning filter 32 and output to the TV tuner 33.The high-frequency signal supplied to the TV tuner 33 is selectively received by a desired signal and converted to a first intermediate frequency. The video signal e supplied to the video detection circuit 34 and detected by the video detection circuit 34 is output to an output terminal 35.
Is supplied to the next stage, and the presence or absence of the video signal e is detected by the signal detection device 36, and the output is supplied to the input tuning filter / TV tuner control device 37 as a detection signal. The control device 37 searches the signal frequency in the reception area in the initial state, and confirms the presence or absence of the signal frequency by the presence or absence of the video signal e.

 FIG. 2 shows a circuit diagram of the input tuning filter 32.

The input tuning filter 32 is connected to an input terminal 41 and has a choke coil 42 for grounding a DC component, a first switching diode 44 and a tuning capacitor 45 which are turned on by a switching potential applied from a first switching voltage terminal 43. And a first tuning coil 46, a series resonance circuit connected to the input terminal 41, a variable capacitance diode 48 to which a reverse bias potential is applied from a tuning voltage terminal 47, a coupling capacitor 49, and a second switch voltage. A second switching diode 51 which is rendered conductive by a switching potential applied from a terminal 50;
, A parallel resonance circuit composed of a series circuit consisting of
Tuning capacitors 54, 55 connected to both ends of 44, 51, bias resistors 56, 57, 58, and an output terminal connected to the amplification circuit 53
59 and is formed from. The trap center frequency of the series resonance circuit is set around channel 2 (99 MHz), and the trap center frequency of the parallel resonance circuit is determined by the reverse bias capacitor of the variable capacitance diode 48, the coupling capacitor 49, and the second tuning coil 52. 6 (181.
It is set so that the frequency of channel 11 (211.25 MHz) is attenuated from 25 MHz).

With the above configuration, the control device 37 receives the second switch diode 51 when receiving the channel 1 to the channel 3.
, A higher potential than the second switch voltage terminal 50 is applied. Then, the reception frequency of channel 1 to channel 3 is 2
Double, ie, the frequencies of channels 6 to 11 are attenuated by the parallel resonance circuit. Further, when receiving the channel 11 from the channel 6 and when the channels 1 to 3 are set in the same area, the control device 37 connects the first switch voltage terminal 43 to the first switch diode 44. A high potential is applied through. Then, a half of the reception frequency of channels 6 to 11, ie, the frequencies of channels 1 to 3, is attenuated by the series resonance circuit, and when the channels 1 to 3 are not stationed, the first switch diode By not conducting 44, the passage loss (about 1 dB) caused by the trap of the series resonance circuit is reduced. A reverse bias potential is applied to the variable capacitance diode 48 via the tuning voltage terminal 47.

As described above, it has a high interference rejection ability in relation to the frequency where the secondary distortion exists, and can prevent occurrence of a beat on the screen.

Effect of the Invention As described above, according to the present invention, channel 1 in the VHF band
When receiving the channel 3 from the VHF band, the first mode is selected, the second switch diode is turned on, the channel 11 is received from the VHF band 6 and the channel 1 to the channel 3 is received in the same area. When the station is stationed, the second mode is selected and only the first switch diode is turned on, thereby exhibiting a high interference rejection ability in relation to the frequency in which the second-order distortion exists. Can be prevented from occurring. In the same area, VHF channel 1 to 3
By not conducting the first switch diode when is not stationed, the passage loss caused by the trap of the series resonance circuit can be reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram of a video detector using an input tuning filter according to an embodiment of the present invention, FIG. 2 is a circuit diagram of the input tuning filter, and FIG. 3 is a circuit diagram of a conventional input tuning filter. . 32: input tuning filter, 44: first switch diode, 45: tuning capacitor, 46: first tuning coil, 48: variable capacitance diode, 49: coupling capacitor, 51: second Switch diode, 52... Second tuning coil.

Claims (1)

(57) [Claims] A first switch diode and a tuning capacitor interposed between a high-frequency signal input terminal and ground;
And a second tuning coil, a series circuit comprising a tuning coil, a series resonant circuit, a variable capacitor diode, a coupling capacitor, and a second switch diode interposed between the high frequency signal input terminal and the output terminal. And a first mode in which only the second switch diode is conducted, and a reverse bias tuning potential is applied to the variable capacitance diode. And a second mode for selecting the input tuning filter.