JP3157372B2 - filter - 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 device for a television receiver. More specifically, the present invention relates to a tuner device capable of switching a trapping frequency by controlling conduction / non-conduction of a switching diode. It is about filters.

[0002]

2. Description of the Related Art In recent years, with the expansion of the reception range of a tuner device, interference with a reception frequency from another frequency has become a serious problem.

FIG. 2 is a circuit diagram showing a VHF tuner section in a conventional television receiver. In the figure,
Reference numeral 3 denotes an input terminal to which a trap circuit for attenuating harmful signals in an intermediate frequency band used in a television receiver or a frequency band of a citizen band is connected, and 1 denotes a filter (FM trap circuit). ) And is configured as follows.

The input terminal 3 is connected to a coil L1, one end of a capacitor C1 and an anode of a diode D1, and a capacitor C2 and a resistor R1 are connected to a cathode of the diode D1. The other end of the capacitor C2 is connected to the other end of the coil L1 and the capacitor C1. The other end of the capacitor C2 is connected to the VHF input tuning circuit via the filter 2 formed by a parallel circuit of the coil L2 and the capacitor C3.

In the filter 1, the coil L1 and the capacitor C1 are set such that the resonance frequency is in the FM band when the switching diode D1 is non-conductive.
On the other hand, the capacitor C2 is a capacitor for cutting DC, and is set to a sufficiently large capacitance value so that the switching diode D1 can effectively pass a signal when conducting.

The filter 2 is an image trap circuit, and the resonance frequency is set to the image frequency of the receiving channel having the highest VHF by the coil L2 and the capacitor C3.

[0007]

However, the above-mentioned conventional circuit requires two resonance circuits such as the filters 1 and 2 in order to attenuate harmful signals from the FM band and image frequency. There were problems such as an increase in pattern area and an increase in material cost. An object of the present invention is to provide a trap circuit that eliminates the above-mentioned cost increase factors and that can be simplified by simple circuit means.

[0008]

Means for Solving the Problems To solve the above problems,
In the present invention, a signal path connecting the input terminal and the output terminal is interposed,
In a filter for selectively forming an image trap and an FM trap in response to switching of a switching diode between conduction and non-conduction when receiving a VHF, the filter includes a coil, first and second capacitors, and a switching diode. The coil and the first capacitor are connected in parallel, the anode side of the switching diode is connected to one end of the second capacitor, and the switching diode and the second capacitor connected in series are connected to the coil and the first capacitor. Connected in parallel with the capacitor of the filter, the cathode side of the switching diode of the filter is connected to the input terminal side, the switching diode and the non-connection side of the second capacitor is connected to the output terminal side, the switching diode and the second Of the switching diode between the second capacitor By inputting the switching control signal of the passing / non-conduction, there is provided a filter characterized by selectively forming said image trap and FM traps.

[0009]

With the above construction, the signal of the image frequency of the highest receiving channel is attenuated at the time of normal VHF reception, and the signal of the interference frequency is attenuated at the time of receiving a channel near the frequency of FM broadcast. Is effectively supplied to the input tuning circuit.

[0010]

An embodiment of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a circuit diagram showing a VHF tuner section of a television receiver to which the filter of the present invention is applied. This tuner device is for US channels,
The second to B channels can be received on the low channel, and the C to KK channels can be received on the high channel. An FM trap is set at the time of reception of six channels, and a signal near 92 MHz is set to be attenuated.

The filter 10 of the present invention shown in FIG. 1 is different from the conventional filters 1 and 2 shown in FIG. 2 in that the connection direction (anode, canode) of the switching diode D1 is reversed. , The coil L2 and the capacitor C3 are eliminated.

Reference numeral 5 is a low channel selection terminal, and 6 is a high channel selection terminal, to which 12 volts is applied when each is selected. Therefore, the switching diode D1 of the filter 10 always has a higher potential on the cathode side than on the anode side regardless of the selection of the low channel and the high channel, and is in a non-conductive state. Therefore, the coil L1 is set to 1
If 3 (nH) and the capacitor C1 are set to about 9 (pF), the resonance frequency F1 becomes

[0014]

(Equation 1)

F1 = 465 (MHz), and a trap can be formed near the image frequency of the KK channel.

Next, 12 volts is applied to the terminal 4 in order to operate the FM trap when receiving 6 channels. 6
Since the channel is a low channel in this tuner device, 12 volts is also applied to the terminal 5. However, the voltage applied from the terminal 5 is divided by the resistors R3 and R4, and the switching diode D1
Is lower than the potential on the anode side, the switching diode D1 becomes conductive.
At this time, if the capacitor C2 is set to about 220 (pF), the combined capacitance of the filter 10 becomes 229 (pF), and if the resonance frequency F2 is calculated by the above equation, F2 = 9.
It becomes 2.24 (MHz), and the signal of the frequency in the FM band can be attenuated.

[0017]

As described in detail above, according to the present invention, in the signal path connecting the input terminal and the output terminal, the image trap and the FM trap are switched according to the switching of the conduction / non-conduction of the switching diode when receiving the VHF. Are selectively formed, so that the constants of the parallel resonance circuit formed when the switching diode is in a conductive state and the parallel resonance circuit formed when the switching diode is in a non-conductive state can be changed. It has an excellent effect that it can be removed.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a tuner device to which the present invention is applied.

FIG. 2 is a circuit diagram showing a conventional tuner device.

[Explanation of symbols]

 1 filter 2 filter 3 signal input terminal 4 FM trap selection terminal 5 low channel selection terminal 6 high channel selection terminal 10 filter

Claims (1)

(57) [Claims] A signal path connecting an input terminal and an output terminal;
In a filter for selectively forming an image trap and an FM trap in response to switching of a switching diode between conduction and non-conduction when receiving a VHF, the filter includes a coil, first and second capacitors, and a switching diode. The coil and the first capacitor are connected in parallel, the anode side of the switching diode is connected to one end of the second capacitor, and the switching diode and the second capacitor connected in series are connected to the coil and the first capacitor. Connected in parallel with the capacitor of the filter, the cathode side of the switching diode of the filter is connected to the input terminal side, the switching diode and the non-connection side of the second capacitor is connected to the output terminal side, the switching diode and the second Of the switching diode between the second capacitor By inputting the switching control signal of the passing / non-conduction, filter, characterized by selectively forming said image trap and FM traps.