KR20030067876A - Adjacent channel trap circuit of color television tuner - Google Patents

Abstract

PURPOSE: An adjacent channel trap circuit of a television tuner is provided to improve audio and burst characteristics of SECAM L' without affecting standard characteristic of PAL and SECAM L. CONSTITUTION: An adjacent channel trap circuit of a television tuner having a frequency converter(34) and a SAW filter(35) includes a 40.9MHz trap unit(341), an RC filter(342), and a switch(343). The 40.9MHz trap unit traps the frequency of 40.9MHz included in the primary IF frequency of the frequency converter. The RC filter is placed between the output terminal of the 40.9MHz trap unit and the input terminal of the SAW filter, and cuts off a DC component included in the output signal of the 40.9MHz trap unit. The switch switches according to a switching signal SW to bypass the output signal of the frequency converter to the SAW filter.

Description

Adjacent channel trap circuits for television tuners {ADJACENT CHANNEL TRAP CIRCUIT OF COLOR TELEVISION TUNER}

The present invention relates to an adjacent channel trap circuit of a television tuner. In particular, in the European television broadcasting PAL or SECAM system, the audio and burst characteristics of SECAM L 'can be achieved without affecting the standard characteristics of PAL and SECAM L. The present invention relates to an adjacent channel trap circuit of a television tuner, which can be improved and also, due to a simple circuit, to achieve process improvement and cost reduction.

The configuration of a general color television tuner is shown in FIG. 1, and FIG. 1 is a schematic diagram of a general television tuner. Referring to FIG. 1, a general television tuner performs a high pass through a high frequency signal which is a television broadcast signal through an antenna ANT. A high pass filter 11, an RF amplifier 12 for amplifying the high frequency signal through the high pass filter 11 with a set gain, and a band pass filter for band-passing the high frequency signal through the RF amplifier 12 ( 13), a primary frequency converter 14 for mixing a high frequency signal through the band pass filter 13 with an internal oscillation frequency to provide a primary IF signal, and a primary through the primary frequency converter 14; SAW filter 15 for band-passing an IF signal, a primary IF amplifier 16 for amplifying the primary IF signal through the SAW filter 15 to a set gain, and the primary IF amplifier 16 1st IF signal to internal oscillation frequency And a secondary frequency converter 17 for providing a secondary IF signal, and a secondary IF amplifier 18 for amplifying the secondary IF signal through the secondary frequency converter 17 with a set gain. have.

The color television standard system includes NTSC system, PAL B / G and SECAM system. According to each standard, frequency band, field frequency, horizontal frequency, video bandwidth channel bandwidth, voice / video carrier spacing, residual sideband, Image modulation polarity and voice modulation are different from each other. For example, the NTSC method has a bandwidth of 1 channel and the interval between voice and video carriers at 6 MHz and 4.5 MHz, and the PAL B / G and SECAM methods have a bandwidth of 1 channel. And an interval between audio / video carriers is 8 MHz (or 7 MHz) and 6.5 MHz (or 5.5 MHz).

In such a television broadcast, since an audio carrier or a video carrier of an adjacent channel is close to a desired channel, a carrier of the adjacent channel is used by using a trap circuit to increase the removal ratio for the audio or video carrier of the adjacent channel. Is removing.

FIG. 2 is an adjacent channel trap circuit diagram of a color television using the conventional SECAM L standard and the SECAM L 'standard. Referring to FIG. 2, 41.9 included in the primary IF signal through the primary frequency converter 24 is shown. A 41.9 trap section 214 and a 40.4 MHz trap section 243 are connected in series to trap the frequencies of 4 MHz and 40.4 MHz, respectively. A switching section is provided between the 41.9 trap section 214 and the 40.4 MHz trap section 243. In the SECAM L standard having the frequency band shown in FIG. 3A according to an external switching signal SW, the output signal of the 41.9 trap unit 214 is trapped to trap 40.4 MHz, which is a voice carrier of an adjacent channel. The output signal of the 41.9 trap unit 214 is configured in the SECAM L 'standard having a frequency band shown in FIG. 3B by providing a 40.4 MHz trap unit 243 as an input terminal. To the output of the 40.4 MHz trap section 243. Without going through the 40.4MHz trap unit 243 is configured to communicate only 41.9 trap 214.

Since the trap circuit of the conventional color television tuner implements and uses two trap circuits, there is a problem that an increase in volume and an increase in production cost are inevitable as the number of used parts increases.

In order to solve this problem, another conventional adjacent channel trap circuit as shown in FIG. 4 may be used.

FIG. 4 is another adjacent channel trap circuit diagram of a color television that uses the SECAM L standard and the SECAM L 'standard in common. Referring to FIG. 4, the first IF signal included in the primary IF converter 24 is included in the primary IF signal. A 40.9 trap unit 344 traps a frequency band including 40.4 MHz to 41.9 MHz as a center trap point, and a capacitance value is set at the rear end of the 40.9 trap unit 344 according to the switching signal SW. It includes a color compensation circuit unit 345 that is variable to compensate for the burst. In this way, the trap position in FIG. 4 is 40.9 MHz, which is close to the SECAM L 'voice carrier, degrades the characteristics by degrading the voice level, and includes a color compensation circuit for burst (color signal) correction.

Since the trap circuit of the conventional color television tuner uses one trap circuit and a color compensation circuit, the trap circuit is reduced to one stage, but the trap circuit is commonly used for the SECAM L standard and the SECAM L 'standard. When applied to the SECAM L 'standard, because the color compensation circuit is used to prevent burst deterioration, there is still a problem that the volume increase and the production cost increase are inevitable with the increase of the used parts.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and therefore, an object of the present invention is to provide audio and audio information of SECAM L 'without affecting the standard characteristics of PAL and SECAM L in the PAL or SECAM system, which is a European television broadcasting system. It is to provide an adjacent channel trap circuit of a television tuner that can improve the burst characteristics and can achieve process improvement and cost reduction due to a simple circuit.

Schematic diagram of a typical television tuner.

2 is a conventional adjacent channel trap circuit diagram.

3A and 3B are frequency band diagrams of desired channels.

4 is another conventional adjacent channel trap circuit diagram.

5 is a desired channel frequency band and a trap frequency characteristic diagram.

6 is an adjacent channel trap circuit diagram of a television tuner according to the present invention.

Explanation of symbols on the main parts of the drawings

34: frequency converter 35: SAW filter

341: 40.9 MHz trap section 342: RC filter

343: switching unit

As a technical means for achieving the above object of the present invention, in the adjacent channel trap circuit applied to the European color television tuner including a frequency converter and a SAW filter, the first IF frequency of the frequency converter. 40.9MHz trap unit for trapping the frequency of 40.9MHz included in; An RC filter disposed between an output terminal of the 40.9 MHz trap unit and an input terminal of a SAW filter to block a DC component included in an output signal of the 40.9 MHz trap unit; And a switching unit configured to switch according to a switching signal to bypass the output signal of the frequency converter to the SAW filter.

Hereinafter, the configuration and operation of the adjacent channel trap circuit of the European color television tuner according to the present invention will be described in detail with reference to the accompanying drawings. In the drawings referred to in the present invention, components having substantially the same configuration and function will use the same reference numerals.

6 is an adjacent channel trap circuit diagram of a television tuner according to the present invention. Referring to FIG. 6, the adjacent channel trap circuit of the European color television tuner according to the present invention includes a frequency converter 34 and a SAW filter 35. It applies to European color television tuners, in particular SECAM L or PAL standard (hereinafter referred to as "SECAM L standard"), SECAM L 'standard.

The adjacent channel trap circuit of the European color television tuner according to the present invention includes a 40.9 MHz trap unit 341 for trapping a frequency of 40.9 MHz included in the primary IF frequency of the frequency converter 34, and the 40.9 MHz trap unit ( It is provided between the output terminal of the 341 and the input terminal of the SAW filter 35, and according to the RC filter 342 and the switching signal SW to cut off the DC component included in the output signal of the 40.9MHz trap unit 341 The switching operation is configured by a switching unit 343 for bypassing the output signal of the frequency converter 34 to the SAW filter 35.

The 40.9 MHz trap unit 341 is configured by connecting a capacitor C1 in series to an LC parallel circuit composed of a coil L1 and a capacitor C2.

The switching unit 343 is configured by connecting a collector terminal to an output terminal of the frequency converter 34, an emitter terminal to an output terminal of the SAW filter 35, and a switching signal SW terminal to a base terminal. do.

Operation of the preferred embodiment of the present invention configured as described above will be described in detail below based on the accompanying drawings.

The adjacent channel trap circuit of the television tuner of the present invention is applied to a color television tuner that uses the SECAM L standard method and the SECAM L 'standard method in common among European color television tuners, where each standard method is adjacent to a desired frequency band. Since the effects of the carriers are different from each other, it is to improve the characteristics of the desired frequency band by performing the function of selectively trapping the carriers of the adjacent channel that affects significantly. This will be described in detail below.

Referring to FIG. 6, a first IF frequency band output from the frequency converter 34 of the European color television tuner to which the trap circuit of the present invention is applied, in the SECAM L standard, as shown in FIG. An audio carrier (SIF) of 32.4 MHz and an image carrier (PIF) of 38.9 MHz are included, and an audio carrier (SIF) of 40.4 MHz of an upper adjacent channel is adjacent. In the SECAM L 'standard, as shown in FIG. 3B, a 33.9 MHz video carrier (PIF) and a 40.4 MHz audio carrier (SIF) are included in a desired band, and a 41.9 MHz video carrier (PIF) of an upper adjacent channel is included. Is close.

As described above, it can be seen that the frequencies of the adjacent channels, which adversely affect the desired channel, are different for each standard method. In the present invention, the 40.9 MHz trap function is switched according to the switching signal SW.

For example, in the SECAM L standard method (channel band: 32.15 MHz to 40.15 MHz), the switching signal SW is provided at a low level so that the NPN transistor Q1 of the switching unit 343 of the present invention is turned off. Accordingly, the output frequency of the frequency converter 34 is provided to the SAW filter 35 after passing through the 40.9 MHz trap unit 341 and the RC filter 342, respectively. At this time, in the 40.9 MHz trap section 341, the trap frequency f = 1 / (2π * sqrt {L1 * CT}) is determined by the combined value CT of the internal coils L1 and the capacitors C1 and C2. It is set to be 40.9MHz in advance and traps the 40.9MHz center frequency, which is the adjacent frequency of the desired band of the SECAM L standard method. As the 40.9 MHz frequency is trapped, the size of the 40.4 MHz voice carrier (SIF) of the adjacent channel is also reduced, thereby reducing the adverse effect of the 40.4 MHz voice carrier (SIF) of the adjacent channel on the desired band.

On the other hand, in the SECAM L 'standard method (channel band: 32.65 MHz to 40.65 MHz), the switching signal SW is provided at a high level so that the NPN transistor Q1 of the switching unit 343 of the present invention is turned on. Accordingly, the output frequency of the frequency converter 34 is directly provided without a trap to the SAW filter 35 through the switching unit 343 without passing through the 40.9 MHz trap unit 341. Here, in the SECAM L 'standard method, since the 41.9 MHz video carrier (PIF) of the adjacent channel is farther away from the desired frequency band than the SECAM L standard method, the influence on the desired frequency band is less.

In addition, since the present invention does not pass through the trap in the SECAM L 'standard method, the voice characteristic and the burst characteristic are not degraded without the need to add a separate color correction circuit as in the prior art.

In the present invention described above, the audio and burst characteristics of SECAM L 'are improved without affecting the standard characteristics of PAL and SECAM L, and the additional circuits are saved and characteristically stable even when the same circuit is used. Due to the audio noise of SECAM L 'in the conventional method, a defective rate can be reduced for a product determined to be defective in the process, thereby improving the process and reducing the material cost.

As described above, the trap circuit to which the present invention is applied may include a band elimination filter.

According to the present invention as described above, in the PAL or SECAM system, which is a European television broadcasting system, it is possible to improve the audio and burst characteristics of SECAM L 'without affecting the standard characteristics of PAL and SECAM L. The simple circuit has the special effect of achieving process improvement and cost reduction.

The above description is only a description of specific embodiments of the present invention, and the present invention is not limited to these specific embodiments, and various changes and modifications of the configuration are possible from the above-described specific embodiments of the present invention. It will be apparent to those skilled in the art to which the present invention pertains.

Claims (3)

In an adjacent channel trap circuit applied to a European color television tuner comprising a frequency converter 34 and a SAW filter 35, A 40.9 MHz trap unit 341 for trapping a 40.9 MHz frequency included in the primary IF frequency of the frequency converter 34; An RC filter 342 disposed between an output terminal of the 40.9 MHz trap unit 341 and an input terminal of the SAW filter 35 to block a DC component included in an output signal of the 40.9 MHz trap unit 341; And And a switching unit 343 for switching in accordance with a switching signal SW to bypass the output signal of the frequency converter 34 to the SAW filter 35. . The method of claim 1, wherein the 40.9MHz trap unit 341 is An adjacent channel trap circuit of a television tuner, characterized in that a capacitor is connected in series to an LC parallel circuit. The method of claim 1, wherein the switching unit 343 A television tuner comprising a collector end connected to an output end of the frequency converter 34, an emitter end connected to an output end of the SAW filter 35, and a switching signal SW end connected to a base end. Adjacent channel trap circuits.