JPS62209910A - Band rejection filter - Google Patents

Abstract

PURPOSE:To improve simply and inexpensively the interrupting characteristic due to a lower side sideband by connecting in parallel at least three branches of the branch to connect serially the first and second indactances, the branch to connect serially the first capacitance and the first switch and the branch to have the second capacitance. CONSTITUTION:The signal inputted by an input terminal removes a channel frequency selected and designated by a system changing-over part 3 and a channel changing-over part 2 by passing through a frequency variable type band rejection filter. By turning on or off a switch D1 as the system changing- over part 3, a high frequency current flowing through a capacitance C2 is turned on or off, indactances L1 and L2 or the parallel resonance frequency of a parallel resonancing circuit composed of switches S1 and C1 are wholly shifted. In short, the frequency shifting is executed to a frequency band to be used respectively by one TV broadcasting system and the second TV broadcasting system RF converters. Further, the frequency to delete the band in respective frequency bands is changed over by turning on or off the switch S1 of two channel changing-over parts.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a frequency switching type band-elimination filter used in high frequency equipment such as an RF converter used in a VTR.

(Prior art) In recent years, VTRs have become widespread throughout the world, and are used in multiple regions using different television broadcasting systems, such as China and P.R. using the I'AL-D system.
VTRs of the type that can be used in both regions such as Southeast Asia using the AL-B system are being produced, and RF converters that can be used with different television broadcasting systems and broadcast frequencies of 4fF are also being produced. Switchable types have come into use.

An RF converter has the function of converting video signals and audio signals recorded on video tape, etc. into RF signals that can be received by a television (hereinafter referred to as TV).
This is a one-sided sideband system that requires only the upper sideband for the F-fold signal and video carrier wave, and the lower sideband is an unnecessary component that causes interference to the TV channel adjacent to the lower side.

In general, the RF output signal of the RF converter for VI (FI11) may be removed using a band-stop filter for the lower sideband, especially the frequency corresponding to the lower audio subcarrier. The majority.

Normally, in actual use, an RF converter is used by selecting an empty channel that is not used in broadcast waves in the area, so it is an output switching type for 2 or more channels, and the 4+F band elimination filter mentioned above is also linked. The configuration is such that the settings are switched by

The following will be explained based on the drawings.

Figure 5 shows the RF output spectrum of a conventional 2-channel switching RF converter, where 4 is the video carrier in the high channel, 5 is the upper audio subcarrier, 6 is the lower audio subcarrier, and 10 is the 41F region. This is the characteristic of the cancellation filter, and the image carrier wave at the low side channel7. Upper audio subcarrier8.
The lower audio subcarrier 9° band-elimination filter 11 similarly exhibits characteristics for the low side channel. Therefore, in a two-system switching type RF converter, a 4JF filter for lower side wave 4fF removal that can switch frequencies for 2 systems x 2 channels is used.
A region cancellation filter is required.

FIG. 6 is a block diagram showing the configuration of a band-stop filter used in a conventional two-system switching RF converter, in which 12 is a system switching section, 13 is a channel switching section, 14
．． 15, 16, and 17 are 44F band cancellation filters with a fixed frequency corresponding to the frequency of each channel of each system) A channel is selected, a branch channel on the B side or H side is selected by the channel switching unit 13, and the signal passes through a frequency-fixed 4) F-band elimination filter connected in series to each branch channel. The lower sideband is removed.

Such conventional methods have the problems of having a complicated circuit configuration, requiring a large mounting space, and requiring a large number of component parts, resulting in high costs. In some cases, the RF multiplied signal was output through a band-elimination filter for removal. However, this type of RF converter has the disadvantage that the lower sideband IF is output at the same level as the upper sideband, which considerably worsens the interference characteristics given to the lower adjacent channel. there were.

(Problems to be Solved by the Invention) The present invention is intended to solve the above-mentioned problems, and has a relatively simple circuit configuration, a small mounting space, excellent mass production, and inexpensive interference characteristics due to the lower side wave 41F. The purpose is to make people feel better.

(Means for solving the problem) In order to solve this problem, the present invention provides a branch path in which a first inductance and a second inductance are connected in series, and a branch path in which a first inductance and a second inductance are connected in series.
At least three branches are connected in parallel, including a branch in which the capacitance and the first switch are connected in series, and a branch having the second capacitance; This is a band-elimination filter consisting of a circuit connected to a second switch.

(Function) With the above configuration, the present invention can be mass-produced with a small number of parts and mounting space, and can improve the interference characteristics due to the lower sideband at a low cost.

(Example) Hereinafter, one example of the present invention will be described based on the accompanying drawings. FIG. 1 is a block diagram showing the configuration of a band-stop filter according to an embodiment of the present invention, in which 1 is a variable frequency band-stop filter, 2 is a channel switching section, and 3 is a system switching section. be. The signal inputted from the input terminal is passed through a variable frequency band-elimination filter to remove the channel frequency selected and designated by the system switching section 3 and the channel switching section 2.

FIG. 2 shows a basic operating circuit of an embodiment of the present invention. 0N10FF switch D as method switching unit 3
By setting the high frequency current flowing through the capacitance of C2 to 0N10FF L, L, , L2 or switch S□
, C unit to shift the parallel resonance frequency of the parallel resonance circuit as a whole.

Fig. 3 shows the operating characteristics when the basic operating circuit of Fig. 2(a) is operated, and the switch D1 is turned ON.
If it is, it corresponds to the frequency of fAl or fAl,
When turned off, it works as a band-elimination filter at a frequency corresponding to fB□ or fiz. In other words, this indicates that the frequencies desired to be used in the RF converters of one TV broadcast method A and the second TV broadcast method B are frequency shifted to the F range. Furthermore, the frequency that you want to eliminate within each frequency band is selected by switching the switch S of the channel switching section 2.
By applying 0N10FF to □, -fAx and fAl 1
9J changes like fllt and fIl□.

2(b), (C), (d), and (e) are equivalent circuits when the channel switching unit 2 and system switching unit 3 are switched, respectively. This is an equation that logically calculates the frequency at which the fF region is eliminated.

In the case of Fig. 2(b), when switch D1 is turned on, C
A high frequency current flows through the capacitance of 2. Further, in the switch S0, a high frequency current also flows through the inductance L2 when the switch S0 is in an open state. In other words, parallel resonance is formed between the series-connected inductance of 5L□ and the parallel-connected capacitance of C1 and C2, and the parallel resonance frequency fA is fA1=l/2
π L, +L, calculated by C1C2/Ct÷C2,
At this frequency, the impedance between the human power outputs becomes maximum and it operates as a band-stop filter.

Similarly, in the case of FIG. 2(C), switch Dll and switch S1
Both are ON, and the parallel resonance frequency fA2 is fA2=l/
Calculated by 2πJ mushroom π7 in 10,000.

In the case of Fig. 2 (d), both switches Die and switch S□ are 0.
At 1iF, the logical formula is fA□=1/2πJ and πη; YT In the case of Fig. 2 (c), switch D is OFF, switch S0 is OFF, and the logical formula is fB2 = 1/2 x It becomes π7r.

Therefore, there is always a frequency between fA and fB2.

fA□<f, 2 It is also clear that the relationship - holds true.

As described above, according to this embodiment, it is possible to switch the synchronization frequency of the band-stop filter with a simple circuit configuration, and there is also one circuit for switching the channel B; This can be achieved with a single circuit. Since the number of component parts is small, the area required for mounting can be reduced, which is advantageous in terms of cost, and has the advantage of being excellent in mass production and having extremely high practical value.

In one embodiment, the switch S is illustrated as a mechanical switch, but the same effect can be obtained even if an electrical switching element is used.

(Effects of the Invention) As described above, according to the present invention, it is possible to provide a frequency-switchable band-stop filter that has a simple circuit configuration, is inexpensive, has a relatively small mounting area, and is highly suitable for mass production. It will be done.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of a band-stop filter according to an embodiment of the present invention, and FIG. 2 is a basic operating circuit diagram. Figure 3 is an operating characteristic diagram, Figure 4 is a specific circuit diagram, Figure 5 is an RF output spectrum diagram of some conventional RF converters,
FIG. 6 is a block diagram of a bandstop filter of a conventional two-system switching RF converter. DESCRIPTION OF SYMBOLS 1... Frequency variable band-stop filter, 2... Channel switching section, 3... System switching section, 4... Video carrier wave of high side channel. 5 ... Upper audio subcarrier of high side channel, 6
...Lower audio subcarrier of the high side channel. 7...Video carrier wave of the low side channel, 8...Subcarrier for low side channel-1 sidetone, 9...Lower side audio subcarrier of the low side channel. 10...Characteristics of the high-side channel band-stop filter,
11...Characteristics of the low-side channel band-stop filter,
12... System switching unit, 13... Channel switching unit, 14, 15, 16.17... Fixed frequency band elimination filter. Patent applicant: Matsushita Electric Industrial Co., Ltd.), 1

Claims (1)

[Claims] At least three branches are connected in parallel: a branch where the first inductance and the second inductance are connected in series, a branch where the first capacitance and the first switch are connected in series, and a branch where the second capacitance is connected in series. , and further the first or second
A band-stop filter consisting of a circuit in which a second switch is connected between either end of an inductance.