KR910009483Y1 - Low pass filter of bs tuner - Google Patents

Abstract

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Description

Broadband Input Filter Circuit for BS Tuner

1 is a block diagram of a conventional BS tuner.

2 is a block diagram of a BS tuner of the present invention.

3 is a conventional input filter circuit diagram.

4 is an input filter circuit diagram of the present invention.

5 is a frequency characteristic diagram of a conventional input filter circuit.

6 is a frequency characteristic diagram of an input filter circuit of the present invention.

* Explanation of symbols for the main parts of the drawings

F ₁ ': Input filter D ₂₁ -D ₂₄ : Barrier cap

L ₂₁ -L ₂₆ : coil R ₂₁ -R ₂₅ : resistance

The present invention relates to a BS tuner that tunes a broadcast wave received by a BS antenna. In particular, the BS tuner improves the filtering characteristics of an input tuning circuit of a BS tuner, thereby simplifying the configuration of the BS tuner circuit and improving selection noise and image talk. It relates to a wideband input filter circuit.

BS broadcasting system is a system that emits radio waves from the ground to broadcasting satellites and sends broadcasting signals to general homes.

The receiving system of the BS broadcasting system receives the 12GHz or 4GHz broadcasting wave transmitted from the broadcasting satellite through the BS antenna, converts the LNB to the RF signal of the IGHz band (strictly the first 1F signal), and then transmits the signal through the coaxial cable. The satellite broadcast signal is input to the indoor BS tuner, and the RF signal of the LNB input to the BS tuner passes through an input filter having a filtering band of 950-1750MH ₂ , and then an IF signal (strictly a second 1F signal) in the mixer. ) And then provided as a baseband signal to the TV set through an FM demodulator.

A general example of such a configuration of BS BS is shown in FIG.

As referred to herein, the satellite broadcast signal of the 4GHz or 120Hz band is converted into the RF signal of the 1NB band from the LNB and then the first IRF amplifier A ₁ , the first equalizer EQ ₁ , and the second RF amplifier EQ ₂ , The second filter (EQ ₂ ) is sequentially input to the input filter F ₁ .

The first and second equalizers EQ ₁ and EQ ₂ are provided to compensate for the frequency gain characteristic of the RF signal of the LNB because the frequency gain characteristic of the LNB is significantly decreased near the high frequency region.

The output outside the second equalizer EQ ₂ is configured to be converted into an IF signal (second IF signal) by mixing at the oscillation frequency of the OSC (O ₁ ) in the mixer M ₁ through a filter F ₁ , IF signal output from the mixer (M ₁ ) is configured to be provided to the FM demodulation stage (not shown) through the waveform shaping helical filter (HF ₁ ), AGC amplifier (A ₃ ) and IF amplifier (A ₄ ) in turn. have.

FIG. 3 shows a detailed circuit configuration of the second equalizer EQ ₂ and the filter F ₁ in the BS tuner block. Here, the second equalizer (EQ ₂ ) is composed of a condenser (C ₁ -C ₄ ), a coil (L ₁ -L ₂ ) and a resistor (R ₁ , R ₂ ), the first equalizer (EQ ₁ ) also It has the same configuration as that of the second equalizer (EQ _2).

The input filter F ₁ includes a low pass filter part, an impedance batching part, a high pass filter part, and a rear stage resistor part.

The low pass filter part is composed of a coil (L ₃ -L ₆ ), a condenser (C ₅ -C ₁₀ ) and the barrier cap diode (D ₁ , D ₂ ). Here, the coils L ₃ -L ₆ are implemented as strip lines on the substrate, and the tuning voltages V _T are applied to the barrier cap diodes D ₁ and D ₂ .

The impedance matching unit is implemented by connecting three resistors R ₃ -R ₃ in a π type.

The high pass filter unit is implemented as a loil (L ₇ -L ₉ ) and a capacitor (C ₁₁ -C ₁₅ ). The rear end resistor is implemented by resistors R6 and R7.

Therefore, when the RF input signal of the LNB through the first and second RF amplifiers A ₁ and A ₂ and the first and third equalizers EQ ₁ and EQ ₂ is input to the filter F ₁ , the low pass filter unit Filtered by a low pass frequency determined by the capacitance of the coil (L ₃ -L ₆ ), condenser (C ₅ -C ₁₀ ) and the capricap diodes (D ₁ , D ₂ ), the barrier cap diodes (D ₁ , D) ₂ ) The characteristic is that if the value of the DC tuning voltage (V _T ) is small, its capacity is increased and its capacity is small if the value of the DC tuning voltage (V _T ) is large, so it is filtered according to the change of the tuning voltage (V _T ). Tuning frequency fo To change. That is, when the tuning voltage V _T is high, the filtering tuning frequency fo is high, and when the tuning voltage V _T is low, the filtering tuning frequency fo is low.

In this way, the RF signal passing through the low pass filter part of the input filter F ₁ is input to the high pass filter part through an impedance matching part composed of resistors R ₃ -R ₅ .

The filtering frequency of the high pass filter unit is determined by the coils L ₇ -L ₉ and the capacitors C ₁₁ -C ₁₂ , and each of the coils L ₈ , L ₉ has a condenser C ₁₄ -C ₁₅ . In addition, the LC image trap is applied. The reason for this is to remove the video frequency (1930 MHz = 970 + 2 x 479.5) of the 24 channel frequency (70 MHz) of BS broadcasting.

Accordingly, the input filtering band by the high pass filter unit and the low pass filter unit covers 950-1750MH ₂ and is provided to the mixer M ₁ through the rear end resistors R ₆ and R ₇ .

The image removal ratio of the input filter F ₁ as described above is a relatively low 47 Hz level as shown in FIG.

However, the conventional input filter circuit has a complicated structure and a two-stage equalizer is required to maintain the filtering frequency gain evenly.

The object of the present invention is to provide a wideband input filter circuit for a BS tuner that does not require an equalization circuit installed at the front of the input filter and can maintain a high level of image rejection ratio and obtain broadband filtering characteristics.

Hereinafter, the present invention will be described with reference to the accompanying drawings.

Claim by the block diagram of the subject innovation turns 2, RF signal from the LNB is then amplified in the RF amplifier (A ₁₎ the input filter (F ₁ ') integrated input be connected to, and, wherein the input filters (F _1' is filtered in) RF signal to be output it is mixed in the oscillation frequency of OSC (O ₁₎ from the mixer (M ₁₎ is configured to be connected to the output IF signal.

The IF signal of the mixer M ₁ is configured to be provided to the FM demodulation stage (not shown) in sequence through the waveform shaping helical filter HF ₁ , the AGC amplifier A ₂ , and the IF amplifier A ₄ .

Since the RF amplifier A ₁ has the same configuration as the existing RF amplifier, the description thereof will be omitted.

The input filter F ₁ ′ has a circuit configuration different from that of the existing input filter.

A detailed circuit configuration for this is shown in FIG.

As can be seen here, the input filter F ₁ ′ is divided into a low pass filter part and a high pass filter part.

The low pass filter of the input filter F ₁ ′ is coil (L ₂₁ -L ₂₄ ), condenser (C ₂₂ -C ₂₅ ), barrier cap diodes (D ₂₁ , D ₂₄ ) and bias resistor (R ₂₁ -R _25). The coils (L ₂₁ -L ₂₄ ) are provided as serial strip lines on the transmission line of the RF signal, and each coil (L ₂₁ -L ₂₄ ) is a respective barrier cap diode (D ₂₁ , D ₂₄₎ ) And the capacitors (C ₂₂ -C ₂₅ ) are connected to ground, and each capacitor (C ₂₂ -C ₂₅ ) has a bias resistor (R ₂₁ -R) of the barrier cap diodes (D ₂₁ , D ₂₄ ). ₂₅ ) are connected more in parallel.

In addition, the tuning voltage (V _T ) passes through the bias resistor (R ₂₁ ) and is connected to the cathode axis of each of the baricap diodes (D ₂₁ , D ₂₄ ) through the coils (L ₂₁ -L ₂₄ ) in sequence. .

The high pass filter part of the input filter F ₁ ′ is composed of condensers C ₂₆ and C ₂₇ and coils ₂₅ and L ₂₆ , and the coil L ₂₅ and the coil C ₂₆ are image trap circuits. Is being prepared.

Here, reference numerals C ₂₁ and C ₂₆ are capacitors for binding between the RF amplifier A ₁ and the mixer M ₁ provided at the front and rear ends of the input filter F ₁ , and C ₂₉ is a DC blocking capacitor.

Referring to the operation and effects of the present invention configured as described above are as follows.

As referred to in FIGS. 2 and 4, the RF signal (first-order IF conversion signal) input from the LNB is amplified by the RF amplifier A ₁ and then the low pass filter part of the input filter F ₁ ′. Is entered.

At this time, the low pass filter unit changes the filtering frequency by changing the capacitance of each barcap diode (D ₂₁ -D ₂₄ ) according to the size of the tuning voltage (V _T ). ₂₂₎ and capacitor (C _23), varicap diode (D ₂₃₎ and a capacitor (C _24), varicap diode (D ₂₄₎ and the cone tensor (C _25), varicap diode (D ₂₄₎ and a condenser (C ₂₅ As the synthesized capacity of C) changes, it is possible to take the filtering band to a wide bandwidth up to 1800MHz.

In particular, since the variable cap diodes (D ₂₁ -D ₂₄ ) at each stage of the low pass filter part are directly controlled by the tuning voltage (VT) through each coil (L ₂₁ -L ₂₄ ), a flat gain characteristic appears over the entire filtering band. In addition, since the bandwidth of the typical BS tuner is 27 MHz, the use of a plurality of tuning circuits (filtering circuits) as in the present invention improves the rejection of adjacent channel interference and improves the selectivity.

The RF signal passing through the low pass filter part is input to the mixer M _{1 as} a wideband RF signal of 950-1800 MHz through the high pass filter part by the coils L ₂₅ and L ₂₆ and the condenser C ₂₇ .

The capacitor C ₂₆ added to the coil L ₂₅ of the high pass filter part is applied to the trap at the image signal frequency.

As described above, the RF signal output through the wideband filtering by the input filter F ₁ ′ is mixed with the oscillation frequency of the OSC (O ₁ ) in the mixer M ₁ and then output as an IF signal of 479.5 MHz, and the helical filter (HF _1). The IF signal is then shaped.

Since helical filter (HF ₁₎ IF signal (strictly speaking, the second IF signal) output from the FM demodulation stage via the automatic gain AGC amplifier (A ₁₎ and the IF amplifier (A ₁₎ which is controlled by the AGC signal (shown O) to provide the final IF signal.

6 shows the improved gain characteristics obtained in the present invention.

As described above, the present invention implements the input filter circuit of the BS tuner as a tunable filtering circuit using a plurality of variable cap diodes, so that the equalization circuit of the input filter stage can be eliminated, and the adjacent channel interference cancellation capability is improved. In addition, the unique effect of bringing the filtering band to the wide band is shown.

Claims (1)

In the BS broadcast tuner input filter circuit, a coil L ₂₁ -L ₂₄ , which is implemented as a stripline, is arranged in series on an RF signal transmission line of an LNB through an RF amplifier A ₁ and the coil L ₂₁ -L. ₂₄ ) connects each series synthesizing circuit by each of the barrier cap diodes (D ₂₁ -D ₂₄ ) and each capacitor (C ₂₁ -C ₂₄ ), and the barrier cap diodes (D ₂₁ -D ₂₄ ) The low pass filter unit is formed by connecting the coils (L ₂₁ -L ₂₄ ) in order to apply the integrated tuning voltage (V _T ), and the coil (L ₂₅ , L ₂₆ ) and the capacitor ( Broadband input filter circuit for a BS tuner comprising a high pass filter boot according to C ₂₆ , C ₂₇ ).