KR900011294Y1 - C.a.t.v. tuner - Google Patents

Abstract

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Description

Tuner for CATV

1 and 2 are block schematic diagrams showing a conventional tuner circuit.

3 is a block diagram of a tuner of the present invention.

4 is a main circuit diagram of FIG.

5 is a main circuit diagram of the local oscillation diagnosis of FIG.

6 is a main circuit diagram of the RF amplifier stage of FIG.

* Explanation of symbols for main parts of the drawings

12: single band tuner part 13: 2 band tuner part

14 signal selector 16 power circuit

20: diode 21: first voltage terminal

22: 2nd voltage terminal 24, 25, 27, 37, 53: switching diode

30: local oscillation stage 31: active element for oscillation (transistor)

41: amplification element (FET) 42: bias circuit

This invention devises a CATV tuner, in particular, a switch of a CATV tuner which constitutes each of two channels of a low band, a middle band, a high band, a super high band, and a high band of a VHF as a pair of tuners. It relates to a ching circuit.

In the US channel allocation method, a 133-channel CATV tuner is used.

This tuner has a reception band of 133 channels including 82 channels of UHF and VHF for general broadcasting and 51 channels for CATV. Specifically, the tuner is composed of a plurality of tuner parts and, as shown in FIG. It is comprised as three sets of tuner parts divided into the tuner part 1, the hyper tuner part 2, and the VHF tuner part 3. As shown in FIG.

Among them, the VHF tuner section 3 is a two-band tuner circuit, and an electronic tuner for converting a tuning coil using a switching diode 8 for band conversion is used.

FIG. 2 shows the main part of the band conversion circuit in the VHF tuner section 3, and the RF amplifier stage 5, the mixing stage 6, and the tuner section according to the voltage supplied to the band conversion terminal 4. As shown in FIG. Band selection is performed by conducting or non-conducting each switching diode 8 which performs band conversion of the tuning circuit of the local oscillation stage 7.

However, band selection is performed by changing the voltage level to the conversion terminal 4 as described above.

The so-called voltage conversion method requires a separate tuner operation power supply terminal and makes it difficult to control the operating voltage between bands for characteristics.

Therefore, it is difficult to apply and control other operating voltages for the equalization of the oscillating forces between the bands of the local oscillation stage 30, and this level of uniformity involves complicated circuits.

Accordingly, the present invention has been proposed in view of the above and aims to provide a new and improved CATV tuner that can be applied to any of so-called voltage conversion or terminal conversion.

In the first aspect of the present invention, the CATV tuner is configured to cover two sets of tuners that divide the low, middle, high, super high, and hyper bands of the VHF in a predetermined frequency range. The second band tuner part covering the channel allocated to the first and second bands in the first tuner part, and the single band tuner part 12 covering the channel of the third band in the second tuner part 13. Was used.

In this case, the channel of each band is designed to obtain a stable characteristic as a whole, so that the two-band tuner unit is set to cover 105 channels, as the channel cover range of each band is specifically shown below.

First band... Low band (2-6 channels) and part of middle band (A-5 to A-3 channels) Rest of second band middle band (A-2, AI channels) High band 7 to 13 channels and super high band Part 1 (JR channel) of the third band... A simplified circuit is provided that can be divided into three bands of individual channels such as the rest of the super high band (SW channel) and the hyper band (AA-WW channel), and can be applied to the selection of each band by a terminal conversion method. will be.

That is, the CATV tuner of the present invention covers the first to third bands of the VHF as two sets of tuners of the two-band tuner portion 13 and the single-band tuner portion 12, and simultaneously operates an operation power supply circuit for driving each tuner portion. The invention has been devised to supply the operating voltage to each tuner section from each group of voltage terminals.

Specifically, the diode 20 is inserted in the forward direction between the two-band tuner unit 13 and the first voltage terminal 21 of the first band selection, and the forward voltage drop is applied to the voltage and the terminal of the band selection. It is used as a positive conversion method.

According to the second aspect of the present invention, the switching diode used for band conversion in the local oscillation stage 30 of the two-band tuner 13 is connected in series with a DC blocking capacitor in series with the oscillating active element and the tuning coil. It is inserted in between to allow the selection of the first band and supply voltage to the active element.

That is, the voltage supply from the first voltage terminal 21 gives the oscillation operation of the first band, while the voltage is supplied from the second voltage terminal directly connected to the operating voltage supply side of the oscillation active element to select the second band. The terminal conversion was made possible.

In addition, in the voltage conversion method, the operating voltage is always supplied to the second voltage terminal 22 and the band conversion voltage is supplied to the first voltage terminal 21.

According to the above circuit configuration, when the first band is selected, the tuning coil is directly grounded without being affected by the switching diode, thereby increasing Q of the tuning circuit.

As a result, a high Q local oscillation circuit is formed to ensure stable oscillation over a wide range.

The stable oscillation operation with respect to such a first band is extremely advantageous since the cover range of the two-band tuner of the wide band tuner, such as the 133-channel CATV, is relatively high.

Therefore, in this paper, the band conversion method can be applied to any of voltage conversion and terminal conversion, and stabilization of oscillation at the time of selecting the first band is achieved.

According to the third aspect of the present invention, a switching diode in which the operating voltage for the RF amplifier stage of the two-band tuner unit is used for band selection in the terminal conversion method is effectively used.

In other words, an operation voltage supply method is disclosed in which the conduction current of the switching diode is kept constant despite the output change of the amplifying element 41 accompanying the AGC operation.

Specifically, the FET 41 and the bias circuit of the AGC-equipped RF amplifier 40 are connected in series with this switching diode in series. When the second band is selected, the voltage from the second voltage terminal 22 is sequentially changed. The switching diode in the direction is removed and supplied as the operating voltage of the amplifier and the bias circuit 42.

On the other hand, when the first band is selected, the voltage from the first voltage terminal 21 is applied to the connection point in the opposite direction to the switching diode and supplies the drain current and the bias current of the FET amplifying element 41.

That is, with respect to the switching diode, the first voltage terminal 21 is connected as the reverse bias and the second voltage terminal 22 is the forward bias, so that the operating current of the RF amplification only 40 is supplied.

Here, the change portion of the switching diode, which depends on the change of the output drain current accompanying the AGC operation of the FET amplification element at the time of selecting the second band, is canceled as a change in the opposite direction of the source bias current, resulting in a substantially constant current. Keep the value.

As a result, the change in reactance of the switching diode, which occurs depending on the current value, does not occur and is substantially constant, and the change in response of the tuner characteristic accompanying the change in reactance is reduced.

In particular, the circuit configuration of this paper stabilizes the conduction current of the switching diode used for band conversion, thereby maintaining the tuner characteristics.

EMBODIMENT OF THE INVENTION Hereinafter, the Example which concerns on this specification is described in detail, referring drawings.

3 is a block diagram of a CATV tuner according to the present invention, in which the UHF tuner section 11, the single band tuner section 12, and the two band tuner section 13 supply the operating voltage from the operating power supply circuit 14. Is driven.

Here, the operating voltage is supplied from each of the voltage terminals 21 to 23 to the two sets of tuners of the VHF, and the first voltage terminal 21 and the two band tuner portion 13 are characterized by the present design. The diode 20 is inserted.

The input signal is input to the input terminal of each band of U.IN or V.IN. A signal selector 16 is provided at the input terminal V.IN of the VHF, and the tuner unit 12 (13) in response to the band selection, respectively. Is delivered.

Each tuner section has a high frequency amplification stage (RF), a mixing stage (MIX), and a local oscillation stage (OSC), and is configured in the same manner as a typical UHF-VHF electronic tuner.

That is, each IF output of the UHF tuner section 11 and the single band tuner section 12 is amplified and derived from the mixing stage of the two-band tuner section 13.

FIG. 4 is a circuit diagram showing one part of the VHF in FIG. 3 specifically, and describes one oscillation terminal group of the power supply circuit 14, the signal selector 16, and the two-band tuner section 13 in detail.

A first to third voltage terminals 21 to 23 corresponding to each of the bands of the two-terminal voltage terminals of the VHF of the power supply circuit l4; specifically, the second to the two-band tuner portions 13; The first terminal 21 and the second terminal 22 each include the first band (for eight channels of the second to sixth channels of the low band and the A-5 to A-3 channels of the middle band) and the second band mid. The operating voltage is supplied to enable the tuning operation of A-2, A-1, A to I channels of the band, 7th to 13th channels of the high band, and 27 channels of the JR channel of the super high band). Configure the optional terminal conversion method.

In the case of using the voltage conversion method, an operating voltage may be supplied to the first voltage terminal 21 to apply a band switching switching voltage to the second voltage terminal 22.

On the other hand, the operating voltage of the single-band tuner 12 is supplied from the third voltage terminal 23 and is divided into two channels of S to W channels of the third band (super-high band) and AA to WW channels of the hyperband. Tuning).

In addition, although not shown, 70 channels of the UHF tuner portion are added to the 133-channel CATV to form the tuner.

Although not shown in the drawing, this power supply circuit 14 is provided with an AGC or AFT signal terminal in addition to the tuning voltage terminal, and operates the tuner to perform various controls.

The signal selector 16 is a signal separation switching diode connected to each power supply terminal for supplying an RF input signal from the VHF input terminal to either the single band tuner 12 or the two band tuner portion 13. (24) or (25) is used.

In particular, in selecting the two-band tuner part 13, a reverse flow prevention diode 26 is provided on the first voltage terminal 21 side and a band is provided on the second voltage terminal 22 side to select the first or second band. A conversion switching diode 27 is inserted to transmit the input signal of the selected band to the RF medium end of the tuner section, respectively.

On the other hand, the diode 20, which is a feature of the present design, is inserted between the first voltage terminal 21 and the two-band tuner portion 13, and the diode 20 is supplied when the voltage is supplied from the first voltage terminal 21. The voltage drop portion of is used.

In other words, the insertion of the diode allows the band supply by the voltage terminal conversion method to supply the voltage to the first and second voltage terminals 21 and 22, and consequently the terminal conversion and the voltage conversion of the band selection. It will provide a new tuner that can be used in combination.

The two-band tuner section 13 generates a predetermined IF output signal by receiving the supply of the operating voltage from the power supply circuit 14 and the VHF input signal from the signal selector 16. (30) consisting of the RF amplifier stage 40 and the mixing stage 60

The RF amplification stage 40 and the mixing stage 60 are coupled by a double tuning circuit 50 between the stages.

The tuning circuit 50 includes a tuning coil of the high channel coil 51 and the low channel coil 52 and a switching diode 53.

The local oscillation circuit 30, which is one feature of the present invention, enables the adoption of both methods of band conversion as described above, and is uniform with respect to the selection of the first and second bands (hereinafter referred to as low-mid high band). It is designed to get one characteristic.

That is, in the conventional circuit, the Q of the circuit resulting from the insertion of the switching diode in parallel with the tuning coil when the low band is received is reduced. However, the circuit of the present invention eliminates this and stabilizes the oscillation operation over the wideband and provides CATV. Provide appropriate circuitry for the tuner.

Specifically, the oscillation circuit shown in FIG. 5 is a transistor 31 of the oscillation active element, the variable capacitance diodes 32 and 33 for voltage tuning, the high and low channel coils 34 and 35, and the capacitor 36 that is characteristic of the present invention. And a series circuit of switching diode 37, the series circuit comprising a connection point a of both coils 34 and 35 for the high and low channels and an operating voltage supplying side of the transistor 31. inserted between (b).

At the same time, the connection point c of the capacitor 36 and the switching diode 37 is supplied with the voltage from the second power supply terminal 22 via the choke coil 38, and the electrode b of the transistor 31 is also provided. The DC blocking capacitor 39 is inserted between and the input, and the operating voltage is transmitted through the second power supply terminal 22 and the switching diode 37 or the first power supply terminal 21 and the backflow prevention diode 28. It is applied to (31).

In addition, a tuning voltage from the tuning terminal (not shown) is applied to the variable capacitance diodes 32 and 33 to be used for channel selection of each band.

As described above, in addition to the terminal voltage conversion, the band selection is also possible by supplying the operating voltage and the switching voltage to each terminal.

According to the above configuration, the selection of the first and second bands (low and high bands) is performed as the switching diode 37 as well as the voltage supply function to the transistor 31.

The wide band oscillation is enabled for high Q when the first band is selected to stabilize the oscillation operation.

On the other hand, it is possible to adjust the operating voltage between the bands, which is advantageous for the uniformity of the bands.

6 is a main circuit diagram of the RF amplifier stage 40 with AGC according to another aspect of the present invention, and shows the FET 41 and the bias circuit 42 of the RF amplifier.

The FET 41 is supplied with an RF input signal and an AGC control signal to its gate circuit, and the output side of the FET is coupled to the mixed element FET 61 of the mixing stage 60 via the double modulation circuit 50.

Here, the bias circuit 42 is connected to the first power supply terminal 21 via two series of backflow preventing diodes 29 via the voltage dropping diode 20 and the switching band diode 53 for band conversion. It is also connected to the second power supply terminal 22 via both, and the FET 41 is driven by AGC control by receiving a voltage supply from either terminal.

Specifically, the bias circuit 42 includes the second gate resistors 45 and 46 and the source bleedy resistors 46 and 47, which are connected to the bleedy resistor via the connection point 43. Alternatively, the operating voltage is supplied from the second power supply terminal 21 or 22.

At the same time, the driving voltage of the FET 41 is also applied via the choke coil 48 at the connection point 43 as a drain voltage, so that an amplification operation by AGC control is obtained.

In this case, the AGC operation changes the drain current. When the second band is selected, the current flowing through the switching diode 53 includes the current to the bias circuit 42, which appears as a canceling effect, resulting in a diode current. It maintains constant and shows stable amplification characteristic.

In other words, despite the AGC effect, the reactance of the switching diode for band conversion is kept substantially constant by constant operation current, thereby exhibiting stable tuner characteristics.

This is because the decrease in the drain current accompanying the AGC operation increases the current flowing through the bleedy resistors 46 and 47 of the source bias, and the operating current of the bias circuit 42 together with the operating current of the FET 41 is increased. By supplying past the switching diode 53, homogenization of the diode current is obtained.

Therefore, suppression of fluctuations in reactance for the squelch diode 53 of the single phase double tuning circuit 50 contributes to stabilization of the tuner response.

Claims (3)

A signal selector 14 for separating input signals from the VHF input terminals into first and second bands and third bands, and a two-band tuner section 13 for tuning a desired channel in the separated first and second bands; An operation power supply circuit 16 including first to third voltage terminals 21 and 23 installed corresponding to each band of the single band tuner unit 12 for tuning a desired channel in the separated third band; The diode 20 is inserted between the electric two-band tuner unit 13 and the electric first voltage terminal 21, and a predetermined band is converted into voltage by a voltage supply from each of the above-described voltage terminals, or by a terminal. A tuner for CATV, characterized by being selected as a conversion method. 2. The switching diode (27) according to claim 1, wherein the two-band tuner section (13) is a coupling coil for a high channel and a low channel, and a coupling diode 27 coupled to a connection point of the tuning coil via a DC blocking capacitor. A local oscillation stage 30 including an oscillation active element 31 having an electrode connected to the operating voltage supply side connected to the diode 27 and electrically connected to the connection point of the electric capacitor and the switching diode 27; CATV tuner to supply the operating voltage from 1 voltage terminal. 2. The second band tuner section (13) according to claim 1, wherein the second band tuner section (13) comprises an amplifying element (41) with an AGC control section, an output side double-tuning circuit containing a bias circuit (42) and a switching diode (13), The operating voltage of the switching diode 27 is supplied in the opposite bias in the first voltage terminal 21 and in the forward bias in the second voltage terminal 22 and the amplification described above. Either one of the operating voltages of the element 41 and the bias circuit 42 is supplied from one of the voltage terminals, and the current of the switching diode 27 is stabilized in a conductive state when the second band is selected. Tuner for CATV.