JP2971656B2 - Filter device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a filter device used as an input filter of a double super tuner employing a double super heterodyne system.

[0002]

2. Description of the Related Art FIG. 4 is a block diagram of a double super tuner. In FIG. 4, reference numeral 60 denotes an input filter;
1 is an automatic gain control circuit (AGC), 62 is an RF amplifier,
63 is a first mixer, 64 is a voltage controlled oscillator (VCO),
65 is a PLL (phase locked loop), 66 is a first intermediate frequency amplifier, 67 is a band pass filter (BPF), 6
8 is the second mixer, 69 is the second local oscillator circuit, 70 is the second mixer
It is an intermediate frequency amplifier.

The operation of the double super tuner will be described below. RF input to double super tuner
The signal (frequency f1) passes through one of the four filters switched by the reception channel in the input filter 60, passes through the AGC 61, is amplified by the RF amplifier 62, and is frequency-f3 = f2-f1 by the first mixer 63. (F2
Is converted to the first local oscillation frequency from the VCO 64). After that, the signal is amplified by the first intermediate frequency amplifier 66,
After passing only the frequency f3 in F67, the frequency is converted to the frequency f5 = f4-f3 (f4 is the second local oscillation frequency) in the second mixer 68 and amplified in the second intermediate frequency amplifier 70.

A conventional filter device used as the input filter 60 of the double super tuner will be described in more detail with reference to FIG. FIG. 5 is a block diagram of a conventional filter device. This filter device has a VL filter (up to 132 MHz) of 20, V
An H filter (132 to 243 MHz) 22, a VSH filter (243 to 471 MHz) 24, and a UHF filter (471 to 770 MHz) 26 are provided, and the four filters are switched by switches 71 to 86. J is the RF input terminal of the double super tuner,
K to N are input terminals of the filters 26, 24, 22, 20;
O to R are output terminals of the filters 26, 24, 22, 20;
S is an input terminal of the AGC 61 at the next stage.

The filter design of this conventional filter device is composed of a spiral coil and a capacitor of a printed foil capable of producing a filter without adjustment, and the RF input terminal J of the double super tuner and the high frequency of the double super tuner on the pattern. The distance between the input terminal K of the UHF filter 26 and the output terminal O of the UHF filter 26 and the AGC input terminal S of the next stage
Between the RF input terminal J and the low frequency V
The distance between the input terminal N of the L filter 20 and the distance between the output terminal R of the VL filter 20 and the AGC input terminal S are the longest.

[0006]

The UHF filter 26 which passes the highest frequency band in the above-mentioned conventional filter device.
FIG. 6 shows an equivalent circuit when is turned on. 6, 87, 89, 91, 93, 95, and 97 are coils,
88, 90, 92, 94, 96 and 98 are capacitors. Here, each of the filters 26, 24, 22, 20 shown in FIG.
Foil patterns KL, KM, KN connecting the inputs of
5 correspond to the coils 87, 89, and 91, respectively, and the inductance components of the printed foil patterns OP, OQ, and OR connecting the outputs of the filters in FIG. 5 correspond to the coils 93, 95, and 97, respectively. . The switches 73, 75, 77, 81, 83, 8 in FIG.
When the switch diode used for the switch 5 is turned off and the switch diode used for the switches 74, 76, 78, 82, 84, 86 is turned on, the switches 73, 75, 77, The minute capacitances of 81, 83, 85 have capacitors 88, 90, 92, 94,
96 and 98 respectively.

When the UHF filter 26 is turned on, the filter device shown in FIG. 5 is equivalent to a configuration in which a trap circuit including a coil and a capacitor shown in FIG. 6 is formed. Pattern K
Coils 91 and 97 corresponding to N and OR and a capacitor 9
The traps by 2,98 occur in the band of the UHF filter 26, and these influence the attenuation of the in-band characteristics of the UHF filter 26. This is shown in FIG. In FIG. 7, the horizontal axis represents frequency, and the vertical axis represents amplitude. As shown in FIG. 7, it can be seen that the high band around 800 MHz is attenuated by the trap at point a. When an air-core coil is used for filter design, the attenuation and disturbance of the in-band characteristics can be corrected by adjusting the air-core coil.
Coil 9 composed of printed foil pattern KN, OR
At 1, 97, the inductance component is fixed, and the in-band characteristics of the UHF filter 26 cannot be corrected by adjusting the coil.

An object of the present invention is to provide a filter device capable of eliminating attenuation and disturbance of the in-band characteristics of a filter in the highest frequency band without changing the in-band characteristics of each filter.

[0009]

According to a filter device of the present invention, a filter having the highest frequency band among a plurality of filters formed by a capacitor and a printed foil has a longest connection distance from a high-frequency input terminal and a next-stage input terminal. And a coil is inserted in at least one of the input-side common line and the output-side common line between the filter of the highest frequency band and the filter adjacent thereto.

[0010]

According to the structure of the present invention, the filter of the highest frequency band is made longer in distance from the high-frequency input terminal and the input terminal of the next stage. The coil is inserted in at least one of the input-side common line and the output-side common line between the input-side common line and the output-side common line when the filter of the highest frequency band is turned on. The low-pass filter formed by the inductance and the small capacitance of the input-side switch and the output-side switch that are turned off allows the band of the filter in the highest frequency band to pass, and traps do not occur in the band. Attenuation and disturbance of the in-band characteristics of the filter in the high frequency band can be eliminated.

[0011]

An embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a circuit configuration diagram of a filter device according to one embodiment of the present invention. This filter device is similar to the conventional device shown in FIG.
Is used as the input filter 60 of the double super tuner shown in FIG. In FIG. 1, 1 is an input-side common line composed of a pattern BE, 2, 3, 21, 23, 25, 27,
Reference numerals 36 to 43 denote resistors for passing a switch current, reference numerals 4 to 19 denote switch diodes, reference numerals 28 to 35, 44, 45, capacitors, 46, an output-side common line composed of a pattern FI, and 20, 22, 24, 26 shown in FIG. Is a filter composed of a capacitor and a spiral coil made of printed foil, and La is an air-core coil. Vcc is a power supply voltage, and BVL, BVH, BVSH, and BU are band selection voltages. A is the R of the double super tuner.
F input terminal (high-frequency input terminal), B to E each filter 20,
22, 24, 26, input terminals F to I are filters 20,
Output terminals 22, 24 and 26 and X are input terminals of the AGC 61 (FIG. 4) at the next stage.

In this filter device, the input side of the VL filter 20 is connected to the RF input terminal A via the switch diode 4, and the input side of the VH filter 22 is connected to the RF input terminal A via the switch diode 8 and the pattern BC. And the input side of the VSH filter 24 is connected to the RF input terminal A via the switch diode 12 and the pattern BD, and the input side of the UHF filter 26 is connected to the RF input terminal A via the switch diode 16 and the pattern BE. ing. The air-core coil La is inserted in the pattern DE of the input-side common line (pattern BE) 1. The output side of the VL filter 20 is connected to the switch diode 5.
, The output of the VH filter 22 is connected to the input X of the next stage via the switch diode 9 and the pattern FG, and the output of the VSH filter 24 is connected to the switch diode 13 and The input terminal X of the next stage is connected via the pattern FH, and the output side of the UHF filter 26 is connected to the input terminal X of the next stage via the switch diode 17 and the pattern FI.

When the UHF filter 26 that passes the highest frequency band in this filter device is on,
Switch diodes 6, 7, 10, 11, 14, 15,
16 and 17 are turned on, and the switch diodes 4, 5, 8,
9, 12, 13, 18, and 19 are off. FIG. 2 shows an equivalent circuit in this case. In FIG. 2, 47 to 52 are coils, and 54 to 58 are capacitors. Here, FIG.
The inductance components of the printed foil patterns BC, CD, DE connecting the inputs of the respective filters 20, 22, 24, 26 correspond to the coils 47, 48, 49, respectively, as shown in FIG.
Printed foil pattern F connecting the outputs of each filter
The inductance components of G, GH, and HI are the coils 52, 5
1, 50 respectively. Further, the series capacitance of the switch diode 4 and the capacitor 28 in FIG. 1 corresponds to the capacitor 53 in FIG. 2, and similarly, the switch diodes 5, 8, 9, 12, 13 and the capacitors 29, 30, 3
1, 32, and 33 are connected to the capacitor 54 of FIG.
~ 58. The air-core coil La inserted between the patterns DE is also indicated by La in FIG.

In FIG. 2, tentatively, capacitors 54 to 58
Is set to 0.5 pF, and the air-core coil La is adjusted so that the sum of the inductances of the coils 47, 48, 49 and the air-core coil La becomes 80 nH.
Thus, a low-pass filter having a pole is formed, and as shown in FIG. 3, good in-band characteristics of the UHF filter 26 are obtained. In this way, by configuring the low-pass filter equivalently to the UHF filter 26, the bandpasses outside the band of the UHF filter 26, does not adversely affect the band of the UHF filter 26, and Can be increased to compensate for the high-frequency range that tends to be attenuated.

As described above, according to this embodiment, the connection distance between the UHF filter 26 that passes the highest frequency band and the RF input terminal A is the longest, and the UH filter that passes the highest frequency band is
By making the connection distance between the F filter 26 and the input terminal X of the next stage the longest and inserting the air-core coil La between the patterns DE, when the UHF filter 26 that passes the highest frequency band is on, By forming a low-pass filter that allows the band of the UHF filter 26 to pass through, it is possible to eliminate attenuation and disturbance of the in-band characteristics of the UHF filter 26.

Although the air-core coil La is inserted between the patterns DE in this embodiment, the same effect can be obtained by inserting an air-core coil between the patterns HI on the output side of the UHF filter 26.

[0017]

According to the filter device of the present invention, the filter of the highest frequency band is set so that the distance from the high-frequency input terminal and the input terminal of the next stage becomes longer, and the filter of the highest frequency band and the filter adjacent thereto are arranged. A coil is inserted in at least one of the input common line and the output common line between the input common line and the output common line when the filter of the highest frequency band is turned on. The low-pass filter formed by the inductance of the input and the minute capacitance of the input-side switch and the output-side switch that are turned off passes the band of the filter of the highest frequency band, and traps do not occur in the band. Attenuation and disturbance of the in-band characteristics of the filter in the highest frequency band can be eliminated.

[Brief description of the drawings]

FIG. 1 is a circuit configuration diagram of a filter device according to an embodiment of the present invention.

FIG. 2 is an equivalent circuit diagram when a UHF filter is turned on in the filter device of the embodiment.

FIG. 3 is a diagram showing in-band characteristics of a UHF filter in the filter device of the embodiment.

FIG. 4 is a block diagram of a double super tuner.

FIG. 5 is a block diagram of a conventional filter device.

FIG. 6 is an equivalent circuit diagram when a UHF filter is on in a conventional filter device.

FIG. 7 is a diagram showing in-band characteristics of a UHF filter in a conventional filter device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Input-side common line 4-19 Switch diode 20 VL filter 22 VH filter 24 VSH filter 26 UHF filter 46 Output-side common line A RF input terminal (high-frequency input terminal) X Next-stage input terminal La Air-core coil

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H04B 1/16-1/26

Claims (1)

(57) [Claims] 1. A capacitor for passing a frequency band obtained by dividing an arbitrary frequency band into a plurality of filters and a plurality of filters made of printed foil are arranged in parallel, and an input side of each of the plurality of filters is connected to a high frequency input terminal. Connected to the input side common line via respective input side switches, and connected to the output side common line connecting the output side of each of the plurality of filters to the input terminal of the next stage via the respective output side switch. The filter device, wherein the filter of the highest frequency band among the plurality of filters is arranged so that the connection distance from the high-frequency input terminal and the input terminal of the next stage is the longest, and the filter of the highest frequency band is provided. A coil is inserted in at least one of an input-side common line and an output-side common line between the filter and an adjacent filter. Filter device.