JPS62287720A - Input filter circuit - Google Patents

Abstract

PURPOSE:To attain a filter circuit with a large attenuation characteristic with less circuit constitution by connecting the 1st filter circuit switched to a different filter characteristic and the 2nd filter characteristic switched to a different filter characteristic in cascade. CONSTITUTION:In receiving a TV signal from an input terminal 1, the signal is amplified by a high frequency amplifier circuit 3 through an input filter switched by a reception band and the result is outputted from an output terminal 3 from an output terminal via the 1st mixing circuit 4, a band pass filter 6, the 2nd mixing circuit 7 and the 2nd IF amplifier 9. The input filter 2 consists of an HPF 11 and an LPF 12 and consists of the filter circuit 43 switched into the 1st high pass filter characteristic and the 1st low pass filter characteristic by switching diodes 16-19 and the 2nd filter circuit 44 consisting of the BPF 13, the HPF 14 and switching diodes 20-25 and switched into the 2nd bypass filter and band pass filter characteristics and the 2nd low pass filter characteristic by connecting in cascade through a capacitor 26.

Description

Detailed Description of the Invention 6. Detailed Description of the Invention [Field of Industrial Application] The present invention relates to an input filter configuration of a double conversion tuner that receives a signal band such as a television signal by dividing it into a plurality of signal bands. .

[Conventional technology]

Regarding the input filter circuit of the double conversion tuner, please refer to Japanese Patent Application Laid-Open No. 60-74731 1% Opening No. 59-56.
No. 429 and Japanese Unexamined Patent Publication No. 57-3439 disclose a circuit that selects a receiving band by providing switching diodes at the input and output of a signal band selective filter (hereinafter referred to as BPF) and connecting them in parallel. Further, regarding filter circuits that allow shared use of elements and change the pass band frequency of the BPF, Japanese Patent Laid-Open No. 54-87456 and Japanese Patent Laid-Open No. 60-55740 can be cited.

[Problem that the invention seeks to solve]

In the above-mentioned conventional technology, each filter obtains the necessary range attenuation, so when a large amount of attenuation is required, the number of circuit components such as capacitors and coils increases.

Furthermore, since the filters are configured in parallel and switched by switching diodes, they are not completely turned off due to the reverse capacitance of the switching diodes, and the U
)(F(attenuation degree of I band or Vl when receiving U4F
(A sufficient degree of attenuation in the F signal band cannot be obtained.

Furthermore, when elements are shared and the selected frequency range of the BPF is changed over multiple bands, the number of circuit elements increases.

The object of the present invention is to provide a multi-band switching type that can obtain a large amount of attenuation with a small number of circuit components, especially V) (F' times signal attenuation when receiving UHF signal, V) (F' times signal attenuation when receiving UHF signal). The purpose is to obtain an input filter circuit.

[Means for solving problems]

For this purpose, filter circuits whose filter characteristics are switched are connected in series, for example, a first filter circuit whose filter characteristics are switched to a first filter characteristic and a second filter characteristic, a third filter characteristic, and a fourth filter characteristic.

by cascading a second filter circuit that switches to a fifth filter characteristic, or a first filter characteristic;
A first filter circuit that switches to a second filter characteristic and a fifth filter characteristic and a second filter circuit that switches to a fourth filter characteristic, a fifth filter characteristic, and a sixth filter characteristic are connected in cascade. This is achieved by

[Effect]

By cascading the first filter circuit and the second filter circuit, for example, the first filter characteristic and the third filter characteristic or the fourth . By cascading the fifth filter characteristics, the sixth. In order to obtain the seventh filter characteristic, one filter circuit can be used for two filter characteristics, and circuit components can be shared, reducing the number of circuit components, and the cascade connection of filters ensures out-of-band attenuation. Possible 0 [Example] An example of the present invention will be described below with reference to FIG.

FIG. 1 is a block diagram of a double conversion tuner using the input filter circuit of the present invention, 1 is a signal input terminal, and 2 is the input filter of the present invention.

5 is a high frequency amplifier, 4 is a first mixing circuit, 5 is a first local oscillation circuit, 6 is a band pass filter, 7 is a second mixing circuit,
8 is a second local oscillator, 9 is a second IF amplifier, 30
is a connection point between the input filter circuit 2 and the high frequency amplifier.

A TV or CATV signal of 50 to 850 MIh is inputted from an input terminal 1, passed through an input filter 2 which is switched depending on the receiving band, amplified by a high frequency amplifier circuit 3, and then inputted to a first mixing circuit 4. The input signal is sent to @11 mixed circuit 4 at the first
Frequency 2150 to 29 input from local oscillation circuit 5I
The first signal of 3000MHz is generated by the local oscillation signal of 50MHz.
The frequency is converted to an IF frequency and the first IF frequency is passed through the band/(frequency 5044 MH passed through the Sfiltalo and inputted to the second mixing circuit 7 and inputted from the second local oscillation circuit 8)
44 MHz by local oscillation signal of z (1) 2nd IF
Convert it to frequency! The signal is output from the amplified output terminal 10 by the 2 IF amplifier 9. Input filter 2 is high frequency amplifier 3
．． This is a filter for improving second-order intermodulation interference characteristics generated in the first mixing circuit 4. Input filter 2 is HP
It consists of FII and LPF 12, and switching diodes 16, 17, 18, and 19 determine the first high-pass filter characteristic (1 (PFI)) and the first port-bass filter characteristic (
A first filter circuit 43 that switches to
(It consists of P F13, BPF14, BPF15, and switching diode 20.21.22.23.24゜25, and has a second high-pass filter characteristic (BPF2), a band-pass filter characteristic (BPF), and a second low-pass filter characteristic (LPFl). ) are connected in cascade by a capacitor 26.The switching circuits for each band are omitted.The filter characteristics of the input filter circuit are shown in FIG. HPFll of the filter circuit 45, 101 is L P 112
, 102 is the BPF 15 of the second filter circuit 44,
Reference numeral 103 indicates the attenuation characteristic of the B P F14 filter, and 104 indicates the attenuation characteristic of the HP F13 filter. In the figure, the reception frequency bands are divided into B1. B1. BII[,B
IV, BI is up to 100MHz, BI is 1
From 00 to 210 MHz.

TV V) (F band or band for receiving CATV signals, B I [ha 210~450 Mk Mateno CAT
The BM receives a UHF band signal of 470M1lIz or higher. B1. BI, BI [When receiving, the 4!1 filter circuit 43 makes LPFl2 conductive to attenuate the BIT/band, which is a signal in the UHF band. In the second filter circuit 44, when receiving BI, the BPF 15 is made conductive, and the BI
When receiving, BPF14 is made conductive, and when receiving BIII, 1 (PF13 is made conductive, and combined with the filter characteristics of LPFll of the filter circuit 43 of 1!1, approximately 210 to 450
Obtain the MIIz bandpass filter characteristics. At this time T
B1.V is the VHF band signal reception band. The signal attenuation characteristics of BV, which is the UHF band of P Fli, and the L P F15 when receiving BI or BPF14 when receiving B The out-of-band attenuation characteristics of each BIIi' are superimposed, and the amount of attenuation of the UHF band signal during VHF band reception can be increased.
The difference signal component of the UHFW two-wave signal due to the second-order intermodulation distortion in the mixing circuit 4 is converted to Vt (F band), which improves the interference characteristics.On the other hand, when receiving the BY UHF band, the first filter circuit 45 In the second filter circuit 44, the HP F12 is made conductive, and the HPF'13 is made conductive in the second filter circuit 44.
TV scratch signal V) (BI becomes F band, HP F13 attenuation of BI frequency band, 1 (PF12 Bl, B1.B
I signal attenuation is superimposed, and V when receiving UHF band (BV)
Increases the degree of attenuation of HF band signals. This allows VHF
When receiving a band signal, the high frequency amplifier 3 and the first mixing circuit 4
The interference characteristics are improved in that the sum or difference signal component between the VHF band signal and the UHF imperial signal due to second-order intermodulation distortion is converted into the UHF band.

FIG. 3 shows an input filter circuit showing a second embodiment of the present invention, and parts having the same functions as those in FIG. 2 are given the same numbers and their explanations will be omitted. Input filter circuit 2 is HPF! A, B
PF32. The filter circuit of M3, which consists of BPF34 and the filter is selected from switching diodes 57, 38, 59, 40, 42, and the filter circuit of @B have different attenuation characteristics 1 (PF34, B P F5
5. LPF56 and switching diode 20~
A fourth filter circuit whose filter is selected by 25 is cascade-connected by a coupling capacitor 26. FIG. 4 shows the attenuation characteristics of each filter in FIG. 3. In Figure 4, the reception band is divided into five, and CAT
This is intended to improve the intermodulation interference characteristics when the V signal is damaged. Bl is up to 100Mff, BI[is 100
VHF band up to 210 M'riz (7) TV
-CATV signal, B M 210~500MH
z, BIV receives CATV signals of 300 to 450 MHz, and BV receives signals of TV UHF band of 470 Ml1z or higher. The figure shows the BPF of the third filter circuit 45.
The attenuation characteristic of BPF31 is set to 105, and the attenuation characteristic of BPF32 is set to 1.
On 06.

BPF33 decrease! The l characteristic is shown in 107. Furthermore, the attenuation characteristic of the BPF 34 of the filter circuit 46 of the conduit 4 is set to 108.

The attenuation characteristics of the BPF 35 are shown at 109, and the attenuation characteristics of the BPF 36 are shown at 110. The BPF 35 of the fifth filter circuit 45 is used when receiving BI, BI, and Bffi, and the BPF 36 is used when the fourth filter circuit 46 receives BI.

B ■ At the time of reception, the B P F35 is made conductive to obtain band characteristics, and at the time of BI [reception, HPF5a is made conductive, and with the attenuation characteristics of the third filter circuit 45 and the LPFS5, the band characteristics of 210 to 300 MHz are obtained. It has gained. At this time, Ml of BI and BII (at the time of F band reception, the UHF band attenuation characteristic of BPF31 of the third filter circuit 45 and the L P F36. B P F35 of the fourth filter circuit)
The band attenuation characteristics of the UHF band are superimposed, and the degree of signal attenuation of the U) (F band at the time of VHF band reception is increased. Also, BM.

When receiving BV, the fourth filter circuit 46 makes the HPF 54 conductive, and when receiving R■ in the third filter circuit, B
Makes P F32 conductive, and also makes HPF31 conductive when receiving BV.
are made conductive and each receiving 1M band is selected. At this time, when the By UHF band is received 1, the fourth filter 46 is
Attenuation characteristics of PF34 and HPF61 of quasi-3 filter 45
V l(F band signal attenuation degree is superimposed, a L(F'
It is possible to increase the signal attenuation in the VHF band during reception5, thereby improving the intermodulation interference characteristics due to the JHF signal during VHFVJ reception or the VHFM signal during Ul(F band reception. In the embodiment of the present invention shown in FIGS. 1 and 3, the bandpass filter characteristics of the reception band are cascaded and shared, and the V) TF band or UHF band is
It has the attenuation characteristics of a band, and has the advantage of being able to simplify the bottom of the circuit groove.

FIG. 5 is an input filter circuit showing a fifth embodiment of the present invention. 50 to 54 are band switching signal voltage terminals, as shown in the figure.
A suffix of B1-B5 is attached. 55-59 are switching diodes, 60-64 are coils, 65-
69H capacitor, 70~72H coupling capacitor, 73
77 are bypass capacitors, and 78 to 82 are bypass resistors. The circuit shown in FIG. 5 has a weak reception band of 4 bands from BI to B 'Iti', similar to the first embodiment of the present invention shown in FIG. a fifth filter circuit 4B that switches depending on the characteristics and the LPF characteristics;
A sixth filter circuit 49 in which HPF, LPF, and BPF are switched is connected in cascade. In the fifth filter circuit, when a voltage is applied to the band switching terminal B1, the switching diode 55 becomes conductive, the switching diode 56 becomes non-conductive, and the input and output of the fifth filter circuit are grounded by the coils 60 and 61, respectively. Input and output are capacitors 65.
66, and when a voltage is applied to the band switching voltage terminal B2, the fifth switching diode 56 becomes conductive, the switching diode 55 becomes non-conductive, and the input and output of the filter circuit are connected to the capacitors 65 and 66. The input and output are connected to the coil 60.6.
Low-pass filter characteristics connected by 1 (this switches). Also, in the sixth filter circuit 49, when a voltage is applied to the band switching terminal B5, the switching diode 59 becomes conductive, and the switching diodes 57 and 58 become non-conductive.
As shown in Figure 6(a), the input and output are capacitors 68.6
9 is grounded, and coils 62 and 63 are connected to input and output. Further, when a voltage is applied to the band switching voltage terminal B3, the switching diode 57 becomes conductive, the switching diodes 58 and 59 become non-conductive, and the sixth
As shown in Figure (b), the input and output terminals are grounded through coils 62 and 63, and the input and output terminals are connected through capacitors 68 and 69, exhibiting high-pass filter characteristics. Furthermore, band switching voltage terminal B3. B4. A voltage is simultaneously applied to B5,
As shown in FIG. 6(c), a capacitor 68 and a coil 62# are connected to the input and output, and a capacitor 69 and a coil 63
Two parallel resonant circuits and a capacitor 64
BPF % property is obtained by a series resonant circuit formed by the coil 67 and the coil 67. In the embodiment of the present invention, the value of capacitor 64 is approximately 17 pF, and the inductance of coil 67 is approximately 75 pF.
nH, the value of the capacitor 68.69 to 50 pF, and the value of the coil 62.65 to about 45 nH, and the cutoff frequency of the LPF characteristic of the sixth filter circuit 49 is set to 1.
00MH2, HPFe property/71) cutoff frequency to 200 MHz, BPF% band to 100~
I have been able to select 210MH2. Also, the value of the coil 60.61 of the filter circuit 48 of $5 is selected to be 20 nH, the value of the capacitor 65.66 is selected to be 7 pF,
The characteristic cutoff frequency is selected around 460MHz. Figure 7 shows the voltage applied to the band switching voltage terminal when receiving each band of BI-BIV. 1H1" indicates that a positive voltage is applied, and 'GND' indicates that the ground potential is applied. There is. B.I.

B1. When receiving BI, the fifth filter 48 applies a positive voltage to B2 to provide LPFW characteristics, and when receiving BI, the sixth filter applies voltage to switching terminal B5 to provide LPF characteristics. BI [When receiving, band switching terminal B3. B4
．． Apply a positive voltage to the BS, and add 100 to 210 Ml (z
Obtain the BPF characteristics of Furthermore, when receiving BI, a positive voltage is applied to the band switching terminal B3, and the H of the fifth filter circuit is
Due to the PF characteristics, a BPF % property with a passband of 210 to 460 M) is obtained. Further, when receiving the UHF band of BM, the fifth filter circuit 48 applies a positive voltage to the band switching terminal B1, and sets the I (PF characteristic) to the sixth filter circuit 48.
A positive voltage is applied to the band switching terminal B5 in the filter circuit 49 to obtain HPF characteristics. With these configurations,
When receiving VHF band BI and BII, in addition to the UHF band signal attenuation of the sixth filter circuit 49, the degree of attenuation due to the LPF characteristics of the fifth filter circuit 48 is taken into consideration, and the UHF band signal attenuation when receiving VHF band signals is Signal attenuation can be increased. Furthermore, when receiving BIV in the UHF band, in addition to the attenuation of the VHF band in the fifth filter circuit 48, the signal increases due to the )(PF characteristics of the sixth filter circuit 49, and V)(
By UHF band signal when receiving F no signal, or U) (F
Intermodulation interference characteristics caused by VHF band signal leakage when receiving a negative signal can be improved. Furthermore, the circuit configuration of the embodiment uses a coil and a capacitor in common for each filter characteristic, resulting in a configuration with a small number of circuit components.

FIG. 8 shows an input filter circuit configuration showing a fourth embodiment of the present invention. Similar to the second embodiment of the present invention shown in FIG. ing. In this embodiment, the fifth filter circuit 48 in the embodiment shown in FIG.
Characteristics, BPF characteristics.

It is constructed by cascade-connecting filter circuits that switch to LP'F characteristics. 8. Components in FIG. 8 having the same functions as those in FIGS. 1 and 5 are designated by the same numbers and their explanations will be omitted.

In FIG. 8, 49 is a first filter circuit, and 111-113 are band switching terminals, which are indicated by suffixes 81-B3. 8
8-90 are coils, 91-93 are capacitors, 94-9
6 is a bypass capacitor, 85 to 87 are switching diodes, and 97 to 99 are bias resistors. Also the 6th
The filter circuit is the same as the embodiment shown in FIG. 5, and the circuit components are given the same numbers, but the band switching terminals 52 to 54 have different suffixes from B4 to B6. In the seventh filter circuit, a positive voltage is applied to the band switching terminal B3 to set the cutoff frequency to 300 MHz, and the PF characteristic is set, and a positive voltage is applied to the band switching terminal BI to set the cutoff frequency to about 470 MHz. HPF characteristics and B1°B2. Applying a positive voltage to BS at the same time,
B with passband characteristics of i0MHz to 460MI]z
Switched to PF characteristics. FIG. 9 shows the switching state during reception of each band. B1. Bl [, B
When receiving I, the band switching terminal is set to 'Hi' in the seventh filter circuit 49, and an LPF with a cutoff of 500MdZ is used.
In the sixth filter circuit 48, a band voltage is applied as in the embodiment of the present invention shown in FIG.
, Bll, BI[. Naori I [During reception, the cutoff frequency of the LPF characteristic of the seventh filter circuit is 300Mh, so 200 to 500M1
(Has BPF characteristics with Z as passband. BIV, B
When receiving V, the sixth filter circuit 48 sets the band switching terminal B4 to 'H1' to set the cutoff frequency to 300M.
1 of H2 (assumed to be a PF characteristic. In the seventh filter circuit 49, when receiving BIV, a positive voltage of 1H1" is applied to all band switching terminals B1 to B5, and the passband is set to 500 to 45.
Obtain BPF characteristics at 0 MHz. Furthermore, when receiving BV, a positive voltage of 'H1' is applied to the band switching terminal B1, and the BV
Receives the Ul(F-no signal).

In this embodiment as well, as in the embodiment shown in FIG.
) (Degree of attenuation of UHF band signal when receiving F band and UHF
It is possible to increase the degree of attenuation of the V) 1F signal during band reception and improve intermodulation interference characteristics. Also in this embodiment, the coil and capacitor are shared to obtain filter characteristics, resulting in a configuration with a small number of circuit components.

In the embodiments shown in FIGS. 1 and 2, the case is shown in which two or three filters are switched in the front stage, the rear stage, but a configuration in which four or more filters are switched, In addition to connection, a cascade connection configuration of three or more stages is also possible.

〔Effect of the invention〕

According to the present invention, since circuit components can be shared for a plurality of filter characteristics, a filter circuit with large attenuation characteristics can be realized with a small number of circuit components. Furthermore, a filter circuit that can switch the reception band to a large number of bands with a simple configuration is possible. In addition, U The intermodulation interference characteristics caused by VHF band signals can be improved.

[Brief explanation of the drawing]

FIG. 41 is a circuit block diagram showing the first embodiment of the present invention,
@Figure 2 is an attenuation characteristic diagram of the filter circuit of the first embodiment, Figure 3 is a circuit block diagram of the second embodiment, Figure 4 is its attenuation characteristic diagram, and Figure 5 is the example of $3. 6 is an equivalent circuit diagram explaining its operation, FIG. 7 is a diagram explaining its switching operation, FIG. 8 is a circuit diagram showing an embodiment of WI4, and FIG. 9 is an explanation of its switching operation. This is a diagram. 2...Input filter circuit 3...Outside the high frequency amplifier
1 Figure 212] Class 3 Figure 4 Figure 6 (21 M 7 Figure

Claims (1)

[Claims] 1. A first filter circuit that switches between a low-pass filter and a high-pass filter, and a second filter circuit that switches between a low-pass filter, a high-pass filter, and a band-pass filter are connected in cascade, and the first filter circuit switches between a low-pass filter, a high-pass filter, and a band-pass filter. The cut-off frequency of the low-pass filter and the cut-off frequency of the high-pass filter of the second filter circuit are close to each other, and the cut-off frequency of the low-pass filter of the second filter circuit and the low-pass cut-off frequency of the band-pass filter are close to each other, and the cut-off frequency of the high-pass filter is close to each other. A filter circuit characterized in that a frequency and a high-frequency cutoff frequency of a bandpass filter are close to each other. 2. The first filter circuit consists of a parallel connection of a low-pass filter and a high-pass filter in which switching diodes are arranged in series with the signal transmission line on the input and output sides, and the second filter circuit consists of 2. The filter circuit according to claim 1, comprising a parallel connection of a low-pass filter, a high-pass filter, and a band-pass filter each having a switching diode arranged in series on a signal transmission line. 5. The input and output of the second filter circuit are connected by a series connection of a first coil and a second coil, and the input and output are connected by a series connection of a first capacitor and a second capacitor. The input and output are connected by series connection of the third coil, the third capacitor, and the first switching diode, the connection point of the first coil and the second coil is grounded by the second switching diode, and the first 2. The filter circuit according to claim 1, wherein a connection point between the capacitor and the second capacitor is grounded through a fifth switching diode.