JPH02148922A - Input circuit for bs tuner - Google Patents

Abstract

PURPOSE:To reduce the number of components and to reduce cost by providing plural series circuits each consisting the connection of an input terminal, a high pass filter and an attenuator in this order and a switch circuit inputting an output of the plural attenuators to a single input stage RF circuit alternative ly. CONSTITUTION:Attenuators 13A,13B each consist of 4 diodes D... combined in a lattice, the bypass diode D and the main path diode D... are subject to control by an AGC voltage and a current acting like pi type attenuator is given to the attenuators to adjust the attenuation of a 1st IF signal. The switch circuit 14 passes the 1st IF signal of any band selectively depending whether diodes DA, DB connected to series between the attenuators 13A,13B and the input stage RF circuit 15 are conductive or not by band selection voltages VA, VB. Thus, a switch changing over two reception antenna outputs or over selectively is not required and the cost is reduced.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides an input circuit for a BS chainer that inputs a desired signal using a switch (hereinafter referred to as an AB switch) that selectively switches the outputs of two or more receiving antennas. Regarding.

[Conventional technology]

Satellite broadcasting in a communication system using satellites may have a plurality of bands, for example, the C band using the 4Gu band and the Ku band using the 12 GHz band. In order to receive these broadcasts, it is necessary to provide dedicated receiving antennas (1) and (2) for each band as shown in FIG. Each receiving antenna (1) (2) converts the received radio wave into a 1 GHz band first) F signal using its converter (la) (2a) and outputs the signal. In order to input these first) F signals to the BS tuner (3), an AB switch (4) has conventionally been used to selectively switch the input.

AB switch (4) and BS tuner (3) shown in Figure 3
In the connection diagram, (5) (5) is a high-pass filter with a built-in AB switch that removes noise from the first F signal, (
6) is an electronic switch, (7) is a high-pass filter with a built-in BS tuner that removes noise, (8) is an attenuator that receives the AGC signal and adjusts the input level, and (9) is an RF circuit at the input stage.

As shown in FIG. 4, the electronic switch (6) is constructed by providing two switch circuits (6a) in parallel in which four PIN diodes (D) are combined in a ladder shape. Each switch circuit (6a) receives a switch signal (S-) and generates a switching voltage vl, which is generated by a band switching circuit (6b).
By setting one of V to s Hm level and the other to 'L'' level, one of the main path diode CD) and the side path diode (D) is made conductive and the other is non-conductive. This switch switches the circuit state to open or short circuit.

Switching voltages v1 and v2 are two switch circuits (6a)
(6a) are inputted in a mutually inverted relationship, so when one switch circuit (6a) opens and passes the first) F signal, the other switch circuit (6a) shorts and the first 1) Cut off the F signal.

The above attenuator 8) is a combination of four PIN diodes (D) in a ladder shape as shown in Figure 5.
The amount of attenuation of the first IF signal is adjusted by flowing a current that is controlled by the AGC voltage and acts as a π-type attenuator through the side path PIN diode (D) and the main path PIN diode CD. Due to its structure, the impedance of this attenuator (8) is always kept constant (for example, 75Ω).

[Problem to be solved by the invention]

The conventional input method described above has the problem that the AB switch (4) is separately provided, which increases the number of parts and increases the cost. In other words, since the ON B switch is an independent component, it must be built into a special shielded case with connection terminals, and a high-pass filter (5
) (5), and it is necessary to incorporate many circuits common to the input stage of the BS chainer, such as providing a band switching circuit (6b).

In addition, band switching is performed by opening one switch circuit (6a) of the electronic switch (6) to allow the first IF signal to pass, and at the same time, shorting the other switch circuit (6a) to fi (impedance 0). Therefore, a problem arises in that the reflected waves generated due to the impedance mismatch of the switch circuit (6a) in the cut-off state interfere with the other switch circuit (6a) in the open state, resulting in radio interference.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an input circuit for a BS tuner that can significantly reduce the number of parts and realize cost reduction, as well as minimize interference between receiving bands.

[Means to solve the problem]

The present invention provides an input for a BS tuner that includes a plurality of series circuits in which an input terminal, a high-pass filter, and an attenuator are connected in sequence, and a switch circuit that selectively inputs the outputs of the plurality of attenuators to a single input stage RF open circuit. Disclose the circuit.

[Effect]

The present invention incorporates the AB switch function into the BS tuner by connecting a switch circuit after a plurality of attenuators for each band, thereby greatly reducing the number of common parts such as high-pass filters. This makes it possible to reduce costs.

Furthermore, since the attenuator is placed on the input terminal side of the switch circuit, there is no reflection of the input 1)F signal, and radio wave interference between bands can be minimized.

〔Example〕

The present invention will be described with reference to one embodiment.

In FIG. 1, (1) and (2) are receiving antennas for satellite broadcasting, and (la) and (2a) are their converters. (
10) is the input stage of the BS tuner (1)) (1
)) is the input terminal, (12) (12) is the high-pass filter that removes noise, <13A) (13B) is the AG
(14) is an electronic switch circuit; (15)
has an input stage RF open circuit.

In the above circuit configuration, the attenuator (13A) (13
B) and a specific example of the switch circuit (14) are shown in FIG.

The attenuators (13A) (13B) combine four diodes (D) and - in a ladder shape, and the side path diodes <
The amount of attenuation of the 1st) F signal is adjusted by flowing a current that is controlled by the AGC voltage and acts as a π-type attenuator through D) and the main path diode (D). The attenuators (13A) (13B) have the same configuration as shown in FIG. Switch circuit (1
4) Attenuator (13A) (13B) and input stage RF
A diode (DA) connected in series between the open circuit 15)
Depending on whether or not (DB) is made conductive at the band selection voltage VA%VB, the first F signal of either band is selectively passed.

Note that the AGC voltage is a transistor (16A) (16B) that is turned on and off by the band selection voltage ■A1Va.
are added to the attenuators (13A) and (13B) through them.

In the above configuration, when receiving the C band of 4 Gtlz band, the band selection voltage vA becomes "H° level,"
The band selection voltage Va becomes °L". This band selection voltage vA causes the transistor (15A) to conduct and the attenuator (13A) to pass the first) F signal with an attenuation amount corresponding to the AGC voltage. 1) The F signal is the conductive diode (DA) of the switch circuit (14)
The signal passes through and is input to the input stage RF open circuit 15).

On the other hand, when receiving this C band, the band selection voltage vB is “L”
level, the transistor (16B) is non-conducting and the AGC voltage is not applied to the attenuator (13B), which is at maximum attenuation. Also, the diode (DB) of the switch circuit (14)
is also non-conducting. Therefore, the first IF signal of the Cu band of the 12Gz band is not input to the input stage RF open circuit 15).In particular, the impedance of the attenuator (13B) does not change even if it is in the state of maximum attenuation, so the amount of reflection is There is very little interference to C-band radio waves.

On the other hand, when receiving the Cu band of the 12GIIz band, the band selection voltage ＾ becomes “L” level and the band selection voltage V
a becomes H” level. Then, the attenuator (13A
) (13B) and the diode (D
The operation of A) (DB) is opposite to the above explanation,
Cu band 1st) F signal only input stage RF open circuit 15
) will be entered.

Note that, unlike the switch circuit (6) of the dedicated AB switch (4) mentioned earlier, the switch circuit (14) adopts a simple configuration that controls conduction/non-conduction using only one diode (Da) (Da). This is because the attenuators (13A) and (13B) can almost completely control the passing and blocking of the 1st) F signal, and this switch circuit (1)
4) may be configured by a switch using mechanical contacts.

[Effects of the Invention] According to the present invention, the function of the conventional AB switch is incorporated into the input stage of the BS chainer with a simplified circuit configuration, which eliminates the need for a dedicated AB switch, making it possible to significantly reduce costs. Become.

In particular, since a structure is adopted in which as many attenuators are provided as the number of input terminals and a switch circuit is disposed at the subsequent stage, it is possible to minimize received fδ interference between each band caused by reflection by the switch circuit.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the input circuit of a BS chainer according to the present invention, and FIG. 2 is a circuit diagram specifically showing the main part of FIG. 1. Figure 3 is a diagram showing how to connect a satellite broadcasting antenna to a BS tuner using a conventional AB switch, and Figure 4 is a diagram showing how to connect a satellite broadcasting antenna to a BS tuner using a conventional AB switch.
Circuit diagram showing a specific example of the switch circuit of the B switch, No. 5
This figure is a circuit diagram of the attenuator of the BS tuner shown in FIG. 3. (1))...-input terminal, (12)--high pass filter, (13A) (13B)...attenuator,
(14)...Switch circuit, (15)...Manual stage RF circuit. Patent applicant: Kansai NEC Corporation (7th generation)
Mr. Gangwon Province Go 1.
；□jjisu・j□ IQ Figure 1 Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] (1) Input of a BS tuner equipped with a plurality of series circuits in which an input terminal, a high-pass filter, and an attenuator are connected in sequence, and a switch circuit that selectively inputs the outputs of the plurality of attenuators to a single input stage RF circuit. circuit.