JPH0339406B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a filter circuit such as a tuner that divides a signal band such as a television signal into a plurality of signal bands and receives the signal, and is particularly suitable for obtaining gain attenuation. Regarding the filter configuration.

[Background of the invention]

FIG. 1 shows a filter circuit consisting of a plurality of filters that switch reception bands using diodes. 1 is a signal input terminal, 2 is a signal output terminal, 3,
4, 5 and 6 are power supply terminals for band switching, 7 is a high pass filter, 8, 9 and 10 are band pass filters, 11 to 20 are switching diodes, 21 to 28 are resistors, 29 to 35
is a high frequency grounding capacitor.

This filter circuit is a filter circuit installed at the input section of the tuner for dividing and receiving television signals in the band of 50 to 900 MHz.The high-pass filter 7 has a circuit configuration as shown in FIG. A signal input terminal, 37 is a signal output terminal, 38 to 42 are capacitors, and 43 and 44 are coils. The bandpass filters 8, 9, and 10 have a circuit configuration as shown in FIG. 3, where 45 is a signal input terminal, 46 is a signal output terminal, 47 to 50 are capacitors, and 51 to 53 are coils. The pass band of band pass filter 10 is 50 to 90 MHz, the pass band of band pass filter 9 is 100 to 170 MHz, the pass band of band pass filter 8 is 170 to 270 MHz, and the pass band of high pass filter 7 is 270 to 900 MHz. .

For example, when trying to receive a signal in the passband of a bandpass filter of 100 to 170MHz, a positive voltage is applied to the band switching power supply terminal 5, the diodes 15, 16, 19, and 20 are made conductive, and the other With all diodes non-conducting,
A signal from a signal input terminal 1 is outputted from an output terminal 2 via a bandpass filter 9 to obtain a desired signal. Usually, a high resistance (about 100KΩ) is connected in parallel to each diode so that a uniform reverse bias is applied to each diode when the diode becomes non-conductive, but this is omitted here. When signals are selected through filters 8 and 10, they are received in a similar manner. When receiving a signal band from 270 to 900 MHz, apply a positive voltage to the power supply terminal 3, make the diode 11 conductive via resistors 21 and 22, and make the diode 12 conductive via resistors 24 and 25. , all other diodes are non-conducting.

Here, the reception band is switched by applying a positive voltage to the power supply voltage terminal or leaving it open, so the loss in the passband is minimized without changing the attenuation degree of the passband of each band. death,
The purpose is to increase the degree of attenuation outside the band as much as possible. Therefore, when gain attenuation by AGC is required, a variable attenuator composed of a PIN diode etc. should be used in the next stage of this filter, or
Alternatively, an RF amplifier capable of AGC operation is required.

[Purpose of the invention]

An object of the present invention is to provide a filter circuit that can change the amount of gain attenuation within a passband using AGC.

[Summary of the invention]

The present invention reduces the operating current of a diode in a conductive state in a filter circuit that selects one of a plurality of filters corresponding to a plurality of divided signal bands by making the diode conductive or non-conductive and passes a signal. is changed by the AGC signal to change the amount of attenuation in the passband.

[Embodiments of the invention]

A circuit diagram of a filter circuit according to an embodiment of the present invention is shown in FIG. In FIG. 4, elements having the same functions as those in FIG. 1 are denoted by the same numbers, and explanations thereof will be omitted.

56 is a high frequency grounding capacitor, 57 and 58 are diodes, 59 is a resistor, 60 is a power supply terminal, 61
64 is a transistor, 65 to 72 are resistors, 7
3 to 76 are power supply terminals corresponding to the band switching power supply terminals 3 to 6 in FIG. 1, and 77 is an AGC signal application terminal.

Transistors 61 to 64 apply voltage to the band switching power supply terminal of the signal band to be received.
By changing the current flowing through the diodes 11 to 18 by changing the AGC signal applied to the terminal 77 via the AGC signal, the impedance of the diodes 11 to 18 is changed. At this time, diode 11
By changing the current flowing through ~18, the voltages at the signal input terminal and signal output terminal 2 change, whereby the voltage applied to the terminal 60 causes the resistors 59 and 21 to change.
Alternatively, the current flowing through diode 57 or diode 58 via 25 changes. As a result, the amount of attenuation can be changed by the diode. Furthermore, diodes 11, 13, 1
By optimizing the impedance of the conductive diodes 5 and 19 and the impedance of the diode 57, it is possible to maintain the input VSWR at the signal input terminal at a substantially constant value. Furthermore, the VSWR at the output terminal can be made good for the same reason.

If VSWR at the input and output is not a concern, diodes 57 and 58 can be omitted.

Note that it is effective for the diode used in the present invention to be a PIN diode that has a low operating resistance value during low current operation, a small inter-terminal capacitance during reverse bias, and a relatively large change in operating resistance due to current.

〔Effect of the invention〕

According to the present invention, it is possible to realize a filter circuit that is capable of gain attenuation and has good input and output VSWR, and in combination with an RF amplifier that does not require AGC operation, allows gain attenuation by AGC, and It is also possible to eliminate the variable attenuator using the PIN diode, which simplifies the circuit configuration and is also effective in suppressing the interference characteristics generated by the RF amplifier.

[Brief explanation of drawings]

Fig. 1 shows a filter circuit consisting of a 4-division filter that performs band switching using switching diodes, Fig. 2 shows a circuit diagram of a high-pass filter, Fig. 3 shows a circuit diagram of a band-pass filter, and Fig. 4 shows an embodiment of the present invention. It is a filter circuit diagram showing. 1...Signal input terminal, 2...Signal output terminal, 3,
4, 5, 6... Power supply terminal for band switching, 7... High pass filter, 8, 9, 10... Band pass filter, 11 to 18, 57, 58... Diode, 60
...Power terminal, 61-64...Transistor, 73-
76...Power supply terminal for band switching, 77...AGC signal application terminal.

Claims (1)

[Claims] 1. In order to receive one signal band out of a plurality of signal bands, the signal input terminals of a plurality of filters provided for each signal band are connected to the signal input terminals via diodes, and The signal output terminals of the plurality of filters are connected to the signal output terminals through diodes, and the diodes of the input terminals and output terminals corresponding to the signal band to be received among the plurality of filters are made conductive.
A filter circuit characterized in that a diode in which the current flowing through the diode is controlled by an AGC signal and the operating current is controlled by the current flowing in the diode is connected at high frequency between a signal input terminal, a signal output terminal, and ground. .