JPS6229221A - Trap circuit for satellite broadcast television receiver - Google Patents

Abstract

PURPOSE:To prevent mixing of noise and to improve picture and sound quality by providing a trap circuit eliminating a microwave signal within a prescribed band from an intermediate frequency signal to the post-stage of an intermediate frequency amplifier. CONSTITUTION:A satellite broadcast television signal in 3.7-4.2GHz received by an antenna becomes the 2nd intermediate frequency signal whose center frequency 70MHz via a down-converter and a tuner circuit 2, amplified by an intermediate frequency amplifier circuit 3 and inputted to a trap circuit 5. When microwaves of 60, 80MHz exist and a switch 26 is turned off, a reverse bias is impressed to diodes 22, 23, which are turned off, and the frequencies 60 and 80MHz are trapped by the trap circuits 8, 9 to prevent mixture of noise. When microwaves of 60, 80MHz do n¦t exist, the switch 26 is turned on, the trap circuits 8, 9 are both short-circuited and no trap circuit is operated, then a sufficient band width is obtained and the picture and sound quality is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a trap circuit for removing microwave signals existing near a second intermediate frequency (70 MHz) in a satellite television receiver. be.

``Prior art'' Generally, satellite television broadcasts receive signals from communication satellites at 3°7 to 4°.
．． After receiving the 2Gllz signal with the antenna and amplifying it, the block down converter converts it to 430~930MHz.
A first intermediate frequency signal of z is obtained. This 430-930M
The 11z signal becomes a second frequency multiple of 70 MHz in the tuner circuit. The output waveform at that time has a center frequency of 70Mt (at z,
It has a frequency band of at least ±10 M1lz on both sides.

``Problem to be solved by the invention'' However, there is an area where microwave signals (M r ) (M 2 ) of 60 MHz and 80 MHz exist in a place exactly ±IOM) lz away from 70 M1 lz, and this microwave There was a problem in that the signals (Ml) (M2) became noise and mixed into the television signal.

``Means for Solving Problems'' The present invention has been made to solve the above-mentioned problems, and it amplifies the intermediate frequency signal output from the tuner circuit with an intermediate frequency amplifier, and further performs video detection. In this receiver, a trap circuit for removing microwave signals within a certain band from the intermediate frequency signal is provided at a stage subsequent to the intermediate frequency amplifier. This trap circuit consists of an upper trap circuit for removing microwaves and a lower trap circuit for removing microwaves.

"Operation" When the 70 MHz intermediate frequency signal output from the tuner circuit is set as the center frequency, microwaves that are ±10 MHz away from the center frequency are removed by the trap circuit, thereby preventing noise from entering. Also, when there is no microwave, turn on the switch and short-circuit the trap circuit with the switching diode. Then, since the trap circuit is not activated, sufficient bandwidth can be obtained and image and sound quality can be improved.

"Example" An embodiment of the present invention will be described below based on the drawings.

In Figure 1, (1) is the first frequency of 430 to 930 MHz.
An input terminal for an intermediate frequency signal, this input terminal (1) is coupled to a tuner circuit (2), an intermediate frequency amplification circuit (3),
Furthermore, a microwave trap circuit (5) and a video detection circuit (6) are connected via a coupling capacitor (4).
, coupled to the output terminal (7).

The trap circuit (5) consists of a lower microwave removal trap circuit (8) that removes 60 MHz microwaves and an upper microwave removal trap circuit (9) that removes 80 MHz microwaves. , these trap circuits (8) and (9) are coils (10), (11), and capacitors (12), respectively.
(13) (14), (15) (16) (17),
The resistors (18), (19), (20) and (21) form a so-called bridged T type. Furthermore, switching diodes (22) and (23) are connected in parallel to the trap circuits (8) and (9), respectively, and a resistor (24) is connected to the anode side of one of the diodes (23).

Power supply (
10B) is connected to the cathode side of the other diode (22), and a reverse bias power supply (10B) is connected to the cathode side of the other diode (22) via a resistor (27).
are combined.

In the above configuration, 3, 7 received by the antenna
~4.2 GHz satellite broadcast television signal is down-converted to obtain a first intermediate frequency signal of 430~930 M)lz.

This is input to the tuner circuit (2) via the input terminal (1) to obtain a second intermediate frequency signal with a center frequency of 70 MHz. This second intermediate frequency signal is transmitted to the intermediate frequency amplifier circuit (3).
The signal is amplified and input to the trap circuit (5).

Here, if microwaves of 60 MHz and 80 MHz are not present, the switch (26) is turned on. Then, the potential on the anode side of one diode (23) (
vl) becomes higher than the other cathode side potential (v2), and the two trap circuits (8) and (9) are both short-circuited by the diodes (22) and (23). Therefore, the output of the intermediate frequency amplifier circuit (3) passes through the trap circuit (5) with the dotted line characteristic (A) shown in FIG. 2, and is sent to the video detection circuit (6).

When microwaves of 60 MHz and 80 MHz are present, when the switch (26) is turned off, a reverse bias is applied to the diodes (22) and (23) to turn them off. Therefore, the output of the intermediate frequency amplifier circuit (3) is 60MHz in these trap circuits (8) and (9).
and 80MHz part are trapped, 60MHz and 8
The 0 MHz microwave is removed, resulting in a solid line characteristic (B) in FIG. 2, and this output is sent to the next stage video detection circuit (6).

"Effects of the Invention" Since the present invention is configured as described above, when microwaves exist within the band of the second intermediate frequency signal in satellite broadcast television, they can be removed by the trap circuit to prevent noise from being mixed in. . Furthermore, if the trap circuit is short-circuited using a switch when microwaves are not present, the bandwidth can be sufficiently widened and the image quality and sound quality can be improved.

[Brief explanation of the drawing]

FIG. 1 is an electric circuit diagram showing an embodiment of a trap circuit of a satellite broadcast television receiver according to the present invention, and FIG. 2 is a frequency characteristic diagram. (1)...Input terminal, (2)...Tuner circuit, (
3)...Intermediate frequency amplification circuit, (5)...Trap circuit, (6)...Video detection circuit, (7)...Output terminal, (8)...Lower microwave removal (9) Upper microwave removal trap circuit, (22) (23) Switching diode, (26) Switch.

Claims (3)

[Claims] (1) In a receiver that amplifies the intermediate frequency signal output from the tuner circuit with an intermediate frequency amplifier and further performs video detection, the microwave signal within a certain band is removed from the intermediate frequency signal at the subsequent stage of the intermediate frequency amplifier. A trap circuit for a satellite broadcast television receiver, characterized in that it is provided with a trap circuit for. (2) The trap circuit for a satellite broadcast television receiver according to claim 1, wherein the trap circuit comprises an upper microwave removal trap circuit and a lower microwave removal trap circuit. (3) A trap circuit for a satellite broadcast television receiver according to claim 1, wherein the trap circuit is turned on and off by a switching diode.