JPH03278729A - Satellite broadcast receiver tuning circuit - Google Patents

Abstract

PURPOSE:To prevent the occurrence of disturbance even when a 1st intermediate frequency signal of a satellite broadcast and that of satellite communication are transmitted in one cable by making a PIN diode conductive in the case of receiving a low frequency satellite broadcast and making the PIN diode nonconductive in the case of receiving a high frequency satellite communication. CONSTITUTION:A control means 63 is connected to a series resonance circuit via PIN diodes 62, 67 or high resistance resistors 60, 68 respectively and in the case of receiving a satellite broadcast signal of 1, 3 channels, the control means 63 applies a voltage to PIN diodes 62, 67 to make the PIN diodes 62, 67 conductive,thereby attenuating a local oscillating frequency band with a trap circuit 34. In the case of receiving a satellite broadcast signal at a high frequency, the control means 63 applies no voltage to the PIN diodes 62, 67 then the PIN diodes 62, 67 are nonconductive. Thus, the high frequency satellite broadcast signal is not attenuated. Consequently, disturbance is eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a second frequency converter which is a tuning circuit for a satellite broadcast receiver.

Conventional technology After converging the 12 GHz band radio waves emitted from satellite broadcasting with a parabolic antenna, a low noise converter
The satellite method can be received by converting the frequency to a first intermediate frequency in the IGHz band and inputting the signal to an indoor satellite receiver via a coaxial cable. In a satellite broadcasting receiver, one channel is selected from among several channels of signals, and then FM demodulation is performed to obtain a video signal and an audio signal. A conventional example will be described below with reference to the drawings.

FIG. 3 shows an example of a block diagram of a conventional satellite broadcasting receiver. In FIG. 3, 37 is an input terminal for the first intermediate frequency signal. 38 is a preamplifier circuit, and 39 is an image filter. 40 is a frequency mixer. 41 is a local oscillator. 42 is a band pass filter. 43 is an FM demodulator. 44
is an FM demodulation output terminal.

The operation of the satellite broadcast receiver channel selection circuit configured as described above will be explained below with reference to FIGS. 3 and 4.

A tuning function in which a first intermediate frequency signal is input to the input terminal 37, amplified by the preamplifier circuit 38, passed through the image filter 39, and mixed with the local signal created by the local oscillator 41 by the frequency mixer 40. In addition, the bandpass filter 42 selects only one wave to be demodulated by the FM demodulator 43, and plays the role of removing noise and interference.

Next, the frequency characteristics of the image filter 39 are shown in FIG.
is passed through (lossily), and its image frequency (
By attenuating frequencies (1836 to 2136 MHz) by 30 dB or more, image interference during channel selection is removed. (Reference: Satellite Broadcasting Receiver Part 1 Target Ratings, June 1980, published by Radio Technology Association) Problems to be Solved by the Invention In recent years, video signal distribution services using communication satellites are about to start. In the case of satellite communication, various bands are assumed for the first intermediate frequency, among which 136
0-1770 MHz is going to be used. If the first intermediate frequency band is set in this way, it will not overlap with the first intermediate frequency band of satellite broadcasting, so there is an advantage that both can be transmitted using two cables.

When satellite broadcasts are received by a conventional satellite receiver from a cable through which such transmission is carried out, the image filter 39 prevents the satellite communication signals from interfering with the image of the satellite broadcast signals.

However, when the frequency of the satellite communication signal matches the local oscillation frequency of the satellite broadcast, the satellite broadcast signal and the satellite communication signal cause a mixing effect in the frequency mixer 40, and the second intermediate frequency component (402, 73M H
z), so interference may occur. That is, the conventional image filter 39 has a frequency of 1880 MHz.
In the above, although it has sufficient attenuation characteristics of 30 dB or more, it has almost no attenuation characteristics at 1400 to 1500 MHz. Therefore, when the satellite communication first intermediate frequency signal has a higher level than that of satellite broadcasting, satellite broadcasting When receiving a channel on the lower side of the channel, if there is a satellite broadcast signal that is higher than the frequency of that channel by the second intermediate frequency, the problem is that they generate interference signals in the second intermediate frequency band. had.

In view of the above problems, the present invention provides a tuning circuit for a satellite broadcasting receiver that does not cause interference even when the first intermediate frequency signal of satellite broadcasting and that of satellite communication are transmitted through a single cable. This is what we are trying to provide.

Means for Solving the Problems As a means for solving the above points F and ff8, the satellite broadcasting receiver tuning circuit of the present invention passes the first intermediate frequency band of satellite broadcasting and blocks the image frequency band. an image filter; and an anode terminal of a PIN diode, which uses the output signal of the image filter as an input signal, connects a capacitor to one terminal of a first microstrip line, and has a cathode' terminal grounded to one terminal of the capacitor. and a control means connected to the anode terminal via a high resistance;
consisting of a second series resonant circuit having the same configuration as the first series resonant circuit, and a second microstrip line connecting the first and second series resonant circuits to each other,
a trap circuit whose resonant frequency is almost the same as the local oscillation frequency when receiving a low-frequency satellite broadcasting signal; a frequency mixer whose input signal is the output signal of the trap circuit; It has a configuration including a local oscillator that supplies an oscillation signal.

According to the above-described configuration, the number of traps is formed by the first microstrip line and the capacitor, and the resonant frequency is set to the local oscillation frequency band when receiving low-frequency satellite broadcasting. has been done. In addition,
A PIN diode as a switch circuit is connected to the trap circuit, and when receiving satellite broadcasting of a high-frequency channel, the control means does not apply voltage to the PIN diode and turns the PIN diode into non-conducting state. The signal is transmitted to the next stage frequency mixer without being attenuated, and when receiving satellite broadcasting on a low-frequency channel, a voltage is applied to the PIN diode by the control means and passed through the PIN diode, and the local oscillation frequency is adjusted. The band is attenuated by the trap circuit described above. In this way, the signal is transmitted to the frequency mixer in the next stage, so that no interference occurs.

Embodiment Hereinafter, a satellite broadcast receiver channel selection circuit according to an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows a circuit diagram of a satellite broadcasting receiver tuning circuit according to an embodiment of the present invention.

In FIG. 1, 70 is an image filter, and 34 is a trap circuit. 35 is a frequency mixer, and 36 is a local oscillator. 49.50.52.53.54.56.57.5
8.64°65, 15.17.24 is a microstrip line, and shows an example of the dimensions (W-width, L-length) when the printed circuit board is a glass epoxy base material.

62 and 67 are PIN diodes, 12.14 is a Schottky barrier diode, 23 is a variable capacitance diode, 2
8 is a high frequency transistor, 13 is a balun transformer, 16
, 18.21.25.31.29.34.51.55.
61.59°66, 69 is a chip capacitor, 22.2
746.30.32°33, 60.68 are chip resistors. 48 is an input terminal, 19 is an output terminal, 20 is a frequency control terminal, 45 is a power supply voltage terminal for the local oscillator 36, 72
is the control means output terminal.

A trap circuit is formed by the microstrip line 58 and the capacitor 59, and its resonant frequency is
It is set to the local oscillation frequency band of the 1.3 channel of satellite broadcasting. Furthermore, the series resonant circuit and the trap circuit formed by the microstrip line 65 and the capacitor 66 constitute a series resonant circuit,
Its resonant frequency is set to the local oscillation frequency band of 1.3 channel satellite broadcasting. Further, the series resonant circuit and the microstrip line 64 determine the degree of coupling between the resonant circuits. Their series resonant circuits each include a PIN diode 62.67 and a high resistance 60°68
A control means 63 is connected through the PIN diode 62.67, and when receiving a 1.3 channel satellite broadcasting signal, the control means 63 applies a voltage to the PIN diode 62.67 to make the PIN diode 62.67 conductive. , the local oscillation frequency band is attenuated by the trap circuit 34. When receiving high-frequency satellite broadcasting signals, the control means 63 does not apply voltage to the PIN diode 62.67.
7 is made non-conductive to prevent high frequency satellite broadcasting signals from being attenuated.

The control means 63 can be easily realized by a band switching circuit such as a PLL synthesizer controlled by a micro combinator or the like.

FIG. 2 shows the frequency characteristics between input and output when the PIN diode is conductive and non-conductive.

First, when the PIN diode 62.76 is conductive, there is an attenuation of about 25 dB or more in the local oscillation frequency band, which is 400 MHz higher than the passband (characteristic A). When the PIN diode 62.67 is non-conductive, As shown in characteristic B, there is no attenuation in the input/output frequency characteristics, which causes g*a
0 frequency mixer 35 that can remove the interference caused by
is a single balanced mixer, and is composed of a Schottky barrier diode 12°14 and a balun transformer 13. The balun transformer 13 is a local oscillator 36
The strip line 15.1? serves to perform unbalanced/balanced conversion of the output from the ? and switch the Schottky barrier diodes 12, 14. , the chip capacitors 16 and 18 constitute a low-pass filter, which filters the second intermediate frequency signal (
The local oscillator 36, whose cutoff frequency is set to 550 MHz, passes only the 400 MHz band) and removes the first intermediate frequency signal and local oscillation signal. Variable capacitance diode 23 and microstrip line 2
The configuration is such that four resonators are connected and the oscillation output is extracted from the emitter.

Note that the trap circuit 34 is arranged between the image filter 70 and the mixer circuit 35, but the image filter 70
It is also possible to arrange it before the mixer circuit 35, and there are basically no restrictions as long as it is before the mixer circuit 35.

Effects of the Invention As described above, the present invention provides a PIN as a switch circuit.
A parallel resonant circuit connected to a diode is placed in front of the frequency mixer, and the control means applies a control voltage to the PIN diode to create conduction and non-conduction states, thereby changing the frequency characteristics between the input and output of the parallel resonant circuit. This is to control the interference generated between the first intermediate frequency signal and the interference signal in the local oscillation frequency band by attenuating the local oscillation frequency band of the signal input to the frequency mixer. The practical effect of removing this is great.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a satellite broadcast receiver tuning circuit according to an embodiment of the present invention, FIG. 2 is a frequency characteristic diagram between input and output of a trap circuit according to an embodiment of the present invention, and FIG. 3 is a conventional Block diagram regarding the channel selection circuit of the satellite broadcasting receiver in the example, No. 4
The figure is a frequency characteristic diagram between the input and output terminals of the image filter. 48...Input terminal, 49.50.52.53.
54.56.57°5B, 64.65.15.17.
24...Microstrip line, 62.6
9...PIN diode, 51.55°61,
59.66, 69.11.16.18.21.25.3
L 29°34... Chip capacitor, 12
．． 14...Shi5-key barrier diode, 1
3... Balun transformer, 19... Output terminal, 20... Frequency control terminal, 23...
... Variable capacitance diode, 45 ... Local oscillator power supply voltage terminal, 72 ... Control means output terminal.

Claims (1)

[Claims] an image filter that passes a first intermediate frequency band of satellite broadcasting and blocks the image frequency band; an output signal of the image filter is used as an input signal; a capacitor is connected to one terminal of a first microstrip line;
a first series resonant circuit comprising a PIN diode having a grounded cathode terminal connected to one terminal of the capacitor, and a control means connected to the anode terminal via a high resistance; It is composed of a second series resonant circuit having the same configuration as the resonant circuit, and a second microstrip line that connects the first and second series resonant circuits to each other, and whose resonant frequency is a low-frequency satellite broadcasting signal. A trap circuit having a local oscillation frequency substantially equal to the local oscillation frequency when receiving the signal, a frequency mixer receiving the output signal of the trap circuit as input, and a local oscillator supplying the local oscillation signal to the frequency mixer. When receiving a low frequency satellite broadcast signal, the control means applies a voltage to the PIN diode to make the PIN diode conductive, and when receiving a high frequency satellite broadcast signal, the control means applies a voltage to the PIN diode. A satellite broadcasting receiver channel selection circuit characterized by making a PIN diode non-conductive.