OUTDOOR UNIT LOW NOISE CONVERTER FOR SATELLITE BROADCAST RECEPTION USE

Abstract: In an outdoor unit low noise converter for satellite broadcast reception use preferably comprising a 2-band LNB converter (LNB: Low Noise Block Downconverter)for receiving two frequency bands, the converter is capable of receiving a plurality of bands by one converter including the same number of terminals by making use of power supply voltages fed via the IF output.

Description: The present invention relates to a multiple-band low noise converter as used in outdoor reception of satellite broadcast signals. The document EP-A-0 149 533 describes a converter of the above type, said converter comprising: a wide-band low noise amplifier; a mixing means comprising local oscillator means, said mixing means outputting an IF signal to an IF output terminal; and switching means for switching between different frequencies of said local oscillator means, each frequency determining a frequency band to be received. In this prior art converter, the mixing means comprises a single voltage controlled oscillator as local oscillator. The control voltage for adjusting the frequency of the local oscillator is adjusted in relation with a control voltage supplied to the IF output terminal. It is the object of the present invention to provide a converter having simple construction and having the function of the above discussed prior art converter. The converter of the present invention is characterized in that a power divider is arranged at the output side of said wide-band low noise amplifier for distributing the output signal of said amplifier into different branches; said mixing means comprises a bandpass filter and a mixer with a local oscillator in each branch, the frequency of said local oscillator being allocated to the pass characteristic of said bandpass filter in a way that the output signal is within a certain band of the IF signal; and said switching means is arranged to selectively switch one of the outputs of said mixers to the output terminal of said converter. This converter has simple construction, as no mixers and oscillators operating in a broader band are necessary, but as only oscillators operating at a fixed frequency and mixers operating in a narrow band, as fixed by the bandpass filter in each branch, are required. These an other objects and features of the present invention will become clear from the following description taken in conjunction with the preferred embodiments thereof with reference to the accompanying drawings, in which: Fig. 1 is a circuit diagram of a two-band low noise converter according to a first embodiment of the present invention; Fig. 2 is a graph showing the relationship between two bands received with the converter according to Fig. 1; Fig. 3 is a circuit diagram of a converter according to a second embodiment of the present invention, in which embodiment a voltage for band switching is supplied via the IF output terminal of the converter; Fig. 4 is a diagram of a circuit for adjusting a threshold voltage; Fig. 5 is a plan view onto a converter equipped with the circuit according to Fig. 3; and Fig. 6 is a diagram to illustrate band selection by using a control voltage and the threshold voltage as adjusted e. g. with the circuit of Fig. 4. The circuit construction in a first embodiment of the present invention is shown in Fig. 1. Fig. 2 shows the frequency relation of a plurality of bands to be received. Here, the ECS band of 10.95 GHz through 11.7 GHz and the Europe Ku band of 11.7 GHz through 12.5 GHz, two bands, are switched for reception. A low noise amplifier 2 has a wide band so that the signals of 10.95 GHz through 12.5 GHz may be amplified. A power divider 7 divides the amplified output signal into two for connection to each of a first band passing type filter 3A with, for example, 10.95 GHz through 11.7 GHz being a passing band and, a second band passing type filter 3B with, for example, 11.7 through 12.5 GHz being a passing band. A first mixer circuit 7A composed of a mixer 4A and a local oscillator 5A of a 10.00 GHz is connected to the first band passing type filter 3A, and a second mixer circuit 7B composed of a mixer 4B and a local oscillator 5B of 10.75 GHz is connected to the second band passing type filter 3B. The output switching operation into the after IF amplifier 6 is selected in relation with the control of the oscillating operation of the respective local oscillator 5A, 5B with voltages B1, B2 as power supply, and diode switches 8A, 8B connected in series respectively to mixers 4A, 4B. It is to be noted that diode switches 8A, 8B are adapted to turn on, off through the operative cooperation in common with the controlling operation of the local oscillators with the voltages B1, B2. In the first mixer circuit 7A, the signals of 10.95 GHz through 11.7 GHz which have passed through the first band passing type filter A are converted into the frequencies of 950 MHz through 1700 MHz (750 MHz in band width). In the second mixer circuit 7B, similarly the signals of 11.7 GHz through 12.5 GHz which have passed through the second band passing filter 3B are converted into the frequencies of 950 MHz through 1750 MHz (800 MHz in band width). In this manner, frequencies are selectively outputted into the IF amplifier 6 within the range of 950 MHz through 1750 MHz, with the band width not being made larger and being within the range of 750 MHz through 800 MHz. In the above description, two bands are provided; more bands may be used. In the first embodiment of the present invention, a useful low noise converter for satellite broadcasting reception is provided, which is capable of receiving a plurality of bands by one converter for frequency converting operation. The second embodiment of the present invention will be fully described with reference to Figs. 3 through 6. Fig. 5 shows an appearance view of a 2-band LNB1 in accordance with the present invention. Referring to Fig. 5, external terminals are an input waveguide 14 (generally the input terminal is made of a waveguide, but may be made of a coaxial cable instead) to be connected with an antenna and an IF output terminal 12 only. Accordingly, the airtight construction does not change because of the two bands. The IF output terminal 12 serves also as a power supply. Band switching will be described by use of the circuit diagram of Fig. 3. Referring to Fig. 3, the power supply voltage to be supplied through the IF output terminal 12 is drawn out by a coil L to be supplied to a power supply circuit 15. It is divided by resistors R1, R2 to be compared with a reference voltage Vs by a comparator 16; the output is inputted to the switching circuit 17 such as a relay or the like. As shown in Fig. 6, in the switching circuit 17, a band 1 is selected if the voltage is 12 through 15V, a band 2 is selected if the voltage is 16 through 24V, with, for example, 15 through 16V being a threshold voltage (boundary). The power supply circuit 15 is composed of a three-terminal regulator outputting voltages P1, P2, P3 to a radio frequency signal amplification converting portion 18, the outputs P1 through P3 being provided as -3V, 5B, 12V. It is to be noted that C is a capacitor for DC cut use, R3 is a resistor which causes hysteresis characteristics so as to prevent the output of the comparator from being unstable near the threshold voltage. Also, as shown in Fig. 4, a variable resistor VR is inserted for adjustment in order to prevent a variation of the threshold voltage caused by a variation of the reference voltage Vs. According to the second embodiment of the present invention, a useful 2-band LNB is provided which is capable of receiving two frequency bands by one LNB to simplify the construction and to reduce the cost, and also is higher in airtightness to simplify the construction of the LNB itself. Although the present invention has been fully described in connection with the preferred embodiments thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications are apparent to those skilled in the art. Such changes and modifications are to be understood as included within the scope of the present invention as defined by the appended claims unless they depart therefrom.

Claims: A multiple-band low noise converter for outdoor satellite broadcast reception comprising a wide-band low noise amplifier (2); a mixing means (7A, 7B) comprising local oscillator means (5A, 5B), said mixing means outputting an IF signal to an IF output terminal (12); and switching means (17; 8A, 8B; B1, B2) for switching between different frequencies of said local oscillator means, each frequency determining a frequency band to be received; characterized in that a power divider (7) is arranged at the output side of said wide-band low noise amplifier (2) for distributing the output signal of said amplifier into different branches; said mixing means comprises, in each of said branches, a bandpass filter (3A, 3B) and a mixer (4A, 4B) with a local oscillator (5A, 5B), the frequency of said local oscillator being allocated to the pass characteristic of said bandpass filter in a way that the output signal is within a certain band of the IF signal; and said switching means (17; 8A, 8B; B1, B2) is arranged to selectively switch one of the outputs of said mixers to the output terminal of said converter. A converter according to claim 1, characterized in that said switching means (17) activates only the local oscillator (5A, 5B) within the selected branch. A converter according to one of the claims 1 or 2, characterized in that said IF output terminal (12) serves as a power supply; and said switching means (17) is responsive to the voltage as applied to said IF output terminal, to switch between said different branches depending on the value of said voltage.

Inventors: NOBORU, MITSUHIRO, YAMAUCHI, MIYOSHI
Applicants: SHARP KABUSHIKI KAISHA
Application year: 1988
Main classification: H03D7
IPC codes: H03J5, H03D7