LOW NOISE CONVERTER

Abstract: A two-band low noise converter for receiving at least two frequency bands comprising switch means (3) for switching a frequency band to receive from one band to another and control means (2, 5, TR) which detects the level of a power-supply voltage to be fed through an IF output terminal (1) and, when the level is low, operates the switch means.

Description: BACKGROUND OF THE INVENTION The present invention relates to a low noise converter (Low Noise Block Downconverter: hereinafter "LNB") for receiving at least two frequency bands, and more particularly, to a construction of an LNB for switching between reception bands in accordance with a power-supply voltage level. Conventionally, as is shown in Fig. 2, a power-supply voltage fed through an IF output terminal is fetched by a coil L. The fetched power-supply voltage is divided by resistors R1 and R2, and is compared with a reference voltage by a comparator 2. The reference voltage is provided through a voltage stabilizer from the power-supply voltage. When an output of the comparator 2 is higher than the reference voltage and higher than a threshold voltage of a transistor TR, the transistor TR is switched on. By this, a relay 3 as a switch relay means is operated to switch a frequency band to receive. R3 is a resistor to cause hysteresis characteristics. D is a diode to protect the transistor TR. C is a condenser to cut a direct current. And, output of a three-terminal regulator 4 is supplied to each circuit inside the LNB. However, with the above conventional circuit, the relay 3 is operated when the power-supply voltage is high, which causes increase of power consumption and further causes temperature rise inside the LNB. SUMMARY OF THE INVENTION Accordingly, it is an aim of the present invention to provide an LNB which alleviates some of the aforementioned problems. Briefly described, in accordance with the present invention, a low noise converter is provided for receiving a plurality of frequency bands and having switch means for switching between said bands in accordance with the level of a power supply voltage fed through an IF output terminal, wherein said switch means when energised consumes power derived from said power supply voltage, and wherein control means is provided for controlling the energisation of said switch means in accordance with said power supply voltage level, characterised in that said control means is so arranged that said switch means is energised when the power supply voltage is below a reference voltage level. BRIEF DESCRIPTION OF THE DRAWINGS The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention and wherein: FIG. 1 is a circuit diagram which shows an embodiment of the present invention; and FIG. 2 is a circuit diagram showing a conventional example. DESCRIPTION OF THE PREFERRED EMBODIMENTS Like reference characters in FIG. 1 designate corresponding parts to that in FIG. 2. FIG. 1 is a circuit diagram showing an embodiment of the present invention. A comparator 2 compares a power-supply voltage with a reference voltage. The output of the comparator 2 is first inverted by an inverter 5. When the output of the inverter 5 is higher than a threshold voltage, a transistor TR is switched on and a relay 3 is operated. As is described above, the relay 3 is operated when the power-supply voltage is low, thus the current becomes increased. However, as the power-supply voltage is low, the power consumption (product of current and power-supply voltage) is reduced. Consequently, temperature rise inside the 2-band LNB is inhibited. For example, when the operating current of the relay 3 is 10 mA, the current as for portion without the relay 3 is 150 mA, the power-supply source voltage of low voltage is 13 V, and the power-supply source voltage of high voltage is 17 V, in a conventional circuit (in which the relay 3 is operated when the voltage is high), power consumption of low voltage is 13 V × 0.15 A = 1.95 W while power consumption of high voltage is 17 V × (0.15 + 0.01) A = 2.72 W. On the other hand, in a circuit of the present invention, power consumption of low voltage is 13 V × (0.15 + 0.01) A = 2.08 W, while power consumption of high voltage is 17 V × 0.15 A = 2.55 W. The largest power consumption of each case: the conventional circuit - - - 2.72 W; the present embodiment - - - 2.55 W. As power consumption reflects calorific power, the present invention consumes less electric power, thus causes less calorific power. In the present embodiment, an inverter 5 is used, but instead of an inverter, it is also possible to invert the polarities of the input side of the comparator 2. As described above, according to the present invention, a relay is operated when a power-supply source voltage is low. Therefore, a useful 2-band LNB is provided in which power consumption is reduced and at the same timereduces calorific power inside the LNB.

Claims: 1. A low noise converter for receiving a plurality of frequency bands and having switch means (3) for switching between said bands in accordance with the level of a power supply voltage fed through an IF output terminal (1), wherein said switch means when energised consumes power derived from said power supply voltage, and wherein control means (R1, R2, 2, 5, TR) is provided for controlling the energisation of said switch means in accordance with said power supply voltage level, characterised in that said control means is so arranged that said switch means is energised when the power supply voltage is below a reference voltage level. 2. The low noise converter according to claim 1, wherein said control means comprises a comparator (2) and an inverter (5) which inverts polarities of output of said comparator. 3. The low noise converter according to claim 1, wherein said control means comprises a comparator (2) at an input side of which polarities of input are inverted. 4. The low noise converter according to claim 1, wherein said switch means is a relay (3). 5. The low noise converter according to claim 1, wherein said control means comprises a comparator (2), and an inverter (5) which inverts polarities of output of said comparator, and wherein said switch means is a relay (3). 6. The low noise converter according to claim 1, wherein said control means comprises a comparator (2) at an input side of which polarities of input are inverted and wherein said switch means is a relay (3).

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