High impedance circuit

• US 20030022653A1
• Filed: 07/18/2002
• Published: 01/30/2003
• Est. Priority Date: 07/26/2001
• Status: Active Grant

• Current Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Original Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Inventors: Okahashi, Tetsuhide
• Granted Patent: US 7,218,910 B2
• Time in Patent Office: Days
• US Class Current: 455/334
• CPC Class Codes: H04B 1/18 Input circuits, e.g. for coupling to an antenna or a transmission line coupling networks between antennas or lines and receivers independent of the nature of the receiver H03H

Abstract

A high impedance circuit of the present invention includes an LC parallel resonance circuit for raising circuit impedance, and a diode, which is connected in parallel to the LC parallel resonance circuit, causing a loop current to flow back via the diode and an inductor in the LC parallel resonance circuit so that a counter electromotive force, due to a surge voltage, which occurs across the inductor is cancelled. A low noise block downconverter which includes a high impedance circuit having a high impedance prevents peripheral circuits from being destroyed by a counter electromotive force, due to a surge voltage, which occurs across the inductor. For this, a diode is provided to cause a loop current to flow back via the diode and the inductor so that the counter electromotive force is cancelled. This makes it possible to cancel the counter electromotive force, to lower the voltage across the inductor to a forward voltage of the diode, and to prevent the destruction of the peripheral circuits such as the high impedance circuit.

Claims

1. A high impedance circuit, comprising:

an LC parallel resonance circuit for raising circuit impedance; and

a diode, which is connected in parallel to said LC parallel resonance circuit, causing a loop current to flow back via said diode and an inductor in said LC parallel resonance circuit so that a counter electromotive force, due to a surge voltage, which occurs across the inductor is cancelled.

2. The high impedance circuit according to claim 1, wherein said diode has a forward voltage smaller than the electromotive force.

3. The high impedance circuit according to claim 1, wherein said diode is a pair of counter serial zener diodes.

4. The high impedance circuit according to claim 3, wherein a sum of the forward voltage and a zener voltage of the pair of counter serial zener diodes is smaller than the counter electromotive force.

5. A low noise block downconverter, comprising:

(a) a receiving circuit for selecting a target broadcast and receiving signals from a satellite of a broadcast thus selected in response to a control pulse for selecting a target satellite, which is transmitted from a receiver, and for amplifying signals thus received and outputting the signals to the receiver;

(b) a regulator IC producing a source voltage for being supplied to said receiving circuit in accordance with a direct current for power source inputted to said regulator IC;

(c) an LC parallel resonance circuit electrically separating said regulator IC from the control pulse; and

(d) a diode, which is connected in parallel to said LC parallel resonance circuit, causing a loop current to flow back via said diode and an inductor in said LC parallel resonance circuit so that a counter electromotive force, due to a surge voltage, which occurs across the inductor is cancelled.

6. A system for receiving satellite broadcasts, comprising:

a receiver outputting a control pulse for selecting a target satellite; and

a low noise block downconverter, including;

(a) a receiving circuit for selecting a target broadcast and receiving signals from a satellite of a broadcast thus selected in response to the control pulse, and for amplifying and outputting signals thus received;

(b) a regulator IC producing a source voltage for being supplied to said receiving circuit in accordance with a direct current for power source inputted to said regulator IC;

(c) an LC parallel resonance circuit electrically separating said regulator IC from the control pulse;

(d) a diode, which is connected in parallel to said LC parallel resonance circuit, causing a loop current to flow back via said diode and an inductor in said LC parallel resonance circuit so that a counter electromotive force, due to a surge voltage, which occurs across the inductor is cancelled.