Antenna switching circuit and communication system using the same

• US 6,704,550 B1
• Filed: 09/12/2000
• Issued: 03/09/2004
• Est. Priority Date: 09/14/1999
• Status: Expired due to Term

• Current Assignee: Sony Semiconductor Solutions Corporation (Sony Group Corp.)
• Original Assignee: Sony Corporation (Sony Group Corp.)
• Inventors: Fukui, Daisuke, Kohama, Kazumasa
• Primary Examiner(s): Chin, Vivian
• Assistant Examiner(s): TRAN, TUAN A
• Application Number:
  US09/660,399
• Time in Patent Office: 1,274 Days
• Field of Search: 455/78-83, 455/296, 455/114, 333/101, 333/103-105, 333/124, 333/127-128
• US Class Current: 455/114.2
• CPC Class Codes: H04B 1/48 in circuits for connecting transmitter and receiver to a common transmission path, e.g. by energy of transmitter H04B1/46 takes precedence

Abstract

An antenna switching circuit and communication system capable of reducing a high-order harmonic component radiated from the antenna used for transmission and reception. A fundamental wave passes through a signal transmission line between an antenna switch and a transmitting circuit, a filter circuit is connected for reflecting the high-order harmonic component, the high-order harmonic component generated due to linear distortion of the antenna switch is propagated toward the antenna and the transmitting circuit, the high-order harmonic component is reflected at a node of the filter circuit, and the reflected signal is propagated toward the antenna through the antenna switch. By suitably controlling a reflection characteristic of the filter circuit and a line of the signal transmission line, the high-order harmonic components on the transmission line are cancelled out and the high-order harmonic component from the antenna can be decreased.

Claims

1. A communication system comprising:

an antenna;

a reception circuit receiving a signal received at the antenna;

a transmission circuit sending a transmission signal to be transmitted to the antenna;

a switch circuit provided between the antenna and the transmission circuit; and

a filter circuit provided between the switch circuit and the transmission circuit;

wherein the filter circuit reflects a signal component having a predetermined high frequency band in the transmission signal toward the switch circuit.

2. A communication system according to claim 1, wherein a first signal transfer line having a predetermined impedance is provided between the switch circuit and the filter circuit.

3. A communication system according to claim 2, wherein a second signal transfer line is provided between the transmission circuit and the filter circuit.

4. A communication system according to claim 1, wherein the filter circuit comprises at least a capacitor and inductor one end of which is connected to a reference potential point.

5. A communication system comprising:

an antenna;

a reception circuit receiving a signal received at the antenna;

a transmission circuit sending a transmission signal to be transmitted to the antenna;

a switch circuit provided between the antenna and the transmission circuit;

a filter circuit provided among the switch circuit, the transmission circuit and the reception circuit, said filter circuit passing a fundamental wave component in the transmission signal and reflecting a signal component having a predetermined high frequency band in the transmission signal toward said switch circuit.

6. A communication system according to claim 5, wherein a first signal transfer line having a predetermined impedance is provided between the switch circuit and the filter circuit.

7. A communication system according to claim 6, wherein a second signal transfer line is provided between the transmission circuit and the filter circuit.

8. A communication system according to claim 5, wherein the filter circuit comprises at least a capacitor and inductor one end of which is connected to a reference potential point.

9. An antenna switching circuit for enabling a transmitting circuit and a receiving circuit to share a single antenna and for switching the antenna to the transmitting circuit at the time of transmission or the receiving circuit at the time of transmission or reception, comprising:

an antenna switch connecting the antenna to the transmitting circuit at the time of transmission and connecting the antenna to the receiving circuit at the time of reception, and

a filter circuit which is connected to at least a signal transmission line between the antenna switch and the transmitting circuit and reflects back a signal of a predetermined high frequency band propagated through the signal transmission line toward said antenna switch.

10. An antenna switching circuit according to claim 9, wherein the filter circuit has a high impedance characteristic with respect to the signal of the high frequency band.

11. A communication system for transmission and reception sharing a single antenna, comprising:

a transmitting circuit for transmitting a high frequency signal by using the antenna;

a receiving circuit for receiving a radio signal by the antenna;

an antenna switch for connecting the antenna to the transmitting circuit at the time of transmission and the antenna to the receiving circuit at the time of reception; and

a filter circuit which is connected to at least a signal transmission line between the antenna switch and the transmission circuit and reflects back a signal of a predetermined high frequency band propagated through the signal transmission line;

wherein a high-order harmonic component generated in the antenna switch corresponding to a transmission signal output by the transmitting circuit is propagated toward both the antenna and the transmitting circuit, and

wherein the filter circuit reflects back the high-order harmonic component propagated toward the transmitting circuit and causes the reflected signal to be propagated toward the antenna through the antenna switch.

12. A communication system according to claim 11, wherein an amplitude of the high-order harmonic component reflected by the filter circuit is controlled by a reflection characteristic of the filter circuit.

13. A communication system according to claim 11, wherein a phase of the high-order harmonic component reflected by the filter circuit is controlled by a length of the signal transmission line between the filter circuit and the antenna switch.

14. A communication system according to claim 11 By wherein the reflection characteristic of the filter circuit and a length of the signal transmission line between the antenna and the antenna switch are controlled so that the high-order harmonic component propagated from the antenna switch in the signal transmission line between the antenna switch and the antenna and the high-order harmonic component reflected by the filter circuit become substantially the same in amplitude and inverse in phase.

15. A communication system according to claim 11, wherein the filter circuit comprises a capacitor and inductor connected in series between a predetermined node on the signal transmission line between the antenna switch and the transmitting circuit, and a reference potential.

16. A communication system according to claim 15, wherein the reflection characteristic of the filter circuit is controlled by values of the capacitor and inductor which constitute the filter circuit.