Wireless handset

• US 6,198,441 B1
• Filed: 07/14/1999
• Issued: 03/06/2001
• Est. Priority Date: 07/21/1998
• Status: Expired due to Term

• Current Assignee: Hitachi, Ltd.
• Original Assignee: Hitachi, Ltd.
• Inventors: Okabe, Hiroshi, Takei, Ken
• Primary Examiner(s): Wong, Don
• Assistant Examiner(s): TRAN, THUY V
• Application Number:
  US09/353,284
• Time in Patent Office: 601 Days
• Field of Search: 343/702, 343/745, 343/850, 343/852, 343/860, 343/861, 455/179.1, 455/182.1, 455/183.1, 455/183.2, 379/398
• US Class Current: 343/702
• CPC Class Codes: H01Q 1/243 with built-in antennas

Abstract

A wireless handset with a built-in tunable antenna has a circuit that tunes the center frequency of impedance matching of the antenna to a call frequency. The wireless handset is used in a communication system that switches between a plurality of call channels. For each call, by adaptively changing the center frequency of impedance matching of the antenna to the frequency used for the call, the frequency band that the antenna should have can be decreased. A first control signal containing call frequency information or data used in a central processing unit to generate the first control signal is used to generate a second control signal in a control signal generator, whereby the center frequency of impedance matching of the tunable antenna can be tuned to a call frequency without having to provide an additional circuit for specifying the call frequency information.

Claims

1. A wireless handset with a built-in tunable antenna, comprising a built-in antenna provided within a case of the wireless handset, an RF circuit part connected to the built-in antenna, a logical circuit part connected to the RF circuit part, and a frequency synthesizer connected between the logical circuit part and said RF circuit, which generates a local oscillation frequency signal in said frequency synthesizer in accordance with a first control signal from a central processing unit contained in said logic circuits part and performs sending/receiving operations with a frequency determined by said local oscillation frequency signal in said RF circuit, wherein said built-in antenna is a tunable antenna including a control circuit for center frequency of impedance matching and a control signal generator is provided within said central processing unit or in the outside connected to the central processing unit and is connected to said control circuit for center frequency of impedance matching, wherein said control signal generator can retain in tabular form or find by computation a relationship between a frequency determined by said local oscillation frequency signal in said RF circuit, said local oscillation frequency signal being set by said first control signal, and a second control signal to be fed to said control circuit for center frequency of impedance matching to tune a center frequency of impedance matching of said tunable antenna to the frequency, and wherein when said first control signal sent to said frequency synthesizer or data used in said central processing unit to generate the first control signal is input to the control signal generator, the control circuit generates a second control signal by referring to the retained relationship or performing computations, and controls a center frequency of impedance matching of said tunable antenna by applying said second control signal to said control circuit for center frequency of impedance matching.

2. A wireless handset with a built-in tunable antenna according to claim 1, wherein said control circuit for center frequency of impedance matching is a circuit that changes a center frequency of impedance matching of said tunable antenna in accordance with a DC voltage value of said second control signal input to the control circuit for center frequency of impedance matching, wherein said control signal generator comprises a frequency to voltage conversion table retaining a relationship between input and output signals so as to output a specific digital signal for a specific input signal, and a digital to analog converter that generates a DC voltage in accordance with a digital signal output from the frequency to voltage conversion table, and wherein there is retained in said frequency to voltage conversion table a relationship between said first control signal or data used in said central processing unit to generate the first control signal, and a digital signal for letting said digital to analog converter generate a second control signal having a DC voltage value which enables a center frequency of impedance matching of a tunable antenna to tune to a call frequency determined by said first control signal.

3. A wireless handset with a built-in tunable antenna according to claim 2, wherein a specific receive frequency signal is received while changing a DC voltage value of said second control signal applied to said control circuit for center frequency of impedance matching, and said frequency to voltage conversion table can be reset so that the DC voltage value of a second control signal with which the highest received signal strength is obtained in said RF circuit is made to correspond with the frequency of said specific receive frequency signal.

4. A wireless handset with a built-in tunable antenna according to claim 1, wherein said control circuit for center frequency of impedance matching is a circuit that changes a center frequency of impedance matching of said tunable antenna in accordance with a DC voltage value of said second control signal input to the control circuit for center frequency of impedance matching, wherein said control signal generator comprises an arithmetic and logic circuit that generates a digital signal in accordance with an input signal, and a digital to analog converter that generates a DC voltage in accordance with a digital signal generated by the arithmetic and logic circuit, wherein a frequency to voltage conversion table is provided connected to said arithmetic and logic circuit, and there is retained in the frequency to voltage conversion table a relationship between said several first control signals or data used in said central processing unit to generate the first control signals, and a digital signal for letting said digital to analog converter generate a second control signal having a DC voltage value which enables a center frequency of DC voltage value which enables a center frequency of impedance matching of a tunable antenna to tune to a call frequency determined by said first control signal, and wherein a digital signal for letting said digital to analog converter generate a second control signal having a DC voltage value which enables a center frequency of impedance matching of a tunable antenna to tune to a call frequency determined by said first control signal is generated by said arithmetic and logic circuit that compensates data related to input and output signals from data retained in said frequency to voltage conversion table by approximate computations.

5. A wireless handset with a built-in tunable antenna according to claim 1, wherein said tunable antenna is a tunable slot antenna comprising a conductive flat cubic which is cuboid as a whole, a slim strip conductor disposed along with the direction of the resonant axis of internal space of the conductive flat cubic and in insulation from the conductive flat cubic, a slot for sending and receiving radio waves, formed across the strip conductor on the top of the conductive flat cubic, and a slip island conductor disposed in insulation from the conductive flat cubic within the slot, wherein RF power is supplied between a coupling part set in said strip conductor and the wall face of said conductive flat cubic, and wherein a variable capacitance circuit connected between said island conductor and the wall face of said conductive flat cubic is provided as said control circuit for center frequency of impedance matching.

6. A wireless handset with a built-in tunable antenna according to claim 5, wherein said control circuit for center frequency of impedance matching comprises a variable capacitance diode connected between said island conductor and the wall face of said conductive flat cubic, and an element for blocking first RF power, connected between said island conductor and the end or proximity thereof of said strip conductor that is far from a coupling part thereof, wherein a DC voltage to change the capacity of said variable capacitance diode is applied from said coupling part to said variable capacitance diode via said slip conductor and said element for blocking RF power, and wherein said second control signal is supplied to said coupling part via a second element for blocking RF power, and the exchange of send/receive signals between said RF circuit and said coupling part is made via an element for blocking DC power.

7. A wireless handset with a built-in tunable antenna, comprising a receive-only built-in antenna, an outer antenna for sending and receiving, an RF signal switching circuit connected between said built-in antenna and said outer antenna, an RF circuit part connected to said RF signal switching circuit, a logical circuit part connected to said RF circuit part, a frequency synthesizer connected between said logical circuit and said RF circuit, and a received signal strength detector provided within said RF circuit or in the outside connected thereto and connected to said logical circuit part, which generates a local oscillation frequency signal in said frequency synthesizer in accordance with a first control signal from a central processing unit contained in said logic circuits part, performs sending/receiving operations with a frequency determined by said local oscillation frequency signal in said RF circuit, and performs diversity receiving wherein an antenna with which higher received signal strength is detected in said received signal strength detector is used for receiving when an antenna connected with said RF circuit by said RF signal switching circuit is said built-in antenna or said outer antenna, wherein said built-in antenna is a tunable antenna including a control circuit for center frequency of impedance matching and a control signal generator is provided within said central processing unit or in the outside connected to the central processing unit and is connected to said control circuit for center frequency of impedance matching, and wherein the control signal generator generates a second control signal from said first control signal sent to said frequency synthesizer or data used in said central processing unit to generate the first control signal and controls a center frequency of impedance matching of said tunable antenna by applying said second control signal to said control circuit for center frequency of impedance matching.

8. A wireless handset with a built-in tunable antenna according to claim 7, wherein after a call is received by said outer antenna while said central processing unit changes the frequency of a local oscillation frequency signal generated by said frequency synthesizer to change a received frequency of said RF circuit, a first control signal for defining, as a call receive frequency, a frequency with the highest received signal strength detected in said received signal strength detector is sent from said central processing unit to said frequency synthesizer, a second control signal is generated in the control signal generator from said first control signal or data used in said central processing unit to generate said first control signal, and the second control signal is input to said control circuit for center frequency of impedance matching so as to tune a center frequency of impedance matching of said tunable antenna to the call receive frequency.