Wireless communication apparatus having automatic antenna tuning function

A wireless communication apparatus comprising

• an oscillator circuit,
• a receiving circuit which receives a reception signal via an antenna and applies an output signal of said oscillator circuit to convert a frequency of said reception signal to a lower frequency,
• a voltage detection circuit for detecting a level of signal power received by said receiving circuit,
• a variable-impedance matching circuit controllable for effecting impedance matching between said antenna and said receiving circuit,
• a first switch, controllable for connecting a selected one of said receiving circuit and said oscillator circuit to said matching circuit,
• a second switch, controllable for selectively connecting said antenna to said receiving circuit and disconnecting said antenna from said receiving circuit,
• a signal processing apparatus for processing an output received signal from said receiving circuit, when said first switch connects said receiving circuit to said matching circuit and said second switch disconnects said antenna from said receiving circuit, and
• a control circuit for controlling said connection and disconnection operations of said first switch and said second switch, and for controlling an impedance of said matching circuit to bring an output voltage value of said voltage detection circuit close to a predetermined reference voltage value, when said first switch connects said oscillator circuit to said matching circuit and said second switch connects said antenna to said receiving circuit, with an output signal of said oscillator circuit thereby inducing resonance of said antenna.

A wireless communication apparatus comprising

• a receiving circuit which receives a reception signal via an antenna,
• a variable-impedance matching circuit controllable for effecting impedance matching between said antenna and said receiving circuit,
• a voltage detection circuit for detecting a level of signal power received by said receiving circuit,
• an oscillator circuit generating an oscillator signal having a frequency that differs from a frequency of said reception signal,
• a current limiting resistor,
• a first switch, controllable for connecting a selected one of said receiving circuit and said oscillator circuit to said matching circuit,
• a second switch, controllable for selectively connecting said current limiting resistor between said antenna and said receiving circuit and disconnecting said current limiting resistor from between said antenna and said receiving circuit,
• a signal processing apparatus for processing an output received signal from said receiving circuit, when said first switch connects said receiving circuit to said matching circuit and said second switch disconnects said antenna from said receiving circuit,
• a control circuit for controlling said connection and disconnection operations of said first switch and said second switch, and for controlling an impedance of said matching circuit to bring an output voltage value of said voltage detection circuit close to a predetermined reference voltage value, when said first switch connects said oscillator circuit to said matching circuit and said second switch connects said current limiting resistor between said antenna and said receiving circuit, with an output signal of said oscillator circuit thereby inducing resonance of said antenna.

A wireless communication apparatus including

• an antenna, and a receiving circuit which receives via said antenna a reception signal having a predetermined reception signal frequency,
• a voltage detection circuit coupled to receive an output signal from said receiving circuit, for generating a detection voltage indicative of a value of signal power received by said receiving circuit,
• a matching circuit connected to said antenna and to an input terminal of said receiving circuit, adjustable for establishing an impedance matched condition whereby an impedance of said antenna corresponds to an input impedance of said receiving circuit at said reception signal frequency and a resonance frequency of said antenna corresponds to said reception signal frequency,
• an oscillator circuit generating an oscillator signal,
• switch means coupled to each of said oscillator circuit, said receiving circuit and said matching circuit,
• a control circuit for controlling said switch means to selectively establish a tuning mode in which said oscillator signal is applied to said matching circuit and said matching circuit is disconnected from said input terminal of said receiving circuit, and a reception mode in which said oscillator signal is isolated from said matching circuit and said matching circuit is connected to said input terminal of said receiving circuit, and for controlling said matching circuit during operation in said tuning mode to adjust a capacitance value of a variable capacitor of said matching circuit in accordance with said detection voltage;
• wherein:
• a frequency of said oscillator signal differs from said reception signal frequency by a fixed amount, and said apparatus comprises a memory having stored therein a reference voltage value, comprising a value of said detection voltage derived beforehand during operation in said tuning mode under said impedance matched condition;
• and
• said control circuit comprises tuning circuit means functioning when said tuning mode is entered subsequent to deriving said reference voltage value, said tuning circuit means comprising:
• initial value determining means configured for comparing said detection voltage with said reference voltage value and for determining an initial adjustment value of said capacitance value based on a result of said comparison, and
• capacitance adjustment means configured for successively adjusting said capacitance value while successively comparing said detection voltage with said reference voltage value, and for halting said successive adjustment when said detection voltage is judged to coincide with said reference voltage value, said successive adjustment commencing from said initial adjustment value.