Wireless communication circuit and wireless communication apparatus using the same

1. A wireless communication circuit, provided with an amplifier for amplifying an inputted signal so as to output thus amplified signal to an antenna, said wireless communication circuit comprising:

a switch configured to be supplied predetermined plural constant voltages and to select one of the predetermined plural constant voltages as a constant voltage supplied to the amplifier, the predetermined plural constant voltages also being supplied to at least one of a plurality of circuits, other than the amplifier, either contained in the wireless communication circuit or electrically connected to the wireless communication circuit;

control means for controlling the switch to select said one of the predetermined plural voltages as the constant voltage supplied to the amplifier in accordance with a power which should be outputted by the amplifier; and

a detector to detect an output of the amplifier; and

a controller to adjust transmission power of the antenna to be constant in response to the detected output of the amplifier, wherein

the constant voltages of the predetermined plural constant voltages are different from one another.

2. The wireless communication circuit as set forth in claim 1 , wherein the control means controls the switch so as to select a constant voltage, enabling the power which should be outputted by the amplifier to be outputted, which is as low as possible, out of the plural constant voltages.

3. The wireless communication circuit as set forth in claim 1 , wherein:

in case where each of the constant voltages is supplied as a power source voltage, a gain of the amplifier is set to be a predetermined gain so as to correspond to the constant voltage that has been supplied, and

the control means causes the switch to select a constant voltage from the constant voltages so as to control the gain of the amplifier.

4. The wireless communication circuit as set forth in claim 1 , wherein the power which should be outputted includes an output power, predetermined as a communication power for a concealed communication, which enables transmission as a lower communication power than in a normal communication.

5. The wireless communication circuit as set forth in claim 4 , wherein the communication power for the concealed communication is set to be a value which allows a communication with a device positioned within a distance of 4 [m] of the wireless communication circuit.

6. The wireless communication circuit as set forth in claim 4 , wherein a communication power X [dBm] defined as the communication power for the concealed communication may be set to be −10 [dBm] or less when a communication power is Pout, on the basis of expression with [mW], and X [dBm]=10·log(Pout [mW]/1 [mW]).

7. The wireless communication circuit as set forth in claim 4 , wherein the communication power for the concealed communication may be set to be a value which allows a communication with an apparatus in contact with an apparatus having the wireless communication circuit.

8. The wireless communication circuit as set forth in claim 4 , wherein the concealed communication power is set to be in a range of from +10 [dB] to 20 [dB] in accordance with a lowest receivable power of a communication end.

9. The wireless communication circuit as set forth in claim 1 , comprising:

a modulation circuit for modulating an inputted signal so as to output thus modulated signal to the amplifier; and

a modulation gain adjustment circuit for changing a gain of the modulation circuit in association with switching of the switch.

10. The wireless communication circuit as set forth in claim 1 , comprising:

a modulation circuit for modulating an input signal so as to output thus modulated signal to the amplifier; and

a modulation gain adjustment circuit for changing a gain of the modulation circuit in accordance with a detection result of an output power of the amplifier and for changing a process of controlling the gain of the modulation circuit in association with switching of the switch so as not to saturate the amplifier.

11. The wireless communication circuit as set forth in claim 1 , comprising a power source for supplying the constant voltages, wherein at least one level of the constant voltages supplied by the power source is changeable.

12. A wireless communication apparatus, comprising a wireless communication circuit, provided with an amplifier for amplifying an inputted signal so as to output thus amplified signal to an antenna, said wireless communication circuit including:

a switch configured to be supplied predetermined plural constant voltages and to select one of the predetermined plural constant voltages as a constant voltage supplied to the amplifier, the predetermined plural constant voltages also being supplied to at least one of a plurality of circuits, other than the amplifier, either contained in the wireless communication circuit or electrically connected to the wireless communication circuit;

control means for controlling the switch to select said one of the predetermined plural voltages as the constant voltage supplied to the amplifier in accordance with a power which should be outputted by the amplifier;

a detector to detect an output of the amplifier; and

a controller to adjust transmission power of the antenna to be constant in response to the detected output of the amplifier, wherein

said wireless communication apparatus is mobile, and

the constant voltages of the predetermined plural constant voltages are different from one another.