Patent ID: 8064854
Filing Date: 2011-11-22
Classification: G07C

Abstract:
1. A radio transmitter device comprising: an antenna for transmitting a radio wave, the antenna having a first terminal and a second terminal; a power circuit for receiving a battery voltage and supplying a drive output voltage to the antenna; a switching circuit provided between the power circuit and the antenna for switching over a direction of application of the drive output voltage between a first direction and a second direction, which are from the first terminal to the second terminal and from the second terminal to the first terminal, respectively; a driver circuit for driving the switching circuit in response to a carrier wave frequency of the radio wave; and a modulator circuit for modulating in an ON/OFF manner an output of the driver circuit by a digital baseband signal of a frequency lower than the carrier wave frequency, wherein the power circuit is a variable power circuit, which includes a command input circuit for inputting a command value of the drive output voltage and a voltage converter circuit for converting the battery voltage to the drive output voltage in accordance with the command value, the command value being variable so that a range of reach of the radio wave transmitted from the antenna is varied in correspondence to the command value, the switching circuit includes an H-bridge circuit of a first switching transistor, a second switching transistor, a third switching transistor and a fourth switching transistor; the first switching transistor is provided between the power circuit and the first terminal; the second switching transistor is provided between the first terminal and a ground; the third switching transistor is provided between the power circuit and the second terminal; the fourth switching transistor is provided between the second terminal and the ground; the antenna receives the drive output voltage in the first direction when the first switching transistor and the fourth switching transistor are turned on, and the second switching transistor and the third switching transistor are turned off; the antenna receives the drive output voltage in the second direction when the second switching transistor and the third switching transistor are turned on, and the first switching transistor and the fourth switching transistor are turned off, the driver circuit includes a first drive transistor, a second drive transistor, a third drive transistor and a fourth drive transistor for turning on and off the first switching transistor, the second switching transistor, the third switching transistor and the fourth switching transistor, respectively; the modulator circuit includes a carrier wave signal circuit, a modulation circuit and a logic circuit; the carrier wave signal circuit produces a carrier wave signal in a pulse form of the carrier wave frequency; the modulation circuit modulates the carrier wave signal in an ON/OFF modulation manner in accordance with the digital baseband signal, and produces a modulated pulse signal including the ON-modulation period and an OFF-modulation period; and the logic circuit converts the modulated pulse signal into four input drive signals for the first to the fourth drive transistors so that only the first and the fourth switching transistors are turned on to apply the drive output voltage to the antenna in the first direction when the modulated pulse signal is at a first signal level in the ON-modulation period of the modulated pulse signal, only the second and the third switching transistors are turned on to apply the drive output voltage to the antenna in the second direction when the modulated pulse signal is at a second signal level in the ON-modulation period of the modulated pulse signal, and all the first to the fourth switching transistors are turned off during the OFF-modulation period of the modulated pulse signal.