Patent Application
20080039903
The invention will now be described in more detail, by way of example only, with reference to the accompanying drawings, in which
The electronic device shown in
The electronic device includes a dual purpose inductor 101, which serves as an antenna for communications purposes in the communications mode and as an inductive element for power conversion purposes in the power conversion mode. In this mode the inductor 101 is connected to an internal power source so that the power converter 104 can convert energy from the internal-source to power the communications system 100. The power converter can be a ‘Buck’ or ‘Boost’ type converter. ‘Buck’ converters are used for reducing the voltage, while ‘Boost’ converters are used for increasing voltages. These converters use an inductor as an energy storage device, and are commonly known to those skilled in the art as switching regulators.
During reception of communications signal by the device, the power converter 104 is normally switched off, and the inductor 101, which also serves as an energy storage device, is connected to a receiver 106 to function as an antenna for communications purposes.
In the communication mode, the inductor 101 picks up electromagnetic energy from the external source.
Switch unit 106 comprising switches 102 and 103 serves to connect the inductor 101 to either the power converter 104, or the receiver 106. A microcontroller 105 controlling the switches 102 and 103 connects the switches according to the requirements of allowable latency and the length of the messages to be received, and the overall power requirements of the circuitry fed from the power converter 104. The switches may be actuated on a regular time multiplexed basis, or irregularly as a result of telecommand signals received, or as commanded by another system, for example a microcontroller.
The switches 102 and 103 may be unipolar or bipolar transistors. Desirably, they show a very low resistance in the ‘ON’ state, and low capacitance in the OFF state. Switches 102 and 103 may also be mechanical switches or relays.
The operational frequency of power converter 104 is chosen with regard to the ratio of the input to output voltage of the converter, the desired efficiency, the possibilities of interference with other circuitry in close proximity to the converter, and the available values of inductance in physical sizes consistent with the application. A typical frequency could be in the 1 to 2 MHz region.
The operational frequency of receiver 106 is chosen with regard to the value of inductor required by the converter 104, the radiated power level allowed (in this respect, it should be noted that in general, the radiated power allowed at the ISM frequencies is higher than at other frequencies) and the available values of inductance in physical sizes consistent with the application. Typical frequencies for such use are 6.78, 13.56 and 27.12 MHz.
Capacitor 105 may not always be needed, although the received signal will be greater when the circuit consisting of the inductor 101 and the capacitor 105 is resonant. However, such resonance is not necessary for the system contemplated by the invention to work.
In the case that the capacitor 105 is used, the value of inductor 101 is chosen to provide both the correct inductance value for the power converter 104 requirements, and to resonate with the capacitor 105 at the frequency at which it is required to receive a signal. The sensitivity of the receiving system is proportional to the physical size of the inductor, but radiation from the inductor when being used in the power conversion circuitry can also be increased, although in that case difficulties in meeting requirements on emissions covered by EMC (Electro Magnetic Compatibility) requirements may be experienced.
Numerous modifications may be made without departing from the spirit and scope of the invention as defined in the appended claims.
