Radio frequency transmission of an electrical signal occurs in a broad frequency spectrum from several megahertz (MHz) to tens of gigahertz (GHz). Common RF transmission systems include an antenna that transmits and receives RF signals and a low noise amplifier that amplifies an input RF signal from the antenna and a power amplifier to generate an amplified signal to be delivered to the antenna. The power of the output signals from the power amplifiers are required to be controlled within stringent specifications as well as regulatory standards, to assure the quality of the RF transmission signals. Moreover, many portable wireless systems are required to increase or reduce the transmitted power depending upon signal strength, transmission range, the types of digital signal modulation such as Quadrature Phase Shift Keying (QPSK) and Orthogonal Frequency Division Multiplexing (OFDM), as well as surrounding interfering signals. These requirements can be met by a power sensing circuit that samples the output power of the power amplifier and outputs a power sensing signal for power control. However, variations in power sensing signals due to temperature and DC bias are also passed on to the power output through the control loop. Variations in power sensing signals can significantly affect the qualities of the output RF signals. A need therefore exists for accurate and reliable techniques for power sensing for RF power amplifiers with good temperature and DC bias compensations.
USPTO Backgrounds
USPTO Backgrounds