Method and apparatus for increasing the efficiency of a transmitter
AssigneeTelefonaktiebolaget LM Ericsson (publ)
InventorBo Lindell
Life of this patent
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Abstract
The present invention relates generally to the field of RF transmitters, and more particularly to a method and apparatus for increasing the efficiency of transmitters which are capable of transmitting at different power levels in each of at least two frequency bands. An inventive method is presented as well as an inventive transmitter comprising at least one power amplifier in which the load in the transmission line is varied as the output power is varied, in order to keep the efficiency of the power amplifier at a high level.
Claims17
1) A transmitter for transmitting RF signals at at least two power levels in each of at least two frequency bands, the transmitter comprising at least one power amplifier connected to a working load, the transmitter being characterised by
- a first electronic circuit connected, in parallel to the working load, to the at least one power amplifier at a line length from the at least one power amplifier, the first electronic circuit comprising a reactive impedance and a switching device connected in series, the reactive impedance and the line length having been chosen so as to provide, when the switching device is closed, a load selected with regard to the efficiency of the at least one power amplifier when the transmitter transmits at one of the at least two power levels;
- wherein, if the at least one power amplifier is more than one power amplifier,
- the line length at which the first electronic circuit is connected to the power amplifiers is different for each power amplifier.
10) The transmitter of any of the above claims, wherein
- the reactive impedance of the first electronic circuit is formed by a capacitor and an inductor, the capacitor and the inductor being connected in parallel or in series.
11) The transmitter of any of the above claims, wherein
- the line length(s) and the reactive impedance of the first electronic circuit have been chosen so that ratio of the load when the switching device is open and the load when the switching device is closed equals the ratio of the power level for which the transmitter is designed to transmit when the switching device is closed and the power level for which the transmitter is designed to transmit when the switching device is open.
12) The transmitter of any of the above claims, wherein the working load is an antenna.
14) A method for improving the efficiency of a transmitter upon changing the output power level at which the transmitter transmits, the transmitter being capable of transmitting at at least two power levels in each of at least two frequency bands, the dual mode RF transmitter comprising a power amplifier connected to a working load, the method characterised by the following steps:
- connecting an electronic circuit, in parallel to the working load, to the at least one power amplifier at a line length from the power amplifier, the electronic circuit comprising a switching device and a reactive impedance, the line length and the reactive impedance being chosen to form an optimal load with regard to the efficiency of the at least one power amplifier when the transmitter transmits in one of the frequency bands at one of the at least two power levels;
- and, if the transmitter transmits at the power level and in the frequency band for which the line length and the reactive impedance are chosen to form an optimal load, then
- closing said switching device and;
- if the transmitter transmits at a power level and/or in a frequency band for which the line length and the reactive impedance are not chosen to form said optimal load, then
- opening said switching device.
Dependencies are inferred from the claim text.