Efficiency of power amplifiers in devices using transmit beamforming
Systems and methods for optimizing the efficiency of each of a plurality of power amplifiers that amplify a corresponding one of a plurality of radio frequency signals for transmission by a corresponding one of a plurality of antennas. Using transmit beamforming, the power of each amplified signal output by the power amplifiers may not be the same for all the power amplifiers, and may vary with changes in the communication channel between the transmitting device and receiving device. Each of the plurality of power amplifiers is controlled to operate with one or more operating parameters that optimize the efficiency for an output power level of corresponding ones of the radio frequency signals. By adjusting one or more operating parameters of each power amplifier according to changing requirements (e.g., the destination device and channel conditions), the efficiency of each power amplifier can be optimized. Consequently, one or more of the power amplifiers are operated with one or more operating parameters that reflects the output power actually needed for the corresponding radio frequency signal to be transmitted.
1. A method for simultaneously transmitting a plurality of radio frequency signals, comprising steps of:
a. weighting each of a plurality of digital baseband transmit signals with a corresponding one of a plurality of transmit weights to produce a plurality of digital weighted signals;
b. converting each of the plurality of digital weighted signals to a corresponding analog signal and then to a radio frequency signal;
c. supplying each of the radio frequency signals to a corresponding one of a plurality of power amplifiers that amplify the corresponding radio frequency signal; and
d. supplying each of the radio frequency signals to a corresponding one of a plurality of self-bias boosting circuits associated with corresponding ones of the plurality of power amplifiers, wherein each self-bias boosting circuit biases the corresponding power amplifier according to a level of the corresponding radio frequency signal supplied to it; and
e. amplifying each radio frequency signals with a corresponding one of the plurality of power amplifiers for simultaneous transmission.
2. A method for simultaneously transmitting a plurality of radio frequency signals, comprising steps of:
a. weighting each of a plurality of digital baseband transmit signals with a corresponding one of a plurality of transmit weights to produce a plurality of digital weighted signals;
b. converting each of the plurality of digital weighted signals to a corresponding analog signal and then to a corresponding radio frequency signal;
c. supplying each of the radio frequency signals to a corresponding one of a plurality of power amplifiers that amplify the corresponding radio frequency signal; and
d. controlling at least one operating parameter of each of the plurality of power amplifiers according to the transmit weight applied to produce the corresponding radio frequency signal to optimize efficiency of each power amplifier depending on the amount of amplification necessary for the corresponding radio frequency signal.
3. The method of claim 2 , wherein the step of controlling comprises generating a voltage or current bias for each power amplifier that optimizes the efficiency for the corresponding amount of amplification required.
4. The method of claim 2 , and further comprising the step of referring to a look-up-table that indexes transmit weights to values for the operating parameter.
5. The method of claim 2 , and further comprising the step of computing values for the operating parameter based on the transmit weights.