High efficiency RF and microwave power amplifiers with non-constant envelope signals.

摘要

In modern wireless communications, the modulation schemes require highly linear power amplifiers since the high data rate is demanded while the bandwidth is restricted. However, the conventional linear power amplifiers suffer from the degradations of power efficiency because the highest efficiency can not be maintained when the envelope varying signals are amplified. This dissertation tackles those technological barriers through the several novel approaches from architecture to circuit perspectives. First architectural approach, the dual-mode power amplifier maintains the relatively high efficiency until the output power is backed-off by 6 dB. This approach saves DC power by reducing the size of power amplifier when the output power is backed-off. The size of overall power amplifier is controlled by turning on and off the small power amplifiers. The technical challenge is to implement a lossless divider and combiner network with the matched impedances regardless of the number of active power amplifiers. A proposed divider and combiner network meet this requirement. Secondly, a novel signal processing techniques, envelope delta-sigma modulation, utilizing high efficiency switching power amplifiers are presented. This approach provides a new paradigm of linear amplification in digital fashion. Using class D amplifier, the feasibility of this approach is evaluated. In addition to that, a novel power amplifier, class ED is proposed for this advanced signal processing techniques. Thirdly, a new concept of pulsed load modulation (PLM) is introduced. The proposed amplifier maintains the maximum efficiency over a wide range of output power level. The essential idea is to synthesize the load impedance for optimum efficiency using switched resonator concepts. A high-Q, bandpass filter in conjunction with two pulse-biased power amplifiers connected with a lambda/4 transmission line constitute the switched resonator. Ideally, for a pair of identically sized and biased class B amplifiers, the maximum efficiency of 78.5% is maintained for up to 6 dB backoff in the output power. The concept is validated by building power amplifiers at 1.87 GHz with a pair of discrete FETs and at 17 GHz with 0.15 mum GaInAs pHEMT technology. The measured results demonstrate that with the proposed approach, significant efficiency improvement is obtained over conventional Class B amplifiers. Lastly, a new power efficient combiner design method is presented for millimeter wave power amplifiers. In conventional integrated power amplifiers, most of estate are wasted in power combiner and divider layouts. By utilizing these unoccupied areas as low loss capacitances, high efficiency power combining and compact power amplifier design are achieved. This concept is proved by building 2 W, 44% PAE, 34 GHz power amplifiers using 0.15 mum pHEMT technology.