| In modern wireless communication system, in order to achieve high-speed data transmission in a limited frequency range, complex and high spectral efficiency modulation modes are widely used. Modulation signals have high power to average power ratio(PAPR) and the envelope of the signal also show a non-constant envelope characteristic, which lead to low efficiency of radio frequency power amplifiers(RF PA).In order to improve the efficiency of RF PA in modern wireless communication system efficiently, the wide-bandwidth envelope tracking(WBET) technology which can achieve high efficiency in wide power range has become one of efficiency enhancement technology has been proposed. This thesis is based on 0.18?m SiGe BiCMOS process, design and research the WBET PA circuit of modern WBET system, including a highlinearity SiGe HBT power amplifier and a wide-bandwidth high-efficiency highperformance CMOS supply modulator.In the modern WBET system, a high-linearity power amplifier is generally used to improve the linearity of the whole system. In this thesis, the SiGe HBT power amplifier works in the class AB mode, can be used for WLAN 802.11 g band. The power amplifier circuit use two stage structure, supply voltage is 3.3V. Both the driving stage and the power stage use linearity-bias circuit to improve the linearity of the WBET system. Simulation results shows, under the working frequency of 2.4GHz, the HBT power amplifier can output 25.25 dBm of linear power,32.5dBm of saturated power, power gain is 27.3dB, peak power added efficiency is 30.2%, input matching S11 is less than-11.59 dB, output matching S22 is less than-13.51 dB, reverse isolation S12 is less than-34.8dB.In modern WBET system, high performance supply modulator is the most important module of WBET PA, is the core of WBET technology, the design of high performance supply modulator has been the most important factor to limit the development of the WBET technology. In this thesis, supply modulator is adopted by a linear amplifier and a switch supply working parallel, supply voltage is 3.3V, load is 5?. The linear amplifier can provide peak linear current is 300 mA, push-pull output stage have a device size of 2.88 mm ? 200 nm, 0.88 mm ? 200nm; The switch supply have a device size of 8mm ?400nm, 2mm ? 400 nm. Performance analysis points out that the supply modulator is suitable for processing the OFDM signal which power is mainly concentrated in the DC and the low frequency part. Simulation result shows that the SM has an output swing of 0.26V~2.8V, a 3dB bandwidth of 22.58 MHz, a phase margin of 63.27 degree, can be used for 10 MHz baseband signal applications, and has a certain margin. Functional verification results show that the supply modulator can modulate the supply voltage according to the amplitude of the envelope signal, and adjust the voltage of the power amplifier dynamically.The HBT power amplifier has high linear output power, high saturate output power, and power added efficiency is not bad, can be used in 2.4GHz WLAN 802.11 g band after further optimization. The supply modulator has correct function, high efficiency, but the DC power consumption is still high, can be used as high performance supply modulator for wide-band envelope tracking power amplifier system after further optimization. |
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