Design And Realization Of Gain Adjustable Doherty Power Amplifier Based On Time Division Duplex

With the rapid development of wireless mobile communication, TD-LTE standard, a new 4G standard, which independent intellectual property rights of our country, has become the evolution of the third generation mobile communication standard TD-SCDMA to the fourth generation mobile communication standard. Both TD-SCDMA system and TD-LTE system are time-division wireless system, its operation mode is based on time division duplex mode, also known as TDD. TDD wireless frame structure is divided by different time slot, the downlink data transfer through the cross slot, and the rate of the uplink and downlink time slot is flexible to configure. For the time division radio system, in order to reduce the interference of the receiving unit and the power consumption of the system, the RF power amplifier system, which is the largest energy consuming, work only in the slot in the transmit time. Due to the characteristics of uplink and downlink signal work time, switching time of the RF power amplifier is strictly limited, it must start the RF power amplifier in the open time and work in stable state. Therefore, this thesis research the link characteristics of the RF power amplifier for TDD system, explore the establishment of the T/R switch link, improve the low SNR gain.Due to using orthogonal frequency division multiplexing (OFDM) modulation In the TD-LTE system, the OFDM modulation signal has a high peak to average ratio. In order to improve the efficiency of the amplifier, RF power amplifier take the Doherty technology, so that when it take a larger rollback in peak power, it also can keep high efficiency. Therefore, this thesis research on the simulation design of Doherty power amplifier in a transmitting system.Based on the simulation design and study in the Doherty power amplifier transmission system, the bi-directional amplifier is designed, including transmitting and receiving system, high and low gain control circuit and a switch circuit. In order to reduce the distortion of the output signal, transmitting system can amplify signal, which take the form of promoting power amplifier and Doherty power amplifier circuit and add in the link of pre-distortion module. The receiving system adopts low noise amplifier, and the high and low gain control circuit is designed, using bypass model to realize high and low gain control.