The Design Of Broadband RF Power Amplifier

With the rapid development of wireless communication technology, mobile internet networking technology and internet of things, growing number of protocol standards have born. In order to increase the system integration, to integrate a variety of communication systems into one chip has been a hotspot of multiband applications. This paper is to design a broadband power amplifier (PA) based on multi-mode multi-band transceiver.In this paper, a broadband PA is designed for GSM/TD-SCDMA/WLAN systems with bandwidth from 0.8 to 2.4GHz in 0.13μm SiGe HBT process has been described. Due to the high linearity requirements of the application systems and a wide operating frequency, the PA adopts common emitter using a two-stage pseudo-differential structure which works in AB class. Multi-stage LC broadband matching network applied in input, which will be impedance conjugate match with the input transistor of the first stage, so that power can be effectively transmitted to drive stage and achieve good VSWR. Adopting multi-stage LC matching circuit in output, which uses load matching to achieve optimum load in the entire frequency band to obtain maximum output power. In order to expand the bandwidth and obtain a flat gain characteristics, compensated matching technique in the inter-stage and the negative feedback technology in the first stage have been used. The principle of matching compensation technology is match at high frequencies, and a bit mismatch at low frequencies to obtain flat gain. An adaptive bias control circuit is used to provide bias current of the power transistor which can improve efficiency and linearity. Because of the output power is large and bandwidth is relatively wide, so the output matching network is implements in the PCB. Broadband output matching network consists of transmission line and discrete capacitors is realized off chip.The chip size of the broadband PA is 1.60 mm× 1.74mm. The post-simulation results show the largest gain is 26.23dB at 846MHz and 3dB band-width is 690MHz-2470MHz. Input VSWR throughout the operating band is less than 2.1, while the circuit is in a stable state during the entire operating band. The power gain during the entire band reaches 23dBm, and output ldB compression point is greater than 26dBm, and the saturation output power is greater than 29dBm with the power added efficiency (PAE) better than 38%. The post-simulation shows the results reached the design requirements.