Research On The Key Building Blocks Of Wireless Transceiver

RF wireless transceivers have been used in all aspects of social life currently.This article will focus on the two key building blocks of the wireless transceiver,one is the rectifier circuit and the other is the variable gain amplifier.Wireless charging has a broad market prospects.Receivers for implanted biomedical equipment are basically using wireless charging technology for power supply.With the development of wireless charging technology,more and more wireless receivers will be powered by wireless charging in future.The rectifier circuit is one of the important parts in the wireless charging system.The received RF power could be converted to DC power only through the rectifier circuit.The converted DC power will supply the load.The power conversion efficiency(PCE)of the rectifier circuit determines the PCE of the whole wireless system.Current researches focus on improving the PCE of the circuits with small input power.However,there are few public researches concern about high power rectifier circuits.In this article,traditional structures of rectifier circuits are analyzed and a circuit topology suitable for high power rectifier is proposed.The width of MOS transistors used in the rectifier circuit might reach up to tens of thousands of microns when the input power is very large.It is of great significance to find a way to quickly and accurately determine the size of the MOS transistors.There are almost no papers focus on the complete theoretical derivation of the rectifier circuits.In this article,the whole working process of the proposed rectifier circuit is analyzed in detail.The optimal width-length ratio of the MOS transistors under the given power and PCE is obtained through some reasonable simplification and approximation.The circuit is simulated in Cadence environment based on the TSMC 0.18um CMOS process.The difference between the theoretical result and the simulation result is acceptable,which is instructive for designing the high power rectifier circuit.A high-speed comparator is needed for the proposed rectifier circuit,so the structure of the comparator is also compared and analyzed,and the appropriate comparator structure is proposed.The layout design is completed using Virtuoso.The variable gain amplifier(VGA)is an important module in the receiver.Using VGA,the gain of the receiver can be changed as the amplitude of the input signal changes.At present,the researches of VGA are mainly focused on low-voltage low-power,high gain range,large bandwidth,achieving gain linearity of dB more accurately and other fields.In this paper,a VGA with the gain of more than 30 dB and band-width over 50 MHz under 1.2V supply voltage is designed.In order to ensure that the establishment of the entire AGC loop is constant,the gain of the proposed VGA must be dB-linear.The working principle as well as advantages and disadvantages of the commonly used VGA structures are analyzed,finally the Gilbert unit is used as the main part of the proposed VGA.The method of constructing the approximate exponential function is used to realize the dB linear variation of the gain.A zero point is introduced at the output terminal to increase the bandwidth.In order to make the VGA be able to work in the case of 1.2V supply voltage,an auxiliary amplifier is used to improve the structure of the Gilbert unit,reducing the number of transistors accumulated in the Gilbert unit.The design is also simulated in the Cadence environment based on the TSMC 0.18um CMOS process and the layout design is also completed.At the end of the paper,the basic rules,some dos and don'ts and design skills of the layout design are introduced.