Study And Design Of Automatic-Gain-Control Front-End Chip In Human Body Communication Receiver

Human body communication（HBC） was first proposed by Massachusetts Institute of Technology（MIT）, the human body is treated as a signal transmission path for the signal transmitting on the body surface or inside. Based on the HBC technology, the communication between the portable electronic devices held by people can be realized. Compared with wireless communication technology, there are many advantages such as convenient connection, less affection by external noise, small external radiation, low power consumption and high security.Currently, there are two main methods coupling the signal to the human channel in the HBC system: galvanic coupling and capacitive coupling. In Galvanic coupling, the human body is as a conductor, which need to use a wire to elicit the signal from the human body, thus the bandwidth is narrow. In Capacitive coupling, without a wire, an electrode can be kept in a certain distance with the human body and the other electrode can be suspended, thus the bandwidth is wide.In this thesis, according to the requirements of the wide bandwidth in HBC system, a wide bandwidth, wide input dynamic range, high input impedance and high gain receiver front-end chip for capacitive coupling was designed, which have a single-ended to differential amplifier（LNA） with wideband and low noise, filter circuit, wideband automatic gain control amplifier（AGC）.In the human channel, due to the high input impedance, the input signal is in the low and middle frequency band, a single-ended to differential LNA consisting a cascode and a common-source amplifier circuit was proposed, which has the features of high input impedance, wideband, noise cancellation, high gain and do not need a large area of the inductor and the capacitor element. On the other hand, the degree of attenuation would change with the signal transmission distance, human joints and carrier frequency change, which means that the dynamic range of the received signal is large, therefore, it is very important to automatically adjust the gain of the amplifier circuit depending on the different amplitude of the input signals. Thus, a new AGC circuit was proposes with low complexity, low power consumption, wide range of dB-linear and wideband because of using utilizes linear in dB（dB-linear） approximation method、active load and zero-pole compensation technology.The proposed front-end receiver chip for HBC was implemented and verified by 180 nm CMOS technology with a supply voltage of 1.8V. The post simulation results showed that the bandwidth of the LNA was 1MHz⁵37MHz, the input equivalent noise was 2.301nV/ （Hz）^1/2, the gain was 22 dB, the current consumption was 767 μA; The gain control range of the AGC was-25⁶7dB, the d B-linear range is 62dB（the error is less than ±1dB）, the bandwidth is 1MHz¹25MHz, the current consumption was 1.6mA. It was demonstrated that the designed chip can meet the requirements of the signal gain and bandwidth in HBC system.