Design And Study Of AGC Loop Algorithm For RF Receiving Channel

Zig Bee technology as one of the main technology in wireless sensor networks which has the advantages of low power consumption, low cost and large capacity network is widely used in industrial control, intelligent household and environmental monitoring, etc. Automatic gain control system as an important part of Zig Bee RF receiver could change gain automaticlly when it faces different strength of the signal to provide a stable level for the next circuit. Therefore, high-performance automatic gain control system helps to improve the quality of Zig Bee communication network.The RF recevier in this paper takes low intermediate frequency receiver structure to meet the requirements of Zig Bee technology of low power consumption and low cost. Automatic gain loop abandons the traditional analog control and adopts digital signal control way. Digital automatic gain control can directly produce gain change in the form of index which has the very high linearity and saves the index produce circuit to reduce the design difficulty. Because the gain of the RF low noise amplifier could be controled by the digital automatic gain control algorithm module,so the demand of the gain of the automatic gain loop is reduced to reduce the design difficulty. The PGA modules of automatic gain loop adopts the combination of coarse and fine tuning parts which not only has high precision, but also has a larger range of gain. Only need to fine the tuning part of the amplifier gain variable, the gain of the coarse is fixed and through the digital signal to control the opening and closing which further reduces the design difficulty.The range of the algorithm is 102 d B, which has 2d B precision. The low noise amplifier module variable range is 32 db which had three states:-2d B, 14 d B and 30 d B. The variable range of the programmable amplifier in the loop is 70 db which is divided into coarse and fine tuning parts. The coarse part is made of four fixed gain amplifiers whose gain is 14 d B and the fine tuning part is an amplifier whose variable range is 14 d B and change precision variable is 2d B controlled by different resistances. On the basis of the results of the five peak detector to control the two parts which is the low noise amplifier module and the programmable gain amplifier module. And at last it is joined the gain distribution adjustment module to optimize the noise factor in the circuit. The algorithm is simulated in the Model Sim SE and compiled by the Design Compiler. Finally, we completed floorplan and routing in the Soc Encounter.