Design and implementation of fast convergence and large dynamic digital Automatic Gain Control

Abstract

In the digital receiver, Automatic Gain Control (AGC) is usually adopted to solve the large fluctuation of received signal and improve the quality of received signal. Linearly Digital AGC (LDAGC) has the disadvantages of long convergence time and small dynamic range, which is not suitable for burst communication. And Logarithmic Space Linearly Digital AGC (LSLDAGC) has high complexity for using logarithmic and exponential operations, which is difficult for hardware implementation. In this paper, a new Approximate Logarithmic Space Linearly Digital AGC (ALSLDAGC) with faster convergence speed and larger dynamic range, compared with LDAGC, has been designed and implemented on FPGA. The proposed ALSLDAGC also has lower complexity than LSLDAGC by replacing logarithmic and exponential operations with multiply operations. The simulation results show that ALSLDAGC can cope with input signal within 70dB fluctuation. And our tests on FPGA show that the fluctuations of ALSLDAGC output signal are only 0.2dB and 0.8dB under continuous and burst communication respectively, and the performance degradation is less than 0.1dB compared with ideal digital amplifier when the average amplitude of input signal is attenuated from 0dB to 36dB.