| The performance of a receiver front-end makes a huge difference in the communication link. Both well-defined system parameters and appropriate architecture design do have a significant influence on the performance, cost, and marketability of a receiver. Automatic gain control (AGC) circuit maintains an accurately desired output level with input signals of variable strength, so that circuits following the AGC circuit require less dynamic range. As for the reason, AGC has been widely used in modern communication receivers.The desired signal with variable strength the antenna receiving can be amplified to an optimized input level for the baseband analog-to-digital converter (BB-ADC) by the use of an AGC circuit. It can also contribute to maximize the dynamic range of receivers in order to have enough capacity to deal with input signals of variable strength. So as to reduce the quantization noise attached by BB-ADC module as low as possible, AGC circuits offer an optimized signal-to-noise and distortion ratio (SNDR) and obtain a minimum error code.This work presents the analysis and design of an AGC circuit in a RF receiver. While an AGC circuit for the utilization of digital television tuners has been designed, an AGC algorithm just has been verified with the aid of simulation tools.Firstly, according to several fundamental parameter specification for the RF receiver, noise, linearity and dynamic range in analog or RF circuits are simply analyzed and calculated.Secondly, this work describes a gain adjustment method for settings and allocations of several variable gain modules. It is maintained a rule of the gain adjustment in terms of the optimized SNDR as well.Finally, two achievement methods for AGC circuits are presented with and without time constants, so as an analysis of the AGC circuit in a digital television tuner. Simultaneously, an AGC algorithm is successfully completed. Simulation results show that requirements of AGC system are satisfied concurrently. |
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