In the paper, a high-precision all-digital automatic gain control (AGC) algorithm for broadband real-time spectrum analyzer is proposed, which provides gain to weak signals, after the large signals and out-of-band noise have been filtered out, to ensure that weak signals have sufficient bit resolution, accuracy and quantization noise ratio in the output formatter. The effective mathematical analysis of the scheme is given and the important parameters which affect the performance is discussed in detail. By selecting the appropriate parameters, the simulation results are very approximate to theoretical value. The maximum dynamic range can be obtained about 96.328dB, the minimum level resolution of the input weak signals can be achieved about, and the output gain resolution is acquired 0.000367dB. For these considerable merits, the scheme is quite suitable for high-resolution broadband real-time spectrum analysis system, and also can be applied in other digital analysis system.
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