Baseband demodulation preprocessing system

Abstract

The system comprises an amplifier, a mixer and a limiting circuit. Said amplifier makes pre-amplification for the received RF analog signals. Said mixer converts the amplified RF analog signals and LO signal to intermediate frequency analog signals through a nonlinear transform. Said limiting circuit is connected to the amplifier and the mixer in series to limit the interference signal level higher than desired signal. The invention can provide anti-interference process for both analog demodulation system and digital demodulation system.

Description

technical field [0001] The invention relates to a baseband signal processing system in a communication system, in particular to a demodulation preprocessing system of a baseband intermediate frequency signal. Background technique [0002] The so-called baseband intermediate frequency signal demodulation preprocessing includes: converting the radio frequency signal into an intermediate frequency signal and providing it to the demodulation unit, and anti-interference processing before demodulation. In the preprocessing system, how to improve the anti-interference performance, and then improve the signal quality sent to the demodulation unit is the key in the preprocessing system. [0003] In the field of communication, interference is an important factor affecting the normal operation of base stations. One of the factors causing interference is: due to limited frequency resources, the frequencies used by different communication systems are close to each other, which causes in...

AI Technical Summary

Problems solved by technology

The defect of this method is that: the adaptive filter is a digital filter, and its essence is to realize the filtering in the digital domain through a certain software algorithm. Therefore, the adaptive filter cannot be applied to the filtering of the intermediate frequency noise of the analog system; The device needs to work in a certain level range (that is, has a certain dynamic range). When the interference signal level is strong, in the digital filter system, due to the dynamic limitation of the analog / digital converter (A / D), the analog interference cannot be The signal is converted into a digital signal without distortion, and then filtered out by an adaptive filter; the filtering principle of the adaptive filter is to dynamically find the interference frequency and filter out the signal of the interference frequency

like figure 1 As shown in Fig. 1, the input signal carries the interference signal. After being output by the adaptive filter, although the interference signal is filtered out, the useful signal also has a spectral loss in the interference frequency range.

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