Radio frequency front-end based on high-intermediate frequency superheterodyne and zero intermediate frequency structure

Abstract

The invention discloses a radio frequency front-end based on the high-intermediate frequency superheterodyne and zero intermediate frequency structure, which includes a transmitting module and a receiving module, wherein, the receiving module includes the following devices connected in turn with each other: a transceiving antenna, a low-pass filter, a superheterodyne unit, an IF band-pass filter, a zero-IF unit, a analog-to-digital converter and a digital baseband module of which the output is communicated with the transmitting module. The zero-IF unit includes the following devices which are also connected in turn with each other: a zero-IF mixer, an active low-pass filter and a variable gain operational amplifier of which the output is communicated with the input of the ADC; the inputs of the zero-IF mixer are communicated with the output of the IF band-pass filter and the second LO respectively. The present invention avoids the image interference, improves the system integration and decreases the system consumption.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This application claims priority from PCT application Ser. No. PCT / CN2012 / 081282, filed Sep. 12, 2012 and CN Application No. CN201210300528.1, filed Aug. 22, 2012, the contents of which are incorporated herein in the entirety by reference.FIELD OF THE INVENTION[0002]The present invention relates to a radio frequency front-end, and more particularly, to a radio frequency front-end based on high-intermediate frequency superheterodyne and zero intermediate frequency structure.BACKGROUND OF THE INVENTION[0003]Among the numerous wireless access systems, the core element of the communication facilities is the RF front-end chip. The RF front-end is mainly used for amplifying, frequency converting, filtering and quantizing the weak signal received from the antenna of the receiver, and demodulating it to the baseband signal. Thus, design of the RF front-end circuit shows significant importance to the design of the whole receiver and has direct inf...

AI Technical Summary

Benefits of technology

[0005]The object of the present invention is to provide an improved radio frequency front-end based on the high-intermediate frequency superheterodyne and zero intermediate frequency structure which effectively eliminates the image interference, improves the sensitivity and reliability of RF front-end circuit and also decreases the tuning ratio of LO.

[0013]The radio frequency front-end of the present invention having the first IF of 2.45 GHz has the following advantages: A. Eliminating the image interference. When the frequency of the input RF signal ranges from 100 MHz to 1.2 GHz, the corresponding image interference frequency is from 3.7 GHz to 4.8 GHz which is out of the range of the input signal channel, thus avoiding the image interference. And the image suppressing filter and IF filter are not required accordingly, and further, improving the system integration and decreasing the system consumption; Meanwhile, comparing the LO tuning range between the conventional superheterodyne structure of which is 100 MHz to 1.2 GHz and the present invention of which is 1.25 GHz to 2.35 GHz, the center frequency increases from 650 MHz to 1.8 GHz, and the tuning ratio decreases from 85% to 30%, which dramatically reduces the design difficulty of the frequency synthesizer and makes it easy to implement the high-intermediate frequency superheterodyne structure. B. The technical solution of the present invention has high feasibility because the post processing technique for 2.45 GHz IF signal is rather matured.

Problems solved by technology

However, an IF filter with high-quality factor is necessity of filtering the image interference effectively, which is unrealizable in the existing CMOS process.

Furthermore, as shown in FIG. 2, the IF of the superheterodyne structure is normally lower than the frequency of the RF signal, which leads to the existence of a fatal defect of image interference for the receiver.

The image interference frequency of the RF front-end of the conventional superheterodyne structure totally falls in a narrow range around the useful channel, which has the defects of difficulty in distinguishing the two kinds of signals.

The structure has a low sensitivity and is hard to integrate.

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