Zero intermediate frequency radio receiver second-order inter-modulation automatic correcting circuit

Abstract

The present invention discloses an automatic correcting circuit of second-order intermodulation performance for a zero-IF wireless receiver. A carrier wave with the frequency fLO as a local oscillation signal is respectively input in a frequency mixer and an input terminal of a correction signal generator. The correction signal generator outputs a correction signal with the frequency 1 / 2fRF to a balance unit, and the correction signal is converted by the balance unit into one differential signal to an FR input terminal of the frequency mixer. One DC deviation signal is generated through the frequency mixer and is output to an A / D converter circuit for converting into a digital signal and entering a digital correcting circuit. The digital correcting circuit selects a corresponding control electrical level according to the size of the DC deviation signal to adjust the frequency mixer and make the DC deviation signal to be the lowest value. The invention can effectively suppress the intermodulation interference caused by even-order nonlinearity, avoid the signal receiving block caused by the even-order and the increase of the error rate, and ensure the normal operation of the system. The automatic correcting circuit of the invention can be used for the wireless FR direct variable frequency receiver.

Description

technical field [0001] The invention relates to a radio frequency receiver, in particular to an automatic calibration circuit for second-order intermodulation performance of a zero-IF wireless receiver. Background technique [0002] The traditional RF receiver adopts a superheterodyne structure, and its circuit structure is as follows: figure 1 shown. It uses two frequency conversions to convert the RF signal to the high-frequency and then to the baseband, and uses an off-chip high-quality factor filter between the modules, so it has the advantages of high sensitivity and good selectivity. Obviously, in the superheterodyne structure, the intermodulation products generated by the even-order nonlinearity are filtered out by the off-chip filter and the coupling capacitor between the modules, and will not interfere with the intermediate frequency signal. However, due to the off-chip filter and a large number of external components, the system integration level is difficult to ...

AI Technical Summary

Problems solved by technology

However, the DC offset caused by even-order nonlinearity and self-mixing caused by carrier leakage will directly interfere with the zero-IF signal

Intermodulation products generated by even-order nonlinearities fall within the signal frequency band and cannot be filtered out by capacitors or filters

[0004] The use of differential circuits can effectively suppress even-order nonlinear products, but the asymmetry of the circuit and the deviation of the process are inevitable. The resulting DC deviation and second-order intermodulation products will cause signal reception blockage and increase the bit error rate, and even make the system unable to work properly

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