WSN Applied To An Active Research And Design Of A Complex Image Rejection Filter

With the continuous development and innovation in wireless technology, the wireless sensor networks (WSN) are increasing demands on its RF front-end. Low-IF architecture is widely used in the RF receiver, and its main parts include a low-noise amplifier, a down-conversion mix frequency, a phase-locked loop frequency synthesizer, an image rejection filter and an IF amplifier processing circuit. Because the complex filter can achieve image rejection, which just eliminate the image interference problem in low-IF architecture. This advantage has become one of the most important components of the low-IF receiver.In this paper, we design and implement a bandwidth-variable complex filter with an automatic tuning function, which is fit for WSN low-power and low-IF radio receiver. The design is based on the SMIC0.18μm CMOS(Complementary Metal Oxide Semiconductor) process, we achieve a complex three-order Butterworth passband filter having a center frequency of3MHz, with a-3dB bandwidth and2M/1M/500K/250K configurable features. The simulation results show that the filter passband gain is about10dB, the image rejection is above than35dB, the third-order intercept point (IIP3) is better than24dBm, the noise figure is less than44dB, the current consumption is about1mA. In addition, due to the process, temperature, aging and other conditions, there might be small deviations between the resistors and capacitors and the design value. We propose an automatic tuning circuit which compensate for this deviation effectively. Finally, the flow circuit chip test results verify the correctness of the design theory and methods, and the whole system works perfectly. The performances meet the design requirements of the wireless sensor networks low-power RF receiver.