| Active complex filters are of particular interest as they, unlike traditional filters, perform image rejection in addition to filtering. Complex filters are considered one of the most effective techniques for discarding the image signals in low intermediate frequency (IF) receivers such as Bluetooth applications.;Alternatives of realizing voltage and current-mode complex filters based on transconductance, transresistance, and current amplifiers are systematically developed. Several new complex filters are presented. These designs are developed from their respective basic complex integrator which is utilized to obtained complex filters from their second-order two-integrator loop lowpass biquad. It is shown that this approach leads to not only most efficient circuit realizations but also advantageous features in terms of image rejections and selectivity characteristics. Detailed frequency domain analysis of the proposed filters is giving and their frequency characteristics are identified. Various amplifiers are realized utilizing the second generation current conveyor (CCII) to promote objective comparison between filters based on different building blocks. Consequently, the comparison shows that the optimum designs in terms of power consumptions are current-mode filters based on the second generation current conveyor and current amplifiers. But further comparisons based on noise performance and filter signal swings show potential advantage of the CA based complex filter. Comprehensive noise analysis and maximum possible signal swing calculations are provided. It demonstrates clearly that the CA based complex filter is expected to provide a better dynamic range. As an application example, a 4th-order complex filter based on the CA is designed for low-IF Bluetooth receiver. Simulation results obtained from a standard 0.18microm CMOS technology verify its proper operation. Simulation results also show that the attainment of the selectivity requirements of the Bluetooth specifications. The filter is designed with 3MHz center frequency and 1MHz bandwidth. The filter shows 43 dB and 56 dB attenuations of blockers at 5MHz and 6MHz, respectively. It is found that the filter exhibits total input referred noise of 180 nA and maximum signal swing of 850 uA. The filter operates from +/-1.5V supply and consumes total power of 1.3 mW. |
