A novel approach based on state space equation is developed that yields a step-gain log-domain CMOS current-mode filter design methodology and the basic circuit unit of the log-domain filter is proposed.According to the methodology

the responding filter has some advantages: low power

low voltage

step gain and adjustable bandwidth.Moreover

the design flow is simple and easy to be optimized.Based on the methodology

a second-order filter (15 μW@1.4V) is presented in the 0.35 μm technology and occupies the area of 150×160 μm.