A 1-V 1.8-MHz CMOS switched-opamp SC filter with rail-to-rail output swing

A low-voltage switched capacitor (SC) filter operated from a single 1 V supply and realized in a standard 0.5-mu m CMOS technology is presented. Proper operation is obtained using the switched-opamp technique without any clock voltage multiplier or low-threshold devices. This makes the circuit compatible with future deep submicrometer technology. As opposed to previous switched-opamp implementations, the filter uses a fully differential topology. This allows operation with a rail-rail output swing and reduction of the number of opamps required to build high-order infinite impulse response (IIR) filters. On the other hand, a law-voltage common-mode feedback (CMFB) circuit is required. In addition, the circuit uses an opamp which is only partially turned off during the off phase. This enables an increase in the maximum sampling frequency. The filter implements a bandpass response (f(s)/f(o) = 4, Q = 7) and it has been characterized with a 1.8 MHz sampling frequency. Its power consumption is about 160 mu W. The filter is still fully functional down to 0.9 V supply voltage.