Active-MOSFET-C single-amplifier biquadratic filters for video frequencies

The authors show how continuous-time active-RC filters can be implemented i n CMOS by replacing all resistors by MOSFETs operating in the linear region . As an example, a 24MHz active-MOSFET-C single-amplifier biquadratic lowpa ss filter with a pole-Q of 3 implemented in a 0.6 mu m CMOS process is disc ussed. By comparing measurements of a test chip, simulations and calculatio ns, the following conclusion is reached: as long as the specifications for frequency, pole-Q, spurious-free dynamic range and supply voltage lie withi n certain limits, then active-MOSFET-C single-amplifier biquads (MOSFET-C S ABs) are preferable, with respect to chip size and power consumption, compa red to multi-amplifier biquads, e.g. integrator-connected biquads. Above th ese limits, the latter must be used.