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

The authors show how continuous-time active-RC filters can be implemented in CMOS by replacing all resistors by MOSFETs operating in the linear region. As an example, a 24MHz activeMOSFET-C single-amplifier biquadratic lowpass filter with a pole-Q of 3 implemented in a 0.6μm CMOS process is discussed. By comparing measurements of a test chip, simulations and calculations, the following conclusion is reached: as long as the specifications for frequency, pole-Q, spurious-free dynamic range and supply voltage lie within certain limits, then active-MOSFET-C single-amplifier biquads (MOSFET-C SABs) are preferable, with respect to chip size and power consumption, compared to multi-amplifier biquads, e.g. integrator-connected biquads. Above these limits, the latter must be used.