Noise performance of low-sensitivity active filters

The noise limitations of some important low-sensitivity RC-active filter realizations are derived; the inherent rms noise (noise from essential network resistors) that exists at the output terminals of a bandpass active filter is determined for two-integrator loop and positive impedance converter filter realizations. Output noise spectral density and total rms output noise are determined for the two-integrator loop section. The noise contributed by the essential circuit resistors and the operational amplifiers is taken into account and it is shown that exact calculation of output noise may be obtained in terms of Q factor and impedance level. The results are used to obtain the theoretical noise limitations of these low-sensitivity active filters. It is found that the deterioration in signal-to-noise ratio (SNR), due to the internal filter noise, is independent of Q factor for high Q realizations.