Noise performance limitations of single amplifiers RC active filters

The noise performance characteristics of single amplifier RC active filters are presented for the cases where the circuits are constructed using the new single-ended Norton quad amplifiers. The power spectral densities and total rms values of the output noise are compared with the same quantities for filters constructed using conventional integrated operational voltage amplifiers. The conditions for minimum noise from the Norton amplifiers are derived, and these minimum levels are compared with those obtained using 741-type amplifiers. When the filters are constructed using infinite gain embedded amplifiers, for certain ranges of Q-factor and passband gain the Norton amplifiers can be biased to give comparable noise performance to the 741 amplifiers, and it is shown that the bias networks required differ significantly from those chosen in most specification sheets for these devices. For positive-gain structures, the 741 amplifiers are shown to be superior in most applications.