ABSTRACT
This chapter provides a development of lowpass and bandpass filter characterizations appropriate for measurement signals and develops filter error analyses for the more frequently required lowpass realizations. Lowpass filters are frequently required to bandlimit measurement signals in instrumentation applications to achieve a frequency-selective function of interest. In 1955 R. P. Sallen and E. L Key of MIT published a description of 18 active filter networks for the realization of various filter approximations. The most important parameter in the selection of operational amplifiers for active filter service is open-loop gain. The choice of resistor and capacitor tolerance determines the accuracy of the filter implementation such as its cutoff frequency and passband flatness. Computer simulation of first- through eighth-order Butterworth and Bessel lowpass filters were obtained with the structure displayed. When signal phase accuracy is essential for phase-coherent applications, ranging from communications to audio systems including matrixed home theater signals, then Bessel lowpass filters are advantageous.
