tailieunhanh - Multisensor thiết bị đo đạc thiết kế 6o (P3)

ACTIVE FILTER DESIGN WITH NOMINAL ERROR Although electric wave filters have been used for over a century since Marconi’s radio experiments, the identification of stable and ideally terminated filter networks has occurred only during the past 35 years. Filtering at the lower instrumentation frequencies has always been a problem with passive filters because the required L and C values are larger and inductor losses appreciable. The band-limiting of measurement signals in instrumentation applications imposes the additional concern of filter error additive to these measurement signals when accurate signal conditioning is required. . | Multisensor Instrumentation 6a Design. By Patrick H. Garrett Copyright 2002 by John Wiley Sons Inc. ISBNs 0-471-20506-0 Print 0-471-22155-4 Electronic 3 ACTIVE FILTER DESIGN WITH NOMINAL ERROR 3-0 INTRODUCTION Although electric wave filters have been used for over a century since Marconi s radio experiments the identification of stable and ideally terminated filter networks has occurred only during the past 35 years. Filtering at the lower instrumentation frequencies has always been a problem with passive filters because the required L and C values are larger and inductor losses appreciable. The band-limiting of measurement signals in instrumentation applications imposes the additional concern of filter error additive to these measurement signals when accurate signal conditioning is required. Consequently 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. The excellent stability of active filter networks in the dc to 100 kHz instrumentation frequency range makes these circuits especially useful. When combined with well-behaved Bessel or Butterworth filter approximations nominal error bandlimiting functions are realizable. Filter error analysis is accordingly developed to optimize the implementation of these filters for input signal conditioning aliasing prevention and output interpolation purposes associated with data conversion systems for dc sinusoidal and harmonic signal types. A final section develops maximally flat bandpass filters for application in instrumentation systems. 3-1 LOWPASS INSTRUMENTATION FILTERS Lowpass filters are frequently required to band-limit measurement signals in instrumentation applications to achieve a frequency-selective function of interest. The application of an arbitrary signal set to a lowpass filter can result in a significant atten- 47 48 ACTIVE FILTER DESIGN WITH NOMINAL