Bandpass Transfer Functions Research Articles

Bandpass filters using Wien's bridge

Bandpass transfer functions are obtained from an active circuit using Wien's bridge and a single operational amplifier. The Q factor is controllable by a single resistance independently of the resonant frequency, and one version of the circuit has a low output impedance.

Synthesis of Rational Transfer Function Approximations Using a Tapped Distributed RC Line With Feedback

This paper describes a simple procedure for synthesizing an active distributed RC network which, by using dominant poles and zeros, realizes a very accurate approximation of an arbitrary stable rational transfer function. The network uses a single uniformly distributed RC line with taps spaced along its length. A linear combination of tap voltages is added to the input signal to form the driving voltage for the RC line; the output signal is also a linear combination of the tap voltages. The network offers a number of significant advantages. Since it realizes a nearly rational transfer function, the approximation problem can be conveniently solved using readily available results on rational function approximation. Also, the network uses only one uniform RC line, the transfer function can be changed simply by changing resistor values, and the frequency can be scaled by minor connection changes. Thus one standard network with minor modification is useful for a wide variety of applications. This paper develops the design procedure and derives the various sensitivity functions of importance. Two example designs are carried out: an approximation to a second-order low-pass transfer function and an approximation to a second-order band-pass transfer function with a Q of 100. The sensitivities for the examples are very reasonable and the measurements made on laboratory models indicate excellent agreement with theoretical predictions.

Correction of seismograms for the transfer function of the seismometer

abstract If digitized seismic data is collected through a seismometer whose transfer function is known, it is not difficult to design a digital filter which will substitute a given band-pass transfer function for that of the seismometer. Various filters of this kind have been applied to digitized records of teleseisms registered on a Benioff short-period vertical seismometer at Chester, New Jersey. After digital filtering on a computer, the resulting data is converted to analog form and recorded on a seismograph drum for visual examination. These records indicate, (1) over the frequency range of interest for teleseismic registration, the seismograph may be regarded as a constant leading phase shift of 270 degrees, a 0.35 second time delay, and a phaseless amplitude function, (2) that it may not be easy to improve on the transfer function of the Benioff instrument for the detection of first motion, and (3) that some additional high-pass filtering might improve the signal-to-microseism ratio at times when the 2-4 second microseism level is high.