Audio Applications for Op Amps, Part III
by Bruce Carter
Advanced Analog Products, Op amp Applications
Texas Instruments, Incorporated
Introduction
This is the third in a series of articles on single-supply audio circuits. The reader is encouraged to review the introductory material in the first article which concentrated on low-pass and high-pass filters. The second article concentrated on audio notch filter applications and curve-fitting filters. This last article focuses on the use of a simulated inductor as an audio-circuit element.
The Simulated Inductor
Fig. 1: A Simulated Inductor Circuit
A simulated inductor circuit (see Fig. 1) reverses the operation of a capacitor -- an inductor resists any change in its current, so when a dc voltage is applied to an inductance, the current rises slowly, and the voltage falls as the external resistance becomes more significant.
In practice it is a little different: The fact that one side of the inductor
is grounded precludes its use in low-pass and notch filters, leaving only
high-pass and bandpass filters as possible applications.
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