A test-tone generator uses a Wien-bridge oscillator with and in its Wien network

PHYSICS · Multi-part · Fermi University Physics · Electronics, Instrumentation & Communication · Feedback, operational amplifiers and analogue signal processing · Feedback, operational amplifiers and analogue signal processing

Electronics for Measurement, Ch Active filters, oscillators and timers

Problem

A test-tone generator uses a Wien-bridge oscillator with

R = 12\,\mathrm{k}\Omega

and

C = 6.8\,\mathrm{nF}

in its Wien network, followed by a monostable timer built from a comparator with

R = 47\,\mathrm{k}\Omega

C = 220\,\mathrm{nF}

and a positive-feedback fraction

\beta = 0.5

, whose capacitor charges from

0\,\mathrm{V}

towards its rail and triggers when it crosses

\beta

of the rail voltage. ((a)) Before any bench measurement is taken, predict the oscillator's frequency and the gain the amplifier must supply. ((b)) Predict the monostable's output pulse width, using the charging solution

v(t) = V(1 - e^{-t/RC})

from the

RC

charging equation.

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