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GATE 2021 EE – Question 62

Analog and Digital Electronics · Schmitt triggers, Sample and hold circuits, A/D and D/A converters · 2 marks · Numerical answer

A CMOS Schmitt-trigger inverter has a low output level of 0 V and a high output level of 5 V. It has input thresholds of 1.6 V and 2.4 V. The input capacitance and output resistance of the Schmitt-trigger are negligible. The frequency of the oscillator shown is ________ Hz. (Round off to 2 decimal places.)

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Correct answer: 3150.00 to 3170.00

Explanation

The capacitor charges from 1.6 V to 2.4 V towards 5 V in $RC\ln\frac{5-1.6}{5-2.4}=0.2683RC$, and discharges from 2.4 V to 1.6 V towards 0 V in $RC\ln\frac{2.4}{1.6}=0.4055RC$. The period is $0.6738\times10\text{ k}\Omega\times47\text{ nF}=0.3167$ ms, so $f\approx3157$ Hz.