Question

(a) Design a inverting Schmitt trigger circuit to be used as a zero crossing detector with transition voltages about ±25 mV. Assume the saturation voltages for the op–amp are ±13 V. Draw the voltage transfer characteristic (VTC), i.e., vout vs. vin.

(b) Design an astable multivibrator to produce a square signal with a frequency of 1 kHz using C=0.01 µF, R1 = 30 kΩ, and R2 = 20 kΩ. Sketch the circuit waveforms (vo, v +, and v −) assuming a saturation voltage of ± 12 V.

(c) State the Barkhausen criterion (i.e., gain and phase-shift requirements for a closed–loop system to sustain steady-state oscillations). Draw a Wien-Bridge oscillator (no need to add gain stabilization). Indicate the nominal closed-loop gain for sustained oscillation, an write an expression for the frequency of oscillation as a function of component values.

+Vs R1 Vs reset discharge 8 4 7 output threshold|6 timer R2 trigger 2 0V control C1 0.01 μF (if required) 0V
The circuit below shows a 555 timer configured as an astable multivibrator. Using a capacitor C1 = 0.01 uF, select resistor values R1 and R2, and for the circuit to output a square signal of frequency f = 1 kHz and 75% duty cycle. Sketch the output waveform if Vs = 5V, indicating its amplitude, period, as well as TH, and TL (duration of the positive and negative parts of the cycle, respectively).

Answer 1

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