GATE 2014 EE (EE2) – Question 59
The oscillator shown uses ideal op-amp and diodes. Its positive and negative output durations are Δt₁,Δt₂. Find $e^{(\Delta t_1-\Delta t_2)/(RC)}$.
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Show answer and explanation
Correct answer: 1.2 to 1.3
Explanation
Ideal diodes select1kΩfeedback for positive output and3kΩfor negative output. With the grounded1kΩresistor,the thresholds are+2.5Vand−1.25Vfor±5Voutput. Charging toward+5from−1.25to+2.5takesΔt1=RC ln[(5+1.25)/(5−2.5)]=RC ln2.5. Discharging toward−5takesΔt2=RC ln[(5+2.5)/(5−1.25)]=RC ln2. Therefore exp[(Δt1−Δt2)/RC]=**1.25**.