2019 Problem 01

Consider the following circuit topology where the input v(in) transitions Hi-Lo-Hi. Assume Rdrv = Rodt = R. 
We make the following two observations.
■ When the input transitions high  low the output net discharges through R; with a time constant τ_fall = RC.
■ When the input transitions low  high the output net charges through R/2; with a time constant τ_rise = (R/2)C.
Choose the correct answer.
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(a) The reasoning is not right. The correct answer should be τ_rise = τ_fall.
(b) The reasoning is not right. The correct answer should be τ_rise > τ_fall.
(c) The reasoning is right. The correct answer is τ_rise < τ_fall.
(d) The reasoning is right for small C. The correct answer is τ_rise < τ_fall.