Question

In lab, we connect the power and ground through two approximately 24-inch 22-gauge copper wires. The total resistance of this 48 inches of wire is about 63mΩ. The total inductance is about 2:0 H. Perform the following two calculations and think about the implications of the result. Consider a circuit that is initially drawing 0mA and then linearly ramps up to a final current of 10mA in 2.5 nanoseconds. (This might be a typical value for a 40MHz clock signal with a 25ns period and 2.5ns rise and fall times.)

      (a) Calculate the voltage drop on the power supply due to the resistance of the wire and the 10mA current.

      (b) Calculate the voltage drop caused by the wire inductance during the rise-time of the current. Recall that v_L(t) = Ldi/dt. (This value is a little pessimistic since parasitic capacitance will tend to decrease the acutal voltage drop, but the answer is still very sobering.)

      (c) Which parasitic causes worse problems at these frequencies and rise times, resistance or inductance?

Answer 1