Exercises S2

1. A clean signal leaves a low impedance output and travels 1 meter on a wire to a gate with an input modeled by an RC circuit. See figure below. What is the propagation delay from the output of chip A until the input of chip B rises above 4 volts?


Assume the output impedance of the chip on the left is so small that we don't need to take account of impedance matching, and that the capacitance & resistance of the 1-meter wire is negligible. [Hint: the circuit on the right is a "leaky integrator" which can be dealt with by the expression (1 - et/t) where t is the product RC]

2. In a TTL NAND gate a signal must pass through 3 transistors before reaching output. Assume the turn-on time for an individual transistor is 5 nsec, and the turn-off time is 12 nsec. (a) If all NAND inputs are connected together and sent from LO to HI, what will be the propagation delay tPHL? Assume that each transistor acts as an inverter and that a transistor is "turned on" with a HI input.
What will be tPLH?

3. List how many different propagation delays it would be required to specify the "AC" performance of a 3-state inverter chip.

4. Draw a test circuit for measuring "maximum clock frequency" in a JK flip flop.

5. A Texas Instruments data book for CMOS chips lists supply current ICC for part 74HCT00 at 2mA, at test conditions VI = VCC or 0 volts. If VI = 2.4 volts, then the data book says
ICC = 2mA, 3 orders of magnitude greater supply current. Why do you think the supply current is so much greater in the second case vs the first?

6. What do you expect Q to be for the following SET, CLOCK and DATA inputs to a D-flip flop?


7. Power delivered to an IC must be dissipated as heat.
By what mechanism(s) does too much heat adversely affect an integrated circuit chip?
How can heat be directed away from a chip?

8. What is the motivation for using BiCMOS logic?

9. The product of delay and power is best in which chip--TTL-AS, CMOS-AC, or BiCMOS?

*10. A space craft heading toward Mars needs digital electronics. Considering that the craft must be away from power supplies on earth, and is exposed to radiation, including ionizing radiation from the sun, which logic family do you think would be best for the Mars mission?

11. A lava lamp is a soothing application of a light bulb's heat to the generation of chaotic oscillations. The up-down oscillations of the oil blobs in a lava lamp are chaotic because they have no single period of oscillation. Find and observe a lava lamp. Where does the energy come from which drives the oscillations?