CMOS Logic Design Basics: Inverter, NAND, and NOR Quiz Quiz

Explore fundamental concepts in CMOS logic design with this quiz on inverters, NAND gates, and NOR gates. Assess your understanding of circuit operation, transistor arrangements, voltage behavior, and logic functionality within CMOS digital circuits.

1. CMOS Inverter Output Behavior

   In a standard CMOS inverter, what will be the output voltage if the input is connected to a high logic level (VDD)?

   1. C. Midway between VDD and 0 V
   2. D. Floating voltage level
   3. B. High logic level (VDD)
   4. A. Low logic level (0 V)

   Explanation: When the input of a CMOS inverter is high, the NMOS transistor turns on, and the PMOS turns off, pulling the output to a low logic level (0 V). The correct behavior is an inverted signal at the output. Option B is incorrect because a high input does not yield a high output in an inverter. Option C, a midway voltage, could only occur during switching transients but not in steady state. Option D, a floating voltage, suggests improper design or connection, which is not the expected operation.

2. Transistor Arrangement in CMOS NAND

   Which configuration accurately represents the placement of NMOS transistors in a typical two-input CMOS NAND gate?

   1. A. Two PMOS transistors in series
   2. C. Two NMOS transistors in parallel
   3. D. One NMOS and one PMOS in series
   4. B. Two NMOS transistors in series

   Explanation: In a CMOS NAND gate, the two NMOS transistors are connected in series to pull the output low only when both inputs are high. Option A describes the configuration of PMOS transistors, which are arranged in parallel in NAND. Option C describes the NOR gate's NMOS arrangement. Option D mixes transistor types, which doesn't reflect standard CMOS logic gate configurations.

3. Logical Function of a CMOS NOR Gate

   Given two inputs, A and B, which output condition is produced by a CMOS NOR gate when both A and B are at low logic levels?

   1. A. The output remains low
   2. B. The output is undefined
   3. C. The output is high
   4. D. The output toggles rapidly

   Explanation: A CMOS NOR gate outputs high only when all its inputs are low, due to the parallel PMOS path pulling the output up. Option A is incorrect, because a low input at both A and B does not yield a low output for NOR. Option B, an undefined output, would suggest an error or floating node. Option D, rapid toggling, is not characteristic of proper NOR gate operation.

4. CMOS Gate Power Consumption

   Why is the static power consumption in a CMOS inverter ideally very low when holding a steady input level?

   1. B. Only leakage currents flow except during switching
   2. A. Both NMOS and PMOS are fully conducting at the same time
   3. D. The input voltage is always at an intermediate value
   4. C. The output oscillates even with a stable input

   Explanation: During steady-state operation, either the NMOS or PMOS is off, resulting in minimal static power dissipation—mainly from leakage currents. Option A is incorrect because both transistors conducting without switching would increase power usage, which is not typical. Option C is inaccurate, as the output remains stable when the input is steady. Option D suggests the input is never at a valid logic level, which is not the case in normal operation.

5. Input Influence in CMOS NAND Gates

   In a three-input CMOS NAND gate with inputs A, B, and C, what is the logic output when all three inputs are at logic high?

   1. C. Output is alternating high and low
   2. D. Output is disconnected
   3. A. Output is logic high
   4. B. Output is logic low

   Explanation: A NAND gate only produces a low output when all its inputs are high, which causes the series-connected NMOS transistors to conduct and the output to drop low. Option A is incorrect, as it describes an OR or NOR function. Option C, alternating outputs, could indicate instability, but is not normal NAND behavior. Option D, a disconnected output, suggests a fault, not standard operation.