Electronics & Communication Engineering

CMOS (Complementary Metal-Oxide-Semiconductor) uses both NMOS and PMOS transistors, offering very low static power consumption, high noise immunity, and wide supply voltage range (3-15V). TTL (Transistor-Transistor Logic) uses bipolar junction transistors, providing faster switching speeds and better current driving capability but higher power consumption. CMOS dominates modern ICs due to its scalability and power efficiency, while TTL is used in legacy systems and high-speed applications.

Setup time is the minimum time the data input must be stable before the clock edge for reliable sampling. Hold time is the minimum time the data must remain stable after the clock edge. Violating setup time causes metastability where the output may settle to an unpredictable state. Violating hold time can cause the flip-flop to capture incorrect data. In VLSI design, timing analysis ensures setup and hold constraints are met across all process, voltage, and temperature (PVT) corners.

The Nyquist theorem states that to accurately reconstruct a signal from its samples, the sampling frequency must be at least twice the highest frequency component in the signal (Fs >= 2*Fmax). If this criterion is not met, aliasing occurs where high-frequency components appear as low-frequency artifacts in the sampled signal. This is fundamental in ADC design, digital audio, telecommunications, and any system converting analog to digital signals.

In Amplitude Modulation (AM), the message signal varies the carrier amplitude while frequency remains constant. In Frequency Modulation (FM), the message varies the carrier frequency while amplitude stays constant. FM offers better noise immunity since noise primarily affects amplitude, but requires more bandwidth. AM is simpler and used in AM radio broadcasting, while FM is used in FM radio, TV audio, and two-way radio where quality matters. FM is more power-efficient as the transmitter can operate at constant amplitude.

An interrupt is a signal that temporarily halts normal program execution to handle a high-priority event. When triggered, the microcontroller saves the current state (PC, registers) on the stack, jumps to the Interrupt Service Routine (ISR) to handle the event, then restores the state and resumes normal execution. Interrupts can be edge-triggered or level-triggered, and have priorities. They enable responsive real-time systems without polling overhead. Common sources include timers, external pins, serial communication, and ADC completion.