Question 1

Average power in a digital gate (50% duty) A gate draws 1.8 µA when the output is HIGH and 3.3 µA when the output is LOW. With VCC = 5 V and a 50% duty cycle, what is the average power dissipation (PD)?

Accepted Answer

Introduction / Context: Digital CMOS and TTL families specify supply current in different logic states. Average power dissipation over time depends on the time spent in each state. Here, we compute average current over a 50% duty cycle and multiply by supply voltage. Given Data / Assumptions: I_H (HIGH-state current) = 1.8 µA. I_L (LOW-state current) = 3.3 µA. Duty cycle = 50% HIGH, 50% LOW. VCC = 5 V. Ignore dynamic switching losses for this simple estimate. Concept / Approach: Average current is the time-weighted mean of state currents. With equal time in both states, I_avg = (I_H + I_L) / 2. Average power PD_avg = VCC * I_avg. Step-by-Step Solution: I_avg = (1.8 µA + 3.3 µA) / 2 = 2.55 µA.PD = VCC * I_avg = 5 V * 2.55 µA.PD = 12.75 µW. Verification / Alternative check: Because the duty cycle is symmetric, arithmetic mean is valid. If the duty cycle were not 50%, a weighted average would be used. Why Other Options Are Wrong: 2.55 µW: mistakenly multiplies current average by 1 V or omits VCC.1.27 µW and 5 µW: arithmetic/units errors.5 µW is a round number guess with no basis here. Common Pitfalls: Forgetting to multiply by VCC, mixing µA with mA, or ignoring dynamic (capacitive) power when edge rates are high (not required in this static-state problem). Final Answer: 12.75 µW

Question 2

TTL output stages Which TTL output structure is commonly referred to as a “totem-pole” arrangement?

Accepted Answer

Introduction / Context: TTL logic families use specific output stage topologies to achieve low output impedance and fast transitions. One of the most recognized forms is the totem-pole output. Given Data / Assumptions: Standard TTL outputs often use a push-pull (active pull-up and active pull-down) stack of transistors. This stack is colloquially named “totem-pole.” Concept / Approach: A totem-pole stage places two active devices in series between VCC and ground, one sourcing during HIGH, the other sinking during LOW. This yields low Rout and fast edges, unlike open-collector which requires an external pull-up. Step-by-Step Solution: Identify options: only one is an established TTL output term—“totem-pole.”Select it as the correct descriptor of the push-pull TTL output. Verification / Alternative check: TTL datasheets (e.g., 74LSxx) describe outputs as totem-pole (standard) or open-collector variants. Why Other Options Are Wrong: Diode arrangement: too vague; not the accepted output term.JBT arrangement: not a recognized TTL topology.Base, emitter, collector arrangement: generic transistor anatomy, not an output style. Common Pitfalls: Confusing totem-pole with open collector or tri-state; only totem-pole actively drives both directions (except in high-Z tri-state variants). Final Answer: totem-pole arrangement

Question 3

Nominal logic supply rails What is the nominal dc supply voltage used by classic TTL and many CMOS families in 5 V systems?

Accepted Answer

Introduction / Context: Digital logic families are associated with standard supply voltages. Classic 5 V logic remains common in legacy and mixed-signal designs even as lower-voltage CMOS (3.3 V, 1.8 V) has proliferated. Given Data / Assumptions: Question refers to “TTL and CMOS” without qualifiers, implying the ubiquitous 5 V era. Concept / Approach: Standard TTL (74xx, 74LSxx) is specified at 5 V ± tolerance. Early CMOS 4000B series operated over a wide range (3–15 V) but was frequently used at 5 V for compatibility. Many 74HC/HCT families also target 5 V systems. Step-by-Step Solution: Identify the conventional supply level shared across many TTL and CMOS parts: +5 V. Verification / Alternative check: Look at datasheets for 74LS00 or 74HC00: recommended VCC ≈ 5 V. Why Other Options Are Wrong: +3 V: common in modern low-voltage CMOS but not “nominal” for TTL.+9 V and +12 V: used in analog or power domains, not standard for TTL logic rails. Common Pitfalls: Assuming all CMOS is 3.3 V; many CMOS families are 5 V compatible or specified at 5 V. Final Answer: +5 V

Question 4

Static HIGH-state dissipation Given ICCH = 1.1 mA at VCC = 5 V and the gate is held in a static HIGH output state (no switching), what is the power dissipation PD?

Accepted Answer

Introduction / Context: Static power in logic is simply supply voltage times the specified static current in a particular state. Manufacturers often list ICCH (HIGH) and ICCL (LOW) currents separately. Given Data / Assumptions: ICCH = 1.1 mA. VCC = 5 V. No switching (ignore dynamic power). Concept / Approach: Use PD = VCC * ICC for the given static state. Step-by-Step Solution: PD = 5 V * 1.1 mA = 5.5 mW. Verification / Alternative check: Units: volts * amperes = watts. 5 * 0.0011 = 0.0055 W = 5.5 mW. Why Other Options Are Wrong: 5.5 W: off by a factor of 1000 (mA vs A).5 mW and 1.1 mW: arithmetic errors. Common Pitfalls: Dropping the milli prefix or mixing µA/mA leads to thousandfold mistakes. Final Answer: 5.5 mW

Question 5

ESD and CMOS handling practice Which of the following is NOT a recommended precaution when handling CMOS devices?

Accepted Answer

Introduction / Context: CMOS inputs are susceptible to electrostatic discharge. Proper ESD practice prevents latent or immediate device damage. Some habits reduce charge buildup; others make it worse. Given Data / Assumptions: ESD can destroy gate oxides via high voltage spikes. Grounding and power-off insertion are standard precautions. Certain materials (e.g., wool) promote charge generation. Concept / Approach: Best practice includes working on grounded surfaces, using wrist straps, keeping humidity reasonable, and never hot-plugging unprotected CMOS. Insulative clothing and carpets increase ESD risk and are discouraged. Step-by-Step Solution: Identify clearly bad advice: wearing wool promotes static.Other listed items match standard ESD guidelines (ground everything, power off before insertion). Verification / Alternative check: ESD control manuals recommend conductive mats, wrist straps, and avoiding static-generating materials like wool or some synthetics. Why Other Options Are Wrong: Grounding surfaces and tools reduces ESD risk.Pins-down on grounded surface equalizes potential.Inserting with power off avoids latch-up and transients. Common Pitfalls: Forgetting that humidity affects ESD, and neglecting personal grounding measures when moving around the lab. Final Answer: Wear wool clothing at all times.

Question 6

Unused TTL inputs should be tied LOW.

Accepted Answer

False

Question 7

There are four different logic level ranges for TTL and CMOS: VIL, VIH, VOL, and VOH.

Accepted Answer

True

Question 8

ECL IC technology is faster than TTL technology.

Accepted Answer

True

Question 9

The speed-power product provides a basis for the comparison of logic circuits when power dissipation and propagation delay are important considerations in the selection of the type of logic to be used.

Accepted Answer

True

Question 10

A pull-down resistor must be used with open-collector TTL circuits.

Accepted Answer

False

Question 11

Power dissipation is a measure of a circuit's noise immunity.

Accepted Answer

False

Question 12

CMOS is a more dominant IC technology than TTL.

Accepted Answer

True

Question 13

The total sink current decreases with an increase in each load gate input.

Accepted Answer

False

Question 14

The greater the propagation delay, the higher the maximum frequency.

Accepted Answer

False

Question 15

Metal-oxide semiconductor field-effect transistors (MOSFETs) are the active switching elements in CMOS circuits.

Accepted Answer

True

Integrated Circuit Technologies Questions