Question 1

Troubleshooting digital circuits Which instrument is commonly used when diagnosing digital circuits in the lab or field?

Accepted Answer

Introduction / Context: Practical troubleshooting of digital systems requires tools tailored to observe logic levels, timing, and stimulus/response behavior. Different instruments complement each other to provide a full picture. Given Data / Assumptions: Logic probe: indicates LOW/HIGH/pulse presence on a node. Oscilloscope: shows voltage versus time, timing, rise/fall, and noise. Pulser (signal injector): provides controlled stimuli to verify logic paths. Concept / Approach: No single tool solves every problem. A logic probe quickly checks states, an oscilloscope validates timing and integrity, and a pulser helps isolate faulty stages by injecting known signals. Step-by-Step Solution: List available instruments and their roles.Determine relevance: all are used routinely in digital fault-finding.Therefore, the inclusive choice is correct. Verification / Alternative check: Service manuals and standard lab practices prescribe these tools for board bring-up and repair. Why Other Options Are Wrong: Each single device alone misses some diagnostic dimensions; the combined option is more accurate. Common Pitfalls: Relying solely on a multimeter in digital work; it lacks timing visibility crucial for clocked logic. Final Answer: all of the above

Question 2

IC integration levels An integrated circuit that contains approximately 12 to 100 equivalent logic gates on one chip is classified as which level of integration?

Accepted Answer

Introduction / Context: IC classification by integration level is a historical but still useful way to compare circuit complexity and packaging constraints. These categories appear in datasheets and textbooks. Given Data / Assumptions: Target complexity: roughly 12–100 equivalent gates. Standard categories: SSI, MSI, LSI, VLSI. Concept / Approach: Small-Scale Integration (SSI) typically includes a handful of gates. Medium-Scale Integration (MSI) aggregates tens of gates (dozens). Large-Scale Integration (LSI) spans hundreds to thousands, and Very-Large-Scale Integration (VLSI) covers tens of thousands to billions in modern contexts. Step-by-Step Solution: Match range 12–100 gates → squarely within MSI.SSI is too small; LSI/VLSI are much larger.Therefore, classification is MSI. Verification / Alternative check: Classic TTL MSI families include counters, multiplexers, and adders—typically in the tens of gates range. Why Other Options Are Wrong: SSI: generally 1–10 gates only.LSI and VLSI: exceed 100 gates by large margins. Common Pitfalls: Assuming strict numeric boundaries; while approximate, 12–100 gates is conventionally MSI. Final Answer: MSI

Question 3

PCB assembly methods Compared to through-hole mounting, what is typically true about the need for drilled holes when using surface-mount technology (SMT) on printed circuit boards?

Accepted Answer

Introduction / Context: PCB manufacturing differs for through-hole and surface-mount assembly. Understanding hole requirements helps reduce cost, improve density, and select appropriate components and processes. Given Data / Assumptions: SMT components are soldered to pads on the PCB surface. Through-hole parts require plated through-holes for leads. Mechanical mounting or connectors may still require some holes. Concept / Approach: Because SMT parts do not pass leads through the board, most signal pads do not require drilling. Vias may still exist for inter-layer connectivity, but component-lead holes become largely unnecessary, enabling denser layouts and smaller boards. Step-by-Step Solution: Identify assembly type: SMT.Assess need for drilling: no lead-through holes for most components.Conclusion: component holes are usually unnecessary, though mounting and connectors may still use some. Verification / Alternative check: Modern high-density designs use almost exclusively SMT, reserving through-hole for connectors or high-stress parts. Why Other Options Are Wrong: “Smaller”/“larger”/“same size”: misunderstand the main point; SMT largely eliminates component holes. Common Pitfalls: Confusing component holes with vias; vias are still used extensively even in SMT boards. Final Answer: usually unnecessary

Question 4

In basic electronics and instrumentation, which of the following is NOT an analog device or quantity (i.e., not naturally varying continuously with amplitude over time)?

Accepted Answer

Introduction / Context: Electronics deals with both analog and digital signals. Analog quantities vary continuously, whereas digital quantities assume discrete states. Identifying whether a device is analog or digital helps determine measurement techniques, noise considerations, and interface circuitry. Given Data / Assumptions: Thermocouple generates a voltage proportional to temperature. Current in a circuit is a continuous physical quantity (amperes). A light switch is considered an on/off selector. A microphone converts sound pressure to a voltage that varies smoothly. Concept / Approach: An analog device produces or responds to signals that change smoothly over time. A digital device primarily has discrete states such as HIGH/LOW or ON/OFF. Decide for each option whether its primary behavior is continuous or discrete. Step-by-Step Solution: Thermocouple: output voltage varies continuously with temperature → analog.Circuit current: a continuous variable measured in amperes → analog.Audio microphone: outputs a voltage that follows air pressure over time → analog.Light switch: intended to be either closed or open (two discrete states) → digital behavior. Verification / Alternative check: Consider how you would measure each signal on an oscilloscope: the thermocouple, current (via shunt), and microphone all show smooth waveforms. The light switch shows two levels with transitions. Why Other Options Are Wrong: Thermocouple: analog voltage proportional to temperature.Current flow: continuous physical quantity.Audio microphone: analog transducer.Mercury thermometer: analog scale reading. Common Pitfalls: Confusing the installation of a switch in an analog circuit with the switch itself being analog. The device's primary operation is binary even if used within analog systems. Final Answer: Light switch

Question 5

Digital fundamentals: What are the only two symbols (digits) used to represent numbers in the binary number system commonly used in computer logic?

Accepted Answer

Introduction / Context: The binary number system underpins all digital electronics and computing. Understanding its digits and place-value representation is foundational for logic design, microprocessors, and data encoding. Given Data / Assumptions: Binary is base-2. Digits available in a base-b system are 0 through b − 1. We are asked specifically for the symbols used as digits. Concept / Approach: In any positional system with base b, exactly b distinct digits exist. For binary (b = 2), the allowed digits are 0 and 1. Numbers are formed by weighting each position by powers of 2 (1, 2, 4, 8, ...). Step-by-Step Solution: Identify base → 2.Enumerate digits → 0 to b − 1 → 0 and 1.Confirm with examples: binary 1011 = 18 + 04 + 12 + 11 = 11. Verification / Alternative check: Think in terms of logic levels: digital circuits represent LOW and HIGH, which correspond naturally to 0 and 1. Why Other Options Are Wrong: 0,1,2: includes a third digit not allowed in base-2.0 through 8: describes base-9.1,2: excludes 0 and includes an illegal digit for binary.0 and 9: mismatched base-10 digits only. Common Pitfalls: Confusing the count of bits with allowed digits, or assuming binary must exclude zero. Zero is a valid binary digit. Final Answer: 0,1

Question 6

In data conversion terminology, a DAC (digital-to-analog converter) performs which function?

Accepted Answer

Introduction / Context: Mixed-signal systems require converting between digital codes and real-world analog signals. A digital-to-analog converter (DAC) is essential in audio playback, instrumentation, motor control, and waveform generation. Given Data / Assumptions: DAC receives binary (or coded) digital words. Output should be a corresponding analog level (voltage or current). No amplification is implied unless specified; conversion is the core function. Concept / Approach: A DAC maps a digital code to a proportional analog quantity. For an n-bit DAC with reference Vref, the smallest analog step is typically Vref / (2^n). The output may be a staircase that can be smoothed by a reconstruction filter. Step-by-Step Solution: Identify device → DAC.Define action → digital code → analog magnitude (voltage or current).Exclude unrelated actions such as A/D or amplification. Verification / Alternative check: Audio DACs convert 16-bit or 24-bit PCM data into line-level analog voltages for speakers after buffering and filtering, confirming the role. Why Other Options Are Wrong: Analog-to-digital is ADC, not DAC.Amplification may follow a DAC but is not inherent to conversion.Frequency spectrum conversion is unrelated. Common Pitfalls: Assuming a DAC inherently amplifies or filters. Those are separate stages (op-amp buffer, active filter). Final Answer: digital data into an analog signal

Question 7

Digital logic levels (generic TTL-like): Which range is typically considered an INVALID region for a binary signal, i.e., neither a guaranteed LOW nor a guaranteed HIGH?

Accepted Answer

Introduction / Context: Digital logic families specify valid input voltage thresholds to ensure robust interpretation of LOW and HIGH. The zone between these thresholds is the undefined or invalid region where reliable operation is not guaranteed. Given Data / Assumptions: Assume TTL-like thresholds: VIL(max) ≈ 0.8 V and VIH(min) ≈ 2.0 V at a 5 V supply. Any voltage below VIL(max) is a valid LOW; any above VIH(min) is a valid HIGH. Between those limits is not guaranteed. Concept / Approach: Define valid regions and identify the gap. The invalid region is the interval between the maximum recognized LOW and the minimum recognized HIGH. Step-by-Step Solution: VIL(max) = 0.8 V.VIH(min) = 2.0 V.Invalid region = 0.8–2.0 V. Verification / Alternative check: Compare with CMOS at 5 V (typical higher margins), but the most commonly taught TTL thresholds set the classic undefined zone at about 0.8–2.0 V. Why Other Options Are Wrong: 0.7–2.8 V: overbroad and does not match standard TTL specs.0.8–3 V or 0.7–2.5 V: do not reflect standard guaranteed thresholds.0–5 V: entire supply span, not an invalid region. Common Pitfalls: Assuming the midpoint (around 2.5 V) is valid. Unless specified by a particular logic family, it is in the no-man's-land for TTL. Final Answer: 0.8–2 volts

Question 8

Number systems conversion (binary fraction to decimal): Convert the fractional binary number 0000.1010 to its decimal (base-10) value.

Accepted Answer

Introduction / Context: Binary fractions use negative powers of 2 to represent values to the right of the binary point. Proficiency with these conversions is essential for fixed-point arithmetic, digital signal processing, and interpreting DAC/ADC resolutions. Given Data / Assumptions: Binary value: 0000.1010 (leading zeros do not affect magnitude). We use positional weights 2^−1, 2^−2, 2^−3, 2^−4 ... for fractional bits. Concept / Approach: Sum contributions of each bit multiplied by its positional weight. For a binary fraction b1 b2 b3 b4 after the point: value = b12^−1 + b22^−2 + b32^−3 + b42^−4. Step-by-Step Solution: Bits after point: 1 0 1 0.Compute contributions: 12^−1 = 0.5, 02^−2 = 0, 12^−3 = 0.125, 02^−4 = 0.Sum = 0.5 + 0.125 = 0.625. Verification / Alternative check: Convert 0.625 to binary by repeated multiplication by 2: 0.6252=1.25 → 1; .252=0.5 → 0; .52=1.0 → 1; .02=0 → 0. Thus .1010, confirming the result. Why Other Options Are Wrong: 0.50: corresponds to .1000.0.55: not a power-of-two fractional combination.0.10: decimal 0.10 is not equal to binary .1010.0.375: corresponds to .0110. Common Pitfalls: Interpreting 0.1010 as a decimal fraction with place values 10^−1, 10^−2, etc., instead of powers of 2. Final Answer: 0.625

Question 9

Number systems conversion (decimal to binary with fractional part): Convert the decimal number 6.75 to binary, using a fixed-point representation with four fractional bits.

Accepted Answer

Introduction / Context: Converting decimal numbers with fractional parts to binary is fundamental in digital systems, especially for fixed-point representation and understanding DAC/ADC step sizes and quantization. Given Data / Assumptions: Decimal value: 6.75. Binary output should show an integer part and four fractional bits. Unsigned positive representation is assumed. Concept / Approach: Split into integer and fractional parts. Convert the integer by successive division by 2. Convert the fraction by successive multiplication by 2, recording carries. Step-by-Step Solution: Integer 6 → binary: 6 / 2 = 3 r0; 3 / 2 = 1 r1; 1 / 2 = 0 r1 → read MSB to LSB: 110.Fraction .75 → multiply by 2: 0.752 = 1.5 → bit 1, remainder .5..52 = 1.0 → bit 1, remainder .0.With four fractional bits, pad trailing zeros → .1100.Combine: 110.1100. With leading zero formatting to 4 bits integer: 0110.1100. Verification / Alternative check: Back to decimal: 0110.1100 = 6 + 0.5 + 0.25 = 6.75. Correct. Why Other Options Are Wrong: 0111.1100 = 7.75.0110.1010 = 6.625.0110.0110 = 6.375.110.11 is numerically correct (6.75) but does not match the requested four fractional-bit fixed-point formatting used in the options. Common Pitfalls: Stopping fractional conversion too soon or forgetting to pad to a defined number of fractional bits can cause mismatch with fixed-point option formats. Final Answer: 0110.1100

Question 10

Digital logic families: A type of integrated-circuit digital logic technology that uses bipolar junction transistors (BJTs) is known as ________.

Accepted Answer

Introduction / Context: Logic families are categorized by the underlying transistor technology, which affects speed, power consumption, noise margins, and interfacing. Recognizing which families use BJTs versus MOSFETs is fundamental. Given Data / Assumptions: TTL stands for transistor-transistor logic. CMOS uses complementary MOSFETs. NMOS refers to n-channel MOS technology. LSI describes integration scale, not a logic family per se. ECL (emitter-coupled logic) also uses BJTs but is a distinct high-speed family; the common textbook answer contrasting MOS is TTL. Concept / Approach: Identify which option explicitly names a BJT-based family in contrast to MOS-based families. TTL is the canonical BJT logic family in general-purpose digital design. Step-by-Step Solution: List families: TTL (BJT), CMOS (MOSFET), NMOS (MOSFET), LSI (integration level), ECL (BJT but niche).Select most representative BJT-based general family → TTL. Verification / Alternative check: Datasheets for 74xx series identify TTL as BJT based, whereas 74HC/74HCT are CMOS based. Why Other Options Are Wrong: CMOS/NMOS: MOSFET technologies, not BJT.LSI: describes density, not device type.ECL: also BJT but specialized; the course-level contrast usually expects TTL as the standard BJT logic family. Common Pitfalls: Confusing integration scale (SSI/MSI/LSI) with technology, or assuming all modern logic is MOS-only. Final Answer: TTL

Question 11

Digital design fundamentals: A full subtractor circuit requires how many inputs and how many outputs?

Accepted Answer

Introduction / Context: Binary subtractors compute difference bits and borrow bits. A full subtractor, like a full adder, accounts for a borrow from the previous less significant stage, making it useful in multi-bit subtraction. Given Data / Assumptions: Inputs typically: A (minuend bit), B (subtrahend bit), and Bin (borrow-in). Outputs typically: D (difference) and Bout (borrow-out). We assume active-high logic. Concept / Approach: Define the function: D = A ⊕ B ⊕ Bin and Bout = (¬A & B) + (Bin & ¬(A ⊕ B)). This formulation shows the need for three inputs and two outputs. Step-by-Step Solution: Identify required bits: A, B, and Bin → 3 inputs.Compute outputs: D (difference), Bout (borrow-out) → 2 outputs.Therefore: three inputs and two outputs. Verification / Alternative check: Compare to a half subtractor (only A and B, producing D and Bout with no borrow-in) → 2 inputs, 2 outputs. The presence of Bin distinguishes the full subtractor. Why Other Options Are Wrong: Two-input answers describe a half subtractor, not full.Three inputs and one output omit either D or Bout, which is incomplete.Four-input option does not match minimal standard full subtractor design. Common Pitfalls: Confusing full subtractor with full adder or forgetting the borrow-in, leading to an incorrect input count. Final Answer: three inputs and two outputs

Question 12

Demultiplexing concept: A demultiplexer (DeMUX) has which general input/output structure?

Accepted Answer

Introduction / Context: A demultiplexer routes a single data stream to one of many outputs based on select lines. It is the inverse of a multiplexer and is key to signal routing, memory addressing, and time-division systems. Given Data / Assumptions: DeMUX topology: 1 → N routing. Select inputs determine which output is active. Outputs may be active-high or active-low depending on device family. Concept / Approach: Recognize the structural definition: a single data input D, k select lines S(k−1:0), and 2^k outputs Y(2^k−1:0) where only one output conveys D at a time. Step-by-Step Solution: Identify the number of data inputs → one.Account for selection → several select inputs.Outputs → multiple lines (typically 2^k). Verification / Alternative check: Compare to the multiplexer (MUX) structure which has several data inputs, select lines, and a single output; a DeMUX is the mirror image. Why Other Options Are Wrong: One input/one output: that is a buffer, not a DeMUX.Several inputs/one output: describes a MUX.Several inputs/several outputs: too vague; not the canonical DeMUX structure. Common Pitfalls: Confusing select lines with data inputs; select lines choose the destination but are not data channels. Final Answer: one data input and a number of selection inputs, and they have several outputs

Question 13

Technology trend awareness: Over roughly the past three decades, how would you best characterize the advances in digital technologies (integration density, speed, power efficiency, and functionality)?

Accepted Answer

Introduction / Context: Digital technology has experienced rapid evolution driven by semiconductor scaling, architectural innovation, and new materials. This question gauges qualitative awareness of that trend. Given Data / Assumptions: Timeframe: approximately three decades. Metrics: integration density, performance, power efficiency, functionality. General industry perspective rather than a specific numeric law. Concept / Approach: Semiconductor scaling (smaller transistors) and design advances (multi-core CPUs, GPUs, specialized accelerators, FPGAs) have enabled dramatic increases in capability, reducing cost per function and power per operation. Step-by-Step Solution: Consider integration density trends enabling SoCs with billions of transistors.Assess performance-per-watt improvements that made mobile computing ubiquitous.Factor in digital transformation across communications, storage, AI, and embedded control.Select the choice that captures the extraordinary breadth and pace of progress. Verification / Alternative check: Contrast devices from 30 years ago with today's smartphones and cloud data centers; the qualitative difference is massive across metrics. Why Other Options Are Wrong: Slowed considerably or stagnated: inconsistent with the ubiquity and capability of modern systems.Increasing at a decreasing rate: partial truth for some nodes, but overall advances remain extraordinary.Made excellent progress: accurate but understates the magnitude. Common Pitfalls: Over-focusing on a single metric (e.g., raw CPU frequency) rather than holistic advances in architecture and integration. Final Answer: Nothing short of phenomenal

Question 14

Fundamentals of number systems: In the base-10 (decimal) number system used in everyday arithmetic, how many unique digit symbols are available to represent any magnitude before a new place value is required?

Accepted Answer

Introduction / Context: The decimal number system is the default way humans record and compute quantities in daily life. Understanding how many unique digit symbols exist in a positional number system is foundational for conversions, digital design, and computer science concepts such as bases and encodings. Given Data / Assumptions: We are discussing the base-10 (decimal) system. We seek the count of unique digit symbols before place value carries to the next position. No special symbols (such as minus sign or decimal point) are counted as digits. Concept / Approach: In any base-b positional system, there are exactly b distinct digit symbols. Digits fill the ones place from 0 up to b−1; when the count exceeds b−1, the system increments the next higher place (tens, hundreds, and so on). For decimal, b = 10, so there must be 10 unique digit symbols. Step-by-Step Solution: Identify base: b = 10 for decimal.List digit symbols: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9.Count symbols: there are 10 symbols.Therefore, the number of unique digit symbols in decimal is Ten. Verification / Alternative check: Compare to other bases: binary (base 2) has 2 symbols {0,1}; octal (base 8) has 8 symbols {0-7}; hexadecimal (base 16) has 16 symbols {0-9, A-F}. This confirms the rule that the count equals the base value. Why Other Options Are Wrong: One: would describe unary, not decimal. Nine: would omit the digit 0, which is essential for positional notation and place holding. Unlimited: symbols are limited and fixed by the base; decimal has exactly 10. Common Pitfalls: Forgetting that 0 is a digit and must be counted. Confusing the number of digits with the number of values you can write—any value can be written, but using only 10 symbols per place. Final Answer: Ten

Question 15

The voltage levels used to represent binary values (0 and 1) in a digital system are nearly equal in value.

Accepted Answer

False

Question 16

Transistor-transistor logic (TTL) uses the bipolar transistor as its main circuit element.

Accepted Answer

True

Question 17

A graph of phase vs. time is a timing diagram.

Accepted Answer

False

Question 18

One advantage of analog circuits over digital circuits is that it's easier to store data.

Accepted Answer

False

Question 19

The two binary digits are 1 and 2.

Accepted Answer

False

Question 20

Memory devices store binary data.

Accepted Answer

True

Digital Concepts Questions