Question 1

GPIB bus width: Determine the number of dedicated data lines carried by the IEEE-488 (GPIB) bus for parallel data transfer.

Accepted Answer

Introduction / Context: The IEEE-488 General Purpose Interface Bus (GPIB) is a parallel instrument bus widely used in test and measurement. Understanding its signal lines is foundational for system integration. Given Data / Assumptions: GPIB provides distinct groups of lines: data lines, handshake lines, management/control lines, and ground/returns. Only the number of data lines is asked, not the total wire count. Data lines are used to carry a byte at a time in parallel. Concept / Approach: GPIB moves data in 8-bit bytes over dedicated parallel conductors. Separate handshake lines (DAV, NRFD, NDAC) coordinate transfer timing, allowing heterogeneous device speeds. Step-by-Step Solution: Identify the data group: DIO1 through DIO8.Recognize that handshake and management lines are separate and not counted as data lines.Conclude that there are 8 data lines. Verification / Alternative check: Pinout references label the parallel data lines as DIO1–DIO8, confirming an 8-bit data path. Why Other Options Are Wrong: 1 or 4 would indicate serial or nibble-width, which GPIB is not. 16 would imply a wider bus than the standard defines for data. 9 is incorrect; the ninth relevant signals are handshake/control, not data. Common Pitfalls: Confusing total conductor count (including control/handshake/grounds) with the data path width. Final Answer: 8

Question 2

Digital-to-Analog Converter (DAC) concept check: A “monotonicity error” in a DAC means the output fails to always move in the correct direction as the input code increases. Such an error will show up as an incorrect analog output for which set of in…

Accepted Answer

Introduction / Context: Monotonicity is a key performance attribute of a Digital-to-Analog Converter (DAC). A monotonic DAC guarantees that as the digital input code increases by one or more least significant bits (LSBs), the analog output never decreases. This question probes where a “monotonicity error” appears across input codes. Given Data / Assumptions: A DAC converts N-bit digital codes to corresponding analog levels. Monotonic means output never decreases for increasing input codes. Real DACs have component mismatches and nonidealities that can create local errors. We are not assuming catastrophic failure; rather, occasional code-to-code inversions. Concept / Approach: A monotonicity error is a localized violation of the required nondecreasing transfer characteristic. It typically occurs at specific code transitions where element mismatches (for example, in a binary-weighted or segmented architecture) cause the next code step to be smaller than expected or even negative. Therefore, such errors do not necessarily affect every code; they manifest at particular transitions. Step-by-Step Solution: Define monotonic behavior: for any code increment, output must not fall.Identify the failure mode: local negative step or insufficiently positive step at certain transitions.Conclude: the error appears only at those specific input codes where mismatch causes inversion.Hence, it shows up only for certain (scattered) inputs. Verification / Alternative check: Plot the DAC transfer curve. Nonmonotonicity is visible as local dips at certain code boundaries while adjacent regions may behave correctly. Why Other Options Are Wrong: only for higher value inputs: Nonmonotonicity is not confined to large codes.only for lower value inputs: Same reasoning; not restricted to small codes.for all inputs: That would imply a gross failure; monotonicity errors are typically localized. Common Pitfalls: Confusing monotonicity error with integral nonlinearity (INL) or gain error; those can be global without inverting direction.Assuming monotonicity implies perfect linearity; it only guarantees direction, not exact step size. Final Answer: only for certain (scattered) inputs

Question 3

DAC resolution clarification: The “resolution” of a Digital-to-Analog Converter is best expressed as which of the following definitions?

Accepted Answer

Introduction / Context: Resolution specifies the smallest change in output that can be resolved by a DAC. It is a fundamental specification distinct from linearity or accuracy. This item asks for the clearest definition among common, sometimes-confused terms. Given Data / Assumptions: A DAC maps N-bit codes to analog levels. LSB step size is related to full-scale range and the number of bits. Other parameters (DNL, INL, accuracy) are separate characteristics. Concept / Approach: Resolution can be expressed either as the number of bits (N) or as the size of one LSB step. Stating it as “number of bits that are converted to an analog output” is the common textbook definition. Minimum output voltage, deviation from a straight line (linearity), and error are different concepts. Step-by-Step Solution: Relate resolution to bits: higher N → more quantization levels → smaller LSB.Understand that “minimum output voltage” is not a standard metric for resolution.Recognize that “deviation from a straight line” is INL, not resolution.Recognize that “difference between expected and actual outputs” is accuracy or error, not resolution. Verification / Alternative check: Compute LSB: LSB = (Full-scale range) / (2^N - 1). This ties bits directly to output granularity. Why Other Options Are Wrong: minimum output voltage: Depends on offset and reference; not “resolution.”deviation from a straight line: That’s integral nonlinearity.difference between expected and actual outputs: That’s accuracy/total error. Common Pitfalls: Equating high resolution with high accuracy; noise and linearity can limit effective number of bits.Ignoring that effective resolution (ENOB) can be less than nominal N due to noise. Final Answer: number of bits that are converted to an analog output

Question 4

ADC architecture identification: Which Analog-to-Digital Converter compares each bit, one at a time, against the input signal during conversion?

Accepted Answer

Introduction / Context: Understanding ADC architectures is essential in digital electronics and signal processing. Successive-Approximation Register (SAR) converters dominate many medium-speed, medium-resolution applications because of their predictable conversion times and moderate complexity. Given Data / Assumptions: The question references “comparing each bit, one at a time.” Typical SAR operation uses a binary search through bit trials. Other architectures (ramp, dual-slope, tracking) follow different principles. Concept / Approach: A SAR ADC contains a DAC, a comparator, and a SAR logic block. The SAR sets the MSB to 1, compares the DAC output to the analog input, and decides to keep or clear the bit. It proceeds bit-by-bit down to the LSB, completing in N steps for an N-bit resolution. Step-by-Step Solution: Initialize with MSB = 1 and others 0.Compare DAC(MSB trial) to input; keep or clear MSB accordingly.Iterate for each subsequent bit (binary search) until LSB is decided.Return the final N-bit digital result after N comparisons. Verification / Alternative check: Time per conversion is roughly N comparator decisions; datasheets confirm “bit-by-bit trial” behavior. Why Other Options Are Wrong: single-slope ramp: Integrates a ramp until comparator toggles; not bit trials.dual-slope ramp: Integrates input, then discharges with a reference for precision; no bit-by-bit search.tracking: Uses an up/down counter to follow input changes; not a binary search per sample. Common Pitfalls: Confusing SAR with flash ADCs; flash compares in parallel with many comparators at once.Ignoring sample-and-hold needs for stable input during the N decisions. Final Answer: successive-approximation converter

Question 5

ADC architecture identification: Which converter uses an up/down counter and associated circuitry to “track” or follow changes in the analog input signal over time?

Accepted Answer

Introduction / Context: Various ADC structures trade off speed, complexity, and noise immunity. A tracking (or servo) ADC maintains a running estimate of the input and adjusts up or down as the input changes, making it intuitive for slowly varying signals. Given Data / Assumptions: The description mentions an up/down counter following the input. Tracking ADCs use a DAC and comparator in a feedback loop. Other architectures exhibit different, non-tracking behaviors. Concept / Approach: In a tracking ADC, the digital output drives a DAC. The comparator compares the DAC output to the input. If the input is larger, the counter counts up; if smaller, it counts down. Thus, the code “tracks” the analog signal with a rate limited by clock and step size. Step-by-Step Solution: Initialize counter to a starting code.Compare DAC(code) to analog input.If input > DAC, increment; if input < DAC, decrement.Repeat continuously; digital code follows the input trajectory. Verification / Alternative check: Block diagrams in textbooks show the counter–DAC–comparator feedback loop characteristic of tracking ADCs. Why Other Options Are Wrong: single-slope ramp: Uses a counter with a fixed ramp and timing measurement, not continuous tracking.dual-slope: Integrating technique for high noise rejection; no up/down tracking loop.successive-approximation: Bit-by-bit binary search per sample, not continuous up/down following. Common Pitfalls: Assuming tracking ADCs are best for all cases; they can be slower to respond to abrupt changes than SAR or flash.Ignoring the steady-state limit cycle behavior around a changing input. Final Answer: tracking converter

Digital Signal Processing Questions