SAIL MCQs

Explanation: A Johnson or twisted-ring counter feeds the complemented last-stage output back to the first stage and normally produces 2n distinct states.

Explanation: A standard n-stage Johnson counter has 2n states, so five stages provide 10 distinct states.

Explanation: In a synchronous counter, all flip-flops receive the clock together and combinational logic determines which stages toggle. This avoids cumulative ripple clocking between stages.

Explanation: 0111 is decimal 7. Incrementing by one gives decimal 8, represented by 1000 in four-bit binary.

Explanation: An asynchronous clear directly forces the stored state to the reset value independent of the normal clock transition.

Explanation: At 2 MHz, one clock period is 0.5 microsecond. Sixteen clock periods therefore require 16 × 0.5 = 8 microseconds.

Explanation: A serial-in parallel-out (SIPO) register accepts bits sequentially and makes the stored bits available simultaneously at parallel outputs.

Explanation: A parallel-in serial-out (PISO) register loads a word in parallel and then shifts its bits out serially.

Explanation: The organization 2K × 16 means 2048 addressable words, each 16 bits wide. Therefore 16 data lines are required for a parallel word transfer.

Explanation: Setup time requires data to be stable for 3 ns before the active edge, and hold time requires it to remain stable for 1 ns after the edge.

Explanation: Flash memory is generally organized so erase operations affect blocks or sectors, enabling higher density than conventional byte-oriented EEPROM implementations.

Explanation: An ideal 10-bit converter has 2^10=1024 steps. Thus one LSB = 5.12 V/1024 = 0.005 V = 5 mV.

Explanation: A SAR converter determines one output bit per successive approximation step, so an ideal 12-bit conversion requires about 12 bit decisions.

Explanation: A conventional n-bit flash ADC uses one comparator for each decision threshold between adjacent output levels, giving 2^n − 1 comparators.

Explanation: For n=8, the flash ADC comparator count is 2^8 − 1 = 255.

Explanation: An R-2R ladder is constructed using only R and 2R values, simplifying resistor matching and IC implementation compared with a wide range of binary-weighted resistor values.

Explanation: For an unsigned 4-bit DAC, code value increases from 0000 to the maximum code 1111, so 1111 produces the largest ideal output.

Explanation: The sample-and-hold captures the instantaneous analog input and holds it nearly constant so the ADC sees a stable value while conversion is in progress.

Explanation: Selecting one of four chips requires log2(4)=2 selection bits. The lower 10 address bits address locations within each 1K chip.

Explanation: A DRAM cell stores data as capacitor charge that leaks with time, so rows must be periodically refreshed.

Explanation: SRAM uses bistable circuitry and normally offers faster access without refresh, although it uses more devices per bit and has lower density than DRAM.

Explanation: EEPROM is electrically erasable and programmable. Traditional EPROM requires ultraviolet light for erasure, while EEPROM supports electrical rewriting.

Explanation: A BCD digit is valid only from 0000 through 1001. When the binary digit sum exceeds 9, adding 0110₂ corrects the result and generates the appropriate decimal carry.

Explanation: 5+7=12. The initial binary sum 1100 is invalid BCD, so adding 0110 gives 1 0010. Thus the BCD result is 0001 0010, representing decimal 12.

Explanation: Excess-3 represents a decimal digit by adding 3 and encoding the result in four-bit binary. For 6, 6+3=9, giving 1001.

Explanation: Excess-3 is a self-complementing code: complementing all four bits of a digit code gives the Excess-3 code for the 9's complement of that decimal digit.

Explanation: An Arithmetic Logic Unit is a combinational subsystem that performs selected arithmetic and logical operations on binary operands.

Explanation: A barrel shifter uses combinational selection networks to shift or rotate an entire word by a selected number of positions without requiring one clock per bit position.

Explanation: An n-to-2^n decoder generates one output for each possible input minterm. The required minterm outputs can then be ORed to realize an SOP function.

Explanation: Six inputs select 2^6=64 addresses. Each address stores 4 output bits, so total storage is 64×4=256 bits.

Explanation: A PROM is manufactured with a fixed decoding structure and user-programmable storage connections, allowing a desired data pattern or truth table to be permanently programmed.

Explanation: Four binary inputs have 2^4=16 possible combinations. A 4-input LUT stores one output value for each combination, so 16 configuration bits represent an arbitrary four-variable Boolean function.

Explanation: FPGAs combine configurable logic resources with programmable interconnect, allowing the configured circuit's signal paths to be established after manufacture.

Explanation: Substituting the values gives Tclk ≥ 2+11+2+1 = 16 ns.

Explanation: fmax=1/Tmin=1/(16 ns)=62.5 MHz.

Explanation: Hold analysis checks that new data cannot reach the destination flip-flop too soon after the active clock edge, so minimum path delay is critical.

Explanation: A synchronous reset is sampled as part of the clocked logic operation and therefore takes effect at the relevant active clock edge.

Explanation: One-hot encoding assigns one flip-flop to each state and keeps exactly one state bit asserted, so eight states require eight state flip-flops.

Explanation: The minimum n satisfies 2^n≥8. Since 2^3=8, three binary state bits are sufficient.

Explanation: A maximal-length LFSR generates a pseudorandom sequence containing every nonzero n-bit state once per period, giving 2^n−1 states.

Explanation: For n=4, a maximal-length LFSR period is 2^4−1=15 states.

Explanation: With XOR feedback, an all-zero register generally produces zero feedback, so every subsequent state remains all zero unless external logic forces the LFSR out of that state.

Explanation: CRC arithmetic represents bit strings as polynomials with binary coefficients and performs division using modulo-2 operations over GF(2).

Explanation: Over GF(2), addition and subtraction are identical and correspond to XOR; there are no carries or borrows.

Explanation: The remainder from division by a degree-r generator polynomial has at most r bits, so a degree-4 generator produces four CRC bits.

Explanation: An open-collector output provides a transistor path to LOW when active. When inactive, the external pull-up resistor establishes the HIGH level.

Explanation: Because any active open-collector transistor can pull the common node LOW while inactive outputs release it, compatible outputs can share a pull-up line to implement wired logic.

Explanation: A static-0 hazard is a temporary 0→1→0 glitch caused by unequal propagation delays when the correct steady output should remain LOW.

Explanation: A dynamic hazard occurs when unequal delays through multiple paths cause several output transitions before the circuit reaches its final correct value.

Explanation: A carry propagates through the entire group only if every bit position propagates it, so the group-propagate condition is the product P0P1P2P3.

Explanation: A borrow is needed whenever the bit being subtracted, including any incoming borrow effect, exceeds the available minuend value at that position.

Explanation: 14+5=19, which exceeds the 4-bit unsigned maximum of 15. A saturating adder clamps the result to 1111 rather than wrapping around.

Explanation: In 8-bit two's-complement representation the range is −128 to +127, and the code 10000000 represents the minimum value, −128.

Explanation: An arithmetic right shift preserves the sign of a two's-complement value by filling vacated most-significant positions with copies of the sign bit.

Explanation: A one-position arithmetic right shift moves each bit toward lower significance while preserving the sign, corresponding to signed division by 2 under the stated conditions.

Explanation: Cascaded magnitude comparison requires greater-than, equal-to, and less-than status so higher-order groups can determine the overall relation correctly.

Explanation: Without a valid indication, the encoded output corresponding to no active input can be ambiguous with the code for a legitimate input. VALID indicates that an asserted input exists.

Explanation: For an active-LOW decoder, assertion is represented by logic 0, so the selected output is LOW and unselected outputs remain HIGH.

Explanation: Four first-stage 4-to-1 multiplexers select from 16 total inputs, and a second-stage 4-to-1 multiplexer selects one of their four outputs.

Explanation: Four flip-flops can represent 16 binary states. A MOD-10 sequence uses 10 of them, leaving 16−10=6 unused states.

Explanation: A self-starting counter has next-state logic that directs unused states back into the valid sequence, preventing permanent lockout.

Explanation: Dual-port memory provides two access interfaces, enabling two agents or datapaths to access a shared memory array with suitable arbitration or port rules.

Explanation: FIFO means First-In, First-Out: entries leave the buffer in the same order in which they entered.

Explanation: FIFO control logic tracks read and write positions and derives EMPTY and FULL conditions to prevent invalid reads and overwriting of unread data.

Explanation: Dual-slope conversion integrates the input over a defined interval; choosing the interval appropriately can strongly reject periodic interference such as 50/60 Hz mains noise.

Explanation: DNL measures how much each actual transition step or code-bin width differs from the ideal one-LSB size.

Explanation: A missing code is an output value that the converter skips entirely as the analog input is swept through its range, often associated with excessive DNL.

Explanation: Monotonicity means the analog output never reverses direction when the input code changes monotonically in one direction.

Explanation: Settling time is measured from a code transition until the analog output reaches and stays within a specified tolerance around its final value.

Explanation: Eight destinations require log2(8)=3 binary select inputs.

Explanation: A negative-edge-triggered device responds to the falling clock transition, from logic HIGH to logic LOW.

Explanation: Because the next D input is the complement of the current Q, each active edge loads the opposite state. The D flip-flop therefore behaves as a toggle element.

Explanation: At thermal equilibrium, the product of electron and hole concentrations equals the square of the intrinsic carrier concentration: np = ni².

Explanation: Using np=ni², p=(10^10)²/10^16=10^4 cm^-3.

Explanation: From the exponential diode equation, the incremental resistance is approximately rd = nVT/ID at the operating point.

Explanation: rd≈VT/ID=26 mV/1 mA=26 ohm.

Explanation: Increasing reverse bias widens the depletion region. Since junction capacitance is inversely related to depletion width, the capacitance decreases.

Explanation: A reverse-biased varactor exploits the voltage dependence of PN-junction capacitance, making it useful for electronic tuning.

Explanation: In avalanche breakdown, carriers accelerated by a strong electric field create additional electron-hole pairs through impact ionization.

Explanation: Zener breakdown occurs in heavily doped junctions with narrow depletion regions, where a strong field enables tunneling.

Explanation: In a standard bridge rectifier, each nonconducting diode must withstand approximately the peak secondary voltage Vm, unlike a center-tapped full-wave rectifier where the PIV is approximately 2Vm.

Explanation: When one diode conducts, the other can see approximately twice the peak voltage of one half-secondary, so PIV≈2Vm.

Explanation: The standard maximum rectification efficiency of an ideal half-wave rectifier is about 40.6%.

Explanation: The standard maximum rectification efficiency of an ideal full-wave rectifier is approximately 81.2%.

Explanation: Since IE=IC+IB and beta=IC/IB, alpha=IC/IE=beta/(beta+1).

Explanation: Drift is the directed motion of charge carriers caused by an applied electric field.

Explanation: Diffusion results from random carrier motion combined with a concentration gradient, producing net transport from higher to lower concentration.

Explanation: The Einstein relation is D/μ = kT/q, linking carrier diffusion and drift properties at temperature T.

Explanation: Reverse bias increases the junction electric field and expands the depletion region.

Explanation: Channel-length modulation shortens the effective channel as VDS rises, giving the saturation-region output characteristic a finite positive slope.

Explanation: Increasing source-body reverse bias increases the threshold voltage required to form the inversion channel; this is the MOSFET body effect.

Explanation: The cascode keeps the voltage variation across the input transistor's feedback capacitance relatively small, reducing Miller multiplication and improving high-frequency response.

Explanation: alpha=beta/(beta+1)=99/100=0.99.

Explanation: Increasing collector-base reverse bias widens the depletion region into the base, reducing effective base width and changing collector current; this is the Early effect.

Explanation: At a given bias point, BJT transconductance is gm=IC/VT, where VT is the thermal voltage.

Explanation: gm=IC/VT=1 mA/25 mV=0.04 S=40 mS.

Explanation: rπ=beta/gm=100/0.04=2500 ohm=2.5 kOhm.

Explanation: The current ratio is exp(ΔV/VT)=exp(50/25)=e^2≈7.4, assuming the exponential term dominates.

Explanation: After forward conduction, stored minority-carrier charge must be removed before the diode fully blocks reverse current, producing reverse recovery time.

Explanation: Schottky conduction mainly involves majority carriers, so there is little minority-carrier storage and reverse-recovery delay is small.