20+ Digital Design Engineer Interview Questions and Answers

Four people with different travel times need to cross a river in 17 min using a boat with max capacity of 2.

• A and B cross first, taking 2 min.

• A returns alone, taking 1 min.

• C and D cross together, taking 10 min.

• B returns with A, taking 2 min.

• Finally, A and B cross together, taking 2 min.

• Total time taken is 17 min.

• A and B traveled together twice, while C and D traveled together once.

Draw log(Id) vs Vgs for a MOSFET and explain the curve. Questions on subthreshold slope, howVth varies with length, asked to explain what is DIBL

• The curve shows the relationship between drain current and gate-source voltage

• Subthreshold slope is the rate of change of drain current with respect to gate voltage

• Vth varies with length due to the effect of channel length modulation

• DIBL stands for Drain Induced Barrier Lowering and refers to the reduction of the threshold voltage du...read more

I have studied digital design, setup hold time is the time data must be stable before and after the clock edge, fixing it involves adjusting the clock or data path, setup time is more critical, a circuit with fewer stages is better for delay and power.

• Studied digital design

• Setup hold time is the time data must be stable before and after the clock edge

• Fixing setup hold time involves adjusting the clock or data path

• Setup time is more critical than hold time

• A circuit with fewer ...read more

To determine the sign on the opamp and output impedances of transistor circuits without pen and paper.

• Use mental math to determine the sign on the opamp based on the input and feedback signals

• Estimate the output impedance by considering the transistor's characteristics and circuit topology

• Practice mental math and circuit analysis to improve speed and accuracy

• Use simulation software to verify calculations and gain additional insights

The minimum sampling frequency required for a passband signal from 5kHz to 10 kHz is 20 kHz.

• The Nyquist-Shannon sampling theorem states that the minimum sampling frequency should be twice the highest frequency component of the signal.

• In this case, the highest frequency component is 10 kHz, so the minimum sampling frequency required is 20 kHz.

• Sampling at a lower frequency can result in aliasing, where higher frequency components are incorrectly represented as lower frequency c...read more

A 58:1 mux can be implemented using 2:1 mux by cascading multiple levels of muxes.

• Implement a 2:1 mux using 2 input lines and 1 output line.

• Cascading multiple levels of 2:1 muxes can create a 4:1, 8:1, 16:1, and finally a 58:1 mux.

• In this case, you would need 6 levels of 2:1 muxes to create a 58:1 mux.

Delay reduction methods in digital design engineering

• Optimizing clock frequency

• Reducing wire length

• Using pipelining

• Implementing parallel processing

• Minimizing capacitance

• Using faster logic gates

• Reducing fan-out

• Using shorter interconnects

• Optimizing placement and routing

State time analysis is a method used to analyze the behavior of digital circuits over time.

• State time analysis involves creating a state diagram to represent the circuit's behavior.

• The state diagram is used to determine the circuit's output at each clock cycle.

• This analysis is useful for verifying the correctness of digital circuits.

• It can also be used to optimize circuit performance.

• Examples of tools used for state time analysis include ModelSim and Cadence.

Count the number of one's in a vector.

• Iterate through the vector and count the number of ones encountered.

• Use built-in functions like count() or accumulate() in C++.

• In Python, use the count() method or sum() function with a conditional statement.

I have worked on various digital projects including designing and implementing digital circuits, developing microcontroller-based systems, and creating digital signal processing algorithms.

• Designed and implemented digital circuits using Verilog and VHDL

• Developed microcontroller-based systems using Arduino and Raspberry Pi

• Created digital signal processing algorithms using MATLAB and Python

• Worked on FPGA-based projects such as image processing and audio processing

• Designed and i...read more

DDP stands for Design Data Package, which is a collection of documents and files that define a product's design.

• DDP includes design specifications, drawings, schematics, and other relevant documents.

• It is used to communicate the design intent to manufacturers and suppliers.

• DDP ensures that the product is manufactured according to the design specifications.

• It also helps in maintaining the product's quality and consistency.

• DDP is an essential part of the product development pro...read more

A 2:1 mux can be used to design and gate.

• A 2:1 mux has two inputs and one output.

• The output is selected based on the value of the select input.

• To design an AND gate using a 2:1 mux, connect one input to the select input and the other input to the data input.

• Connect the output of the mux to the AND gate output.

• The truth table for the AND gate can be derived from the truth table of the 2:1 mux.

A 4:1 mux can be implemented using two 2:1 muxes by selecting one of the 2:1 muxes based on the select line.

• Use one 2:1 mux to select between the two inputs of the second 2:1 mux based on the select line

• Connect the outputs of the two 2:1 muxes to get the final 4:1 mux output

NAND gate can be implemented using a 2:1 multiplexer by connecting one input to select line and the other input to one of the data inputs.

• Connect one input of the NAND gate to the select line of the 2:1 mux.

• Connect the other input of the NAND gate to one of the data inputs of the 2:1 mux.

• Connect the other data input of the 2:1 mux to ground.

• The output of the 2:1 mux will be the output of the NAND gate.

State diagrams are visual representations of the states and transitions of a system.

• Identify the states of the system

• Determine the events that trigger state transitions

• Draw the state diagram using appropriate symbols and notation

• Label the states and transitions

• Include any necessary conditions or actions for each transition

NOT gate is a logic gate that inverts the input signal.

• Also known as inverter gate

• Produces output that is opposite of input

• Symbol is a triangle with a small circle at the input

• Example: NOT gate with input 0 produces output 1

NAND gate is a logic gate that produces an output that is the inverse of the AND gate.

• It has two or more inputs and one output.

• The output is low only when all inputs are high.

• It is a combination of an AND gate followed by a NOT gate.

• It is commonly used in digital circuits for its versatility and efficiency.

• Example: CD4011B IC contains four 2-input NAND gates.

Mux is used to select one of several input signals and forward the selected input to the output.

• Multiplexers are used in digital circuits to select one of several input signals and forward the selected input to the output.

• Mux is used in data transmission systems to combine multiple data streams into a single stream.

• Mux is used in memory systems to select a particular memory location for read or write operations.

• Mux is used in microprocessors to select a particular register or...read more