VLSI and hardware engineering interview questions

VLSI and hardware engineering interview questions

Explain why & how a MOSFET works

Draw Vds-Ids curve for a MOSFET. Now, show how this curve changes (a) with increasing Vgs (b) with increasing transistor width considering Channel Length Modulation

Explain the various MOSFET Capacitances & their significance

Draw a CMOS Inverter. Explain its transfer characteristics

Explain sizing of the inverter

How do you size NMOS and PMOS transistors to increase the threshold voltage?

What is Noise Margin? Explain the procedure to determine Noise Margin

Give the expression for CMOS switching power dissipation

What is Body Effect?

Describe the various effects of scaling

Give the expression for calculating Delay in CMOS circuit

What happens to delay if you increase load capacitance?

What happens to delay if we include a resistance at the output of a CMOS circuit?

What are the limitations in increasing the power supply to reduce delay?

How does Resistance of the metal lines vary with increasing thickness and increasing length?

You have three adjacent parallel metal lines. Two out of phase signals pass through the outer two metal
lines. Draw the waveforms in the center metal line due to interference. Now, draw the signals if the signals in outer metal lines are in phase with each other

What happens if we increase the number of contacts or via from one metal layer to the next?

Draw a transistor level two input NAND gate. Explain its sizing (a) considering Vth (b) for equal rise and fall times

Let A & B be two inputs of the NAND gate. Say signal A arrives at the NAND gate later than signal B. To
optimize delay, of the two series NMOS inputs A & B, which one would you place near the output?

Draw the stick diagram of a NOR gate. Optimize it

For CMOS logic, give the various techniques you know to minimize power consumption

What is Charge Sharing? Explain the Charge Sharing problem while sampling data from a Bus

Why do we gradually increase the size of inverters in buffer design? Why not give the output of a circuit to
one large inverter?

In the design of a large inverter, why do we prefer to connect small transistors in parallel (thus increasing effective width) rather than lay out one transistor with large width?

Given a layout, draw its transistor level circuit. (I was given a 3 input AND gate and a 2 input Multiplexer. You can expect any simple 2 or 3 input gates)

Give the logic expression for an AOI gate. Draw its transistor level equivalent. Draw its stick diagram

Why dont we use just one NMOS or PMOS transistor as a transmission gate?

For a NMOS transistor acting as a pass transistor, say the gate is connected to VDD, give the output for a square pulse input going from 0 to VDD

Draw a 6-T SRAM Cell and explain the Read and Write operations

Draw the Differential Sense Amplifier and explain its working. Any idea how to size this circuit? (Consider Channel Length Modulation)

What happens if we use an Inverter instead of the Differential Sense Amplifier?

Draw the SRAM Write Circuitry

Approximately, what were the sizes of your transistors in the SRAM cell? How did you arrive at those sizes?

How does the size of PMOS Pull Up transistors (for bit & bit- lines) affect SRAMs performance?

Whats the critical path in a SRAM?

Draw the timing diagram for a SRAM Read. What happens if we delay the enabling of Clock signal?

Give a big picture of the entire SRAM Layout showing your placements of SRAM Cells, Row Decoders, Column Decoders, Read Circuit, Write Circuit and Buffers

In a SRAM layout, which metal layers would you prefer for Word Lines and Bit Lines? Why?

How can you model a SRAM at RTL Level?

Whats the difference between Testing & Verification?

For an AND-OR implementation of a two input Mux, how do you test for Stuck-At-0 and Stuck-At-1 faults at the internal nodes? (You can expect a circuit with some redundant logic)

What is Latch Up? Explain Latch Up with cross section of a CMOS Inverter. How do you avoid Latch Up?

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