The Top Lattice Semiconductor Interview Questions and How to Ace Your Interview

Getting a job at Lattice Semiconductor is a great opportunity for any hardware engineer or recent graduate. As a leader in programmable logic devices, Lattice offers the chance to work on cutting-edge technology and exciting products However, you’ll need to impress in your Lattice interview first

Lattice interviews are centered around technical skills problem-solving abilities, and culture fit. With preparation, research and practice, you can master the Lattice interview process. Read on for an overview of what to expect, the top technical questions you’ll likely encounter, and tips for standing out.

What to Expect in a Lattice Interview

The Lattice interview process typically involves:

• An initial phone screening with a recruiter
• A technical phone interview
• An onsite interview consisting of:
  • A coding challenge
  • Multiple technical interviews focused on architecture, algorithms, data structures
  • A system design discussion
  • Conversations about your experience and cultural fit

The initial recruiter screen aims to verify your resume details and assess basic communication skills.

The technical phone interview provides a high-level evaluation of your technical abilities. Brush up on computer organization, digital logic, Verilog, C/C++, and general hardware engineering basics.

The onsite is where you’ll get deep technical questions. Come prepared to write synthesizeable Verilog code, discuss tradeoffs in digital logic implementations, analyze circuit schematics, and work through complex architecture and design problems.

Throughout the interviews, expect behavioural and situational questions about your work style, how you handle challenges, and your alignment with Lattice’s core values. Bring specific examples of when you demonstrated problem-solving, accountability, passion, and teamwork.

12 Must-Know Lattice Semiconductor Interview Questions

Here are some of the most common Lattice interview questions with guidance on how to approach them:

Technical Questions

1. Explain a multiplexer circuit and how it works.

A multiplexer or “mux” allows multiple input signals to be routed to a single output line. The select lines determine which input is connected to the output.

In a 2:1 mux with inputs A and B and a select line S, when S=0, A is connected to the output. When S=1, B is connected. This works by using S to control transmission gates that open and close paths between the inputs and output.

2. Design a 2-bit comparator using logic gates.

First, let’s define the function. A 2-bit comparator will take in 2-bit inputs A and B and output 1 if A > B, 0 if A = B, and -1 if A < B.

We can break this down into 3 outputs:

• A>B
• A=B
• A<B

To compare the bits A1 and B1:

• A1>B1 is just A1
• A1=B1 is A1′ + B1
• A1<B1 is B1′

We can use similar logic with A0 and B0. Then combine these expressions to get the final comparator outputs.

3. Explain a multiplexer-based RAM architecture.

A RAM can be implemented with a decoder, memory cells, and a mux. The decoder converts the address lines into a 1-hot encoded select line for the mux. The mux routes data from the addressed memory cell to the output. On writes, the mux routes input data to the addressed memory cell. The memory cells store the actual bit values and are typically SRAM cells composed of a flip-flops.

4. How can you detect if two integers have the same remainder when divided by 7?

We can take the bitwise AND of the two integers. If two numbers have the same remainder when divided by 7, their last 3 bits will be the same. Doing a bitwise AND will extract those last 3 bits. If the AND result is anything other than 0, the remainders are the same.

5. Design a circuit that detects when two 8-bit numbers have equal magnitude.

We can compare the two numbers bit-by-bit from MSB to LSB. As soon as we find a bit position that differs between the two numbers, we know the magnitudes are not equal.

To implement this, we can use XNOR gates on each bit pair, followed by a large AND gate on all of the XNOR outputs. If any XNOR output is 0 (indicating a bit mismatch), the AND output will be 0, signaling unequal magnitudes. The circuit will output 1 only if all bits match, meaning the magnitudes are equal.

6. How can you swap the values of two variables without using a temporary variable?

For variables a and b, we can swap them by using the XOR operation like so:

a = a XOR b b = a XOR ba = a XOR b

The XOR “toggles” the bits so each assignment effectively swaps the values in a and b.

Verilog Questions

7. Write a Verilog module for a 4-bit ripple carry adder.

module ripple_carry_4bit (    input [3:0] A,    input [3:0] B,     input Cin,    output [3:0] Sum,    output Cout);wire [3:1] c; // Carry wires// Generate sum and carry bitsfull_adder fa0(A[0], B[0], Cin, Sum[0], c[1]);  full_adder fa1(A[1], B[1], c[1], Sum[1], c[2]);full_adder fa2(A[2], B[2], c[2], Sum[2], c[3]);full_adder fa3(A[3], B[3], c[3], Sum[3], Cout);endmodule

8. Write a testbench for a D-flip-flop.

module dff_test; // Inputs   reg clk;reg d; // Outputwire q; // Unit Under Test  d_flipflop dut (    .clk(clk),     .d(d),    .q(q));    // Clock generationalways #5 clk = ~clk;  initial begin  // Initialize   clk = 0;  d = 0;    // Test with input sequence  #10 d = 1;  #10 d = 0;  #10 d = 1;  #10;  $finish;end      endmodule  

This testbench exercises the DFF by toggling the clock, pulsing the D input, and observing the impact on Q.

9. Describe blocking and non-blocking assignments in Verilog.

Blocking assignments (=) cause the RHS expression to be evaluated and assigned to the LHS before proceeding. This enforces a sequencing of operations.

Non-blocking (<=) assignments allow the RHS and LHS to be evaluated concurrently. The assignment occurs at the end of the time step. This allows for modeling combinational logic and parallelism.

Blocking assignments should be used for clocked, sequential logic. Non-blocking assignments are better for combinational logic.

Design and Architecture

10. Design a vending machine system.

I would decompse the vending machine into the key components:

• Payment processing
  • Validates coins and bills
  • Tracks amount deposited
• Item selection
  • Keypad and display for entering selection
  • Dispensing mechanism to release item
• Inventory tracking
  • Keeps track of inventory per selection
  • Monitors dispensing
• Control logic
  • Handles payment and selection flow
  • Drives dispensing based on payment completion and item availability

The payment processor and selection interface would be the user-facing peripherals. The control logic would tie everything together.

The block diagram would have the peripherals and inventory management feeding into the control unit. The control unit would interface with the dispensing mechanism.

Some major design considerations are:

• Number of item selections
• Type of payment accepted
• Sensor feedback to detect dispensed items
• Physical size and capacity of machine

11. Design a system to track inventory for a small grocery store.

I would use RFID tags on each grocery item to enable automated tracking. RFID readers at store shelving can scan tagged items and report real-time inventory counts to a central database.

The database can decrement item counts as customers checkout items scanned at the register. It can also track items in backstock storage areas through periodic RFID scans.

The system should provide a web interface with dashboard views of:

• Current inventory per item
• Alerts on low stock
• Historical reports on sales patterns

The backend will run on a cloud server to handle heavy transaction loads. It will implement APIs for the RFID readers, registers, and web/mobile dashboards.

Security is also crucial for