Hardware System design Interview topics and tips

Introduction

Interviews preparation topics and tips are tailored towards electronic system design in consumer electronic industry.

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Roles and RESPONSIBILITIES

• Key Responsibilities

  • We work on products such as phone, laptop, wearables, etc.

  • We do schematic capture and PCB board layout

  • We perform electrical validation testing

  • We work with embedded system engineers

  • We work with chip and component suppliers 

  • We go to factory to support building the actual products

• Common Job Titles

  • Hardware system integration engineer

  • Hardware development engineer

  • Hardware System Design engineer

  • System EE

  • Hardware design engineer

  • Hardware engineer - board level and system

Interview Topics 

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• EE Fundamentals

  • Passives 

    • RLC

  • Analog Circuits

    • Opamps

  • Digital Circuits

    • Logic gates

  • Mixed Signal Circuits

    • ADCs, DACs

  • Filter Design

    • Analog passive, active, 1st order, higher order design (i.e Butterworth) 

    • Digital filter design, FIR, IIR (recursive).

  • Transceiver Type

    • Single ended 

    • Differential pair 

    • Termination

  • Signal Integrity

    • Common issues: signal reflection, signal attenuation, and crosstalk

    • Mitigation: proper layout, Impedance control, termination, spacing

  • Circuit Design

    • Reverse voltage protection, soft start circuit, MOSFET load switch, LED driver, temp sensing, current sensing, fault protection, etc.

• Digital Communication Interface

  • High Speed Interconnect Design

  • Physical layer transceiver basics

    • current mode logic driver type

    • voltage mode logic driver type

    • low voltage differential signaling charactercs

      • • i.e differential voltage swings, common voltage, etc.

    • Common communication interface

    • USB, PCIe, MIPI CSI, DSI

  • Low Speed interconnect Design

    • Physical layer transceiver basics

      • Driver output type

        • Open drain, push-pull

      • Common communication interface

        • I2C, SPI, UART

• PCB Fabrication and assembly Manufacturing

  • PCB Fabrication

    • PCB Types

      • PCB/FPCB/Rigid PCB

    • Stackup types

    • Drill technology

  • Assembly

    • Component footprints

    • Component clearance

• PCB Board Design

  • PCB Floor planning

    • Component Placement

    • Pin Breakout

    • Routing planning

    • Power plane planning

    • DFM

    • DFA

  • Stackup

    • PCB Layer definition

      • i.e 4 layered PCB ( L1 -Signal/Components, L2- Ground, L3 - Power, L3 - Signal/Component)

    • PCB Trace width and spacing

    • Via drill size and topology

      • Laser drilled stacked uVias

      • Mechanical drilled through holes Vias.

      • Via Pad size

      • Pad type

        • Solder mask defined, Non-solder mask defined

  • High Speed PCB Design

  • Layout consideration

    • controlled impedance

    • Skew control

    • Termination

    • stitching vias for layer transition

    • line to line spacing to avoid crosstalk

• Hardware System Bringup and Validation

  • Board bring up

    • Boot logic

    • Power on/off sequence

  • In Circuit Testing

    • Impedance (TDR measurements)

    • DCR

    • PDN

  • Functional Circuit testing

    • memory throughput

    • Wi-Fi throughput

    • sensor reads

  • Signal Integrity testing

    • Digital interface PHY timing and voltage

      • Edges (Rise and fall time)

    • Clocks

    • Jitter

    • Eye Diagram

  • Power Integrity testing

    • Voltage regulator ripple, tolerance, line and load regulation

    • Stability test:  large current load step test and phase margin test.

    • Impedance vs frequency for the power delivery network (PDN test)

  • System coexistence test

    • identify aggressor and victim within the electrical system 

    • define acceptance criteria 

    • implement mitigation solution (could be either SW or HW) after the coexistence test results.

  • Thermal

    • Skin temperature cannot exceed certain limit based on the product type at worst case ambient temperature 

    • IC case temperature cannot exceed Manufacture specification under worse case ambient temperature

    • CPU cannot throttle within the operating temperature limit

  • EMC

    • ESD

    • Radiated and conducted Immunity

    • Radiated and conducted Emission

  • Reliability/Environmental

    • Drop test

    • Vibration test

    • Tumble test

    • Thermal and Humidity

    • Long term interoperability test

• System Design

  • Power System

    • DC to DC Switch Mode power regulator

    • Dc to DC Linear power regulator

    • Layout consideration

    • Battery

      • Selection process

      • Charging curve

  • Digital System

    • Processor Selection

      • MCU, Application processor, and Realtime processor

    • Main Memory

      • DDR3/4 SDRAM

    • Storage

      • eMMC, UFS NAND Flash

  • Design an embedded hardware architecture

    • e.g. Tablet, Multimedia Streaming device, wireless game controller.

  • Design an general purpose computer hardware architecture

    • e.g. Phone, Laptop

  • Design a power tree

    • power delivery network for a processor or microcontroller.

Interview Tips

• Preparation is the key!

• Illustrate your thought process! Use the white boards.

• Don't make it Q&A session! Navigate and frame the answer towards your strong areas. Don't just answer the questions be asked, but also expand deeper on how it relates to other disciplines and challenges that you faced.

• Ask for clarification! Make sure you understand the questions. 

• Listen attentively and don't interrupt the interviewers

• Show enthusiasm in the role and ask interviewers about their job roles and team dynamics.

Q&A

What goes on in the mind of interviewers?

• We evaluate on reasoning and clarity of presentation.

• We want to find collaborating and cool teammates whom we want to work with.

• Fundamentals is the bare minimum and open ended questions are where interviewers are looking for creative, critical thinking, and problem solving skills.

Does rejection mean that I am not good enough?

• Interview results are highly depended on the role, level, and the interview panels.

• Some candidate are very smart but they don't fit the generalist EE role.

• Some candidate have many years of experience but do not meet the senior engineering bar. Giving them a lower level is not appropriate.

• Some candidate didn't brush up on the fundamentals.