GD 2nd interview

Question 1

What fundamentally changes when designing PCBs at 10+ Gbps?

Answer 1

Traces behave as transmission lines; impedance control, loss, reflections, crosstalk, and discontinuities dominate performance. Layout is as critical as the schematic.

Question 2

How do you control impedance on a PCB?

Answer 2

By defining stackup, trace width/spacing, dielectric properties, solid reference planes, and validating with field solvers (e.g., HyperLynx).

Question 3

What causes eye diagram closure?

Answer 3

ISI from bandwidth limits, jitter (random and deterministic), noise, attenuation, reflections, and crosstalk.

Question 4

Why are vias a problem at high speeds?

Answer 4

They add parasitic inductance/capacitance and can create stubs that cause reflections; mitigated with back-drilling or blind/buried vias.

Question 5

What is insertion loss vs return loss?

Answer 5

Insertion loss is signal attenuation through the channel; return loss is energy reflected due to impedance mismatch.

Question 6

What layout practices reduce crosstalk?

Answer 6

Adequate spacing, solid reference planes, orthogonal routing between layers, controlled impedance, and minimizing parallel runs.

Question 7

How do you isolate sensitive analog from high-speed digital circuitry?

Answer 7

Functional partitioning, careful return-path control, continuous ground planes, minimizing split planes, and keeping high di/dt currents away from analog sections.

Question 8

What common mistakes cause noise in analog measurements?

Answer 8

Poor grounding, long current loops, power-supply noise, improper probing, and coupling from digital signals.

Question 9

How do you select an op-amp for high-speed or low-noise use?

Answer 9

Based on GBW, slew rate, noise density, input bias/offset, stability with capacitive loads, and supply constraints.

Question 10

Why might you use multiple gain stages instead of one high-gain stage?

Answer 10

To maintain stability, bandwidth, noise performance, and avoid saturation or slew-rate limitations.

Question 11

Why does low ESR output capacitance improve transient response?

Answer 11

It lowers output impedance, supplying immediate charge during load steps before the control loop can respond, reducing voltage droop.

Question 12

How would you debug a DC-DC converter that droops under load?

Answer 12

Apply load steps, observe transient response, check output capacitance ESR/placement, verify compensation, and inspect switching-node behavior.

Question 13

How do you reduce ripple and noise on a switching supply?

Answer 13

Proper LC filtering, good layout/grounding, optimized compensation, shielding, and optionally post-regulation with an LDO.

Question 14

What belongs on a power entry module?

Answer 14

TVS diodes, EMI filtering, inrush current limiting, reverse-polarity protection, and hot-plug protection.

Question 15

How does power noise affect high-speed data links?

Answer 15

It introduces jitter and threshold modulation, increasing bit error rate.

Question 16

A new board draws too much current at power-up. What do you do first?

Answer 16

Current-limit the supply, check for shorts, inspect thermally, isolate rails, and bring up power incrementally.

Question 17

How do you probe a switching node correctly?

Answer 17

Use a short ground spring or differential probe to minimize loop inductance and measurement artifacts.

Question 18

What is a BERT and what does it measure?

Answer 18

A Bit Error Rate Tester measures link integrity by comparing transmitted and received data over time.

Question 19

Why use a sampling oscilloscope for high-speed links?

Answer 19

For extremely high bandwidth, low jitter, and accurate eye-diagram and timing analysis.

Question 20

What electrical issues most commonly impact optical systems?

Answer 20

Power-supply noise, ground noise, jitter, thermal drift, and poor signal integrity.

Question 21

What must be considered when interfacing analog signals to an FPGA?

Answer 21

Signal conditioning, ADC requirements, grounding, noise, timing, and protection of FPGA I/Os.

Question 22

How do you protect FPGA I/O pins?

Answer 22

Series resistors, clamps/ESD diodes, proper sequencing, and avoiding back-powering.

Question 23

What should be simulated vs measured?

Answer 23

Simulate early to guide design decisions; measure to validate assumptions and catch real-world effects.

Question 24

How do you approach vague requirements?

Answer 24

Clarify assumptions, propose an architecture, prototype quickly, validate, and iterate with stakeholders.

Question 25

When do you ask for help?

Answer 25

After isolating the problem, forming hypotheses, and being able to ask a precise technical question.

Question 26

How do you handle technical disagreements?

Answer 26

Data-driven discussion, simulations or measurements, and collaborative decision-making.

Question 27

How do you explain complex technical issues to non-engineers?

Answer 27

Focus on impact, risks, and outcomes using simple language and visuals, not equations.

Question 28

Why General Dynamics and this role?

Answer 28

This role aligns well with my background in mixed-signal PCB design, integration, and test, and it offers hands-on R&D work in a lab-focused environment. The Optical Center of Excellence combines high-speed electronics, systems integration, and mission-driven work, which is exactly the direction I want to grow in.

Question 29

What does your ideal work environment look like?

Answer 29

A collaborative environment with strong technical ownership, access to lab hardware, and opportunities to learn from experienced engineers. I do my best work when I’m close to the hardware and working through problems as a team.

Question 30

Describe a time you had to troubleshoot under time pressure.

Answer 30

During flat-sat integration testing, we were on a tight schedule to verify system-level communication. I created and executed a structured test script so we could isolate failures quickly instead of ad-hoc debugging. By focusing on the highest-risk interfaces first, we confirmed all components could communicate and stayed on schedule.