@LearnEmc

LearnEMC helps companies build the in-house expertise they need to ensure their products will meet electromagnetic compatibility requirements.

 Stoughton, WI
LearnEMC.com
Joined March 2017
  • Tweets465
  • Following77
  • Followers929
319Media
EMC Question of the Week: A 1-volt, 2-Ω source is connected to the 50-Ω, 5-pF input of an oscilloscope through 10 nH of inductance. Which of the plots in the figure most accurately represents the voltage waveform measured by the oscilloscope? Answer at learnemc.com/emc-question-of….
An RLC circuit and four possible output waveforms

ALT An RLC circuit and four possible output waveforms

59
EMC Question of the Week: A 100-MHz sine wave with a peak-to-peak amplitude of 2 volts is measured with a 50-Ω EMI test receiver. A single narrow-band spike is observed at 100 MHz. What is the quasi-peak amplitude of that spike? Answer at learnemc.com/emc-question-of….
representations of a sine wave in the time and frequency domains

ALT representations of a sine wave in the time and frequency domains

60
EMC Question of the Week: 1-kΩ resistors in series with the low-speed inputs of a microprocessor can help a product meet a.) radiated emissions requirements b.) ESD requirements c.) both of the above d.) none of the above Answer at learnemc.com/emc-question-of….
circuit board with components

ALT circuit board with components

1
71
EMC Question of the Week: A 5-MHz square wave has 1-ns transition times and a peak-to-peak amplitude of 1.0 volt. What is the amplitude of the harmonic at 125 MHz as measured on a spectrum analyzer? Answer at learnemc.com/emc-question-of….
time and frequency domain representations of a trapezoidal waveform

ALT time and frequency domain representations of a trapezoidal waveform

1
61
EMC Question of the Week: Each of the four circuits in the figure has a switch that closes at t=0. Which circuit will be the first to develop 9 volts across the capacitor? Answer at learnemc.com/emc-question-of….
Four RC circuits

ALT Four RC circuits

1
81
EMC Question of the Week: What can we conclude from the near-field probe measurement depicted in the photo that shows 40 dB(μV) peaks between 30 and 50 MHz? Full question and answer at learnemc.com/emc-question-of….
near-field probe measurement

ALT near-field probe measurement

103
EMC Question of the Week: Which of the following is a visual aid that is useful for analyzing certain transmission line problems in the frequency domain? a) Bounce Diagram b) Triboelectric Series c) Smith Chart d) Bob Smith Termination Answer at learnemc.com/emc-question-of….
a bounce diagram and a partial mapping of the real and imaginary parts of a complex reflection coefficient on a unit circle

ALT a bounce diagram and a partial mapping of the real and imaginary parts of a complex reflection coefficient on a unit circle

91
EMC Question of the Week: A shielded twisted pair connects a small sensor board to a controller board. The sensor board has a plastic enclosure. How and where should the cable shield be connected? Full question and answer at learnemc.com/emc-question-of….
A small pcb is connected to a shielded twisted wire pair. Question marks appear in boxes connecting the cable shield to the board ground.

ALT A small pcb is connected to a shielded twisted wire pair. Question marks appear in boxes connecting the cable shield to the board ground.

109
EMC Question of the Week: A 1.0-volt, 100-Mbps, single-ended signal driver sends a signal to a matched load on a 1-meter cable. Which of the cable options in the figure is least likely to cause a radiated emissions problem? Answer at learnemc.com/emc-question-of….
a. coax with shield grounded at connector b. coax with shield grounded at source location c. twisted wire pair with one wire grounded at connector d. coax with shield grounded through a 5-mm pigtail

ALT a. coax with shield grounded at connector b. coax with shield grounded at source location c. twisted wire pair with one wire grounded at connector d. coax with shield grounded through a 5-mm pigtail

127
EMC Question of the Week: Class II ceramic capacitors (e.g., X7R) are well-suited for a.) DC power bus decoupling b.) AC power bus decoupling c.) high-pass filtering d.) none of the above Full question and answer at learnemc.com/emc-question-of….
Two SMT components mounted on a printed circuit board

ALT Two SMT components mounted on a printed circuit board

2
3
186
EMC Question of the Week: At 60 Hz, aluminum foil can effectively shield a.) electric fields b.) magnetic fields c.) both of the above d.) none of the above Full question and answer at learnemc.com/emc-question-of….
Depiction of a mouse in a box covered in aluminum foil

ALT Depiction of a mouse in a box covered in aluminum foil

3
259
EMC Question of the Week: How fast can you draw charge from two parallel planes separated by a distance of 0.25 mm when they are initially charged to 1 volt?  Full question and answer at learnemc.com/emc-question-of….
A switch that closes at t=0 causing a short circuit between two planes spaced 0.25 mm apart. The shorting via radius is 0.3 mm. The relative permeability of the dielectric is 4.5. The voltage between the planes was initially 1 volt.

ALT A switch that closes at t=0 causing a short circuit between two planes spaced 0.25 mm apart. The shorting via radius is 0.3 mm. The relative permeability of the dielectric is 4.5. The voltage between the planes was initially 1 volt.

222
EMC Question of the Week: Within the first 200 ps of a sudden demand for current to the BGA in the figure below, where is most of the current coming from? a.) C1 b.) C2 c.) C1 and C2 equally d.) the plane capacitance Answer at learnemc.com/emc-question-of….
Cross section of a 24-layer circuit board showing decoupling capacitors at two locations. C1 is on the backside of the board sharing via connections with a BGA. C2 is on the top side 5 mm away.

ALT Cross section of a 24-layer circuit board showing decoupling capacitors at two locations. C1 is on the backside of the board sharing via connections with a BGA. C2 is on the top side 5 mm away.

1
192
EMC Question of the Week: Assuming the product meets its EMC requirements, this PCB layer is almost certainly a layer devoted to a.) high-speed signals b.) power distribution c.) RTN d.) GND Answer at learnemc.com/emc-question-of….
A section of Layer 6 in an 8-layer printed circuit board

ALT A section of Layer 6 in an 8-layer printed circuit board

1
1
4
319
EMC Question of the Week: The initial spike from an ESD simulator discharged into a calibration target is primarily due to the a.) simulator's capacitor b.) simulator's switch c.) simulator's self-capacitance d.) target's center plate Answer at learnemc.com/emc-question-of….
ESD simulator calibration waveform

ALT ESD simulator calibration waveform

2
222
EMC Question of the Week: Which output in the figure corresponds to the measured voltage from a small 15-nH loop placed over a circuit board trace. The trace carries a current that looks like a 250-MHz square wave. Answer at learnemc.com/emc-question-of….
Possible outputs from a magnetic field probe measuring a 250-MHz square-wave current

ALT Possible outputs from a magnetic field probe measuring a 250-MHz square-wave current

153
EMC Question of the Week: A 1-Gbps signal is routed on a trace that is 0.25 mm above the return plane. This trace should normally have a a.) balanced termination b.) coplanar ground c.) controlled impedance d.) all of the above Full question and answer at learnemc.com/emc-question-of….
microstrip traces on a circuit board connecting to a BGA device

ALT microstrip traces on a circuit board connecting to a BGA device

1
120
EMC Question of the Week: A plane wave is incident on long parallel wires that have different diameters. Which of the following statements is correct? a.) ICM = I1 + I2 b.) IDM = 0 c.) VDM = 0 d.) all of the above Full question and answer at learnemc.com/emc-question-of….
Illustration of an electromagnetic plane wave striking parallel wires with different diameters

ALT Illustration of an electromagnetic plane wave striking parallel wires with different diameters

124
EMC Question of the Week: In order to filter the common-mode power bus noise effectively, which of the components shown in the schematic must be eliminated? a.) L2 b.) L3 c.) CX1 and CX2 d.) CX4 and CX5 Answer at learnemc.com/emc-question-of….
a poor powerline filter design

ALT a poor powerline filter design

1
197
EMC Question of the Week: Small unconnected copper dots or diamonds on the outer layers of a printed circuit board are an example of a.) ground fill b.) via stitching c.) guard posts d.) thieving Answer at learnemc.com/emc-question-of….
circuit board with many small unconnected green dots on its surface

ALT circuit board with many small unconnected green dots on its surface

3
138
Load more