@LearnEmc profile picture
LearnEMC @LearnEmc

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

Joined March 2017
  • Tweets 447
  • Following 78
  • Followers 918
301 Photos and videos
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
47
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
117
EMC Question of the Week: What determines the location of the nulls in the (sin x)/x shape in the plot below? a.) transition time b.) duty cycle c.) fundamental frequency Full question and answer at learnemc.com/emc-question-of….
plot of the harmonics of a 10-MHz trapezoidal waveform with 0.5-ns and 5.0-ns transition times

ALT plot of the harmonics of a 10-MHz trapezoidal waveform with 0.5-ns and 5.0-ns transition times
2
112
EMC Question of the Week: A sine wave has a peak amplitude of 2.0 volts on a 50-Ω scope. The same signal on a 50-Ω spectrum analyzer would be a narrow-band peak with an amplitude of a.) 6 dB(μV) b.) 120 dB(μV) c.) 123 dB(μV) d.) 126 dB(μV) Answer at learnemc.com/emc-question-of….
sine wave displayed on an oscilloscope

ALT sine wave displayed on an oscilloscope
1
148
EMC Question of the Week: One advantage of routing signals on microstrip trace pairs as opposed to stripline trace pairs is that microstrip trace pairs generally a.) radiate less b.) take up less space c.) have better balance d.) have lower loss Answer at learnemc.com/emc-question-of….
microstrip and stripline trace pairs

ALT microstrip and stripline trace pairs
1
2
98
EMC Question of the Week: Differential trace pairs on the outer layer of a printed circuit board 0.25 mm over a solid copper plane should generally a.) be tightly coupled b.) be length matched c.) have coplanar ground d.) all of the above Answer at learnemc.com/emc-question-of….
Four differential signal trace pairs routed on a printed circuit board

ALT Four differential signal trace pairs routed on a printed circuit board
1
4
137
EMC Question of the Week: If a digital signal trace extends a distance that exceeds its "critical length," it's generally necessary to a.) slow the transition time b.) provide a matched termination c.) either (a.) or (b.) d.) none of the above Answer at learnemc.com/emc-question-of….
portion of a circuit board with a single long trace highlighted

ALT portion of a circuit board with a single long trace highlighted
1
94
EMC Question of the Week: A 100-Ω transfer impedance expressed in dB(Ω) is A.) 10 dB(Ω) B.) 20 dB(Ω) C.) 40 dB(Ω) D.) meaningless Answer at learnemc.com/emc-question-of….
A transfer impedance plot with units of dB(ohms)

ALT A transfer impedance plot with units of dB(ohms)
1
125
EMC Question of the Week: A common-mode choke with bifilar windings generally has a.) lower inter-winding capacitance b.) lower leakage inductance c.) lower resistance d.) all of the above Answer at learnemc.com/emc-question-of….
Two winding options for a common-mode choke: sectional and bifilar.

ALT Two winding options for a common-mode choke: sectional and bifilar.
2
157
EMC Question of the Week: A wireless ESD wrist strap dissipates accumulated charge using a.) ionization b.) radiation c.) thermal induction d.) none of the above Answer at learnemc.com/emc-question-of….
Representation of a cordless ESD wrist strap

ALT Representation of a cordless ESD wrist strap
2
100
EMC Question of the Week: What is the best way to connect a decoupling capacitor to a high-speed IC on a board with power and ground planes? Full Question and Answer at learnemc.com/emc-question-of….
Four possible ways to connect a decoupling capacitor to an IC on a board with power and ground planes.

ALT Four possible ways to connect a decoupling capacitor to an IC on a board with power and ground planes.

1
3
174
EMC Question of the Week: What is the primary source of the ringing on the power inverter low-to-high transition shown in the figure? a) load capacitance b) load inductance c) mismatched load d) reverse-recovery current Full question and answer at learnemc.com/emc-question-of….
low-to-high and high-to-low voltage waveforms on the switch node of a buck converter

ALT low-to-high and high-to-low voltage waveforms on the switch node of a buck converter
3
162
EMC Question of the Week: What is the mutual capacitance between a basketball and a tennis ball? Full question and answer at learnemc.com/emc-question-of….
Schematic depiction of the self and mutual capacitances between two spheres.

ALT Schematic depiction of the self and mutual capacitances between two spheres.
52
EMC Question of the Week: When a wire-pair transmission line passes through a metal plate, it's best to model the plate as a a) plane-wave reflector b) lumped inductance c) lumped capacitance d) frequency-selective surface Full question and answer at learnemc.com/emc-question-of….
wire-pair transmission line passing through holes in a metal plate

ALT wire-pair transmission line passing through holes in a metal plate
92
EMC Question of the Week: A shielded cable connects to a circuit board mounted in a plastic enclosure. The cable shield should generally connect to the circuit board a) directly b) through an RC filter c)through a CM choke d) through ferrites Answer at learnemc.com/emc-question-of….
illustration of a shielded cable connecting to a circuit board through an unknown impedance

ALT illustration of a shielded cable connecting to a circuit board through an unknown impedance
103
EMC Question of the Week: What is the difference between differential-mode propagation and odd-mode propagation? a) differential-mode is undefined b) odd-mode is undefined c) a factor of 2 d) there is no difference Full question and answer at learnemc.com/emc-question-of….
Differential voltage source driving one microstrip trace relative to another microstrip trace

ALT Differential voltage source driving one microstrip trace relative to another microstrip trace
1
92
EMC Question of the Week: If the current drawn from a DC-to-DC converter increases from 1 A to 2 A, the differential-mode conducted emissions will increase by approximately a) 3 dB b) 6 dB c) between 0 and 6 dB d) possibly less than 0 dB Answer at learnemc.com/emc-question-of….
conducted emissions test setup showing a DUT with an external load

ALT conducted emissions test setup showing a DUT with an external load
1
87
EMC Question of the Week: In a conducted emissions test, moving the DUT closer to the vertical metal plane (from 40 cm to 20 cm), the value of the parasitic capacitance would increase by approximately a) 0 dB b) 3 dB c) 6 dB d) -6 dB Answer at learnemc.com/emc-question-of….
A conducted emission test setup showing the DUT on a 80-cm wooden table located 40 cm from a vertical metal plane.

ALT A conducted emission test setup showing the DUT on a 80-cm wooden table located 40 cm from a vertical metal plane.
2
91
EMC Question of the Week: In order to filter the common-mode power bus noise effectively, which of the components shown in the figure need to be eliminated? a) L2 b) L3 c) CY1 and CY2 d) CY3 and CY4 Full question and answer at learnemc.com/emc-question-of….
AC Powerline filter schematic showing a common-mode choke with X-capacitors and Y-capacitors on both sides. One side is unbalanced.

ALT AC Powerline filter schematic showing a common-mode choke with X-capacitors and Y-capacitors on both sides. One side is unbalanced.
1
153
EMC Question of the Week: A digital clock driver transmits a signal on a 50-Ω coaxial cable to a 50-Ω load.  What value of source resistance maximizes the power delivered to the load? a) 0 Ω b) 50 Ω c) 100 Ω d) depends on the cable length Answer at learnemc.com/emc-question-of….
voltage source with unknown resistance driving a 50-ohm load through a 50-ohm transmission line

ALT voltage source with unknown resistance driving a 50-ohm load through a 50-ohm transmission line
81
Load more