Download EXPERIMENT EMC1: LAYOUT AND GROUNDING OF

EXPERIMENT EMC1: LAYOUT AND GROUNDING OF
PRINTED CIRCUIT BOARD
OBJECTIVE:
Analyze the conducted electromagnetic interference between the circuits on a
printed circuit board.
Apply various noise reduction techniques, such as decoupling capacitors and Lnetwork filters on the circuit.
LEARNING OUTCOME:
LO2 – Apply good grounding principles with respect to reduced interference.
(cognitive – applying, level 3)
APPARATUS:
1.
2.
3.
4.
5.
6.
Experiment Board (Layout and Grounding)
DC Power Supply
Oscilloscope 100 MHz
Capacitors (0.01 F, 0.1 F, 10 F)
Inductors (100 H, 220 H)
Resistors (100 , 220 )
OVERVIEW:
In this experiment, you can find three types of circuits on a single PCB board.
There is an analog circuit, a digital circuit and an electromechanical circuit. Each of
these circuits has distinctive characteristics. The analog circuit is a low-voltage
(millivolt range) sine-wave oscillator. The digital circuit is a high-voltage (5 volt) fastswitching square-wave. The electromechanical circuit is a high-current motor.
In circuit-1, the power and ground are connected by common traces. In the
first experiment, you will analyze the noise coupled via common impedance
coupling. The analog circuit is taken as the victim circuit. The effect of fast-switching
digital circuit and high-current motor on the victim circuit is investigated.
The experiment board has another group of circuits at the bottom. It is
labeled as Circuit-2. However, in Circuit-2, the ground and power traces are
connected via separate ground. Again, the analog circuit is taken as the victim circuit
and the effects of digital and motor circuit is analyzed.
The last part of the experiment uses Circuit-1. There are slots for, decoupling
capacitors, LC filters and RC filters in the experiment board. Here, you can apply
various sets of decoupling capacitors and filters, at both the victim and source
circuits. The effect in noise reduction can be demonstrated by applying the
appropriate combination of decoupling capacitor and filters.
EXPERIMENT STEPS:
1. At the beginning of the experiment verify that slot C102, C105, C107, C108, C202,
C205, C207 and C208 are open (there are no components connected in these
locations).
2. Apply 5 V DC Power Supply to Circuit-1 of the experiment board.
3. Switch ON the analog circuit (toggle SW103). Display the sine-wave output
(CN103) in the oscilloscope. Sketch the waveform.
4. Switch ON the digital circuit (toggle SW102). Display the digital output (CN102) in
the oscilloscope. Sketch the waveform. Measure the peak-to-peak amplitude of
the noise riding on the sine-wave signal (use proper volt/div setting). Sketch the
waveform.
5. Try disconnecting and then connecting the BNC connector (CN102) on the digital
circuit output of the oscilloscope. Observe carefully any changes in the noise
level on the sine-wave at the moment you disconnect or connect the BNC
connector. Compare the noise level and explain your observation.
6. Turn the digital clock (SW102) OFF. Then, turn ON the electric motor circuit
(toggle SW101). The electric motor should turn on and off at a rate of about 1 Hz.
Observe the changes on the sine-wave.
7. Turn the digital clock (SW102) ON and turn OFF the motor circuit (SW101).
8. Use a probe to examine the DC and AC voltage components on various points of
the 5 V-trace and ground-trace and Vcc pins of the ICs. Describe your
observation.
9. Disconnect the power supply from Circuit-1, and connect it to Circuit-2.
10. Repeat steps 3 to 8 on Circuit-2. Compare the noise amplitude due to the
different layout of Circuit-1 and Circuit-2.
11. Use the available capacitors, inductors and resistors on the relevant sockets on
Circuit-1 of the PCB. Try various configurations of decoupling capacitors and Lnetwork filters to minimize the noise on the sine-wave signal when the digital
circuit is on. Try every logical combination (use the reference number on the
Experiment Board for capacitors and inductors to record the combination) and
record the different magnitudes of improvement on the sine-wave quality.
Name:
Student ID:
Major:
Date:
Table No.:
TE MCE EE
EMC1 ANSWER SHEET:
LAYOUT AND GROUNDING OF PRINTED CIRCUIT BOARD
Answer to Experiment Step 3
Circuit-1
Circuit-2
Answer to Experiment Step 4
Peak to peak:
Circuit-1
Circuit-2
Circuit-1
Circuit-2
Peak to peak:
Answer to Experiment Step 5
Answer to Experiment Step 6
Answer to Experiment Step 8
Answer to Experiment Step 11
(peak-to-peak noise on the sine-wave)
Decoupling capacitor, LC
At the victim circuit
and RC filters
At the source circuit
Comment on the noise levels for common ground traces and separate ground traces.
Comment on the application of decoupling capacitors and filters in noise reduction.