ADM202E/ADM1181A
80
70
60
50
LIMIT
was operated at maximum baud rates and configured like a
typical RS-232 interface. Testing for radiated emissions was
carried out in a shielded anechoic chamber.
dB
µ
V
RADIATED NOISE
40
30
DUT
20
TURNTABLE
10
0
00066-025
ADJUSTABLE
ANTENNA
TO
RECEIVER
0.3
0.6
3
6
1
LOG FREQUENCY (MHz)
10
30
Figure 25. ADM202E Conducted Emissions
Figure 26. Radiated Emissions Test Setup
RADIATED EMISSIONS
Radiated emissions are measured at frequencies in excess of
30 MHz. RS-232 outputs are designed for operation at high
baud rates, while driving cables can radiate high frequency EM
energy. The previously described causes of conducted emissions
can also cause radiated emissions. Fast RS-232 output transitions
can radiate interference, especially when lightly loaded and
driving unshielded cables. Charge-pump devices are also prone
to radiating noise due to the high frequency oscillator and the
high voltages being switched by the charge pump. The move
toward smaller capacitors to conserve board space has resulted
in higher frequency oscillators in the charge-pump design,
causing higher levels of conducted and radiated emissions.
The RS-232 outputs on the ADM202E feature a controlled slew
rate to minimize the level of radiated emissions, yet they are fast
enough to support data rates of up to 230 kBaud.
emissions are well within specifications without the need for
additional shielding or filtering components. The ADM202E
80
70
60
50
dB
µ
V
40
30
20
10
0
START 30.0MHz
STOP 200.0MHz
LIMIT
00066-026
Figure 27. ADM202E Radiated Emissions vs. Frequency
Rev. C | Page 13 of 16
00066-027
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