ADM202E/ADM1181A

Rev. C | Page 13 of 16

LOG FREQUENCY (MHz)

80

70

0

0.3

30

0.6

1

60

50

10

40

30

20

10

LIMIT

36

Figure 25. ADM202E Conducted Emissions

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.

Figure 27 shows radiated emissions vs. frequency. The levels of

emissions are well within specifications without the need for

additional shielding or filtering components. The ADM202E

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.

TURNTABLE

DUT

RADIATED NOISE

ADJUSTABLE

ANTENNA

TO

RECEIVER

Figure 26. Radiated Emissions Test Setup

START 30.0MHz

STOP 200.0MHz

LIMIT

80

70

60

50

40

30

20

10

0

Figure 27. ADM202E Radiated Emissions vs. Frequency