ELECTROMAGNETIC COMPATIBILITY AND MEDICAL DEVICES - Design and Development of Medical Electronic Instrumentation - page 167

J2
B N C

1

20MHz COMB

2

J3
B N C

1

10MHz COMB

+5V

2

IC2

C6
0.01uF

1 1 9
1 11

13

14

A
D
C LK
G
D/U
LOAD

QA
Q Q QD
RCO

J4
B N C

IC3

1

5MHz COMB

8

OUT

2

+5V

12

MX/MN

40MHz_OSC

7

74F191

J5
B N C

1

2.5MHz COMB

2

U4A

J1
B N C

U4B

1
2

3 4

5

6 1

40MHz COMB

74F32

74F32

2

U4C

9
10

8

74F32

U4D

12
13

11

74F32

IC1
LM78L05A/TO39

S1

1 2

VIN VOUT +5V

9V

+ C3
100uF

+ C4
100uF

C5
0.01uF

C7
0.01uF

BT1 C1

0.01uF

C2
0.01uF

3

Figure 4.13 High-frequency clocks and fast logic generate broadband signals extending well into the hundreds of megahertz. This gener-
ator produces various comb patterns which are useful in the calibration of spectrum analyzers.

isolates the device under test from unwanted interference signals on the power line and
provides a test point to probe emissions conducted from the device under test toward the
power line. Figure 4.16 presents the circuit for a 50

Ω /50 µ H LISN following the de fi nition

of standard CISPR-16-1. This circuit provides a 50- output impedance for measurement

of RF emissions produced by the device under test. This impedance was selected because
theoretical and empirical data have shown that the power circuitry statistically looks like a
50-

Ω

impedance to standard electronic equipment, and RF test equipment is typically
designed for 50-

Ω

input. The bandwidth is typically determined by the operating fre-
quency of the potential victims of the device under test's conducted emissions. For the
majority of medical devices, emission measurements are carried out from 150 kHz to
30 MHz. This ensures that devices do not interfere with VLF or HF radio communication
systems and other electronic devices operating at these frequencies.

Ω