Engineering Specification
ES-3U5T-1B257-AA
EMC Design Guide for Printed Circuit Boards
Frame 17 of 78
Rev. A
10/01/2002
Printed copies are uncontrolled
Table 31. Frequency and Impedance
Frequency
Ground plane
impedance
Track
impedance
100 Hz
574 µ 5.74
m
1 kHz
574 µ 5.74
m
10kHz 574
µ 5.76
m
20 kHz
574 µ 5.81
m
50 kHz
574 µ 6.14
m
100 kHz
574 µ 7.21
m
500 kHz
576 µ 22.5
m
1 MHz
582 µ 44
m
2 MHz
604 µ 87.5
m
5 MHz
736 µ 218
m
10 MHz
1.04 m 437
m
20 MHz
1.61 m 874
m
50 MHz
2.62 m 2.18
100 MHz
3.69 m 4.37
200 MHz
5.22 m 8.74
500 MHz
8.26 m 21.8
1 GHz
11.6 m 43.7
Signal grounds usually fall into one of the three categories:
·
Single-point ground
·
Multi-point ground
·
Hybrid ground
Single point grounds, (Figure 33), with regards to noise, are very undesirable because of
the series connection of all the individual circuit grounds. At high-frequencies the
inductances of the ground conductors increase the ground impedance. A single-point
ground is preferable below 1 MHz. Between 1 and 10 MHz a single point-ground can
usually be used, provided the length of the longest ground conductor is less than one-
twentieth of a wave-length to prevent emissions and to maintain a low impedance.
Summary :
Frequency and Impedance Frequency Ground plane impedance Track impedance 100 Hz 574 µ 5.74 m 1 kHz 574 µ 5.74 m 10kHz 574 µ 5.76 m 20 kHz 574 µ 5.81 m 50 kHz 574 µ 6.14 m 100 kHz 574 µ 7.21 m 500 kHz 576 µ 22.5 m 1 MHz 582 µ 44 m 2 MHz 604 µ 87.5 m 5 MHz 736 µ 218 m 10 MHz 1.04 m 437 m 20 MHz 1.61 m 874 m 50 MHz 2.62 m 2.18 100 MHz 3.69 m 4.37 200 MHz 5.22 m 8.74 500 MHz 8.26 m 21.8 1 GHz 11.6 m 43.7 Signal grounds usually fall into one of the three categories: · Single-point ground · Multi-point ground · Hybrid ground Single point grounds, (Figure 33), with regards to noise, are very undesirable because of the series connection of all the individual circuit grounds.
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