CGS702V datasheet(7/10 Pages) NSC

7 / 10 page

EMI Characteristics and Measurements for CGS702

MEASURING THE SPECTRAL CONTENT OF A LOGIC IC

In order to analyze the frequency or spectral content of

logic ICs two measurement techniques have been devel-

oped One method

The Radiated Measurement Method is

based on the system-level FCC certification test methodolo-

gy FCC Open Site Test (OST) 55 The radiated method

utilizes a multilayer PCB with the IC-under-test is mounted

on a grounded adjustable table placed 3 meters from an

antenna mast (see

Figure 3 ) The IC’s input is stimulated by

a known periodic waveform and its output drives a typical

PCB microstrip The 75X microstrip is properly terminated

to prevent reflections from affecting the IC’s spectral con-

tent results

The FCC certification test method is an

open field measure-

ment procedure Therefore the spectral content of the de-

vice-under-test (in this case an IC) cannot be detected be-

low the ambient level of radiation The test-site is perma-

nent and the average ambient noise level remains relatively

constant

The CGS700 and CGS702 were tested for EMI using the

above method A comparison of the EMI results in the form

of spectral content is shown in

Figures 4 and 5

For more details on EMI see Application Note AN-831

Screen Room with 120 dB Shielding

TLF12386 – 9

FIGURE 3 Radiated EMI Measurement Method

CGS702V Datasheet(PDF) 7 Page - National Semiconductor (TI)