AN504 데이터 시트보기 (PDF) - Vishay Semiconductors
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AN504 Datasheet PDF : 12 Pages
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AN504
Vishay Siliconix
S1
50 W
R1
50 W
HP4195A
T1
50 W
HP
41800A
Hi Z
Active
Probe
HP
41800A
Hi Z
Active
Probe
25 W
IN
OUT
DG884
Oscillator Level Set to 0 dBm
75 W
Thru
Termination
FIGURE 15. Network Measurement
FIGURE 16. Output Isolation
To measure the overall distortion of the DG884 setup, two
methods were chosen. Differential gain and phase are well
known to the video community and show how well the overall
signal path maintains a constant small-signal gain and phase
for the low-level color carrier at 4.43 MHz (PAL) or 3.58 MHz
(NTSC) as the brightness (luminance) signal is ramped
through its specified range. The second method uses a
two-tone intermodulation test to determine large signal
performance and arrive at a figure of merit known as third-order
intercept point. This is well known to communication engineers
who need to judge the ability of a channel to resolve small
signals in the presence of many large ones without the benefit
(and complexity) of filter selectivity. The differential gain and
phase measurements were made using a network analyzer
(HP4195A), and a distortion analyzer (Marconi TF2910/4) was
used to provide a cross check. Figure 17 shows the
measurement setup for the analyzer, and Figure 18 shows the
Marconi setup.
www.vishay.com S FaxBack 408-970-5600
6-10
The results from the analyzer are shown in Figure 19 for one
input to one output, and in Figure 20, for one input to four
outputs, the latter being the worst-case loading. The analyzer
test signal was a ramp of 700 mV with a 280 mV peak,
4.43-MHz signal superimposed to represent the dynamics of
a video signal. The analyzer plots clearly show the gain
reduction (negative slope) at peak brightness and also the
phase change .
Tests with the Marconi set up showed that differential gain and
phase measurements were below 0.08% and 0.05_,
respectively, when the test waveform was an EBU
International Test Line signal C. Measurements below 0.1%
and 0.1_ are difficult to resolve with the Marconi setup, which
is why the analyzer method was tried as well.
Document Number: 70610
05-Aug-99
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