AD9201
COMMON-MODE PERFORMANCE
Inspection of the curves will yield the following conclusions:
1. An AD9201 running with AVDD = 5 V is the easiest to
drive.
2. Differential inputs are the most insensitive to common-mode
voltage.
3. An AD9201 powered by AVDD = 3 V and a single ended
input, should have a 1 V span with a common-mode voltage
of 0.75 V.
Attention to the common-mode point of the analog input volt-
age can improve the performance of the AD9201. Figure 29
illustrates THD as a function of common-mode voltage (center
point of the analog input span) and power supply.
–30
–35
2V SPAN
–40
–45
THD – dB
THD – dB
–50
–55
–60
1V SPAN
–65
–70
–10
2V SPAN
–20
–30
–40
–50
1V SPAN
–60
–70
–75
–80
–0.5
0
0.5
1.0
COMMON-MODE LEVEL – V
1.5
–80
–0.5
0
0.5
1.0
COMMON-MODE LEVEL – V
1.5
a. Differential Input, 3 V Supplies
–30
–35
–20
–40
–45
THD – dB
THD – dB
–50
2V SPAN
–55
–60
–65
–70
–75
–80
–0.5
0
1.5
0.5
1.0
COMMON-MODE LEVEL – V
2.0
2.5
1V SPAN
–70
–80
–0.5
–30
–10
c. Single-Ended Input, 3 V Supplies
2V SPAN
–40
–50
–60
1V SPAN
0
1.5
0.5
1.0
COMMON-MODE LEVEL – V
2.0
2.5
b. Differential Input, 5 V Supplies
d. Single-Ended Input, 5 V Supplies
Figure 29. THD vs. CML Input Span and Power Supply (Analog Input = 1 MHz)
–12–
REV. D
AD [ ANALOG DEVICES ]
