Datasheet
AD9233
Rev. A | Page 16 of 44
0
5492-038
AVDD
1V p-p
49.9Ω
523Ω
0.1µF
R
R
C
499Ω
499Ω
499Ω
AD8138
AD9233
VIN+
VIN–
CML
Figure 37. Differential Input Configuration Using the AD8138
For baseband applications where SNR is a key parameter,
differential transformer coupling is the recommended input
configuration. An example is shown in
Figure 38. The CML
voltage can be connected to the center tap of the secondary
winding of the transformer to bias the analog input.
The signal characteristics must be considered when selecting a
transformer. Most RF transformers saturate at frequencies
below a few MHz, and excessive signal power can cause core
saturation, which leads to distortion.
05492-039
2V p-p
49.9Ω
0.1µF
R
R
C
AD9233
VIN+
VIN–
CML
Figure 38. Differential Transformer-Coupled Configuration
At input frequencies in the second Nyquist zone and above, the
noise performance of most amplifiers is not adequate to achieve
the true SNR performance of the AD9233. For applications
where SNR is a key parameter, transformer coupling is the
recommended input. For applications where SFDR is a key
parameter, differential double balun coupling is the recom-
mended input configuration. An example is shown in
Figure 39.
As an alternative to using a transformer-coupled input at
frequencies in the second Nyquist zone, the
AD8352 differential
driver can be used. An example is shown in
Figure 40.
In any configuration, the value of the shunt capacitor, C, is
dependent on the input frequency and source impedance
and may need to be reduced or removed.
Table 8 displays
recommended values to set the RC network. However, these
values are dependant on the input signal and should only be
used as a starting guide.
Table 8. RC Network Recommended Values
Frequency Range (MHz) R Series (Ω) C Differential (pF)
0 to 70 33 15
70 to 200 33 5
200 to 300 15 5
>300 15 Open
AD9233
R
0.1µF
0.1µF
2V p-p
VIN+
VIN–
CML
C
R
0.1µF
S
0.1µF
0
5492-089
25Ω
25Ω
SP
A
P
Figure 39. Differential Double Balun Input Configuration
AD9233
AD8352
0Ω
R
0Ω
C
D
R
D
R
G
0.1µF
0.1µF
0.1µF
VIN+
VIN–
CML
C
0.1µF
0.1µF
16
1
2
3
4
5
11
R
0.1µF
0.1µF
10
8, 13
14
V
CC
200Ω
200Ω
05492-088
ANALOG INPUT
ANALOG INPUT
Figure 40. Differential Input Configuration Using the AD8352