AD6653-150EBZ Analog Devices Inc, AD6653-150EBZ Datasheet - Page 25

• Manufacturer Part Number: AD6653-150EBZ
• Manufacturer: Analog Devices Inc

Specifications of AD6653-150EBZ

• Lead Free Status / Rohs Status: Compliant

Differential Input Configurations
Optimum performance is achieved while driving the AD6653 in a
differential input configuration. For baseband applications, the
AD8138, ADA4937-2, and
excellent performance and a flexible interface to the ADC. The
output common-mode voltage of the AD8138 is easily set with
the CML pin of the AD6653 (see Figure 47), and the driver can
be configured in a Sallen-Key filter topology to provide band
limiting of the input signal.
1V p-p
For baseband applications where SNR is a key parameter,
differential transformer coupling is the recommended input
configuration. An example is shown in Figure 48. To bias the
analog input, the CML voltage can be connected to the center
tap of the secondary winding of the transformer.
2V p-p
0.1µF
Figure 47. Differential Input Configuration Using the AD8138
Figure 48. Differential Transformer-Coupled Configuration
49.9Ω
49.9Ω
499Ω
523Ω
0.1µF
AD8138
499Ω
499Ω
ADA4938-2
ANALOG INPUT
ANALOG INPUT
2V p-p
R
R
R
R
C
C
0.1µF
C
P
differential drivers provide
D
A
0.1µF
0.1µF
R
Figure 50. Differential Input Configuration Using the AD8352
D
Figure 49. Differential Double Balun Input Configuration
0Ω
0Ω
S
VIN+
VIN–
AD6653
VIN+
VIN–
AD6653
R
S
G
16
1
2
3
4
5
CML
AVDD
CML
AD8352
P
V
Rev. 0 | Page 25 of 80
0.1µF
0.1µF
CC
14
0.1µF
8, 13
10
11
25Ω
25Ω
0.1µF
0.1µF
The signal characteristics must be considered when selecting
a transformer. Most RF transformers saturate at frequencies
below a few megahertz (MHz). Excessive signal power can also
cause core saturation, which leads to distortion.
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 AD6653. For applications where
SNR is a key parameter, differential double balun coupling is
the recommended input configuration (see Figure 49).
An alternative to using a transformer coupled input at frequencies
in the second Nyquist zone is to use the
driver, as shown in Figure 50. See the
more information. In addition, if the application requires an
amplifier with variable gain, the
variable gain amplifiers (DVGAs) provide good performance
driving the AD6653.
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 10 displays
recommended values to set the RC network. However, these
values are dependent on the input signal and should be used
only as a starting guide.
Table 10. Example RC Network
Frequency Range (MHz)
0 to 70
70 to 200
200 to 300
>300
0.1µF
200Ω
200Ω
0.1µF
R
R
C
0.1µF
R
R
C
VIN+
VIN–
AD6653
VIN+
VIN–
AD6653
CML
R Series
(Ω Each)
33
33
15
15
CML
AD8375
AD8352
AD8352
or
C Differential (pF)
15
5
5
Open
AD8376
data sheet for
differential
AD6653
digital