CN-0268 Datasheet, PDF (5/6 Pages) Analog Devices – Resonant Approach to Designing a Band-Pass Filter for Narrow-Band, High IF, 16-Bit, 250 MSPS Receiver Front End

Circuit Note
COMMON VARIATIONS
Quite a few combinations of drivers and high speed ADCs are
available; however, for optimum performance, it is important to
pay attention to the input and output impedance of the ADC
driver and the input reactance of the ADC. Each device has its
own unique impedance characteristic. A common variation to
the Figure 1 circuit is the ADL5562 (3.3 GHz bandwidth) driving
the AD9467 with a low-pass, antialiasing filter design for wideband
receiver applications, as described in Circuit Note CN-0227.
Similarly, Circuit Note CN-0110 describes using the ADL5562
differential driver amplifier to drive wide bandwidth ADCs,
such as the AD9445, for high IF ac-coupled applications. Another
alternative where variable gain is desired, the ADL5565 can be
replaced with the AD8375 variable gain amplifier. The AD8375
is a digitally controlled, variable gain, wide bandwidth amplifier
that provides precise gain control across a broad 24 dB gain range
with 1 dB resolution. The AD8376 is a dual version of the AD8375.
Circuit Note CN-0002 describes how to use the AD8376 VGA to
drive wide bandwidth ADCs for high IF, ac-coupled applications.
CN-0268
CIRCUIT EVALUATION AND TEST
The circuit shown in Figure 1 is implemented using the AD9467
evaluation board (AD9467-250EBZ). The bottom side of the
AD9467 evaluation board includes the ADL5562 and a prototype
area for a fourth-order filter. The ADL5562 was replaced with
the ADL5565 because both ADC drivers are pin compatible.
See User Guide UG-200 for the complete schematics, BOM,
and layout for the AD9467-250EBZ board. Table 2 shows the
modifications to the AD9467 evaluation board required to
duplicate the circuit shown in Figure 1. Complete documentation
for this circuit note can be found in the CN-0268 Design
Support package located at: http://www.analog.com/CN0268-
DesignSupport.
This circuit uses the modified AD9467-250EBZ circuit board
and the HSC-ADC-EVALCZ FPGA-based data capture board to
run the tests. The two boards have mating high speed connectors,
allowing for the quick setup and evaluation of the circuit’s
performance. The modified AD9467-250EBZ board contains
the circuit evaluated as described in this note, and the HSC-
ADC-EVALCZ data capture board is used in conjunction with
VisualAnalog evaluation software, as well as the SPI controller
software to properly control the ADC and capture the data.
Application Note AN-835 contains complete details on how to
set up the hardware and software to run the tests described in this
circuit note.
Table 2. AD9467 Evaluation Board Modification for the ADL5565 Driver Option
Reference Designator
Description
R121, R122, C109, C110, C117, R103, C116, R130, C118
DNI
R125, R110, R107, R113, R114, R119, R120
0Ω
T103
Balun, 1:1 impedance ratio
R105, R106
33 Ω
C101, C105, C106, C107
0.1 µF
U100
ADL5565
R117, R118
5.6 Ω
C113, C114
1 nF
L101, L102
39 nH
C119
8.2 pF
L103, L104
150 nH
C120
2 pF
L100
180 nH
R111, R112
155 Ω
R127, R128
15 Ω
Manufacturer
M/A-Com
Analog Devices
Coilcraft
Murata
Coilcraft
Murata
Coilcraft
Part Number
MABA-007159-000000
0805CS
GRM15
0805CS
GRM15
0805CS
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