Circuit Note

CN-0268

Rev. 0 | Page 5 of 6

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.

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

Manufacturer

Part Number

R121, R122, C109, C110, C117, R103, C116, R130, C118

DNI

R125, R110, R107, R113, R114, R119, R120

0 Ω

T103

Balun, 1:1 impedance ratio

M/A-Com

MABA-007159-000000

R105, R106

33 Ω

C101, C105, C106, C107

0.1 µF

U100

ADL5565

Analog Devices

R117, R118

5.6 Ω

C113, C114

1 nF

L101, L102

39 nH

Coilcraft

0805CS

C119

8.2 pF

Murata

GRM15

L103, L104

150 nH

Coilcraft

0805CS

C120

2 pF

Murata

GRM15

L100

180 nH

Coilcraft

0805CS

R111, R112

155 Ω

R127, R128

15 Ω