ADA4961ACPZN-R7 datasheet(21/24 Pages) AD

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Data Sheet

ADA4961

Rev. C | Page 21 of 24

LAYOUT CONSIDERATIONS

When designing the board, take care to minimize the parasitic

capacitance caused by the routing that connects the RF outputs.

A good practice is to avoid any ground or power plane under

this routing region and under the chokes to minimize the

parasitic capacitance.

EVALUATION BOARD

The ADA4961 evaluation board is a 4-layer board built on FR4

material. The board is configured for a single-ended input and a

single-ended output. All RF input and output traces are 50 Ω.

On the RF input, the Mini-Circuits® TCM2-43X balun, a 2:1

impedance balun, is used to match external 50 Ω generators to

the 100 Ω differential input of the ADA4961. On the RF output,

the Mini-Circuits TCM1-43X balun, a 1:1 impedance balun, is

used to convert the differential output of the amplifier to the

single-ended output of the evaluation board.

The outstanding linearity performance over frequency is

achieved in part by the RF outputs having a dc bias to the

supply, typically 5 V for best performance. RF chokes provide

the path to the bias supply from the RF output to the positive

supply rail. It is highly recommended that Coilcraft 0805CS-

471XJLC 470 nH inductors be used for bias. The self resonant

frequency of these inductors is high enough so that it does not

impact the performance of the ADA4961 at up to 4 GHz.

A complete description of operating the evaluation board and

evaluation board software is given in the EV-ADA4961SDP1Z

user guide.

A bill of materials for the RF section of the evaluation board is

given in Table 11.

2nH

470nH

+5.0V

1:2

DIGITAL

INTERFACE

ADA4961

2nH

2pF

MARKI

BAL-0006GSMG

BAND-PASS

FILTER

50Ω

0.1µF

50Ω

+5.0V

2pF

Figure 49. ADC Interface Circuit Using a Low-Pass Antialias Filter

Table 11.

Reference Designator

Description

Manufacturer

Part Number

ADA4961ACPZN-R7

Device under test

Analog Devices, Inc.

ADA4961ACPZN-R7

J1, J2

Input, output SMA connectors

Johnson

142-0701-801

RF input balun

Mini-Circuits

TCM2-43x+

L1, L2

470 nH RF bias chokes

Coilcraft

0805CS-471XJLC

RF output balun

Mini-Circuits

TCM1-43x+

C1, C2, C3, C4

0.1 μF RF dc blocking capacitors

Murata-Erie

GRM155R71C104KA88D

R1, R2

8.87 Ω input matching pad

Panasonic

ERJ2GEJ9R1X

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