AD9739-R2-EBZ datasheet(42/48 Pages) AD

42 / 48 page

AD9739

Data Sheet

Rev. B | Page 42 of 48

Output Stage Configuration

The AD9739 is intended to serve high dynamic range applications

that require wide signal reconstruction bandwidth (that is,

DOCSIS CMTS) and/or high IF/RF signal generation. Optimum ac

performance can only be realized if the DAC output is configured

for differential (that is, balanced) operation with its output

common-mode voltage biased to analog ground. The output

network used to interface to the DAC should provide a near 0 Ω

dc bias path to analog ground. Any imbalance in the output

impedance between the IOUTP and IOUTN pins results in

asymmetrical signal swings that degrade the distortion

performance (mostly even order) and noise performance.

Component selection and layout are critical in realizing the

performance potential of the AD9739.

MINI-CIRCUITS®

TC1-33-75G+

90Ω

IOUTP

IOUTN

70Ω

Figure 66. Recommended Balun for Wideband Applications with Upper

Bandwidths of up to 2.2 GHz

Most applications requiring balanced-to-unbalanced conversion can

take advantage of the Ruthroff 1:1 balun configuration shown in

Figure 66. This configuration provides excellent amplitude/phase

balance over a wide frequency range while providing a 0 Ω dc bias

path to each DAC output. Also, its design provides exceptional

bandwidth and can be considered for applications requiring

signal reconstruction of up to 2.2 GHz. The characterization plots

shown in this data sheet are based on the AD9739 evaluation

board, which uses this configuration. Figure 67 compares the

measured frequency response for normal and mix mode using

the AD9739 evaluation board vs. the ideal frequency response.

–36

–33

–30

–27

–24

–21

–18

–15

–12

–9

–6

–3

500

1000

1500

2000

2500

3000

3500

FREQUENCY (MHz)

IDEAL BASEBAND MODE

MIX MODE

TC1-33-75G

BASEBAND

TC1-33-75G

IDEAL MIX MODE

Figure 67. Measured vs. Ideal Frequency Response for Normal (Baseband)

and Mix Mode Operation Using a TC1-33-75G Transformer on the AD9739

Evaluation Board

Figure 68 shows an interface that can be considered when

interfacing the DAC output to a self-biased differential gain

block. The inductors shown serve as RF chokes (L) that provide

the dc bias path to analog ground. The value of the inductor,

along with the dc blocking capacitors (C), determines the lower

cutoff frequency of the composite pass-band response. An RF

balun should also be considered before the RF differential gain

stage and any filtering to ensure symmetrical common-mode

impedance seen by the DAC output while suppressing any

common-mode noise, harmonics, and clock spurs prior to

amplification.

90Ω

IOUTP

IOUTN

70Ω

RF DIFF

AMP

OPTIONAL BALUN AND FILTER

90Ω

LPF

Figure 68. Interfacing the DAC Output to the Self-Biased Differential Gain Stage

For applications operating the AD9739 in mix mode with output

frequencies extending beyond 2.2 GHz, the circuits shown in

Figure 69 should be considered. The circuit in Figure 69 uses a

wideband balun with a configuration similar to the one shown

in Figure 68 to provide a dc bias path for the DAC outputs. The

circuit in Figure 70 takes advantage of ceramic chip baluns to

provide a dc bias path for the DAC outputs while providing

excellent amplitude/phase balance over a narrower RF band.

These low cost, low insertion loss baluns are available for

different popular RF bands and provide excellent amplitude/

phase balance over their specified frequency range.

MINI-CIRCUITS

TC1-1-462M

90Ω

IOUTP

IOUTN

70Ω

90Ω

Figure 69. Recommended Mix Mode Configuration Offering Extended RF

Bandwidth Using a TC1-1-43A+ Balun

MURATA

JOHANSON TECHNOLOGY

CHIP BALUNS

180Ω

IOUTP

IOUTN

70Ω

Figure 70. Lowest Cost and Size Configuration for Narrow RF Band Operation

AD9739-R2-EBZ 数据表(PDF) 42 Page - Analog Devices

AD9739-R2-EBZ 数据表(HTML) 42 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

数据表下载

链接网址

AD9739-R2-EBZ 数据表(PDF) 42 Page - Analog Devices

AD9739-R2-EBZ 数据表(HTML) 42 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

数据表 下载

链接网址

数据表下载