AD9119BBCZ datasheet(53/66 Pages) AD

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Data Sheet

AD9119/AD9129

Rev. B | Page 53 of 66

For applications that operate the AD9119/AD9129 in Mix-Mode

with output frequencies extending beyond 2.2 GHz, the user may

want to consider the circuit shown in Figure 154. This circuit

uses a wideband balun (for example, −3 dB at 4.0 GHz), with a

configuration that is similar to the example shown in Figure 152,

to provide a dc bias path for the DAC outputs. This circuit was

implemented on an evaluation board, and the frequency response

was measured to compare it with the ideal curve in Figure 146.

The result is shown in Figure 155.

50Ω

MINI-CIRCUITS

TCI-1-13M+

TCI-1-33M+

IOUTP

IOUTN

VDDA

Figure 154. Recommended Mix-Mode Configuration Offering Extended RF

Bandwidth Using TC1-1-13M+ Balun

–36

–33

–30

–27

–24

–21

–18

–15

–12

–9

–6

–3

500

1000 1500 2000 2500 3000 3500 4000 4500 5000

FREQUENCY (MHz)

NORMAL MODE

MIX-MODE

MEASURED NORMAL

MEASURED MIX-MODE

Figure 155. Measured vs. Ideal DAC Output Response; fDAC = 2.6 GSPS

To assist in matching the AD9119/AD9129 output, a Smith chart

is provided in Figure 156. The plot was taken using the circuit

in Figure 154, with the balun and the coupling capacitors

removed, and L = 270 nH. For the measured vs. ideal response of

the DAC output, see Figure 155, which illustrates that a nonideal

response occurs in the second half of the second Nyquist zone.

This area corresponds to the low impedance area between 2 GHz

and 3 GHz, as shown in the Smith chart in Figure 156. Output

matching can be used to compensate for this nonideal response;

the possible reduction in signal bandwidth must be considered if

such matching is used.

1. 300kHz

3.1341

Ω 710.55mΩ 376.96nH

2. 1GHz

54.333Ω –44.210Ω 3.5999pF

3. 2GHz

13.113

Ω –11.207Ω 7.1006pF

4. 3GHz

13.022Ω –14.259Ω 756.48pH

Figure 156. Measured Smith Chart Showing the DAC Output Impedance;

fDAC = 2.6 GSPS

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