AD9233 datasheet(17/45 Pages) AD

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AD9233

Rev. A | Page 16 of 44

AVDD

1V p-p

49.9Ω

523Ω

0.1µF

499Ω

AD8138

AD9233

VIN+

VIN–

CML

Figure 37. Differential Input Configuration Using the AD8138

For baseband applications where SNR is a key parameter,

differential transformer coupling is the recommended input

configuration. An example is shown in Figure 38. The CML

voltage can be connected to the center tap of the secondary

winding of the transformer to bias the analog input.

The signal characteristics must be considered when selecting a

transformer. Most RF transformers saturate at frequencies

below a few MHz, and excessive signal power can cause core

saturation, which leads to distortion.

2V p-p

49.9Ω

0.1µF

AD9233

VIN+

VIN–

CML

Figure 38. Differential Transformer-Coupled Configuration

At input frequencies in the second Nyquist zone and above, the

noise performance of most amplifiers is not adequate to achieve

the true SNR performance of the AD9233. For applications

where SNR is a key parameter, transformer coupling is the

recommended input. For applications where SFDR is a key

parameter, differential double balun coupling is the recom-

mended input configuration. An example is shown in Figure 39.

As an alternative to using a transformer-coupled input at

frequencies in the second Nyquist zone, the AD8352 differential

driver can be used. An example is shown in Figure 40.

In any configuration, the value of the shunt capacitor, C, is

dependent on the input frequency and source impedance

and may need to be reduced or removed. Table 8 displays

recommended values to set the RC network. However, these

values are dependant on the input signal and should only be

used as a starting guide.

Table 8. RC Network Recommended Values

Frequency Range (MHz)

R Series (Ω)

C Differential (pF)

0 to 70

70 to 200

200 to 300

>300

Open

AD9233

0.1µF

2V p-p

VIN+

VIN–

CML

0.1µF

25Ω

Figure 39. Differential Double Balun Input Configuration

AD9233

AD8352

0Ω

0.1µF

VIN+

VIN–

CML

0.1µF

8, 13

VCC

200Ω

ANALOG INPUT

Figure 40. Differential Input Configuration Using the AD8352

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