AD9239 datasheet(21/41 Pages) AD

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AD9239

Data Sheet

For applications where SNR is a key parameter, differential

transformer coupling is the recommended input configuration

(see Figure 47 to Figure 49), to achieve the true performance of

the AD9239.

Regardless of the configuration, the value of the shunt capacitor, C,

is dependent on the input frequency and may need to be reduced

or removed.

*CDIFF IS OPTIONAL

1.25V p-p

33Ω

*CDIFF

50Ω

0.1μF

AGND

ADT1-1WT

1:1 Z RATIO

VIN – x

ADC

AD9239

VIN + x

0.1µF

Figure 47. Differential Transformer-Coupled Configuration

for Baseband Applications

ADC

AD9239

1.25V p-p

2.2pF

0.1μF

ADT1-1WT

1:1 Z RATIO

0.1μF

Ω

250

Ω

VIN + x

VIN – x

Figure 48. Differential Transformer-Coupled Configuration

for Wideband IF Applications

ADC

AD9239

1.25V p-p

0.1μF

ADT1-1WT

1:1 Z RATIO

0.1μF

Ω

250

Ω

VIN + x

VIN – x

Figure 49. Differential Transformer-Coupled Configuration

for Narrow-Band IF Applications

1.25V p-p

Ω

0.1µF

66Ω

VIN – x

ADC

AD9239

VIN + x

4.7pF

0.1µF

BALUN

1:1 Z

BALUN

1:1 Z

Figure 50. Differential Balun-Coupled Configuration

for Wideband IF Applications

Single-Ended Input Configuration

A single-ended input may provide adequate performance in

cost-sensitive applications. In this configuration, SFDR and

distortion performance can degrade due to input common-mode

swing mismatch. If the application requires a single-ended input

configuration, ensure that the source impedances on each input

are well matched in order to achieve the best possible performance.

A full-scale input of 1.25 V p-p can be applied to the ADC’s

VIN + x pin while the VIN − x pin is terminated. Figure 51

details a typical single-ended input configuration.

1.25V p-p

Ω

49.9Ω

0.1µF

25Ω

VIN – x

ADC

AD9239

VIN + x

*CDIFF

*CDIFF IS OPTIONAL

Figure 51. Single-Ended Input Configuration

Rev. E | Page 20 of 40

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