AD6684 datasheet(24/107 Pages) AD

24 / 107 page

AD6684

Data Sheet

Rev. 0 | Page 24 of 107

Analog Input Controls and SFDR Optimization

The AD6684 offers flexible controls for the analog inputs, such

as buffer current and input full-scale adjustment. All of the

available controls are shown in Figure 56.

AIN

CONTROL

(SPI)

10pF

VIN+x

100Ω

VIN–x

AVDD3

VCM

BUFFER

400Ω

100Ω

AVDD3

3.5pF

AVDD3

3.5pF

Figure 56. Analog Input Controls

Using Register 0x1A4C and Register 0x1A4D, the buffer

currents on each channel can be scaled to optimize the SFDR

over various input frequencies and bandwidths of interest. As the

input buffer currents are set, the amount of current required by

the AVDD3 supply changes. This relationship is shown in

Figure 59. For a complete list of buffer current settings, see

Table 46.

10Ω

0.1µF

VIN+x

VIN–x

0.1µF

BALUN

50Ω

AGND

10Ω

50Ω

10Ω

0Ω

2pF

10Ω

0Ω

Figure 57. Differential Transformer Coupled Configuration for First and Second Nyquist Frequencies

10Ω

0.1µF

VIN+x

VIN–x

0.1µF

50Ω

AGND

DNI

50Ω

DNI

10Ω

0Ω

DNI

10Ω

0Ω

BALUN

Figure 58. Differential Transformer Coupled Configuration for Third and Fourth Nyquist Zones

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