AD7762SLASH datasheet(21/23 Pages) AD

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Data Sheet

AD7767

DRIVING THE AD7767

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Rev. D | 21 of 23

ANTIALIASING

The AD7767/AD7767-1/AD7767-2 sample the analog input at a

maximum rate of 1.024 MHz. The on-board digital filter provides

up to 100 dB attenuation for any possible aliasing frequency in the

range from the beginning of the filter stop band (0.547 × ODR) to

where the image of the digital filter pass band occurs. This occurs

at MCLK minus the filter stop band (MCLK − 0.547 × ODR), as

shown in Figure 42.

Figure 42. AD7767/AD7767-1/AD7767 Spectrum

Table 9 shows the attenuation achieved by various orders of

front-end antialias filters prior to the signal entering the AD7767/

AD7767-1/AD7767-2 at the image of the digital filter stop band,

which is 1.024 MHz − 0.547 × ODR.

Table 9. Antialias Filter Order, Attenuation at at First Image Point

Model

Filter Order

Attenuation at 1.024 MHz – 0.547 ×

ODR

AD7767

First

27 dB

Second

50 dB

Third

70 dB

AD7767-1

First

33 dB

Second

62 dB

Third

89 dB

AD7767-2

First

38 dB

Second

74 dB

Third

110 dB

The AD7764 and AD7765 ∑-∆ devices are available to customers

that require extra antialias protection. These devices sample the

signal internally at a rate of 20 MHz to achieve up to a maximum of

156 kHz or 312 kHz output data rate. This means that the first alias

point of these devices when run at the maximum speeds is 19.921

MHz and 19.843 MHz, respectively.

POWER DISSIPATION

The AD7767/AD7767-1/AD7767-2 offer exceptional performance at

ultralow power. Figure 43, Figure 44, and Figure 45 show how the

current consumption of the AD7767/AD7767-1/ AD7767-2 scales

with the MCLK frequency applied to the device. Both the digital

and analog currents scale as the MCLK frequency is reduced. The

actual throughput equals the MCLK frequency applied divided by

the decimation rate employed by the device in use. For instance,

operating the AD7767 device with an MCLK of 800 kHz results in

an output data rate of 100 kHz due to the decimate-by-8 filtering.

Figure 43. AD7767 Current vs. MCLK Frequency

Figure 44. AD7767-1 Current vs. MCLK Frequency

Figure 45. AD7767-2 Current vs. MCLK Frequency

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