EVAL-AD7767-1EDZ 查看數據表（PDF） - Analog Devices
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EVAL-AD7767-1EDZ Datasheet PDF : 24 Pages
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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 of any possible aliasing
frequencies 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 at MCLK − filter stop band (MCLK − 0.547 × ODR),
which is the first alias point. This is illustrated in Figure 42.
fMCLK
DIGITAL FILTER 100dB
ANTIALIAS PROTECTION
DIGITAL FILTER
IMAGE AT fMCLK
BAND OF INTEREST
fMCLK – (0.547 × ODR)
FIRST ALIAS POINT
Figure 42. AD7767/AD7767-1/AD7767 Spectrum
Table 8 shows the attenuation achieved by various orders of
front-end antialias filters prior to the AD7767/AD7767-1/
AD7767-2 at the image of the digital filter stop band, which is
1.024 MHz − 0.547 × ODR.
Table 8. Antialias Filter Order Attenuation at First Alias Point
Model
Filter Order
Attenuation at
1.024 MHz – 0.547 × ODR
AD7767
1st
27 dB
2nd
50 dB
3rd
70 dB
AD7767-1 1st
33 dB
2nd
62 dB
3rd
89 dB
AD7767-2 1st
38 dB
2nd
74 dB
3rd
110 dB
The AD7764 and AD7765 sigma-delta devices are available to
customers that require extra antialias protection. These devices
sample internally at a rate of 20 MHz to achieve up to a maxi-
mum 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 are 19.921 MHz and 19.843 MHz, respectively.
POWER DISSIPATION
The AD7767/AD7767-1/AD7767-2 offer exceptional perform-
ance 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 of each of the
AD7767/AD7767-1/AD7767-2 equals the MCLK frequency
applied divided by the decimation rate employed by the device
AD7767
in use. For instance, operating the AD7767 device with an
MCLK of 800 kHz gives an output data rate of 100 kHz due to
the decimate by 8 filtering.
4.5
4.0
3.5
DIDD
3.0
2.5
2.0
1.5
AIDD
1.0
0.5
IREF
0
0 100k 200k 300k 400k 500k 600k 700k 800k 900k 1000k
FREQUENCY (Hz)
Figure 43. AD7767 Current vs. MCLK Frequency
2.5
2.0
DIDD
1.5
1.0
AIDD
0.5
IREF
0
0 100k 200k 300k 400k 500k 600k 700k 800k 900k 1000k
FREQUENCY (Hz)
Figure 44. AD7767-1 Current vs. MCLK Frequency
1.4
DIDD
1.2
1.0
AIDD
0.8
0.6
0.4
IREF
0.2
0
0 100k 200k 300k 400k 500k 600k 700k 800k 900k 1000k
FREQUENCY (Hz)
Figure 45. AD7767-2 Current vs. MCLK Frequency
Rev. 0 | Page 21 of 24
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