AD7739 datasheet(28/32 Pages) AD

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AD7739

Preliminary Technical Data

Rev. 0 | Page 28 of 32

FREQUENCY RESPONSE

The sigma-delta modulator runs at ½ the MCLK frequency,

which is effectively the sampling frequency. Therefore, the

modulator Nyquist frequency is ¼ of the MCLK.

If chopping is enabled, the input signal is resampled by

chopping. Therefore, the overall frequency response features

notches close to the frequency of 1/channel conversion time.

The typical ADC frequency response plots are given in

Figure 26 and Figure 27. The plots are normalized to 1/channel

conversion time.

Note that these figures apply to each channel separately and are

based on individual channel conversion time. The signal is

effectively resampled once more in the multiplexer by switching

between enabled analog inputs.

NORMALIZED INPUT FREQUENCY

(INPUT FREQUENCY

× CONVERSION TIME)

–120

–100

–80

–60

–40

–20

010

100

CHOP = 1

03742-0-026

Figure 26. Typical ADC Frequency Response, Chopping Enabled

NORMALIZED INPUT FREQUENCY

(INPUT FREQUENCY

× CONVERSION TIME)

–120

–100

–80

–60

–40

–20

010

100

CHOP = 0

03742-0-027

Figure 27. Typical ADC Frequency Response, Chopping Disabled

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