Preliminary Technical Data

AD7766

DIGITAL FILTERING

The AD7766 has an on-board digital FIR filter. The FIR filter’s

decimation rate is preset for each AD7766 model (See Table 6

for details). The digital filter consists of three separate filter

blocks. Figure 19 shows the three constituent blocks of the filter.

The order of decimation of the first filter block is either set as

either 2, 4 or 8. The remaining sections have a decimation rate

of 2. The settling time of the filter implemented on the AD7766,

AD7766-1 and AD7766-2 is related to the amount of

decimation employed, the filter settling time of each device is

shown in Table 7.

Digital Filter

Stage 1

Stage 2

Stage 3

Dec x (2 x n)

Dec x 2

Dec x 2

Data

Stream

SDO

7th Order

Sinc Filter

FIR Filter

FIR Filter

Figure 19.FIR filter stages

(n = 1 for AD7766, n= 2 for AD7766-1, n = 4 for AD7766-2)

The response of the digital filter on board the AD7766 is shown

in Figure 20.. The filter provides stop-band attenuation of

100dB and passband ripple of ± 0.005dB.

0

-20

-40

-60

-80

-100

(Hz)

( dB )

Figure 20.AD7766 Filter Response for AD7766 (MCLK =1Mhz, ODR = 125Khz)