AD7766 datasheet(12/18 Pages) AD

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AD7766

Preliminary Technical Data

Rev. PrD | Page 12 of 18

THEORY OF OPERATION

The AD7766 is high performance 24-bit over-sampled analog to

digital converter combining wide dynamic range and input

bandwidth with an on chip FIR filter while consuming only

20mW max power in a 16 pin TSSOP package. The AD7766 is

available with 3 preset decimation rates, 8, 16 and 32. Table 6

shows the three available models of the AD7766. The three

models differ in the preset decimation rate employed. The

output data rates of the AD7766, AD7766-1 and the AD7766-2

are relative to each of their preset decimation rates.

Table 6. AD7766 Models.

Decimation Rate

Output Data Rate (ODR)

AD7766

125 KHz

AD7766-1

62.5 KHz

AD7766-2

31.25 KHz

In decimate × 8 mode the output will be updated every 8 MCLK

periods, offering a maximum output data rate of 125KHz for

the AD7766 device. The AD7766-1 model is set in decimate ×

16 mode, and the AD7766-2 is preset to decimate × 32. The

decimation ratio of each model indicates the level of filtering

employed in the on-board digital FIR filter. The higher filter

decimation rates provide the user with increased dynamic

specifications; however, there is a trade-off on throughput as the

filter delay increases as higher decimation rates are introduced.

AD7766 TRANSFER FUNCTION

The AD7766 outputs its conversion results in a 2’s complement,

24-bit serial format. The fully differential inputs VIN+ and

VIN- are scaled by the AD7766 relative to the reference voltage

input (VREF+) as shown in Figure 12.

+ = V

REF

- 1LSB

- = 0V

= V

REF

-1LSB

+ = 0V

+ = V

REF

- = V

REF

011…111

011…110

000…010

000…001

000…000

111…111

111…110

100…000

100…001

24-Bits

24-Bit

AD7766

Output

2’s Complement

Figure 12.AD7766 TransferFunction

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