AD9877 datasheet(21/36 Pages) AD

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AD9877

Rev. B | Page 21 of 36

Table 7. Cable Driver Gain Control

Bits [7:4]

CA Interface Transmit Word

0000

0000 0000 (default)

0001

0000 0001

0010

0000 0010

0011

0000 0100

0100

0000 1000

0101

0001 0000

0110

0010 0000

0111

0100 0000

1000

1000 0000

In this mode, the lower bits determine the fine gain setting of

the DAC output.

Table 8. DAC Output Fine Gain Setting

Bits [3:0]

DAC Fine Gain

0000

0.0 dB (default)

0001

0.5 dB

0010

1.0 dB

0011

1.5 dB

...

1110

7.0 dB

1111

7.5 dB

New data is automatically sent over the 3-wire CA interface

(and DAC gain adjust) whenever the value of the active gain

control register changes or a new profile is selected. The default

value is 0x00 (lowest gain).

The formula for the combined output level calculation of the

AD9877 fine gain and the AD8327 or AD8322 coarse gain is

V8327 = V9877(0) + (fine)/2 + 6(coarse) − 19

V8322 = V9877(0) + (fine)/2 + 6(coarse) − 14

where:

fine is the decimal value of Bits [3:0].

coarse is the decimal value of Bits [7:8].

V9877(0) is the level at AD9877 output in dBmV for fine = 0.

V8327 is the level at output of the AD8327 in dBmV.

V8322 is the level at output of the AD8322 in dBmV.

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