AD9148BBCZ datasheet(55/73 Pages) AD

55 / 73 page

Preliminary Technical Data

AD9148

Rev. PrA | Page 55 of 73

The NCO operating frequency, fNCO, is at the DAC rate. The

frequency of the complex carrier signal can be set from dc up to

fDAC/2. The frequency tuning word (FTW) is calculated as

DAC

CENTER

FTW

The generated quadrature carrier signal is mixed with the I and Q

data. The quadrature products are then summed into the I and

Q data paths, as shown in Figure 70.

When using the fine modulator, the maximum signal bandwidth of

0.8 × fDATA is always achieved.

Updating the Frequency Tuning Word

The frequency tuning word registers do not get updated

immediately upon writing as the other configuration registers

do. After loading the FTW registers with the desired values,

Bit 2 of Register 0x5A must transition from 0 to 1 for the new

FTW to take effect.

Phase Offset Adjustment

A 16-bit phase offset may be added to the output of the phase

accumulator via the serial port. This static phase adjustment

results in an output signal that is offset by a constant angle

relative to the nominal signal. This allows the user to phase

align the NCO output with some external signal, if necessary.

This can be especially useful when NCOs of multiple AD9148s

are programmed for synchronization. The phase offset allows

for the adjustment of the output timing between the devices.

The static phase adjustment is sourced from the NCO Phase Offset

Word[15:0] value located in Register 0x58 and Register 0x59.

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