AD9957SLASHPCBZ datasheet(16/61 Pages) AD

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AD9957

Data Sheet

Rev. F | Page 16 of 61

MODES OF OPERATION

OVERVIEW

The AD9957 has three basic operating modes.

•

Quadrature modulation (QDUC) mode (default)

•

Interpolating DAC mode

•

Single tone mode

The active mode is selected via the operating mode bits in

Control Function Register 1 (CFR1). Single tone mode allows

the device to operate as a sinusoidal generator with the DDS

driving the DAC directly.

Interpolating DAC mode bypasses the DDS, allowing the user

to deliver baseband data to the device at a sample rate lower

than that of the DAC. An internal chain of rate interpolation

filters the user data and upsamples to the DAC sample rate.

Combined, the filters provide for programmable rate interpola-

tion while suppressing spectral images and retaining the original

baseband spectrum.

QDUC mode employs both the DDS and the rate interpolation

filters. In this case, two parallel banks of rate interpolation

filters allow baseband processing of in-phase and quadrature

(I/Q) signals with the DDS providing the carrier signal to be

modulated by the baseband signals. A detailed block diagram of

the AD9957 is shown in Figure 25.

The inverse sinc filter is available in all three modes.

PDCLK

I/Q IN

DAC_RSET

IOUT

TxENABLE

FTW

DAC GAIN

CLOCK

SYSCLK

PLL

÷2

REF_CLK

REFCLK_OUT

XTAL_SEL

PARALLEL DATA

TIMING AND CONTROL

AD9957

cos (ωt+θ)

sin (ωt+θ)

DDS

AUX

DAC

8-BIT

POWER

DOWN

CONTROL

RAM

SERIAL I/O

PORT

PROGRAMMING

REGISTERS

I Q

IS QS

OSK

INTERNAL CLOCK TIMING AND CONTROL

DAC

14-BIT

OUTPUT

SCALE

FACTOR

Figure 25. Detailed Block Diagram

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