AD9857SLASHPCB datasheet(10/31 Pages) AD

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AD9857

–10–

REV. 0

MODES OF OPERATION

The AD9857 has three operating modes:

• Quadrature Modulation Mode (Default)

• Single-Tone Mode

• Interpolating DAC Mode

Mode selection is accomplished by programming a control reg-

ister via the Serial Port. The Inverse SINC ﬁlter and output scale

multiplier are available in all three modes.

Quadrature Modulation Mode

In Quadrature Modulation Mode both the I and Q data paths

are active. A block diagram of the AD9857 operating in the

Quadrature Modulation Mode is shown in Figure 16.

In Quadrature Modulation Mode, the PDCLK/FUD pin is an

output and functions as the Parallel Data Clock (PDCLK), which

serves to synchronize the input of data to the AD9857. In this

mode, the input data must be synchronized with the rising edge

of PDCLK. The PDCLK operates at twice the rate of either the

I or Q data path. This is because of the fact that the I and Q data

must be presented to the parallel port as two 14-bit words mul-

tiplexed in time. One I word and one Q word together comprise

one internal sample. Each sample is propagated along the inter-

nal data pathway in parallel fashion.

The DDS Core provides a quadrature (sin and cos) local oscilla-

tor signal to the quadrature modulator, where the I and Q data

are multiplied by the respective phase of the carrier and summed

together, to produce a quadrature-modulated data stream.

All of this occurs in the digital domain, and only then is the digital

data stream applied to the 14-bit DAC to become the quadrature-

modulated analog output signal.

Figure 16. Quadrature Modulation Mode

PARALLEL

DATA IN

(14-BIT)

PDCLK/

FUD

INVERSE

CIC FILTER

INV

CIC

(4 )

CIC

– 63 )

FIXED

INTER-

POLATOR

PROGRAMMABLE

INTERPOLATOR

QUADRATURE

MODULATOR

INVERSE

SINC FILTER

INV

SINC

14-BIT

DAC

DAC_RSET

IOUT

OUTPUT

SCALE

VALUE

TUNING

WORD

TIMING & CONTROL

DDS

CORE

REFCLK

MODE

CONTROL

CLOCK

MULTIPLIER

– 20 )

PROFILE

SELECT

LOGIC

POWER-

DOWN

LOGIC

CONTROL REGISTERS

RESET

CIC

OVERFLOW

TxENABLE

SERIAL

PORT

DIGITAL

POWER-

DOWN

PS1

PLL

LOCK

PS0

CLOCK

INPUT

MODE

AD9857

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