AD9762 datasheet(18/23 Pages) AD

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AD9762

–18–

REV. B

REFIO

FS ADJ

IOUTA

IOUTB

CLOCK

RSET

2k *

RCAL1

CLOCK

I-CHANNEL

50 **

RLOAD

50 **

RLOAD

NYQUIST

FILTER

AND MIXER

REFIO

FS ADJ

IOUTA

IOUTB

CLOCK

RSET

2k *

RCAL2

100

Q-CHANNEL

50 **

RLOAD

50 **

RLOAD

NYQUIST

FILTER

AND MIXER

0.1 F

REFLO

AVDD

* OHMTEK ORNA1001F

** OHMTEK TOMC1603-50F

Figure 57. Baseband QAM Implementation Using Two

AD9762s

It is also possible to generate a QAM signal completely in the

digital domain via a DSP or ASIC, in which case only a single

DAC of sufficient resolution and performance is required to

reconstruct the QAM signal. Also available from several vendors

are Digital ASICs which implement other digital modulation

schemes such as PSK and FSK. This digital implementation has

the benefit of generating perfectly matched I and Q components

in terms of gain and phase, which is essential in maintaining

optimum performance in a communication system. In this

implementation, the reconstruction DAC must be operating at a

sufficiently high clock rate to accommodate the highest specified

QAM carrier frequency. Figure 58 shows a block diagram of

such an implementation using the AD9762.

AD9762

LPF

MIXER

STEL-1130

QAM

COS

SIN

I DATA

Q DATA

CARRIER

FREQUENCY

STEL-1177

NCO

CLOCK

Figure 58. Digital QAM Architecture

AD9762 EVALUATION BOARD

General Description

The AD9762-EB is an evaluation board for the AD9762 12-bit

D/A converter. Careful attention to layout and circuit design

combined with a prototyping area allow the user to easily and

effectively evaluate the AD9762 in any application where high

resolution, high speed conversion is required.

This board allows the user the flexibility to operate the AD9762

in various configurations. Possible output configurations include

transformer coupled, resistor terminated, inverting/noninverting

and differential amplifier outputs. The digital inputs are designed

to be driven directly from various word generators, with the

on-board option to add a resistor network for proper load

termination. Provisions are also made to operate the AD9762

with either the internal or external reference, or to exercise

the power-down feature.

Refer to the application note AN-420 “Using the AD9760/

AD9762/AD9764-EB Evaluation Board” for a thorough

description and operating instructions for the AD9762

evaluation board.

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