AD9750 Просмотр технического описания (PDF) - Analog Devices

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AD9750

10-Bit, 125 MSPS High Performance TxDAC® D/A Converter

Analog Devices 

AD9750

+5V

DVDD

634⍀

1.82V

REFLO

100W

AVDD

500⍀

500⍀

0.1␮F

REFIO

FSADJ

RSET1

2k⍀

I DATA

INPUT

AD9750

(“I DAC”)

LATCHES

U1

DAC

IOUTA

IOUTB

500⍀

CFILTER

500⍀

100⍀

VPBF

BBIP

BBIN

+

CLK

AVDD

Q DATA

INPUT

AVDD REFLO

LATCHES

QOUTA

U2

AD9750

(“Q DAC”)

DAC

QOUTB

REFIO

FSADJ SLEEP

0.1␮F

RSET2

1.9k⍀

RCAL

220⍀

ACOM

DCOM

100⍀

500⍀

500⍀

CFILTER

500⍀

100⍀

500⍀

500mV p-p WITH

VCM=1.2V

BBQP

BBQN

PHASE

SPLITTER

AD8346

NOTE: 500⍀ RESISTOR NETWORK - OHMTEK ORN5000D

100⍀ RESISTOR NETWORK - TOMC1603-100D

Figure 36. Baseband QAM Implementation Using Two AD9750s

VOUT

LOIP

LOIN

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 imple-

mentation, the reconstruction DAC must be operating at a

sufficiently high clock rate to accommodate the highest specified

QAM carrier frequency. Figure 37 shows a block diagram of

such an implementation using the AD9750.

12

12

I DATA

STEL-1130

12

QAM

Q DATA

AD9750

50⍀

LPF

TO

MIXER

50⍀

12 12

SIN

COS

CARRIER 12 STEL-1177

FREQUENCY

NCO

AD9750 EVALUATION BOARD

General Description

The AD9750-EB is an evaluation board for the AD9750 10-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 AD9750 in any application where high

resolution, high speed conversion is required.

This board allows the user the flexibility to operate the AD9750 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 ter-

mination. Provisions are also made to operate the AD9750

with either the internal or external reference, or to exercise the

power-down feature.

Refer to the application note AN-420 for a thorough description

and operating instructions for the AD9750 evaluation board.

CLOCK

Figure 37. Digital QAM Architecture

REV. 0

–17–

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