AD9851-FSPCB データシートの表示（PDF） - Analog Devices

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AD9851-FSPCB

CMOS 180 MHz DDS/DAC Synthesizer

Analog Devices 

AD9851

Rx

RF IN

VCA

I

I/Q MIXER

AND

LOW-PASS Q

FILTER

AD9059

DUAL

8-BIT ADC

8

DIGITAL

8

DEMODULATOR

ADC CLOCK FREQUENCY

LOCKED TO

Tx CHIP/SYMBOL/PN RATE

ADC ENCODE

180MHz

OR 30MHz

REFERENCE

CLOCK

AD9851

CLOCK

GENERATOR

32

CHIP/SYMBOL /PN

RATE DATA

AGC

Rx BASEBAND

DIGITAL DATA OUT

Figure 1. Chip Rate Clock Generator Application in a Spread Spectrum Receiver

IOUT

MICROPROCESSOR

OR

MICROCONTROLLER

DATA

BUS

8-BIT PARALLEL DATA,

OR 1-BIT  40 SERIAL DATA,

RESET, W CLK AND FQ UD

IOUTB

180MHz OR 30MHz

REFERENCE

CLOCK

AD9851

RSET

CMOS

OUTPUTS

QOUT

QOUTB

3.9k

470pF 100k

100k

100

LOW-PASS

FILTER

200

7TH ORDER ELLIPTICAL

70MHz LOW PASS

200 IMPEDANCE

200

VOLTAGE HERE = CENTER POINT

OF SINE WAVE (0.5V TYPICALLY)

USING PASSIVE AVERAGING CIRCUIT

0 TO 1V p-p

SINE WAVE

Figure 2. Basic Clock Generator Configuration

IOUT and IOUTB are equally loaded with 100 . Two 100 k

resistors sample each output and average the two voltages. The

result is filtered with the 470 pF capacitor and applied to one

comparator input as a dc switching threshold. The filtered DAC

sine wave output is applied to the other comparator input. The

comparator will toggle with nearly 50% duty cycle as the sine

wave alternately traverses the center point threshold.

IF FREQUENCY

IN

FILTER

RF

FREQUENCY

OUT

REFERENCE

CLOCK

FILTER

AD9851

DDS

TUNING

WORD

Figure 3. Frequency/Phase-Agile Local Oscillator

for Frequency Mixing/Multiplying

REFERENCE

CLOCK

AD9851

DDS

TUNING

WORD

FILTER

PHASE

COMPARATOR

LOOP

FILTER

VCO

DIVIDE-BY-N

RF

FREQUENCY

OUT

Figure 4. Frequency/Phase-Agile Reference for PLL

REFERENCE

CLOCK

FILTER

PHASE

COMPARATOR

LOOP

FILTER

VCO

RF

FREQUENCY

OUT

AD9851

DDS

TUNING

WORD

REF CLK IN

PROGRAMMABLE

DIVIDE-BY-N FUNCTION

(WHERE N = 232/ TUNING WORD)

Figure 5. Digitally Programmable Divide-by-N

Function in PLL

EZ-KIT LITE

DSP

ADSP-2181

DSP

PROCESSOR

L&R

AUDIO IN

AD1847

STEREO

CODEC

ADSP-2181

BUS

8-BIT

DATA

BUS

INPUT/

OUTPUT

DECODE

LOGIC

AD9851/FSPCB

EVALUATION

BOARD

DAC

OUT

AD9851

DDS

REF

OSC

FM RF

OUTPUT

Figure 6. High Quality, All Digital RF Frequency

Modulation

High quality, all digital RF frequency modulation generation with

the ADSP-2181 DSP and the AD9851 DDS is well documented

in Analog Devices’ application note AN-543. It uses an image of

the DDS output as illustrated in Figure 8.

–10–

REV. D

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