AD9854SLASHPCB datasheet(12/44 Pages) AD

12 / 44 page

AD9854

–12–

REV. 0

FREQUENCY – MHz

1200

1000

800

600

400

200

100

200

300

400

500

MINIMUM COMPARATOR

INPUT DRIVE

VCM = 0.5V

Figure 23. Comparator Toggle Voltage Requirement

LPF

REFCLK

RF/IF

INPUT

I BASEBAND

SIN

LPF

AD9854

Q BASEBAND

LPF

CHANNEL

SELECT

FILTERS

COS

a. Quadrature Downconversion

LPF

REFCLK

SIN

LPF

AD9854

COS

RF OUTPUT

I BASEBAND

Q BASEBAND

b. Direct Conversion Quadrature Upconverter

Figure 24. Director Quadrature Up/Down Conversion

Applications for the AD9854

RF IN

DUAL

8-/10-BIT

ADC

DIGITAL

DEMODULATOR

Rx BASEBAND

DIGITAL DATA

OUT

I/Q MIXER

AND

LOW-PASS

FILTER

VCA

ADC ENCODE

ADC CLOCK FREQUENCY

LOCKED TO Tx CHIP/

SYMBOL/PN RATE

REFERENCE

CLOCK

CHIP/SYMBOL/PN

RATE DATA

AD9852

CLOCK

GENERATOR

AGC

Figure 25. Chip Rate Generator in Spread Spectrum Application

BANDPASS

FILTER

IOUT

AD9854

FUNDAMENTAL

FC – FO

IMAGE

FCLK

FC + FO

IMAGE

BANDPASS

FILTER

FC + FO

IMAGE

AD9854

SPECTRUM

FINAL OUTPUT

SPECTRUM

AMPLIFIER

Figure 26. Using an Aliased Image to Generate a High

Frequency

VCO

LOOP

FILTER

PHASE

COMPARATOR

REFERENCE

CLOCK

FILTER

AD9854

DDS

TUNING

WORD

REF CLK IN

FREQUENCY

OUT

DAC OUT

PROGRAMMABLE

"DIVIDE-BY-N" FUNCTION

(WHERE N = 248/TUNING WORD)

Figure 27. Programmable “Fractional Divide-by-N”

Synthesizer

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