AD9993BBCZ datasheet(28/57 Pages) AD

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Data Sheet

AD9993

Rev. A | Page 27 of 56

APPLICATIONS INFORMATION

DIRECT CONVERSION RADIO APPLICATION

A direct conversion radio application of the MxFE is shown in

Figure 32. The DAC output signals, IOUTA_P/IOUTA_N and

IOUTB_P/IOUTB_N, are differential currents. At 500 MSPS,

DAC output signals fall within the 1st Nyquist zone (dc to

250 MHz). DAC current outputs are converted to a voltage and

then processed by passive low-pass filters (LPF). The low-pass

filters reject out of band signal harmonics and their sampling

images. The filter outputs feed the baseband inputs of a

quadrature modulator. Quadrature modulator baseband inputs

must fall within an allowable voltage range, which gives rise to a

common-mode voltage requirement at the outputs of the DACs.

The MxFE receive signal chain consists of a VGA followed by a

quadrature demodulator, then by a programmable LPF, and

another VGA. The ADRF6518 is an LPF and VGA specifically

designed to drive the analog inputs of high speed ADCs like the

ones on the MxFE. The LPF is an antialiasing filter. At

250 MSPS, the ADC signal bandwidth is 125 MHz.

See the ADRF6518 as ADC Driver section for further

information about this interface.

Figure 32. Radio Signal Chain Example

DATA

ASSEMBLER

PLL AND CLOCK

DISTRIBUTION

OR BYPASS

CLKP

CLKN

STROBE_x

DOUTxA_x/DOUxB_x

DINxA_x, DINxB_x

DCI_x

DCO_x

SERIAL

PORT

LOGIC

RST

SPI_SDI, SPI_SDO

SPI_SCLK

SPI_CS

IOUTA_x

IOUTB_x

REFERENCES

AND BIAS

250MSPS

ADCs

A_VINx, B_VINx

C_VINx, D_VINx

QUAD

MODULATOR

QUAD

DEMOD

ADRF6518

VGA

RF IN

VGA

RF OUT

AD9993

500MSPS

DACs

PASSIVE LPF

PROGRAMMABLE

LPF AND VGA

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